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ENDOCRINE SYSTEM

June 16, 2024

Endocrine system

1. Neuro-endocrine-immune regulation.

2. Hormones and mechanisms of their activity.

3. Endocrine organs classification.

4. Central endocrine organs:

а) hypothalamus;

б) pituitary;

в) epiphysis.

5.Peripheral endocrine glands: thyroid, parathyroid, adrenal

For a multicellular organism to survive and maintain its integriti in a varying, often adverse gain connective tissue, tissue fluid and plasma, Is stabilised by the coordinated regulatory activity of the autonomic and endocrine systems, the latter including the diffuse neure-endocrlne system proper. The autonomic nervous system utilizes conduction and neurotransmitter release to transmit information, it is swift and localised in the responses induced. The diffused neuro-endocrine system uses only secretion: Is slower and the Iiduced responses are less localized because the secretions neurotransmitteres can act on contiguous cells on group of near by cells veached 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.

The close interrelationship of the autonomic and endocrine systems, 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 glands peculiarities

1. Stroma + parenchyma.

2. Endocrine cells.

3. Ductless glands.

4. Well developed microcirculatory bed with fenestrated capillaries

Endocrine system we can classify under folowing basic coponents:

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.

Hormones

1. Proteins derivatives

2. Especially active

3. Selective influence on “target-cells”

Mechanisms of hormones activity

1. Cell membrane permeability changes

2. Activation of intracellular processes.

3. Influence on the chromosomes

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. The hypothalamus contains special neurosecretory cells which are aggregated to from nuclei (30 pairs of nuclei) which are grouped into anterior, middle (medlobasilar and tuberal) and posterior groups.

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 maiuclei: 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. 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.

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. There may be distinguished 3 lobes: anterior, medial and posterior. But hystologically it is more convinient to divide it into adenohypophysis and neurohypophysis.

1). Adenohypophysis includes the pars anterior, intermedia and tuberalis.

2). Neurohypophysis includes the pars posterior.

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 due to presence of secretory granules in it (chromophills). And ofher type of cells arranged in middle part of trabecule, does not stains intenslvely, so called chromophobic cells.

Chromophilic cells are divided into I) acidophils ahd 2) basophils.

I. Acidophils cells: or L-cells:

a). Somatotropes – These are ovoid and usually grouped alongcapillaries: they are largest and most abundant class of adenohypophysial chromophils, secreting somatotropin. Ultrastruturally are seen to contaiumerous 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.

b). Mammotropes-secreting the polypeptide hormone prolactin are dominant in pregnancy and hypertrophy during lactation. They are distinguished by their affinlty to dry erytrosinc and azacarminc. 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). Thyrotropes-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 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.

b). Gonadotropes-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-opiomelanocortlcotropin, 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. They appear to consist of a number of cells of different types, including degranulated secretory cells of the types, stem and yong cells capable of giving rise to chromatophils and follicular cells containing numbers of lysosomes and forming cells clusters around cystes of various sizes (follicular stellate cells): 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 Rathke’s 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, 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. In the fora of releasing factors.

Posterior lobe of hypophysis or neurohypophysis, is mainly made up of ependymocytes. They have spinous processes on their body and are called pituicytes. Processes of pituicytes passes 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 ieurohypophysis. Axons of this neurosecretory cells form the hypothalamo-neurohypophysial bundles. ln posterior lobe of hypophysis, these ends are called Herrings body.

Pineal gland

Epyphysis cerebri participates in regulation of processes which are characterized by rythmizm and periodism eg 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 found in the parenchyma:

1). pinealocytes (endocrinocytus pinealis)

2). gliocytes (gliocytus centrales)

Pinealocytes are found towards the centre of the lobules. They are large neuroglial 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:

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. 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.

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).

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 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.

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.

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.

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 and 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.

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.

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 neuroamioradrenalin 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.

Parathyroid glands

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. Betweeeighbouring 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 iormal 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.

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.

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

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 rnitochondria and agranular endoplasmic reticulum. The mitohondria is characterised 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 non-specialized 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 acidophillic 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 elipsoid while in adrenalin containing cells, the vesicles are paler.

References:

A-Basic:

1. Practical classes materials

http://intranet.tdmu.edu.ua/data/kafedra/internal/histolog/classes_stud/English/medical/III%20term/16%20Endocrine%20%20system.htm

2. Lecture presentations

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. 251-264

4. Wheter’s Functional Histology : A Text and Colour Atlas / [Young B., Lowe J., Stevens A., Heath J.]. – Elsevier Limited, 2006. – P. 328-337

5. Inderbir Singh Textbook of Human Histology with colour atlas / Inderbir Singh. – [4^th edition]. – Jaypee Brothers Medical Publishers (P) LTD, 2002. – P. 299-309

6. Ross M. Histology : A Text and Atlas / M. Ross W.Pawlina. – [sixth edition]. – Lippincott Williams and Wilkins, 2011. – P. 740-780

B – Additional:

1. Eroschenko V.P. Atlas of Histology with functional correlations / Eroschenko V.P. [tenthedition]. – Lippincott Williams and Wilkins, 2008. – P. 383-401

2. Junqueira L. Basic Histology / L. Junqueira, J. Carneiro, R. Kelley. – [seventh edition]. – Norwalk, Connecticut : Appleton and Lange, 1992. – P. 410-443

3. Charts:

http://intranet.tdmu.edu.ua/index.php?dir_name=kafedra&file_name=tl_34.php#inf3