Endocrine
system, hypothalamus. Pituitary gland. Pineal body. Thyroid
and parathyroid glands. ADRENAL GLANDS
1. The general morphofunctional
characteristic of the endocrine system. Endocrine glands classification.
2. Pituitary
gland location and embryonic origin.
3. 2
major divisions of the pituitary and their descriptions.
4. Cell
types in pituitary portions and characteristic staining properties.
5. Hormones
produced by the pituitary, indicating for each one the division and cell type
responsible for its production as well as its target site.
6. Hypothalamus
nuclei. Peculiarities of the neurosecretory cells.
7. Description
of role of the hypothalamus in controlling pituitary function.
8. Description
of blood supply to the pituitary and its role in pituitary function.
9. Pineal
gland general structure and functions.
10. Pinealocytes
and neuroglial cells.
11. Pineal
gland interconnections with the other endocrine glands and nervous system.
12. Age
changes of the pineal gland.
13. The
general morphofunctional characteristic of the endocrine system. Endocrine
glands classification.
14. Location,
shape, and embryonic origin of the thyroid gland.
15. Role
of the pituitary gland and hypothalamus in the regulation of thyroid follicular
activity.
16. Effects
of thyroid hormones on their target tissues.
17. Structure,
function, location, and embryonic origin of the C or parafollicular cells.
18. Description
of the thyroid follicles, follicular cells, basement membrane, colloid,
capillaries of the thyroid gland.
19. Distinguish
between an active and inactive thyroid gland on the basis of follicular
morphologic characteristics.
20. Comparison
of parenchymal cell types of the parathyroid glands (chief cells and oxyphilic
cells) in light and electron microscopes.
21. Role
of the parathyroid hormone in controlling blood calcium and phosphate levels
and the specific effects of this hormone on its target tissues.
22. Factors
that controls the secretory activity of the parathyroid glands.
23. Comparison
of the parathyroid hormone and calcitonin in terms of their source and
function.
24. Describe the
cortex and medulla of the adrenals in terms of their histological structure,
function, location, and embryonic origin.
25. Layers of the
adrenal cortex in terms of each layer’s histological structure, the hormones
secreted, and the layer’s location.
26. Roles of the pituitary, hypothalamus, and kidney in regulation of
adrenocortical hormone secretion.
27. Functional relationship between the adrenal medulla and the nervous
system.
28. Adrenocortical hormones role in adrenomedullary function regulation.
29. Alone endocrine cells origin and location.
30. APUD system. Paracrine
(local) and distant regulation of human organs and systems.
31. Important skin’s functions and relation of them to its structure.
32. Major layers of skin and the basic tissue type that predominates in
each.
33. Cell types commonly found in the epidermis and description of their
structure, function, and location.
34. Layers of the epidermis of thick skin and description of the
distinguishing structural features of each.
35. Steps in the processes of epidermal cell renewal and keratinization in
relation to the epidermal layers.
36. Comparison of the 2 layers of the dermis.
37. Description of the important components of the skin derivatives.
38. Comparison of the 3 types of glands associated with the skin.
For a
multicellular organism survivement and maintainment its integrity in a varying,
often adverse condition, connective tissue, tissue fluid and plasma perform
important functions. They are stabilized by the coordinated regulatory activity
of the autonomic and endocrine systems, the latter including the diffuse
neuro-endocrine system proper. The autonomic nervous system utilizes conduction
and neurotransmitter release to transmit information; it is swift and localised
in the responses induced. The diffuse neuro-endocrine system uses only
secretion: Is slower and the induced responses are less localized because the
secreting neurotransmitteres can act on contiguous cells, on group of nearest
cells reached by diffusion or on distal cells via blood like hormones. The endocrine system proper comprising clustered
cells and discrete ductless glands producting hormones, is even slower and less
localised though its effects are specific and often prolonged. There regulatory
systemes over-lap is form and function, witn a gradation from the neural
autonomic system, through intermediate system proper.
Endocrine cells. The term " endocrine cells " is used in
relation to the cells that synthesize and secrete into the internal environment
of the body a particular hormone. In practice, the term endocrine cells is used
in relation to the secretory cells of the glands of internal secretion,
endocrine single cells and small clusters of them (such as neuroendocrine cells
in the respiratory system ), often combined in the diffuse endocrine system
(eg, enteral endocrine system - a set of all cells of the gastrointestinal
tract, producing biologically active substances regulatory nature). Endocrine
cells are usually found in close contact with blood capillaries. These
capillaries in the endocrine glands have a standard structure: fenestrovannoho
type of endothelium and a wide lumen and a continuous basement membrane .
Endocrine cells have a structure which is determined
by the chemical nature of a hormone synthesized them. For endocrine cells that
synthesize peptides and proteins well developed granular endoplasmic reticulum,
Golgi complex and protein secretory granules are typical. Well developed smooth
endoplasmic reticulum and numerous mitochondria with tubular and vesicular
cristae are typical for cells that synthesize steroid hormones. They also have
lipid inclusions.
The close interrelationship of the autonomic and
endocrine systems, both structural and functional, is exemplified by the
hypothalamus. Though conviniently considered separately, the autonomic, diffuse
neuro-endocrine and endocrine systems are really a single neuro endocrine
regulator of the metabolic activities and internal environment, providing
conditiones in which it can function successfully. There are, in addition to
endocrine glands and diffuse-endocrine system, other hormone producing cells
which form minor components of other systems and are describe with them.
Endocrine system
includes glands and cells, which have general functional feature – they secrete
specific substances called hormones into the circulation, which can regulate
different functions of organs and systems of the human organism. All endocrine
glands have general structural features: 1. they have no excretory ducts; 2.
they have very well developed blood network (capillaries); 3. cells of the
endocrine glands form special accumulations as
follicles, cords, trabeculae or clusters; 4.in
endocrine cells one can find special granules, which contain hormones.
Endocrine system is
classifying under following basic components:
I. Central regulatory formation of endocrine
system,
1. Hypothalamus
2. Hypophysis
3. Epiphysis
II. Peripheral endocrine glands
1. Thyroid gland
2. Parathyroid gland
3. Suprarenal gland: a) cortex, b)
medulla,
III. Organes, having both ehdocrine and non-endocrine
functions.
1. Gonads: a) testis, b) ovary.
2. Placenta
3. Pancreas
IV. Solitary hormone
producing cells.
1. APUD-cells (of nervous origin)
2.
Solitary hormone producing cells (not of nervous
origin).
Hormones as integrators
Hormones have
been defined as products of specialized tissues, which are carried by the blood
system to influence other cells, tissues and organs, or the organism as a whole. The integrative action of hormones consists in the
depression, activation or maintenance of cells other than, as well as,
themselves, as, for example, thyrotrophic hormone of the anterior lobe of the
hypophysis and thyroglobin. Some hormones affect certain organs and tissues
almost specifically, under certain conditions, and there are called target organs;
other hormones have a more general effect, which probably influences some basic
cell reactions about which little is known. The hormones may be secreted almost
as rapidly as they are formed (adrenal cortex), or they may be stored
intercellularly or extracellularly in the gland while the blood level is
maintained (insulin in the pancreatic islets, thyroglobulin in the thyroid
gland colloid). Hormones differ greatly in chemical composition, and include
proteins, polypeptides, modified amino acids, and steroids. Like certain drugs,
vitamins and trace elements, they may be effective in minute concentrations.
Tropic hormon - hormone whosetarget cells are other endocrine cells
(eg, endocrine cells of the anterior pituitary synthesizes and secretes into
the blood ACTH (adrenocorticotropic hormone). Targets for ACTH - endocrine
cells of the adrenal glands cortex, which synthesize glucocorticoids.
Releasing hormones ( releasing factors) [from Eng. releasing hormone
(releasing factor)] - group of hormones synthesized in neurons of the
hypothalamic region of the brain, which targets cells are endocrine cells of
the anterior pituitary (e.g. releasing hormone for synthesizing ACTH cells of
the anterior pituitary - corticoliberin).
Liberin - releasing hormone enhances the synthesis and
secretion of hormones related to endocrine cells of the anterior pituitary
(e.g. corticoliberin activates the secretion of ACTH from ACTH- synthesizing
endocrine cells of the anterior pituitary).
Statin - releasing hormone, unlike liberin inhibiting the
synthesis and secretion of hormones in target cells.
There are next main types of
hormones:
1) oligopeptides (e.g., neuropeptides
), polypeptides (e.g. , insulin );
2) glycoproteins (e.g. tyreotropin
);
3) steroids (such as aldosterone and
cortisol);
4) tyrosine derivatives (e.g.,
iodine-containing thyroid hormones : triiodothyronine - T3 and thyroxine - T4);
5) retinoic acid derivatives (e.g.
vitamin A);
6) eicosanoids ( arachidonic acid
metabolites).
Target cells. The target cell - cell that can record specific
presence of hormone using the receptors and may change mode of operation upon
binding of the hormone (ligand) to its receptor .
Ligand. The term " ligand " means a chemical
compound that binds to another chemical compound, usually with higher molecular
weight. In endocrinology context, the term "ligand" is used in
relation to hormone molecules that bind to specific receptors on their target
cells.
Receptor- high-molecular substance that specifically binds to a
specific ligand , such as a hormone. Receptors liy in glycocalix of target cell
or inside the cell. So, there are two classes of receptors -the nuclear and
membrane .
Membrane. Peptide receptor ligands (e.g., insulin, growth
hormone, different tropic hormones) are usually located in the plasma membrane
of the cell.
Nuclear . Receptors of steroid hormones (eg, glucocorticoids,
testosterone, estrogen ), tyrosine derivatives and retinoic acid have
intracellular localization.
Regulation of target cells
Depending on the distance from the
producer of the hormone to the target cells differentiated endocrine, and
paracrine and autocrine regulation may occur.
Variations of ligands influence on target cells . A - endocrine , B - paracrine , B - autocrine
Endocrine or dystant
regulation. Hormone secretion
occurs in the internal environment, the target cell may be from endocrine cells
arbitrarily far. The most striking example: the secretory cells of the
endocrine glands and hormones of which enter the general circulation system.
Paracrine regulation. Producers of biologically active substances and
target cells located nearby, hormone molecules reach target cell by diffusion
in the intercellular substance. For example, in the parietal cells of the
gastric glands secretion of H stimulates gastrin and histamine, and inhibits
somatostatin and prostaglandins, which are secreted by cells located nearby.
Autocrine regulation. In autocrine regulation cell which is producing the
hormone has receptors for the same hormone (i.e., cell- producing the hormone
at the same time is its own target). As an example of endothelins produced by
endothelial cells and affect the same endothelial cells; T- lymphocytes that
secrete interleukins, have different target cells, including T- lymphocytes.
Mechanisms of hormone action
Hormone molecule that circulates with blood
or lymph, "recognizes" its receptor on the surface of a target cell. Stereochemistry of the highly active center of
hormone molecule and its receptor configuration has decisive role in this
recognition. Here, as in several other vital processes of the body, under the
principle of "key" (hormone ) to " lock " (plasmolemma
receptor). Binding of hormone to the receptor causes a conformational (three-
dimensional) changes in receptor molecules, which, in turn, influences the
enzyme system of cell, including adenilat - cyclase. This enzyme adenylate
cyclase leads to conversion of ATP to cyclic adenosine monophosphate (cAMP).
Molecules of the last one act as a universal stimulator of cells
intracytoplasmic enzymes. It is characteristic that the effect of hormones can
manifest itself not only to strengthen but also in inhibition of cells and
systems. Note that for description of the
universal role of cAMP in the mechanism of hormones action american scientist
E. Sutherland in 1971 was awarded the Nobel Prize.
Interaction between the individual
links of the endocrine system, as well as between endocrinocytes and target
cells is based on the principle of
feedback. Effect of a hormone in the target cell leads to increased production
of certain chemicals. Increasing the concentration of the latter in the
internal environment is the signal to inhibition of endocrinocytes. Conversely,
reducing the concentration of hormone in the blood or lymph is an stimulus for
synthetic activity of endocrinocytes. The principle of feedback remains in
force in the case of depressing (inhibitory) effect of hormones on the target
organ.
All endocrine glands have several
common features of the structure :
1. they are ductless (have no
excretory ducts).
2. They have well-developed vascular
network, especially microcirculatory bed (capillaries of visceral type with
fenestrated endothelium and continuous basement membrane ).
3. Endocrine cells form
characteristic clusters in the form of follicles (vesicles), or trabeculae
(cords), or lobules. So, parenchyma of the gland has sufficient structural or
morphological units - follicles, trabeculae, lobules.
Hypothalmus
Hypothalmus is the highest centre of control and coordination of the
endocrine system. It controls and interprates all the visceral functions of the
organism and unites the endocrine mechanism of regulation with the nervous
regulation and especially with the sympathetic and parasympathetic parts of the
vegetative nervous system. The hypothalamus contains special neurosecretory
cells which are aggregated in nuclei (30 pairs of nuclei) which are grouped into anterior,
middle and posterior groups.
Endocrine function is related to the activities of specific
neurosecretory cells of the anterior and middle hypothalamus. Neurocytes of
posterior nuclei, to a lesser extent, of middle and anterior hypothalamus send
their processes in the sympathetic and parasympathetic nerve trunks to the
relevant objectives (targets), so, they provide nervous regulation of their
activities.
In the
hypothalmus region an eminentia medial is present which forms the neurogemal
centre of the hypothalamo-hypophysial system. It
is formed of ependyma (of individual specialized cells which differentiate to
from Tanicytes).
The tanicytes
are characterized by branched processes which contact with the primary
capillaries of the hypophysial portal system. The hypothalamo-adenohypophysial
system accumulates neurohormones called adeno-hypotrophin released by the
hypothalamus and which pass into the portal system of the hypophysis.
The hypothalamo-neurohypophysial system accumulates
nonapeptides which are released into the blood. The
anterior group of nuclei of the hypothalamus contains two main nuclei: 1) supraoptical nuclei- are formed
by large cholinergic neurosecretory cells which contain secretory granules both
in the perlkaryon and in the processes. The axons of these cells pass
through the medial eminentia and the infundibulum of hypothalamus into the
posterior lobe of the hypophysis. Here they form the terminal buds of Herring
on the wall of blood capillaries. These cells produce neurohormon-vasopressin
also called antidiuretic hormone which controls reabsorption of water in renal
tubules. In recent years it was also proved the important role of vasopressin
in the regulation of body temperature, the cardiovascular system activity, this
hormone is necessary for normal brain development.
2). Paraventricular
nuclei- are composed of a central and peripheral portion,
while the central part is formed of large cholinergic neurosecretory cells
whose axons pass into the posterior lobe of the hypophysis, the peripheral part is made of
small adrenergic neurosecretory cells whose axons pass into the medial
eminence. The cells of the central part release hormone oxytocin which
regulates contraction of the uterus and mammary gland smooth muscles.
In the medial group of nuclei small adrenergic cells are present which
produce adenohypophysotropic neurohormones by means of which the hypothalamus
regulates the activities of the adenohypophysis. These hormones are low
molecular oligopeptides which are divided into liberins (releasing factors) which stimulate the activity of
the anterior and medial lobes of the pitutary, and statins (inhibitory factors) which inhibit their activity.
Some of the important nuclei lie in the region of the tuber cinereum (nucleus arcuatus, nucleus
ventromedialis and nucleus dorsomedialis). The principle areas of
production of liberin and statin includes both ventromedial and arcuate nuclei,
small peptidoadrenergic cells of the paraventricular nuclei and analogous cells
of the grey periventricular matter, preoptic zone of the hypothalamus and
suprachiasmatic nuclei.
Common name of
liberins and statins is releasing factors. Liberins are physiological
antagonists of statins: the first stimulate and
the latest depress production and the output of pituitary hormones into
the bloodstream. Liberins and statins pass to the pituitary through portal
vein: axovasal synapses lie in the medial eminence (primary mesh) from which
blood is collected into the portal vein, which then forms secondary capillary
net in the adenohypophysis. Next liberins are known: folliliberin, lyuliberin,
somatoliberin, prolactoliberin, tyroliberin, melanoliberin, cortycoliberin, a
group of statins include somatostatin, and prolactostatin melanostatin. Names
of hormones of middle hypothalamic nuclei are formed of two parts: the first
part corresponds to the name of pituitary hormone that produces target cell
(e.g. folitropin, lutropin, somatropin), the second part includes the word
liberin, statin or - depending on the physiological action of hormones.
American scientists Tiymen R. and E. Shelley in 1977 were awarded by he Nobel
Prize for the discovery of hypothalamic liberins and statins.
The effects of various hypophyseal
hormones on target organs and the feedback mechanisms that control their
secretion. For definitions of abbreviations
The
hypothalamus begins to develop in the fourth or fifth week of embryogenesis in
the basement of the intermediate brain vesicle.
Hypothalamus
controls the visceral activites of organs by two mechanisms:
1) through its regulation of
hypohysial activity, it is called transadenohypophysial regulation,
2) by sending efferent impulses to
control sympathetic and parasympathetic nervous system. It is called
parahypophysial regulation
Hypophysis
Hypophysis is also known as pituitary
gland. The central endocrine organ whose function is the
regulation of a number of peripheral parts of the endocrine system (the so
-called pituitarydependent) as well as in the implementation of a direct impact
on a number of cells of nonendocrine nature. Pituitarydependent elements of
endocrine system are the thyroid, adrenal cortex, endocrine cells of gonads.
Among nonendocrine cells pituitary gland regulates lactocytes of mammary gland,
melanocytes, adipocytes , chondrocytes, testis spermatogonia and others.
Deposited in pituitary oxytocin and vasopressin - are hormoness that cause
contraction of the smooth muscle cells of the uterus and vascular wall.
There may be distinguished 3 lobes: anterior, medial and posterior. But
hystologically it is more convinient to divide it into adenohypophysis and
neurohypophysis due to the origin and structure. Such structures originate due
to the specific development of pituitary gland in embryogenesis. The pituitary
gland begins to develop in the fourth week of embryogenesis of epithelial and
neural primordia.
The epithelium
of the upper part of oral cavity forms a pouch-like structure which deepens in
direction to future brain and gives rise to adenohypophysis structures. The
distal portion is formed as a result of epithelium growth of the anterior wall
of pituitary pouch, intermediate lobe - from its posterior wall. Towards the
pituitary pouch intermediate brain vesicle produces outgrowth , which is
converted in the future into the funnel of the third ventricle of the brain.
Glia of the distal end of the funnel, growing, forms the neurohypophysis,
proximal part of the funnel becomes a pituitary stem. Adrenocorticotropocytes
in the pituitary gland appears on the fifth week of embryogenesis, cell
producers of other pituitary hormones later - at 13th weeks. By the time the baby is born pituitary
gland differentiation in general is completed. In the postnatal period phasing
of pituitary endocrinocytes activation is observed: in the early postnatal
period mainly somatotropocytes and tyrotropocytes cells are activated, in
puberty activation of gonadotropin-releasing adenocytes is predominant.
Development
of the adenohypophysis and the neurohypophysis from the ectodermal epithelium
of the oral cavity roof and from nerve tissue of the diencephalon floor.
Adenohypophys
is covered with fibrous capsule, parenchyma is represented by cords of
endocrine cells, surrounded by a network of reticular fibers, such fibers also
surround the capillaries with fenestrated endothelium and wide lumen of
secondary capillary network.
Endocrine
cells of the anterior lobe that synthesize peptide hormones contain elements of
granular endoplasmic reticulum, Golgi apparatus, numerous mitochondria and
secretory granules of different diameters. Cells are placed between blood
capillaries and secrete hormones here. They also receive some liberins and
statins from blood.
Specimen of cat pituitary stained with hematoxylin and
eosin. In the left part edenopituitary has typical trabecular arrangement of
adenocytes. Anterior and intermediate pars are separated by split.
1). Adenohypophysis includes the
pars anterior (distalis), intermedia and tuberalis.
2). Neurohypophysis includes the
pars posterior (nervosa).
Sometimes the pars intermedia is
cystic, as it is here. In this particular instance, the pars intermedia is
fused with the pars distalis to the left, and the lumen of Rathke's pouch has
disappeared. The split seen at the right is a fixation artifact; pars nervosa
is at the lower right
Adenohypophysis is highly
vascularized and consists of epithelial cells of varying size and shape
arranged in cords supported by a delicate skeleton of connective tissue. Each
trabecule (cord) is formed of gland cells (adenocytes) of 2 types. One
of them, arranged in perifery of trabecula and stained intensively with special
dies due to presence of secretory granules in it (chromophills).
And ofher type of cells arranged in middle part of trabecule, does not stains
intenslvely, without granules, so called chromophobic
cells.
The latter ones include:
1)
undifferentiated cambial cells, which is a reserve for the replacement of endocrinocytes
who completed their life cycle;
2) cells that
have entered the stage of differentiation, but have not yet accumulated in the
cytoplasm special hormone granules;
3) cells which
at the time of the pituitary gland taking for histological examination threw
their secretory granules outside the cytoplasm;
4) follicular
- stellate cells, whose function is still not clear. Clusters of follicular -
stellate cells can form microfollicular structure with deposition of secretory
products in the lumen of the follicles.
Some stains allow the recognition of cell types of the
pars distalis: chromophils (acidophils and basophils) and chromophobes. Gomori’s
trichrome stain. High magnification.
Pars distalis stained to show the 3
major types of secretory epithelial cells there:
- a = pale chromophobes
- b = blue basophil
- c = red acidophil
Notice
that these cells are characteristically in cord-like clumps. The clumps are
separated by a fine reticular fiber stroma (thin blue lines), where the blood
capillaries lie. All endocrine glands are highly vascularized, since secretions
go directly into capillaries (depending on the organ.) In endocrine glands the
endothelium of these vessel s is typically continuous and fenestrated.
Chromophilic cells are
divided into I) acidophils ahd 2) basophils.
I. Acidophils cells: or L-cells:
a). Somatotrophes - These are ovoid and usually
grouped alongcapillaries: they are largest and most abundant class of
adenohypophysial chromophils, secreting somatotropin. Ultrastruturally are seen
to contain numerous electron dense, spherical secretory phase, relatively small
amount of granular endoplasmic reticulum; the nucleus lies in central part of
the cell. Cells of similar fine structure characterize human eosinophilic
adenoma associated with acromegaly or gigantism.
Pale capillaries between clumps of
acidophils of pars distalis. At the left, on the lower edge of the sinusoidal
wall, is an elongate nucleus of an endothelial cell. EM would show that the
endothelium here is continuous and fenestrated.
Somatotropic
cell from the anterior
pituitary. Notice the numerous, middle-sized
osmiophilic spherical secretory
granules.
Electron
micrograph of a somatotroph (growth hormone–secreting cell) of a cat anterior
hypophysis. Note the numerous secretory granules, long mitochondria, cisternae
of rough endoplasmic reticulum, and Golgi complex. x10,270.
b). Mammotrophes-secreting
the polypeptide hormone prolactin are dominant in pregnancy and hypertrophy
during lactation. They are distinguished by their affinlty to dry erytrosinc
and azacarmine. Their granules are largest in any hypophysial cells (about
500-6OO nm in diameter). Their size is bigger in pregnant and lactating females
than that in non-pregnant females and males. The granules are evenly dense,
ovoid or fuse with lysosomes to form autophagic vacuoles, which degrade unused
granules. In active cells granular endoplasmic reticulum and a Golgi complex
are prominent.
II. Basophils or B-cells:
a). Thyrotrophes-secrete
TSH. They are also called B-basophils. They are elongate, polygonal and lie in
clusters towards the adenohypophysial centre. They usually form cellular cords,
which has no direct contact with capillaries. They are stained selectively with
aldehyde fuscin. Their small granules, peripheral and irregular, are less
electron dense than in other basophils: being 100-150 nm in diameter and among the
smallest granules in adenohypophysial cells.
Mammotroph from the anterior
pituitary. The secretory granules are sparse and eliptical.
b). Honadotropes-also
known as basophils are larger than thyrotrophs, are rounded and usually
situated next to capillaries. They have secretory granules with an affinity for
the periodic acid. In some cells, usually peripheral in lobe, granules are
stained in purple white, in others, more central, they are red, suggesting that
the former secrete FSH and latter LH. It is shown by latest researches that FSH
and LH may coincide in the same cell within the same secretory granules.
Gonadotropes has plevarphic nucleus and spherical granules about 200 nm in diameter, along with this
are present vesicular endoplasmilc reticulum and a well developed Golgi
complex.
Corticotropes are the
fifth group of chromophills. They are an intermediate cells due to their
possibility for staining. The identification of the cells which secrete
adrenocortlcotropin (ACTH) was difficult to achieve until it was realised that
a precursor molecule, pro-oplo-melanocortlcotropin, is cleared into a number of
different molecules including ACTH, B-lipotropIn and B-endorphin. The function
of latter two is unknown, although the opio-gelanocortlcotropin coaplex is also
synthesized in neurons of the central neurvous system and has neuromodulator
function. In human this precursor is glycosylated. Making the granules
PAS-positive. They are also basophilic. These cells are irregular in shape and
size and have short dendritic processes which are inserted along other
neighbouring cells. Their granules are also small (about 200 nm) and difficult to defect
under light microscope.
Chromatophobic cells are predominat cells in anterior
pituitary. They constitute the majority of the cells of the
adenohypophisis (principal cells). They appear to consist of a number of cells
of different types, including degranulated secretory cells of the types, stem
cells capable of giving rise to chromatophils and follicular cells containing numbers of lysosomes
and forming cells clusters around cystes of various sizes: cystes are often
present in the junctional areas with the neurohypophysis and are filled with a
PAS-positive substance of unkrown significance.
Pars intermedia is
a constituent of the anterior pitutary, being derived embryologically from the
cells lining the cavity of Rathkes porch. Pars intermedia has many B-cells and
follicles of chromatophobic cells surrounding PAS-positive colloidal material.
Adenocytes of these pars has capacity to produce proteins or mucous secretion,
which may be stored within adjoining cells. Secreting cells of pars intermedia
have granules containing either -endorphin of -endorphin scattered uniforalyz
these cells contain peptide hormone including ATCH, melanocyte-stimulating
hormone, lipocytestimulating hormone, which assigned to the APUD series, as are
other adenohypophysial secretory cells.
Pars tuberalis. This part
is remarkable for its large number of blood vessels, between which cords of
undifferentiated cells are admixed with some and cells. From pars tuberalis penetrates trabecules in anterior lobe. In
some cells of trabecules are found some basophilic granules, but secretion from
there cells only starts after signals from neurons.
Posterior lobe of
hypophysis or neurohypophysis. Neurohypophysis comprises the posterior lobe of the
pituitary and pituitary part of stalk. Neurohypophysis is mainly made up of ependymocytes (glial cells”) – pituicytes
(the origin of which is related cells which line the wall of the 3rd
ventricle of the brain). It contains also blood vessels, axons of the
hypothalamic- pituitary tract and their endings on blood capillaries (axo-vasal
synapses). Proper endocrine function pf piruicytes is yet unknown, they contain
numerous intermediate filaments, pigment granules and lipid inclusions. In contrast to the anterior pituitary, posterior
lobe (neurohypophysi ) is part of the brain.
Neurohypophysis contains axons and their endings, which belong to neurons with
large perikaryons. These neurons are located in the paraventricular and
supraoptical nuclei of the hypothalamus.
Pituicytes
have spinous processes and send them to adventocytes of blood vessels or basal
membranes of capillaries. Hormones vasopressin and oxytocin secreted by big
peptidocholinergic neurosecretory cells of anterior lobe of hypothalamus are
stored in neurohypophysis. Axons of this neurosecretory cells form the
hypothalamo-neurohypophysial tracts. ln posterior lobe of hypophysis, these
ends are called Herring’s bodies.
Section
of the pars nervosa. Most of the tissue is formed by axons. Herring bodies and
nuclei of pituicytes can be seen as well as erythrocytes (in yellow) within
blood capillaries. Mallory’s trichrome stain. High magnification.
Two pale pink Herring bodies, collections of secretion
in the pars nervosa of the pituitary. They represent accumulations of
neurosecretion within the axons of neurons whose cell bodies lie in the
hypothalamus of the brain.
Pineal gland
Epyphysis cerebri
participates in regulation of processes, which are characterized by rythmizm
and periodism e.g. ovario-menstrual cycle. Such cyclic functions which
keep on charping in their intensity depending upon day or night are called
Circa diem. The capability of epyphysis and regulate rhytmic functions is
assentuated by its capacity and release hormones under the stimulation of
light. The organ is covered with a thin connective tissue capsule from which
arise septas dividing the whole organ into lobules. There are two types of
cells arranged in lobules in the parenchyma:
1). pinealocytes
(endocrinocytus pinealis)
2). gliocytes
(gliocytus centrales)
Pinealocytes
are found towards the centre of the lobules. They are large neurosecretory
cells, containing a large nucleus and large nucleoli. From their bodies arise
long processes simular to dendrites, which undergo branching and intermediate
with the processes of gliocytes. The processes usually are directed towards
capillaries and undergo contact with them. The cells contain both granular and
agranular endoplasmic reticulum, mitochondria and Golgi complex. An organelles
of unusual structure made up of groups of microfibrils and perforated lamellae
may be present called "Canaliculate lamellar bodies". The terminal
buds of the processes of these cells contain aonaalnes and polypeptide
hormones, along with a neurotransmitter gama-amino-bityric acid.
There are two types of pinealocytes: 1) light ones, which contain light homogenous cytoplasm
and 2) dark ones, which contains acidophilic
inclusions.
These two cells are the functional diversity of a single cell. The cell also
contains well developed ribosomes and polysomes. The pinealocytes are separated
from one another by neurogial cells that reseable astrocytes in structure.
Their processes are directed towards the interlobular connective tissue septa.
The
pinealocytes produce a number of hormones. These hormones have chiefly
inhibitory actions on the endocrine system including pitutary, thyroid,
parathyroid, gonads, suprarenalis and pancreas. The hormones reach the
hypophysis through blood or cerebrospinal fluid.
Parenchyma of epiphysis with brain sends.
The epiphysis regulates the function of the gonads by releasing
serotonin. The pinealocytes also produce a class of hormones called
antigonadotropin, which decreases the secretion of luteinazing hormone from the
adenohypophysis. It also produces hormonal factors which increase the amount of
pottasium in blood (mineral metabolism). They produce as many as 40 types of regulatory
peptides-thyroliberin, lueliberin, tyrotropin and vasotocin etc.
Glandula thyroidea
Thyroid gland is peripheral pituitarydependent gland, which differs from all
other endocrine glands in that hormone storage is developed to the highest
degree and reflected morphologically most markedly.
The thyroid gland,
located in the cervical region anterior to the larynx, consists of two lobes
united by an isthmus. Thyroid gland is composed of numerous spherical
follicles. Each follicle consists of a simple epithelium of follicular cells
enclosing a central lumen filled with colloid, a gelatinous substance. In
typical sections, follicular cells range from squamous to low columnar; the
follicles have a variable diameter. It depends on thyroid gland stimulation.
A loose connective
tissue capsule that sends septa into the parenchyma covers the gland. These
septa gradually become thinner; they reach all the follicles, separated from
one another by fine, irregular connective tissue composed mainly of reticular
fibers. The thyroid is an extremely vascularized organ, with an extensive blood
and lymphatic capillary network surrounding the follicles. Endothelial cells of
these capillaries are fenestrated, as they are in other endocrine glands. This
configuration facilitates the passage of the hormones into the blood
capillaries.
Its
function is to synthesize the hormones thyroxine (T4) and
triiodothyronine (T3), which stimulate the rate of metabolism.
The
major regulator of the anatomic and functional state of the thyroid gland is
thyroid-stimulating hormone (thyrotropin), which is secreted by the anterior
pituitary.
Relationship between the
hypothalamus, the hypophysis, and the thyroid. Thyrotropin-releasing hormone
(TRH) promotes secretion of thyrotropin (TSH), which regulates the synthesis
and secretion of the hormones T3 and T4. In addition to
their effect on target tissues and organs, these hormones regulate TSH and TRH
secretion from the pars distalis and the hypothalamus by a negative-feedback.
Solid arrows indicate stimulation; dashed arrows, inhibition.
The morphologic appearance of
thyroid follicles varies according to the region of the gland and its
functional activity. Normally in man there is a preponderance of smaller over
larger follicles. But in certain conditions may increase in size, and the
external surface may be markedly irregular. In man the size the follicles
varies considerably from region to region, with corresponding differences in
the follicular cells and colloid. This has been attributed to cyclic states of
activity, which take place regionally rather than uniformly. In the thyroid of
animals other than man, the folicles are more uniform. In the rat and guinea
pigs the follicles on the periphery of the gland are larger than the more
central ones, and the colloid of the former is more basophile
Low power view of thyroid gland with
its characteristic colloid-filled follicles. This is the only endocrine gland
that typically stores its hormonal secretion extracellularly before releasing
it into the bloodstream.
The gland has
a thin capsule of connective tissue whose extension divide it into masses of
irregular form and size. The structural-functional
units of the gland are follicles, which are spherical vesicles of varying size
and filled with a cavity in the centre. If the thyroid gland is highly
active then the walls of the follicles forms many branched infoldings and the
contour of the follicle becomes stellated. In the cavity of the gland is
present colloid which has a protein called thyroglobulin.
Photomicrograph of a section of
thyroid and parathyroid glands. The thyroid is formed by thousands of spheres called
thyroid follicles. They are filled with a glycoprotein, the colloid, which
appears fragmented here because of an artifact. The parathyroid is separated
from the thyroid by a thin connective tissue capsule nad consists of cords. H&E stain. Low magnification.
The space between
the follicles is fullfilled by a stroma made up of delicate connective tissue
in which there are numerous cappillaries and lymphatics, along with large
number of nerve fibers. In these septas are found compactly arranged groups of
epitheliocytes along with lymphocytes and labrocytes (must cells).
Section of a thyroid showing the
follicles formed by a simple epithelium, containing colloid. H&E stain.
Medium magnification
Thyroid gland cells (thyrocytes). The thyroid epithelium rests on a basal lamina. The
follicular epithelium exhibits all the characteristics of a cell that
simultaneously synthesizes, secretes, absorbs, and digests proteins.
Normally, each follicle of the human
thyroid consists of an outer shell of gland cells thyrocytes that enclosed the
colloid. These cells are commonly low cuboidal,
and are in close relation with the connective tissue and its network of blood
and lymph capillaries. The epithelium of the gland varies in size and
arrangement, depending on age, sex, and season of the year, diet and certain
pathological processes. In general, it is believed that the epithelium is squamous when the gland is underactive
(hypo function), and columnar and folded when it is overactive (hyper function).
There are, however, so many exceptions that it is impossible to determine the
functional state of the gland in all cases through histological examination
along.
The
processes of synthesis and iodination of thyroglobulin and its absorption and
digestion. These events may occur simultaneously in the same cell.
The basal part of these cells is
rich in rough endoplasmic reticulum. The nucleus is generally round and
situated in the center of the cell. It is commonly spheroidal and poor in
chromatin, and contains one or more nucleoli. After stimulation of the gland
cells, the nucleus enlarges and stains more lightly. The apical pole has a
discrete Golgi complex and small secretory granules with the morphologic
characteristics of follicular colloid. Abundant lysosomes and some phagosomes
are found in this region. The cell membrane of the apical pole has microvilli
to be seen only in electron microscope. During functional activity of the
thyroid gland the number and length of this microvilli increase. Cisternae of
rough endoplasmic reticulum are dispersed throughout the cytoplasm.
Mitochondria, which are usually short, thin and rod-like in the human gland,
are more numerous in the apical portion of the cytoplasm.
The gland cells of any one follicle
are more or less uniform, though occasionally some columnar cells may be
present when most cells are cuboidal. Rarely, there may be “colloid cells” of
Langendorff with a dark picnotic nucleus and dense-staining, osmiophilic
cytoplasm. They are probably dead or dying cells.
EM of thyroid cell showing sparse
microvilli on the apical surface that lies next to the stored colloid in the
follicle.
Follicular cells or tyrocytes are found around the follicles and also in
the extrafollicular epithelium. In the follicles these cells form a single layer lying
on a basal membrane forming its outer boundary. Normally the cells are cuboidal
and the colloid in the follicles are distended with abundant colloid. When highly active -
the cells are columnar and colloid scanty. On the apical part of the cell
towards the colloid there is a layer of microvilli. Between neighboring cells
there are well developed polydesmosomal contacts and in mature follicles are
found lateral interdigitation amongst cells of the follicles. The cell shows
well developed organelles especially those concerned with the synthesis of
protein, granular endoplasmic reticulum, Goldgi apparatus, lisosomes,
microtubules, microfilaments etc.
Higher power of thyroid, showing
follicular epithelium, which varies from simple squamous to simple cuboidal in
height, depending on how distended the follicles are. Notice distended
capillaries between follicles.
Colloid. The lumen of the
follicles is normally filled with the characteristic material called colloid.
This is clear, viscous fluid whose consistency varies when the gland is in
different states of activity. It is optically and probably chemically homogenous, except for some
desquamated cells and, under certain conditions, some macrophages. The colloid is thus an active reservoir, which is in
a continual state of flux rather than an inert storage center. During
hypo function colloid becomes watery (liquid), foamy (frothy) and bad staining. During hyper function colloid becomes very dense and solid, well
staining.
Histophysiology
The thyroid is
the only endocrine gland whose secretory product is stored in great quantity.
This accumulation is also unusual in that it occurs in the extracellular
colloid. In humans, there is sufficient hormone within the follicles to supply
the organism for up to 3 months. Thyroid colloid is composed of a glycoprotein
(thyroglobulin) of high molecular mass (660 kDa)
This mechanism maintains
an adequate quantity of T4 and T3 within the organism.
Secretion of thyrotropin is also increased by exposure to cold and decreased by
heat and stressful stimuli.
Synthesis & Accumulation of Hormones by Follicular Cells
Synthesis and accumulation of
hormones take place in four stages: uptake of iodide from the blood, synthesis
of thyroglobulin, release of thyroglobulin, activation
of iodide and iodination of the tyrosine residues of myroglobulin.
1. The uptake of circulating
iodide is
accomplished in the thyroid by a mechanism of active transport, using die
iodide pump. This pump, located within the cytoplasmic membrane of the basal
region of the follicular cells, is readily stimulated by thyrotropin. The
uptake of iodide can be inhibited by such drugs as perchlorate and thiocyanate,
which compete with iodide.
2. The synthesis of
thyroglobulin is similar
to that in other protein-exporting cells. Briefly, the secretory pathway
consists of the synthesis of protein in the rough endoplasmic reticulum, the
addition of carbohydrate in the endoplasmic reticulum and the Golgi complex.
3. The release of
thyroglobulin from formed
vesicles at the apical surface of the cell into the lumen of the follicle.
4. During the activation of
iodide, iodide is
oxidized by thyroid peroxidase to an intermediate, which in turn combines the
colloid with the tyrosine residues of thyroglobulin. In contrast to the first
three processes, iodination of tyrosine residues bound to thyroglobulin takes
place, not inside the follicular cells, but in the colloid, in contact with the
membrane of the apical region of the cells.
5. Hormone exfusion to the
bloodstream.
It is postulated that
the union of the iodinated tyrosine is catalyzed by an enzymatic mechanism.
Thyroglobulin must have the correct spatial configuration for this process to
occur normally. When disease causes the production of abnormal amounts of
thyroglobulin, this process is blocked, resulting in deficient synthesis of
thyroid hormone. The process can also be blocked by drugs (e.g.,
propylthiouracil, carbamazole) that inhibit the peroxidase-catalyzed iodination
of thyroglobulin. Some forms of thyroid dysfunction are related to a genetic
deficiency of peroxidase or the iodide pump.
Liberation of T3 & T4
When stimulated by
thyrotropin, thyroid follicular cells take up colloid by a form of pinocytosis.
Folds of apical cytoplasm (lamellipodia) encircle a portion of colloid and
bring it into the follicular cell. The pinocytotic vesicles then fuse with
lysosomes. The peptide bonds between the iodinated residues and the
thyroglobulin molecule are broken by proteases in lysosomes, and T4,
T3, diiodotyrosine (DIT), and monoiodotyrosine (MIT) are liberated
into the cytoplasm. The free T4 and T3 then cross the
cell membrane and are discharged into the capillaries. MIT and DIT are not
secreted into the blood, because their iodine is removed as a result of the
intracellular action of iodotyrosine dehalogenase. The products of this
enzymatic reaction, iodine and tyrosine, are reused by the follicular cells. T4
is the more abundant compound, constituting 90% of the circulating thyroid
hormone, although T3 acts more rapidly and is more potent.
Thyroxine has a gradual effect, stimulating
mitochondrial respiration and oxidative phosphorylation; this effect is
dependent on mRNA synthesis. T3 andT4 increase the
numbers of both mitochondria and their cristae. Synthesis of mitochondrial
proteins is increased, and degradation of the proteins is decreased.
Most of the effects of
thyroid hormones are the result of their action on the basal metabolic rate;
they increase the absorption of carbohydrates from the intestine and regulate
lipid metabolism. Thyroid hormones also influence body growth and the
development of the nervous system during fetal life.
Thyroid Disorders & Hormone Synthesis
A
diet low in iodine hinders the synthesis of thyroid hormones, causing hypothyroidism. Thyroid hypertrophy as
a result of increased thyrotropin secretion causes the disorder known as iodine
deficiency goiter, which occurs widely in some regions of the world.
The syndrome of adult hypothyroidism, myxedema, may be the result of a number of diseases of
the thyroid gland, or it may be secondary to pituitary or hypothalamic failure. Autoimmune
diseases of this gland impair its function, with consequent hypothyroidism. In Hashimoto thyroiditis it is possible to detect antibodies
against thyroid tissue in the patient's blood. As with other autoimmune
malfunctions, Hashimoto disease is more common in women.
Children
who are hypothyroid from birth are
called cretins; cretinism is characterized by arrested
physical and mental development.
Hyperthyroidism, or thyrotoxicosis, may be caused by a variety
of thyroid diseases, of which the most common form is
Parafollicular cells
Another type of cell,
the parafollicular,
or C (clear) cell, is found as part
of the follicular epithelium. They are located in the wall of the
follicles, lying between basal parts of the two thyrocytes, but their apical
portions do not touch the lumen of the follicle. Parafollicular cells are
somewhat larger than thyroid follicular cells and stain less intensely. They
have a small amount of rough endoplasmic reticulum, long mitochondria, and a
large Golgi complex. The most striking feature of these cells is their numerous
small (100-180 nm in diameter) granules containing hormone. These cells are
responsible for the synthesis and secretion of calcitonin, a hormone whose main effect is to lower
blood calcium levels by inhibiting bone resorption. Secretion of calcitonin is
triggered by an elevation in blood calcium concentration.
Parafollicular
cells called calcitoninocytes. The cells are polyhedral, with oval excentric nuclei.
They lie between the follicular cells and their basement membrane. They may,
however, lie between adjoining follicular cells, but do not reach the lumen.
They may also be arranged in groups within the connective tissue septa.In size
they are very large cells, do not absorb iodine but synthesize neuroamin
noradrenalin and serotonin by means of decarboxylation of tyrosine and
5-hydroxytryptophan with formation of hormone called calcitonin and
somatostatin. The cytoplasm is filled with oxyphilic and acidophilic secretory
granules. The cell shows well developed endoplasmic reticulum (granular), Golgi
complex, mitochondria. They contain small but strongly osmiophilic
granules-release calcitonin. Those which contain large but weakly osmiophilic
granules-release somatostatin. Calcitonin
believes as an anta-gonist to the hormone of parathyroid gland and decreases
calcium ions in the blood.
High
magnification of a section of a thyroid. Calcitonin-producing parafollicular
cells can be distinguished from the follicular epithelial cells because they
are larger and their nuclei stain lighter. H&E stain. High magnification.
Electron
micrograph of thyroid showing 2 calcitonin-producing parafollicular cells and
part of a thyroid follicle. Note 2 blood capillaries at both sides of the
parafollicular cells.
Electron
micrograph of a calcitonin-producing cell. Note the small secretory granules
(SG) and the scarcity of rough endoplasmic reticulum (RER). G, Golgi region.
x5000.
Parathyroid glands
The parathyroids
(peripheral pituitary independent glands) are four small yellow-brown, oval glands—3 x 6
mm—with a total weight of about
The human parathyroid glands, viewed from behind.
Each parathyroid gland
is contained within a connective tissue capsule. These capsules send septa into
the gland, where they merge with the reticular fibers that support elongated cord-like clusters of secretory
cells.
The parenchyma of the
parathyroid glands consists of densely packed groups of two types of cells: the
chief, or principal, cells and the oxyphilic cells, which may form a continuous mass of cells
or may be arranged as anastomosing cords, or less commonly as follicles with a
colloidal material in their lumen.
Low power
of parathyroid, showing a somewhat lobulated appearance and considerable
adipose tissue intermingled with secretory portions.
The chief (principal) cells are the more numerous
and probably the more important. They are small polygonal cells with a
vesicular centrally placed nucleus and a pale-staining, slightly acidophilic
cytoplasm. The
mitochondria are filamentous to granular and sometimes are close to the
nucleus. The Golgi apparatus is short and situated close to the nucleus, with
no evidence of vascular polarity. The cytoplasm is rich in glicogen and
contains numerous fat droplets. Electron microscopy shows irregularly shaped
granules (200-400 nm in diameter) in their cytoplasm. They are the secretory
granules containing parathyroid hormone, which is a polypeptide in its active
form.
Oxyphilic cells are larger polygonal
cells; their cytoplasm contains many acidophilic mitochondria with abundant
cristae. The
nucleus is smaller and darker-staining, embedded in a deeply staining cytoplasm
crowded with granular mitochondria. There is a little or no demonstrable
glycogen or fat in most oxyphile cells. The function of the oxyphil cells is
not known.
With increasing age,
secretory cells are replaced with adipocytes. Adipose cells constitute more
than 50% of the gland in older people.
The parathyroid glands
show certain changes with increasing age:
1.
Increase in amount of connective tissue, including increased number of
fat cells as well as mast cells;
2.
The oxyphilic cells are said to appear at four and one half to seven
years, and to increase in number especially after puberty;
3.
In the closely packed masses of gland cells, some cords and follicles
appear in the year-old infant and increase thereafter; colloidal accumulation
in the lumen of the follicles shows the same tendency.
Histophysiology
Parathyroid
hormone binds to receptors in osteoclasts. This is a signal for these cells to
produce an osteoclast-stimulating factor, which increases the number and
activity of osteoclasts and thus promotes the absorption of the calcified bone
matrix and the release of Ca2+ into the blood. The resulting
increase in the concentration of Ca2+ in the blood suppresses the
production of parathyroid hormone. Calcitonin from the thyroid gland also
influences osteoclasts by inhibiting both their resorptive action on bone and
the liberation of Ca2+. Calcitonin thus lowers blood Ca2+
concentration and increases osteogenesis; its effect is opposite to that of
parathyroid hormone. These hormones constitute a dual mechanism to regulate
blood levels of Ca2+, an important factor in homeostasis.
In addition to
increasing the concentration of Ca2+, parathyroid hormone reduces
the concentration of phosphate in the blood. This effect is a result of the
activity of parathyroid hormone on kidney tubule cells, diminishing the absorption of phosphate and causing an increase of
phosphate excretion in urine. Parathyroid hormone indirectly increases the absorption of Ca2+ from the
gastrointestinal tract by stimulating the synthesis of vitamin D, which
is necessary for this absorption. The secretion of parathyroid cells is
regulated by blood Ca2+ levels.
In hyperparathyroidism, concentrations of
blood phosphate are decreased and concentrations of blood Ca2+ are
increased. This
condition frequently produces pathologic deposits of calcium in several organs,
such as the kidneys and arteries. The bone disease caused by hyperparathyroidism,
which is characterized by an increased number of osteoclasts and multiple bone
cavities, is known as osteitis fibrosa
cystica. Bones from patients with osteitis fibrosa cystica are less resistant
and prone to fractures.
In hypoparathyroidism, concentrations of
blood phosphate are increased and concentrations of blood Ca2+ are
decreased. The bones
become denser and more mineralized. This condition causes spastic contractions
of, the skeletal muscles and generalized convulsions called tetany. These symptoms are caused by
the exaggerated excitability of the nervous system, which is due to the lack of
Ca2+ in the blood. Patients with hypoparathyroidism are treated with
calcium salts and vitamin D.
The functional significance of this gland lies in the regulation of
calcium metabolism. It produce a hormone called parathyrohormone which causes
the release of calcium from bones into the blood. I.e, hypercalcification and
demineralization of bones. The parathormone increases serum calcium by three mechanisms:
1). Increases bone resorption
through stimulation of osteoclastic activity,
2). Insreases calcium reabsorption
from the renal tubules (inhibiting phosphate resorption).
3), Enchancing calcium absorption
from the gut.
There are four
parathyroid glands as a rull. Each gland is covered with a connective tissue
capsule from which some septa extend into the gland substance.
Within the gland a network of
reticular fibres support specialized cells called endocrinocytus
parathyroideus. The parenchyma of the gland is made up of cells that are
arranged in cords, wlth numerous fenestrated capillaries lying in close
relationship to them. Between neighbouring cells there are well developed
desmosomal contacts and interdigitation.
There are two types of cells:
1) Endocrinocytus
principalis
(chief cells) - cytoplasm basophllic, densly collected ribosomes toward the
periphery, which shows a very high activity of the cell (protein synthesis).
Golgl complex highly developed with flattened vesicles and cisternaes, giving
rise to secretory granules 150-200 nm. Mitochondria abundant and of elongated form with
transversaly arranged cristae. The chief cells are divided into light and dark
cells depending upon their state of activity and glycogen contect,
2) Endocrinocytus
oxyphilicus
are found in lesser number and appear only a little before puberty. Their
cytoplasm is densely packed with mitochondria. True secretory granules are
absent. The division of the cells is not based on any morphological difference
but on maturation or functional stapes. Both active and inactive cells contain
glycogen, however the number of inactive cells is more in normal conditions
then active cells. This gland is not under any regulation of hypophysis for its
secretions but works on the basic of concentration of calcium in blood. Its
activity increses under hypocalcification and decreases with
hypercalcification. Parathyrocytes carry receptors which can directly measure
the amount of calcium in the blood.
Section
of a parathyroid gland showing the chief cells of the gland arranged as cords
separated by blood capillaries. H&E stain. Medium magnification.
Parathyroid
at higher power, showing that the cells are actually tightly packed epithelial
cords. The larger, pale pink cells in the middle and to the right are oxyphil
cells; they have a smaller, darker nucleus and relatively larger amount of
cytoplasm than the majority of cells, which are called chief cells (to the left
in the photo). The chie f cells secrete parathormone; the significance of the
oxyphil cells is not clear.
Photomicrograph of a section of a
parathyroid gland. Note a group of large, acidophilic oxyphil cells at the right.
Medium magnification.
Adrenal glands
Glandula suprarenalis is a palsed yellowish
organ formed by the union of two independent hormon producing glands,
comprising of cortex and medulla of different origin, regulatory and
phisiological significance, situated on the superior renal pole. The adrenal
glands are paired organs, which lie near the superior poles of the kidneys,
embedded in adipose tissue. They are flattened structures with a half-moon
shape; in the human, they are about 4-
Examination of a fresh section of adrenal gland shows
it to be covered by a capsule of dense connective tissue. The gland consists of
two concentric layers: a yellow peripheral layer, the adrenal cortex;-and a
reddish-brown central layer, the adrenal medulla. Outside the glands are covered by connective
tissue capsule,which Is divided into two layers-outer (dense) and inner
(loose). Cortex-shows three cellular zones. Under the capsule lies a thin
striated layer of small epithelial cells, whose division participates in
regeneration of cortex. The endocrinocytes corticalls forms an epithelial layer
which is oriented perpendicularly to the surface of the gland. The three
principal cellular zones of the glands are:
1) zona glomerulosa
2) zona fasclculata
3) zona reticularis
Adrenocortical tissue is shown stippled; adrenal medullary tissue is shown
black. Note the location of the adrenal glands at the superior pole of each
kidney. Also there are shown extra-adrenal sites where cortical and medullary
tissues are sometimes found.
The adrenal cortex and the adrenal medulla can
be considered two organs with distinct origins, functions, and morphologic
characteristics that unite during embryonic development. They arise from
different germ layers. The cortex arises from coelomic intermediate mesoderm;
the medulla consists of cells derived from the neural crest, from which sympathetic
ganglion cells also originate. The general histologic appearance of the
adrenal gland is typical of an endocrine gland in which cells of both cortex
and medulla are grouped in cords along capillaries.
Feedback mechanism of ACTH and
glucocorticoid secretion. Solid arrows indicate stimulation; dashed arrows,
inhibition. CRH, corticotropin-releasing hormone, ACTH, corticotropin.
The connective tissue capsule that covers the adrenal
gland sends thin septa to the interior of the gland as trabeculae. The stroma
consists mainly of a rich network of reticular fibers that support the
secretory cells.
Blood Supply
Several arteries that enter at various points around their periphery supply
the adrenal glands. The three main groups are the superior suprarenal artery, arising from the
inferior phrenic artery; the middle suprarenal
artery, arising from the aorta; and the inferior suprarenal artery, arising from the
renal artery. The arterial branches form a
subcapsular plexus from which arise three groups of vessels: arteries of the
capsule; arteries of the cortex, which branch repeatedly to form the capillary
bed between the parenchymal cells (these capillaries drain into medullary
capillaries); and arteries of the medulla, which pass through the cortex before
breaking up to form part of the extensive capillary network of the medulla.
A dual blood supply provides the medulla with
both arterial (via medullary arteries) and venous (via cortical arteries) blood. The capillary endothelium is extremely attenuated and interrupted by
small fenestrae that are closed by thin diaphragms. A continuous basal lamina
is present beneath the endothelium. Capillaries of the medulla, together with
capillaries that supply the cortex, form the medullary veins, which join to
constitute the adrenal or suprarenal vein.
Adrenal Cortex
Because of the differences in disposition and
appearance of its cells, the adrenal cortex can be subdivided into three
concentric layers that are usually not sharply defined in humans: the zona
glomerulosa, the zona fasciculate, and the zona
reticularis. These zones occupy 15%, 65%, and 7%,
respectively, of the total volume of the adrenal glands.
I). Zona glomerulosa is
found in outer region (subcapsular zone) of the gland. It is
formed of small, polyhedral cells (endocrinocytes)
arranded in rounded groups or convoluted columns, with duply staining nuclei,
scanty basophllic cytoplasm with lipid droplets (very few). The cytoplasm
displays many microtubules, large mitochondria and agranular endoplasmic reticulum.
The mitohondria is characterized by lamellated cristae. The agranular
endoplasmic reticulum is represented by small vesicles, between which are
located ribosomes: characteristics of steroid producing cells. The Golgi
apparatus is developed very well. The cells secrete hormone - aldosterone -
mineral - corticold hormone, which affects electrolyte and water balance.
Between the zona glomerulosa and fasciculata a narrow layer of nonspecialized
cells is found. This layer is called intermediate or sudanphobic zone. The
division of cells in this layer participates in the regeneration of reticular
and fascicular zones. The zona glomerulosa is poorly developed in human beings.
2). Zona fascilulata -
consist of large polyhedral cells with basophillc cytoplasm arranged in
straight columns, two cells wide, with parallel fenestrated venous capillaries
between them. The cytoplasm contains vany lipid droplets, phospholipids, fats,
fatty acid, cholesterol embedded in complex agranular endoplasmic reticulum.
The mitochondria are
typically spherical with tubular cristae, the Colgl complex is extensive. The
side of the cells feeing the blood capillaries contains a layer of microvillis.
The granular endoplasmic reticulum is well developed. Ribosomes lie freely in
the cytoplasm. Along with light coloured cells are found dark colored cells
which contain small atount of lipids, but high amount of ribonucleoprotein. In
the dark cells are found well developed agranular endoplasmic reticulum and
granular endoplasmic reticulum. The light and dark cells represent different
functional entities of the endocrinocytes. The dark cells are concerned with
the formation of enzymes which participate in formation of corticosteroid.
Affer secretion of steroid the cell becomes light in color and prepares for the
release of secretion into the blood. Cells of this zone produce glucocorticoid
hormone - corticosterone, cortizon and cortisol (hydrocortizon). These hormones
maintain the carbohydrate balance in the body.
Apart from it, it
controls the guantity of protein and lipids, increases the process of
phosphorylation in the body, leading to the formation of matter, rich in energy
which is released for maintaing the basic processes of life support
glucocorticoid helps in the process of gluconeogenes i.e. formation of glucose
from protein and the deposition of glycogen in liver and myocardium and
mobilization of tissue protein.
High concentratioh of
glucocorticoid causes destriction of lymphocytes and eosinophils in the blood,
causing lymphocytopenia and erytrocytopenia which causes changes in
inflammatory responses of body.
3). Zona retlcuaris
contains branching, interconnected columns of round cells whose cytoplasm
consist of large deposits of agranular endoplasmic reticulum, lysosomes and
pigment bodies which may indicate degenerative processes. The cristae of
mitochondria are tubular in shape. The endoplasmic reticulum is primarily made
up of vesicules with large amount of ribosomes. The cells secrete sex hormones
- progesterone, oestrogen and androgen. However the formation of testosterone
and other androgenic hormones dominate over the development of female hormones.
Between the reticular
zone and the medulla is found a zone of highly acidophilic cells called X-zone.
Adrenal medulla is composed of groups and columns of phacochromocytes seperated
by wide fenestrated capillaries. The chromaffin cells (chromaffinocytes)
synthesis and expel adrenalin and noradrenalln into the sinusoids.
There are two types of
chromaffinocytes depending upon their secreations. Light coloured ones called
epinephrocytes, dark coloured ones norepinephrocytes. The cytoplasm of the cell
is filled with secretory granules of 100-500 nm in diameter. The granules are
filled with protein-kateholamine. In noradrenalin containing cells, the
vesicles are round or elipsold while in adrenalin containing cells, the
vesicles are paler.
Specimen of adrenal gland.
Stained with haematoxylin and eosin.
References. The layer
immediately beneath the connective tissue capsule is the zona
glomerulosa, in which the columnar or
pyramidal cells are arranged in closely packed, rounded, or arched clusters surrounded by
capillaries. The nuclei stain deeply, and the rather scanty cytoplasm contains
basophilic material, which may be diffuse or, as in man, disposed in clumps.
Lipid droplets, when present, are scarce and small in most animals, and may be
numerous in others.
Mitochondria may be filamentous (in man), rodlike (in
the guinea pig and cat), or spherical in the rat. The compact Golgi apparatus
is juxtanuclear and may be polarized toward the capillary surface in some
animals.
The next layer of cells is known as the zona
fasciculata because of the arrangement of the cells in
straight cords, one or two cells thick, that run at right angles to the surface
of the organ and have capillaries between them. The cells of the
zona fasciculata are polyhedral, with a great number of lipid droplets in their
cytoplasm. As a result of the dissolution of the lipids during tissue
preparation, the fasciculata cells appear vacuolated in common histologic
preparations.
This is the region, which may contain mitotic figures.
The mitochondria appear generally to be less numerous than in the outer
cortical zone. The Golgi apparatus is juxtanuclear, and in some animals appear
to be somewhat less compact than in the zona glomerulosa.
The zona reticularis, the innermost layer of the cortex, lies between the zona fasciculata and
the medulla; it contains cells disposed in irregular cords that form an
anastomosing network. These cells are smaller than those of the other two
layers. Lipofuscin pigment granules in the cells are large and quite numerous.
The cytoplasm contains fewer lipid droplets. Toward the medulla there is
variable number of “light” cells and “dark” cells which differ in their
staining affinities. The nuclei of the light cells are pale-staining, while
those of the dark cells are shrunken and hyperchromatic. Mitochondria are few
in the former and numerous in the latter. The Golgi apparatus is compact or
fragmented. The dark cells contain clumps of yellow or brownish pigment. Some
as degenerating cells regards both the light and dark cells. Irregularly shaped
cells with picnotic nuclei—suggesting cellular degradation—are often found in
this layer. Cells of the adrenal cortex have the typical ultrastructure of
steroid-secreting cells.
Fine structure of 2
steroid-secreting cells from the zona fasciculata of the human adrenal cortex.
The lipid droplets (L) contain cholesterol esters. M, mitochondria with characteristic
tubular and vesicular cristae; SER, smooth endoplasmic reticulum; N, nucleus;
G, Golgi complex; Ly, lysosome; P, lipofuscin pigment granule. x25,700.
Histophysiology
Cells of the adrenal cortex do not store their
secretory products in granules; rather, they synthesize and secrete steroid
hormones only upon demand. Steroids, being low-molecular-weight lipid-soluble
molecules, can freely diffuse through the plasma membrane and do not require
the specialized process of exocytosis for their release.
The steroids secreted by the cortex can be
divided into three groups, according to their main physiologic actions:
glucocorticoids, mineralocorticoids, and androgens. The zona
glomerulosa secretes mineraloeorticoids, primarily aldosterone, that maintain electrolyte (eg, sodium and
potassium) and water balance. The zona fasciculata secrete
the glucocorticoids cortisone and cortisol or, in
some animals, corticosterone; these glucocorticoids regulate carbohydrate,
protein, and fat metabofisrn. The zona reticularis
produce androgens and perhaps estrogens
in small amounts.
The location of the enzymes participating in
aldosterone synthesis has been determined through differential centrifugation.
The synthesis of cholesterol from acetate takes place in smooth endoplasmic
reticulum, and the conversion of cholesterol to pregnenolone takes place in the
mitochondria. The enzymes associated with the synthesis of progesterone and
deoxycorticosterone from pregnenolone are found in smooth endoplasmic
reticulum; those enzymes that convert deoxycorticosterone →
corticosterone → 18-hydroxycorticosterone → aldosterone are located
in mitochondria - a clear example of colaboration between two cell organelles.
The glucocorticoids, mainly cortisol
and corticosterone, exert a profound effect on the metabolism of carbohydrates,
as well as on that of proteins and lipids. In the liver, glucocorticoids
promote the uptake and use of fatty acids (energy source), amino acids (enzyme
synthesis), and carbohydrates (glucose synthesis) that are used in
gluconeogenesis and glycogenesis (glycogen assembly). These hormones can
stimulate the synthesis of so much glucose that the resulting high levels in
the blood produce a condition similar to diabetes mellitus. Outside the liver,
however, glucocorticoids induce an opposite, or catabolic, effect on peripheral
organs (eg, skin, muscle, adipose tissue). In these structures, glucocorticoids
not only decrease synthetic activity but also promote protein and lipid
degradation. The by-products of degradation, amino and fatty acids, are removed
from the blood and used by the synthetically active hepatocytes.
Glucocorticoids also suppress the immune response by
destroying circulating lymphocytes and inhibiting mitotic activity in
lymphocyte-forming organs.
The mineralocorticoids act mainly on the
distal renal tubules as well as on the gastric mucosa and the salivary and
sweat glands, stimulating the absorption of sodium. They may increase the
concentration of potassium and decrease the concentration of sodium in muscle
and brain cells.
Dehydroepiandrosterone is the only sex
hormone that is secreted in significant physiologic quantities by the
adrenal cortex. It has virilizing and anabolic effects, but it is less than
one-fifth as potent as testicular androgens. For this reason, and because it is
secreted in small quantities, it produces a negligible physiologic effect under
normal conditions.
As in other endocrine glands, the adrenal cortex is
controlled initially through the release of its corresponding releasing hormone
stored in the median eminence. This is followed by secretion of
adreno-corticotropic hormone, or corticotropin (ACTH), which stimulates the
synthesis and secretion of cortical hormones (eg, glucocorticoids). Free
glucocorticoids may then inhibit ACTH secretion. The degree of pituitary
inhibition is proportionate to the concentration of circulating
glucocorticoids; inhibition is exerted at both the pituitary and hypothalamic
levels.
Adrenal Medulla
The adrenal medulla is composed of polyhedral
parenchymal cells arranged in cords or clumps and supported by a reticular
fiber network. A profuse capillary supply intervenes between adjacent cords,
and there are a few parasympathetic ganglion cells. Medullary parenchymal cells
arise from neural crest cells, as do the postganglionic neurons of sympathetic
and parasympathetic ganglia. Parenchymal cells of the adrenal medulla can be
regarded as modified sympathetic postganglionic neurons that have lost their
axons and dendrites during embryonic development and have become secretory
cells.
Medullary parenchymal cells have abundant
membrane-limited electron-dense secretory granules. These granules contain one
or the other of the catecholamines, epinephrine or nor-epinephrine. The
secretory granules also contain ATP, proteins called chromogranins (which may
serve as binding proteins for catecholamines), dopamine β-hydroxylase
(which converts dopamine to norepinephrine), and opiate-like peptides
(enkephalins).
A large body of evidence shows that two different
types of cells in the medulla secrete epinephrine and norepinephrine. Epinephrine-secreting
cells have smaller granules that are less
electron-dense, and their contents fill the granule. Norepinephrine-secreting
cells have larger granules that are more electron-dense;
their contents are irregular in shape, and there is an electron-lucent layer
beneath the surrounding membrane. About 80% of the catecholamine output of the
adrenal vein is epinephrine.
Diagram of an adrenal
medullary cell showing the role of several organelles in synthesizing the
constituents of secretory granules. Synthesis of norepinephrine and conversion
to epinephrine take place in the cytosol.
All adrenal medullary cells are innervated by
cholinergic endings of preganglionic sympathetic neurons. Unlike the cortex,
which does not store steroids, cells of the medulla accumulate and store their
hormones in granules.
Epinephrine and norepinephrine are secreted in large
quantities in response to intense emotional reactions (e.g., fright). Secretion
of these substances is mediated by the preganglionic fibers that innervate
medullary cells. Vasoconstriction, hypertension, changes in heart rate, and
metabolic effects such as elevated blood glucose result from the secretion and
release of catecholamines into the bloodstream. These effects are part of the
organism’s defense reaction to stress (the fight-or-flight response). During
normal activity, the medulla continuously secretes small quantities of these
hormones.
Medullary cells are also found in the paraganglia
(collections of catecholamine-secreting cells adjacent to the autonomic
ganglia) as well as in various viscera. Paraganglia are a diffuse source of
catecholamines.
Fetal, or
provisional, Cortex
In humans and some other animals, the adrenal gland of
the newborn is proportionately larger than that of the adult. At this early
age, a layer known as the fetal, or provisional, cortex is present between the
medulla and the thin permanent cortex. This layer is fairly thick, and its
cells are disposed in cords. After birth, the provisional cortex undergoes
involution while the permanent cortex—the initially thin layer—develops,
differentiating into the three layers (zones) described above. A major function
of the fetal cortex is the secretion of sulfate conjugates of androgens, which
are converted in the placenta to active androgens and estrogens that enter the
maternal circulation. This layer in adult has no lipid inclusions and can’t be
stained with
Regeneration of the adrenal gland
Cortical cells are particularly susceptible to injury.
They are replaced by mitosis probably throughout the cortex, with a greater
tendency for this to take place in the transition zone between zona glomerulosa
and zona fasciculata. Another layer of stem cells one can find between the
capsule and zona glomerulosa. Between zona reticularis and adrenal medulla is
situated X-zone, in which one can see cells with acidophilic cytoplasm.
Successful transplantation seems to require the presence of a capsule. It is
more successful also in totally adrenalectomized animals. The medulla does not
survive transplantation readily.
Adrenal Dysfunction
A common disorder of the adrenal medulla is pheochromocytoma, a tumor of its
cells that causes hyperglycemia and transient elevations of blood pressure.
These tumors can also develop in extramedullary sites.
Disorders of the adrenal cortex can be
classified as hyperfunctional
or hypofunctional. Tumors of the adrenal cortex can result in
excessive production of glucocorticoids (Gushing syndrome) or aldosterone (
Adrenocortical insufficiency (
Carcinomas of the adrenal
cortex are rare, but most are highly malignant. About 90% of these tumors
produce steroids associated with endocrine glands.
Students’ Practical
Activities:
Students must know and illustrate such histologic
specimens:
Specimen 1. Pituitary gland.
Stained with haematoxylin and eosin.
This speciment from a mid-line section through the
brain and cranial floor illustrates the pituitary gland in situ. The pituitary
is almost completely enclosed in a bony depression in the sphenoid bone, called
the sella turcica. The three major components of the gland, the anterior
pituitary, pars intermedia and the posterior pituitary, are easily seen at this
magnification. The posterior pituitary is connected to the hypothalamus by a
short stalk, the pituitary stalk. H & E section of hypophysis, with the
darker pars distalis on the left and the paler pars nervosa on the right. The
slit between the two parts is the remnant of Rathke's pouch. The very narrow
band of darker-staining cells along the right-hand margin of the slit is all
there is of the pars intermedia.
Illustrate and indicate: 1.Anterior pituitary (adenohypophysis). 2.Pars
intermedia. 3.Posterior pituitary (neurohypophysis).
Specimen 2. Pituitary gland.
Paraldegid and
Cells of the anterior
pituitary, chromophils and chromophobes, form cords of secretory cells, which
are surrounded by a rich network of sinusoidal capillaries. The cromophils are
subdivided into two groups, acidophils and basophils because of their staining
properties with a variety of histological methods. For example in speciment,
acidophils are stained orange and basophils are stained blue. The somatotrophs
and mammotrophs represent the acidophils of traditional light microscopy, the
basophils being the thyrotrophs, gonadotrophs and probably the corticotrophs
(which were formerly thought to be chromophobic). The chromaphobes are the
smallest cell in the anterior pituitary and contain few cytoplasmic granules;
they have little affinity for either acidic or basic dyes and probably
represent resting forms of chromophil cells.The cells of pars intermedia are
basophilic, form irregular clumps lying between the pars anterior and pars
posterior but tending to spill out into the neural tissue of the pars
posterior.
The posterior pituitary
contains the non-myelinated axons of neurosecretory cells, the cell bodies of
which are located in the hypothalamus. Cells called pituicytes similar in
structure and function to the neuroglial cells of the central nervous system
support the neurosecretory cells axons. Most of the nuclei seen in this
micrograph are those of pituicytes. A rich network of fine, fenestrated
capillaries pervades the posterior pituitary.
Pars distalis stained with H
& E. There are several purple basophils in the center and a good clump of
pink acidophils above them. Most of the rest of the cells, rather pale ones,
are the chromophobes.
Detail of the last picture with
purple basophils toward the bottom center, pink acidophils at top center, and
pale chromophobes scattered randomly. Very pale capillaries can be seen to the
immediate left and right of the central clump of cells, lying within the
delicate c.t. framework (stroma). Some secretion has collected in the center of
the p icture. Be sure to consult your handout chart from class for hormones
secreted and target organs affected.
Illustrate and indicate: 1.Adenohypophysis: a) acidophils; b) basophils; c)
sinusoidal capillaries. 2.Cells of the pars intermedia. 3. Neurohypophysis: a)
pituicytes; b) capillaries.
Specimen 3. Pineal gland.
Stained with haematoxylin and eosin.
At a low magnification it is
seen that pineal body is cowered by the connective tissue capsule, from which
the septas appear and divide the parenchyma onto the lobules. At a high
magnification let you find irregular shaped light cells with round shaped
nuclei – pinealocytes. They occupy the middle part of lobules. Glial cells are
smaller and have dark nuclei.
Illustrate and indicate: 1. Capsule. 2. Connective tissue septum. 3. Lobules.
4. Pinealocytes. 5.Neuroglial cells. 6. Pineal send.
Specimen 4. Thyroid gland.
Stained with haematoxylin and eosin.
The
thyroid gland consists of two lobes, connected by the isthmus and is lying in
the neck in front of the upper part of the trachea. The functional units of the
thyroid gland are the thyroid follicles, irregular, spheroidal structures. The
follicles are variable in size and contain a homogeneous, colloid material
which is stained pink in this preparation. The thyroid gland is enveloped in an
outer capsule of loose connective tissue. From the capsule, connective tissue
septa extend into the gland dividing the gland into lobules, and conveying a
rich blood supply, together with lymphatics and nerves.
Thyroid follicles are lined by a
simple cuboidal epithelium which is responsible for the synthesis and secretion
of the iodine-containing hormones T3 and T4. Thyroid
follicles are filled with a glycoprotein complex called thyroglobulin or
thyroid colloid, which stores the thyroid hormones prior to secretion. In
actively secreting thyroid glands, as in these spacement, the follicles tend to
be small and the amount of colloid diminished; the cuboidal lining cells are
relatively tall reflecting active hormone synthesis and secretion. Conversely,
the follicles of the less active thyroid are distended by stored colloid and
the lining cells appear flattened against the follicular basement membrane.
A second secretory cell type is
found in the thyroid gland either as single cells among the follicular cells or
as small clumps in the interfollicular spaces. These are so-called
parafollicular cells. Parafollicular cells synthesize and secrete the hormone
calcitonin in direct response to raised blood calcium levels.
Illustrate and indicate: 1.Capsule.
2.Connective tissue septa. 3.Thyroid follicles: a) simple cuboidal epithelium
(thyrocytes); b) thyroid colloid. 4.Parafollicular cells. 5.Capillaries.
Specimen 5. Parathyroid gland.
Stained with haematoxylin and eosin.
This micrograph shows a parathyroid
gland characteristically embedded in capsule of a thyroid gland. The thin
capsule of the parathyroid gland gives rise to delicate connective tissue
septa, which divide the parenchyma into dense, cord-like masses of secretory
cells. The septa carry blood vessels, lymphatics and nerves.
The parathyroid gland contains
secretory cells with two types of morphological characteristics:
1). Chief or principal cells: these
are the most abundant cells and are responsible for the secretion of
parathyroid hormone. Chief cells have a prominent nucleus and relatively little
cytoplasm which varies in staining intensity according to the degree of
secretory activity of the cell. Actively secreting cells contain much rough
endoplasmic reticulum and stain strongly; in contrast, inactive cells contain
little rough endoplasmic reticulum and stain poorly.
2). Oxyphilic cells: these are larger and much less
numerous than chief cells and tend to occur in clumps. They have smaller,
densely stained nuclei and strongly eosinophilic (oxyphilic) cytoplasm
containing fine granules. Few oxyphil cells are found in the human parathyroid
gland until puberty, after which they increase in number with age. Oxyphilic
cells do not secrete hormones except in certain pathological conditions and their
function is poorly understood.
Illustrate and indicate: 1.Connective
tissue septa. 2. Parathyrocytes. 4. Blood vessels.
Specimen 6. Adrenal gland.
Haematoxylin and Eosin.
The adrenal gland is seen to be divided into an outer cortex and a
pale-stained inner medulla. Capsule, invests the gland and provides external
support for a delicate collagenous framework supporting the secretory cells.
The adrenal cortex can be seen to consist of three histological zones which
are named according to the arrangement of the secretory cells: zona
glomerulosa, zona fasciculata, zona reticularis. The zona glomerulosa lying
beneath the capsule consists of short columnar cells closely packed in ovoid
groups or in columns which may form arcs. The zona fasciculata consists of
polyhedral cells considerably larger than those of the zona glomerulosa. They
are arranged as anastomosing “cords” of cells with a marked radial orientation,
extending between the zona glomerulosa and the reticularis. The zona
reticularis consists of an irregular network of branching cords and clumps of
glandular cells separated by numerous wide capillary sinusoids. The glandular
cells are much smaller than those of the adjacent zona fasciculata.
The adrenal medulla is composed of closely packed clumps of secretory cells
supported by a fine reticular network containing numerous wide capillaries. The
secretory cells of the adrenal medulla have large, granular nuclei and
extensive strongly basophilic cytoplasm.
Illustrate and indicate:1. Capsule; 2. Adrenal cortex: a) zona glomerulosa; b) zona fasciculata; c)
zona reticularis; 3. Adrenal medulla: a) chromaffin cells; b) sinusoidal
capillaries.
Specimen 2. Adrenal cortex.
Note that the cytoplasm of cells zona fasciculata is even richer in smooth
endoplasmic reticulum and lipid droplets that the zona glomerulosa and this may
confer a foamy appearance of the cells. In this specimen you see lipid droplets
in cells of zone fasciculata look like black drops of different sizes. Lipid
droplets of secretory cells of zona glomerulosa, when present, are scarce and
small. Cells of zona reticularis contain few lipid droplets, so cytoplasm
stains more strongly.
Illustrate and indicate: 1. Lipid droplets in the
cytoplasm of secretory cells of zona fasciculate.
REFERENCES:
A-Basic:
1.
Practical classes materials
http://intranet.tdmu.edu.ua/data/kafedra/internal/histolog/classes_stud/English/medical/III%20term/17%20Adrenal%20glands%20and%20diffuse%20endocrine%20system.%20Skin%20and%20its%20appendages.htm
http://intranet.tdmu.edu.ua/ukr/kafedra/index.php?kafid=hist&lengid=eng&fakultid=m&kurs=2&discid=Histology,
cytology and embryology
3. Stevens
A. Human Histology / A. Stevens,
J. Lowe. – [second
edition]. –Mosby, 2000. –
P. 264-274
4.
Wheter’s Functional Histology : A
Text and Colour Atlas / [Young B.,
Lowe J., Stevens A., Heath J.]. – Elsevier
Limited, 2006. – P. 338-341
5.
Inderbir Singh Textbook of Human
Histology with colour atlas / Inderbir Singh. – [fourth edition]. –
Jaypee Brothers Medical Publishers (P) LTD, 2002. – P. 193-206, 309-314,
6.
Ross M. Histology : A Text and Atlas
/ M. Ross W.Pawlina. – [sixth
edition]. – Lippincott Williams and Wilkins, 2011. – P. 780-784
B - Additional:
1.
Eroschenko V.P. Atlas of Histology
with functional correlations / Eroschenko V.P. [tenth edition]. –
Lippincott Williams and Wilkins, 2008. – P. 402-407
2.
Junqueira L. Basic
Histology / L. Junqueira, J. Carneiro, R. Kelley.
– [seventh edition]. –
3.
Charts:
http://intranet.tdmu.edu.ua/index.php?dir_name=kafedra&file_name=tl_34.php#inf3
4. Disk:
http://intranet.tdmu.edu.ua/data/teacher/video/hist/
5.
Volkov K. S. Ultrastructure of the
main components of body /
K. S. Volkov. – Ternopil : Ukrmedknyha, 1999. – P. 36-40, 84-88
http://intranet.tdmu.edu.ua/data/books/Volkov(atlas).pdf
http://en.wikipedia.org/wiki/Circulatory
http://www.meddean.luc.edu/LUMEN/MedEd/Histo/frames/histo_frames.html
http://www.udel.edu/biology/Wags/histopage/histopage.htm