Physiology of blood vessels. Systemic circulation
PHYSIOLOGY OF VENOUS AND LYMPHATIC
SYSTEM. microcirculation
Regulation of blood CYRCULATION
Objectives for
Students’ Independent Studies
You should prepare for the practical class using the
existing textbooks and lectures. Special attention should be paid to the
following:
List:
1. Physiology of blood circulation
a). Common characteristic of blood flow
b).
Blood pressure
c).
Role of changing body position
d).
Local regulatory mechanisms
e).
Functional types of vessels
2. Physiology of venous and lymphatic system. Microcirculation
a).
Peculiarities of microcirculation and lymphatic system
b)
coronary cyrculation
b). Blood flow in veins
c). Lymphatic system
3.
Regulation of blood cyrculation
a). Local
regulation of blood flow
b).
Neuro-humoral regulation of systemic circulation
c).
Haemodinamic in special body conditions
d). Anatomic and
physiological properties of blood circulation system in fetus and children
e).
Condition of blood circulation in aged and old persons
Practical activities:
1).
Measuring arterial pressure by Korotkov’s method
2). Evaluation of arterial pulse
3).
Determination of functional condition superficial, perforant and deep veins4).
Test under the physical load
5). Analyses of electrocardiogram in
person of different age groups6). Sphygmogram – graph registration of arterial
pressure
1. Physiology of blood circulation
a). Common
characteristic of blood flow
The direct effect
of heart contraction is creation of certain level of blood pressure, which is
allows blood circulation.
Blood flow is
continuous, although heart pumps the blood by separate portions. It caused by
functioning of all components of cardio-vascular system: heart, arteries,
arterioles, capillaries, venuls and veins. Besides that continuous blood flow
is caused by extracardial factors as skeletal muscle contraction and pressure
gradient between abdominal and thoracic cavities. Cardiac output depends on
high, mass and area of human body surface. Cardiac output is regulated by
contractive activity of cardiac muscle; valve function of full value; blood
volume, vascular tonus, blood flow in capillaries; value of blood returning to
the heart. In general distribution of cardiac output between different organs
corresponds to its functional activity. Part of common blood supply, which
every organ gets, depends on necessity in O2 and substrates of
energy exchange. Average time of blood circulation measures 20-23 s.
Powers, which causes blood flow
Blood flows in
vessels from high pressure to low. Heart pumping causes initial pressure. The
highest pressure is large arteries ascending from the heart. Pressure in aorta
at the end of systole is 110-
Blood flow is continuous, although heart pumps the
blood by separate portions. It caused by functioning of all components of
cardio-vascular system: heart, arteries, arterioles, capillaries, venuls and
veins. Besides that continuous blood flow is caused by extracardial factors as
skeletal muscle contraction and pressure gradient between abdominal and
thoracic cavities. Cardiac output depends on high, mass and area of human body
surface. Cardiac output is regulated by contractive activity of cardiac muscle;
valve function of full value; blood volume, vascular tonus, blood flow in
capillaries; value of blood returning to the heart. In general distribution of
cardiac output between different organs corresponds to its functional activity.
Part of common blood supply, which every organ gets, depends on necessity in O2
and substrates of energy exchange. Average time of blood circulation measures
20-23 s.
Kinds of blood movements:
laminar
Turbulence
Functional importance of blood circulation
system.
Both pulmonary and systemic circulation,
compose entire system of blood circulation and function in correlation. The
right ventricle is responsible for blood pumping into pulmonary circulation.
Here blood is oxygenated and CO2 is taken out. The left ventricle
pumps blood into systemic circulation. Blood flow in this part of vascular
system provides performing of all other blood functions as regulatory,
protective, excretory and others. Both right and left parts of heart pump equal
portions of blood into corresponding vessels and function in interconnection to
each other. The minute blood volume in pulmonary and systemic circulation is
the same.
Circulating blood volume
Blood flowing in
vessels is similar to stream of fluid in the pipe, but has a lot of
specificities. Fluid stream in the pipe is described by formula:
Q= (P1-P2)/R,
where
Q - fluid volume,
P1 -
pressure in the beginning of the pipe,
P2 -
pressure in the end of the pipe,
R - peripheral
resistance of the pipe.
So fluid volume,
which flows through the pipe is directly proportional to pressure difference
from the end to beginning of pipe; and inversely proportional to peripheral
resistance of pipe. As vessels have elastic walls, the blood flow in it, is
differ from the same in pipe. Vessel cross-section may change due to neural and
endocrine influences according to necessity.
Blood volume
flowing through every part of vascular system per time unit is the same. It
means that through aorta or cross-section of all arteries, capillaries or veins
flows equal volume of blood. This volume per minute is called minute blood
volume and measures in adults in rest 4.0 - 6.5 l/min.
Peripheral resistance of vessels
Peripheral
resistance in vessels according to Poiseuille's formula depends on length of
vessels (l), viscosity of blood (η) and cross-section of vessel (r):
R= 8lŋ/πr.
In accordance to
this formula the highest peripheral resistance might be in the smallest
vessels. In reality the highest resistance is observed in arterioles. Average
blood flow resistance in adults is equal to 900-2500 din·s/sm5
Paradoxes of blood flow.
In capillaries
blood flow resistance is a bit lower because of such mechanism. In capillaries
blood cells move one after another, dividing only by plasma, which decreases
friction between blood cells and capillary wall. On other side, capillaries are
shorter, than arterioles, which caused lower blood flow resistance too.
Viscosity of
blood is also important for resistance of vessels. It depends on quantity of
blood cells, protein rate in plasma, especially globulins and fibrinogen.
Considerable increase of blood viscosity may cause lower blood returning to the
heart and than disorders of blood circulation.
In large arteries
centralization of blood flow is observed. Blood cells moves in the central part
of blood stream, and plasma is peripheral. Instead increase of blood viscosity
in arterioles is caused by higher friction between cells and vessels wall.
Linear velocity of blood flow
Blood flow also is
characterized by linear velocity of blood circulation:
V=Q/πr2,
where
V - linear
velocity,
Q - blood volume,
r - radius of
vessel.
So it is clear
the wider cross-section of vessel the slower linear velocity of blood stream.
In large arteries linear velocity is highest (0.1-0.2 m/s). In arterioles it
measures 0.002 - 0.003 m/s, in capillaries - near 0.0003 m/s. In veins
cross-section decreases and linear velocity increases to 0.001 - 0.05 m/s in
large veins and to 0.1 -
b). Blood pressure
Transversal
pressure - is difference between pressure inside the vessel and squeeze of it
from the tissues. When increasing the tissue pressure to vessel wall, it
closes. Hydrostatic pressure is corresponding to weight of all blood in vessel
when it has vertical position. For vessels of head and neck this pressure
decreases towards the heart. For vessels of limbs it has outward direction.
That is why hydrodynamic pressure in vessels over heart is decreased due to
hydrostatical pressure. Below heart hydrodynamic pressure is increased, because
it is summarized with hydrodynamic pressure.
c). Role of changing body position
In horizontal
position of the body hydrostatical pressure is equal in every part of the body
and hydrodynamic pressure doesn't depend on it. In vertical position
transversal pressure in vessels of limbs creates tension of vessels walls
(Laplas low):
Pt=F/r,
where
Pt –
transversal pressure,
F - vessel
tension,
r - radius of
vessel.
So it is shown
the smaller radius of vessel, the lower tension in vessels walls. Due to this
capillaries with thinnest wall don't crush because of its smallest diameter.
Existence of precapillary sphincters permits proper direction of blood pressure
so that capillaries may close (plasmatic capillaries).
d). Local regulatory mechanisms
Collagen fibers
of vessels walls form net, which prevent its tension or decrease tone. Smooth
muscle cells combine with elastic and collagen fibers in vessels walls.
Contracting and stretching these fibers smooth muscle cells produce active
tension of vessel wall - tonus of vessels.
There are some
mechanisms in regulation of vessel tonus by smooth muscles. When rapid
increasing of blood pressure, smooth muscles contract and decrease tension by
decreasing vessel diameter. In slow rising of pressure tension decrease by
dilation of smooth muscles and increase vessel diameter. These mechanisms occur
more often in veins than in arteries. Veins have equal elasticity in systemic
and pulmonary circulation, but arteries are more extensible in pulmonary
circulation. Arteries in pulmonary circulation contain a lot of elastic and
smooth muscle fibers.
Functional types of vessels
According to
function all vessels may be divided into some groups:
- Elastic (damping)
vessels. Large arteries belong to this group. The main function of these
vessels is to turn ejection of blood into continuous blood flow. It is possible
due to elastic properties of its wall;
- Resistive
vessels are arterioles, precapillary sphincters and venuls. These vessels may
regulate the blood flow in capillaries by changing their tonus;
- Exchange
vessels are capillaries. Their walls due to the special structure permit
exchange of materials between blood and tissues;
-Capacitive
vessels are veins. To sure one-way direction of blood flow veins have valves if
lying below the heart. Veins contain 75-80 % of circulating blood. Veins of
skin and abdominal cavity may function as depot of blood.
2. PHYSIOLOGY OF VENOUS AND LYMPHATIC SYSTEM. microcirculation
a). Peculiarities of
microcirculation and lymphatic system
Functional element of microcirculation
Microcirculatory
part of vascular system performs all blood functions. There are such types of
vessels: arterioles, metarterioles, capillaries and venuls. Mean diameter of
these vessels is less than 100 mcm. Arterioles, capillary bed venuls and
lymphatic capillaries compose functional element of microcirculation. Main
processes as blood-tissue exchange or lymph production are performed there. Mean
diameter of capillaries is 3-6 mcm. The length of capillary vessel is near 750
mcm. Capillaries perform exchange in surface near 14000 mkm2. Blood
flow velocity in capillaries consists near 0.3 mm/s, which permits passing
erythrocytes through capillary in 2-3 s.
(Microcirculation)
Microcirculatory bed and functional types of
capillaries
Depending on structure
it distinguished three types of capillaries: somatic, visceral and sinusoidal.
Capillaries walls are composed from one layer of endothelial cells and basal
membrane. Endothelial cells are active elements of capillary bed.
Endothelial cell may produce enzymes as
antithrombin III endothelial relaxing factor, endothelial contracting factor,
which may activate function of hormones and neurotransmitters on vessel's wall
or cause some physiological effects by it. It was determined that
endotheliocites may contract and become voluminous. Endoteliocytes contain
microfibrills, composed from actin, myosin and other contractive elements. Such
structures are directed along cell basis and binds to cytoplasm in places of
intracellular contacts. When microfibrills contracting two kinds of effects may
be produced: both increasing intracellular split after contraction and
increasing cell height and its' prominence inside the vessel. Capillary wall
has small splits and a lot of pores. In certain organs capillary walls have
some specialties. In kidneys glomeruls, intestinal epithelium, capillaries are
fenestrated. This specialty permits passing through endothelial cells water,
ions and other even rather large molecules as aminoacids or fructose. In red
bone marrow, liver and spleen capillaries have interrupted walls, which let
passing even blood cells.
Interstitial spaces
Intracellular
substance surrounds microcirculatory bed and lymphatic capillaries.
Intracellular substance is composed by net of collagen and elastic fibers,
which form small cavities filled in by gelatin-like substance including
proteins, ions and water. Intracellular space has filter system and
reabsorbtive system. Filter system in composed by capillary bed. Reabsorbtive system
includes lymphatic capillaries and venules. Due to convection and diffusion in
fluid surroundings, intracellular fluid streams from blood capillaries to
lymphatic capillaries.
Lymphatic capillaries
Lymphatic
capillaries begin as one side closed capacities, which are drained by smallest
lymphatic vessels. Lymphatic capillaries have valves, which prevent opposite
movement of lymph. Connective tissue fibers fix outer surface of lymphatic
capillary to surrounding intracellular substance and keep it voluminous shape.
Pressure of lymph inside the capillary is lower than in intracellular space,
which helps to lymph flow. Capillary wall has basal membrane and one layer of
endotheliocytes.
Transport
of substances through capillary membrane
Substances are transported through
capillary membrane are lipid soluble as O2 or CO2 and
water-soluble as ions or glucose. Substances of molecule size more than 6-7 nm
cannot diffuse through intra-endothelial pores. The greater the concentration
difference of a given substance on two sides of capillary membrane, the greater
will bi net rate of diffusion. Forces
that determine fluid movement through capillary membrane are capillary
pressure, interstitial fluid pressure, plasma colloid osmotic pressure and
interstitial fluid colloid osmotic pressure. At arterial end of capillary
pressure is higher than interstitial fluid pressure, which causes filtration.
At venous end of capillary plasma colloid osmotic pressure is lower than
interstitial pressure, which cause reabsorbtion.
b).
Coronary circulation
Anatomic physiology (The 2 coronary arteries that supply the
myocardium arise from the sinuses behind the cusps of the aortic wave at the
root of the aorta. The right coronary artery has a greater flow in 50 % of
individuals, the left has a greater flow in 20 %, and the flow is equal in 30
%.
There are 2
venous drainage systems: a superficial system, ending in the coronary sinus and
anterior cardiac veins, that drains the left ventricle; and a deep system that
drains the rest of the heart.)
Compressive influences
role
(The heart is a muscle that compresses its blood vessels when it contracts. The
pressure inside the left ventricle is slightly greater than in the aorta during
systole. Consequently, flow occurs in the arteries supplying the subendocardial
portion of the left ventricle only during diastole, although the force is
sufficiently dissipated in the more superficial portions of the left
ventricular myocardium to permit some flow in this region throughout the
cardiac cycle.).
Metabolic and chemical factors significance (Factors that cause coronary vasodilatation: O2,
CO2, H+, K+, lactic acid, prostaglandines,
adenine nucleotides, adenosine. Asphyxia, hypoxia, intracoronary injections of
cyanide all increase coronary blood flow 200-300 % in denervated as well as
intact hearts.).
Neural regulation (The coronary arterioles contain alpha-adrenergic
receptors, which mediate vasoconstriction, and beta-adrenergic receptors, which
mediate vasodilatation. Activity in the noradrenergic nerves cause coronary
vasodilatation.).
c). Blood flow in veins (Blood flows through the blood vessels,
including the veins, primarily, because of the pumping action of the heart,
although venous flow is aided by the heartbeat, the increase in the negative
intrathoracic pressure during each inspiration, and contractions of skeletal
muscles that compress the veins (muscle pump).
Morpho-functional
properties of venous system (Veins
are the vessels, which are carry out blood from organs, tissues to heart in
right atrium. Only pulmonary vein carry out blood from lungs in left atrium.
There are superficial (skin) and deep veins.
They are
very stretching and have a low elasticity. Valves are present in veins. Plexus
venosus are depo of blood. Blood moving in veins under gravity.)
Mechanism of regulation (Difference of pressure in venous system is a cause of
blood moving. From the place of high pressure blood moving to the place of low
pressure. Negative pressure in chest is a cause of blood moving. Contraction of
skeletal muscles, diaphragm pump, peristaltic movement of veins walls are the
causes of moving.)
Venous pressure (Venous pressure is pressure of blood, which are
circulated in veins. Venous pressure in healthy person is from 50 to
Speed of blood stream (Speed of vein blood stream depend on diameter
of vessels. In venuls speed of blood moving is lower. In veins of middle
diameter it 7-14 cm/s, in big veins the speed is near 20 cm/s. In big veins
speed of blood moving depend on breathing and heartbeat.)
Venous pulse (Venous pulse is a moving of walls of big veins, which
are depend on heartbeat. The cause of it stop of blood flow from vein to heart
during atrium systole. At these time pressure in it increase. Methods of
investigation of venous pulse are phlebography.)
(Lymphatic system)
c).
Lymphatic system
Morpho-functional properties of
lymphatic system (Lymph system has
capillaries, vessels, where present valves, lymphatic nodes. In
lymphatic nodes are lymphopoiesis, depo of lymph, their function is
barrier-filter. Lymph flow in vein system through the chest lymph ductus.
Functions of lymph: 1. support of constant level of volume and components of
tissue fluid; 2. transport of nutritive substances from digestive tract in
venous system; 3. barrier-filter function. 4. take place in
immunology reactions.)
Composition and properties of lymph
(Lymph is tissue fluid that enters the lymphatic vessels. It drains into the
venous blood via the thoracic and right lymphatic ducts. It contains clotting
factors and clots on standing in vitro. Its protein content is generally lower
than that of plasma but varies with the region from which the lymph drains. It
should be noted that, in most locations, interstitial fluid is not
protein-free; it contains proteins that traverse capillary walls and return to
the blood via lymph. Water-insoluble fats are absorbed from the intestine into
the lymphatic vessels, and the lymph in the thoracic duct after a meal is milky
because of its high fat content Lymphocytes enter the circulation principally
through the lymphatic vessels, and there are appreciable numbers of lymphocytes
in thoracic duct lymph. Time of clotting – 10-15 minutes. There are 3 kinds of
lymph: peripheral, transport, central. The difference between them in cell
quantity level.)
Production of lymph (Fluid
efflux normally exceeds influx across the capillary walls, but the extra fluid
enters the lymph and drains through them back into the blood. This keeps the
interstitial fluid pressure from rising and promotes the turnover of tissue
fluid. The normal 24-hour lymph flow is 2-
Mechanism of lymph flow (Lymph flow is due to movements of skeletal
muscle, the negative intrathoracic pressure during inspiration, the suction
effect of high velocity flow of blood in the veins in which the lymphatic
vessels terminate, and rhythmic contractions of the walls of the large lymph
ducts. Since lymph vessels have valves that prevent backflow, skeletal muscle
contractions push the lymph toward the heart. Pulsations of arteries near
lymphatic vessels may have a similar effect. However, the contractions of the
walls of the lymphatic ducts are important, and the rate of these contractions
increases in direct proportion to the volume of lymph in the vessels. There is
evidence that the contractions are the principal factor propelling the lymph.)
3 Regulation of blood CYRCULATION
a). Local regulation of blood flow
Role of metabolic factors:.
Greater rate of metabolism or less
blood flow causes decreasing O2 supply and other nutrients.
Therefore rate of formation vasodilator substances (CO2, lactic
acid, adenosine, histamine, K+ and H+) rises. When
decreasing both blood flow and oxygen supply smooth muscle in precapillary
sphincter dilate, and blood flow increases. In is a vasodilator substance as
nitric oxide released from endothelial cells released from endothelial cells.
It causes secondary dilation of large arteries when micro vascular blood flow
increases. Cardiac muscle utilizes fatty acids for energy. Cardiac muscle
utilizes glucose through glycolisis that results in formation of lactic acid.
Basal tone of vessels. When arterial pressure suddenly increases local
blood flow tends to increase. It leads to sudden stretch of arterioles cause
smooth muscles in their wall to contract. Than local blood flow decreases to
normal level. Vessel walls are capable to prolonged tonic contraction without
tiredness even at rest. Such a condition is supported by spontaneous myogenic
activity of smooth muscles and efferent impulsation from autonomic nerve
centers, which control arterial pressure. Partial state of contraction in blood
vessels caused by continual slow firing of vasoconstrictor area is called
vasculomotor tone. Due to regulatory nerve and humoral influences this basal
ton changes according to functional needs of curtain organ.
b). Neuro-humoral regulation of
systemic circulation
Afferent link. Nerve receptors, which are capable react to
changing blood pressure, lays in heart cameras, aorta arc, bifurcation of large
vessels as carotid sinus and other parts of vascular system. Irritation of
these mechanical receptors produce nerve impulses, which pass to higher nerve
centers for processing sensory information from visceral organs.
Central link. Vasoconstrictor area of vasculomotor center is located
bilaterally in dorsolateral portion of reticular substance in upper medulla
oblongata and lower pons. Its neurons secrete norepinephrine, excite
vasoconstrictor nerves and increase blood pressure. It transmits also
excitatory signals through sympathetic fibers to heart to increase its rate and
contractility.
Vasodilator area
is located bilaterally in ventromedial of reticular substance in upper medulla
oblongata and lower pons. Its neurons inhibit dorsolateral portion and decrease
blood pressure. It transmits also inhibitory signals through parasympathetic
vagal fibers to heart to decrease its rate and contractility.
Posterolateral
portions of hypothalamus cause excitation of vasomotor center. Anterior part of
hypothalamus can cause mild inhibition of one. Motor cortex excites vasomotor
center. Anterior temporal lobe, orbital areas of frontal cortex, cingulated
gyrus, amygdale, septum and hippocampus can also control vasomotor center.
Efferent link. Stimulation of sympathetic vasoconstrictor
fibers through alfa-adrenoreceptor causes constriction of blood vessels.
Stimulation of sympathetic vasodilator fibers through beta-adrenoreceptors as
in skeletal muscles causes dilation of vessels.
Parasympathetic
nervous system has minor role and gives peripheral innervations for vessels of
tong, salivatory glands and sexual organs.
Mechanical receptors reflexes. These are spray-type nerve endings, which are
stimulated by stretch. In increasing blood pressure, from the wall of carotid
sinus impulses pass through Hering's nerve to glossopharyngeal nerve to
solitary tract in medulla. Secondary signals inhibit vasoconstrictor center and
excite vagal center. It results in peripheral vasodilatation and decreasing
heartbeat. When arterial pressure decreases whole processes lead to exciting
dorsolateral portion of vasomotor center and increasing blood pressure and
heartbeat. Similar reflex mechanism starts from receptors of aortic arc.
Bainbridge reflex
is observed when arterial pressure increases due to increasing blood volume and
blood return. Atria and SA node are stretched and send nerve signals to
vasomotor center. Increasing heart rate and heart contractility prevent damming
up of blood in pulmonary circulation.
Reflexes from proprio-, termo- and
interoreceptors. Contraction of
skeletal muscle during exercise compress blood vessels, translocate blood from
peripheral vessels into heart, increase cardiac output and increase arterial
pressure. Stimulation of termoreceptors cause spreading impulses from somatic
sensory neurons to autonomic nerve centers and so leads to changing tissue
blood supply. Irritation of visceroreceptors results in stimulation of vagal
nuclei, which cause decreasing blood pressure and heartbeat.
c). Haemodinamic in special body
conditions
Changing body position. Change body position from vertical to horizontal
and vice versa is followed by redistribution of blood. Under the influence of
gravity veins in lower half of the body are dilated and may contain additional
near
Regulation of blood flow in
physical exercises. In physical
exercises impulses from pyramidal neurons of motor zone in cerebral cortex passes
both to skeletal muscles and vasomotor center. Than through sympathetic
influences heart activity and vasoconstriction are promoted. Adrenal glands
also produce adrenalin and release it to the blood flow. Proprioreceptor
activation spread impulses through interneurons to sympathetic nerve centers.
So, contraction of skeletal muscle during exercise compress blood vessels,
translocate blood from peripheral vessels into heart, increase cardiac output
and increase arterial pressure.
Changing blood
volume after bleeding. In changing blood volume volumic receptors in vena cava or
atria are activated. These impulses spread to both medulla oblongata and
osmolarity regulating neurons in hypothalamus. In consequence decreasing blood
volume heart activity rises through sympathetic activation and vasopressin in
released from hypophisis.
d). Anatomic and physiological properties of
blood circulation system in fetus and children
Blood circulation in fetus (55 % of the fetal cardiac output goes through
the placenta. The blood in the umbilical vein in humans is believed to be about
80 % saturated with O2, compared with 98 % saturation in the
arterial circulation of the adult. The ducts
venous divert some of this blood directly to the inferior vena cava, and the
remainder mixes with the portal blood of the fetus. The portal and systemic
venous blood of the fetus is only 26 % saturated, and the saturation of the
mixed blood in the inferior vena cava is approximately 67 %. Most of the blood
entering the heart through the inferior vena cava is diverted directly to the
left atrium via the patent foramen oval. Most of the blood from the superior
vena cava enters the right ventricle and is expelled into the pulmonary artery.
The resistance of the collapsed lungs is high, and the pressure in the
pulmonary artery is several mm Hg higher than it is in the aorta, so that most
of the blood in the pulmonary artery passes through the ducts arteries to the
aorta. In this fashion, the relatively unsaturated blood from the right
ventricle is diverted to the trunk and lower body of the fetus, while the head
of the fetus receives the better oxygenation blood from the left ventricle.
From the aorta, some of the blood is pumped into the umbilical arteries and
back to the placenta. The O2 saturation of the blood in the lower
aorta and umbilical arteries of the fetus is approximately 60 %.)
Structural changes cardiovascular
system after birth (Because of the
patent ducts arterial and foramen oval, the left and right heart pump in parallel
in the fetus rather than in series as they do in the adult. At birth, the
placental circulation is cut off and the peripheral resistance suddenly rises.
The pressure in the aorta rises until it exceeds that in the pulmonary artery.
Mean while, because the placental circulation has been cut off, the infant
becomes increasingly asphyxia. Finally, the infant gasps several times, and the
lungs expand. The markedly negative pleural pressure (-30 to
Blood pressure in children (In newborns systolic arterial
pressure is 65-
Regulation of blood circulation
system in children (In
2-3 years after of birth prevent tonic influences of sympathetic nerves on
heart. From 2-3 month begin influence of n.vagus on heart.)
Reactions of cardiovascular system
on physical load (On
dynamic physical load children and teenagers reacted by increase of heart beat,
systolic arterial pressure. When the children and teenagers train to physical
load they increase the reserve possibility of organism and as adaptive reaction
increase rate of heartbeat (not increase the diastolic arterial pressure,
decrease systolic arterial pressure). On static physical load children and
teenagers reacted by increase arterial pressure. Increase of physical load is
preventing development of hypertension.)
e). Condition of blood circulation
in aged and old persons
Common
properties of aged organism is decrease intensity of blood circulation in
different tissues, organs and systems. It presents redistribution of volume of
circulated blood to brain and heart. Elasticity of vessels' wall decrease, that
is why increasing peripheral vessel resistance. In these persons decrease speed
of blood stream (may be it connect with decrease of cardiac output), decrease
speed of capillary blood stream; change character of blood stream regulatory
processes.)
PRACTICAL ACTIVIRIES:
1). Measuring arterial pressure
by Korotkov’s method
Examinee sits at
the table, putting right hand on the level of heart. Give cuff on the middle
1/3 of right shoulder and fix. Cuff is fixed well if you can put under it only
one finger. Find the pulsation of brachial artery. Give ear to cuff
Processing of
arterial pressure data
Pulsation pressure
may be calculated using the formula:
PP=SP-DP, where
PP – pulsation
pressure, SP – systolic pressure, DP – diastolic pressure.
Middle dynamical
pressure is equal to:
PP/3+DP
Peripheral
vessels resistance is calculated as
PVR=MDP·60·1,333/MBV,
where
MBV – minute
blood volume
MBV=PR·PP·100/MDP
Note in the
conclusion, do results normal or not?
|
Classification of blood
pressure for adults |
||
|
Category |
diastolic, mmHg |
|
|
Normal |
≤ 120 |
≤ 80 |
|
120 – 139 |
or 80 – 89 |
|
|
Stage 1 Hypertension |
140 – 159 |
or 90 – 99 |
|
Stage 2 Hypertension |
160 - 179 |
or 100 - 109 |
|
≥ 180 |
or ≥ 110 |
|
2). Evaluation of arterial pulse
Find radial
artery on right wrist of examinee. Press artery by four fingers of your arm to
radial bone of examinee and feel pulsation. Perform this investigation
simultaneously on both arms.
Evaluate, do
pulsation is symmetrical or not. In case of identical pulsation in both hands
count then pulse rate per minute on right wrist.
3). Determination of functional
condition superficial, perforant and deep veins
In horizontal
position lift leg upward (in this position venous blood can flow out of veins).
Put up jute in the upper 1/3 of thigh. Put jute to patient on the legs and take
of a jute. When there is pathology in veins, they will full with blood quickly.
Lying on the back
release veins from blood and put up 3 jutes in the upper and middle 1/3 of
thigh, and under the knee joint. Patient stand up. If there is any
insafficientsy of valves of perforant veins in these zones the blood will full
it quickly.
While talking off
jutes from down ward to upward you observe valve condition of superficial
veins.
Marsh’s test
shows the condition of deep veins. While standing put on jute upper that knee,
in such way we’ll stop the blood in superficial veins. Patient has to walk for
5-10 minutes. Notise if the blood goes out the shin veins if valves of
perforant and deep veins functioning good enough, then veins are release from
blood.
In conclusion show the functional condition of
superficial, perforant and deep veins of legs.
4). Test under the physical
load
Examinee sits on
the chair. Estimate the constant level of both arterial pressure and pulse rate
by measuring every 1-2 min. Examinee changes body position to vertical and
squats 20 times through 20 s.
5). Analyses of electrocardiogram in person of
different age groups
Compare
analyses of electrocardiogram do according to methods, which is present in
methodical instruction to lesson No 30. Present results in the table.
|
No |
Indexes |
I aged group |
II aged group |
|
1 |
Source of impulse |
|
|
|
2 |
Heart rhythm |
|
|
|
3 |
Heart rate |
|
|
|
4 |
Voltage of ECG |
|
|
|
5 |
Electrical power direction |
|
|
|
6 |
Amplitude and duration of ECG components |
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Sphygmogram – graph registration of arterial pressure
Anacrota – à
(ana –
up, crotos
– push). It is the opening of semilunear valves and moving of blood
in aorta.
Catacrota - b (cata – down, crotos – push). It has addition wave – dicrotic. It is end of ventricular
systole, the pressure in ventricle start to decrease.
Incisura (i)
Addition wave ñ or secondary or dicrotic
increase. The close of semilunear valves of
aorta and push the blood from them.
RESUME:
Physiology of
Systemic Circulation
Determined by
Dynamics of blood flow
Anatomy of circulatory system
Regulatory mechanisms that control heart and
blood vessels
Blood volume
Most in the veins (2/3rd)
Smaller volumes in arteries and capillaries
Dynamics of Blood
Circulation
Interrelationships between:
Pressure
Flow
Resistance
Control mechanisms that regulate blood
pressure
Blood flow through vessels
Blood Flow
Recall: Cardiac output - the
total volume of blood pumped by the ventricle per minute
The actual volume of blood flowing through a
vessel, an organ, or the entire circulation in a given period:
Is measured in ml per min.
Is equivalent to cardiac output (CO),
considering the entire vascular system
Is relatively constant when at rest
Varies widely through individual organs,
according to immediate needs
Circulatory Changes
During Exercise
Blood Pressure (BP)
Blood Pressure – The measure of force
exerted by blood against the vessel walls.
Force per unit area exerted on the wall of a
blood vessel by its contained blood
Expressed in millimeters of mercury (mm Hg)
Measured in reference to systemic arterial BP
in large arteries near the heart
Blood moves through vessels because of blood
pressure, gravity, and skeletal pump
The differences in BP within the vascular
system provide the driving force that keeps blood moving from higher to
lower pressure areas
Blood Flow &
Blood Pressure
Blood flow (F) is directly
proportionalto the difference in blood pressure (DP) between two
points in the circulation
F = Flow
α = directly
proportional to
Δ = change in
P = Pressure
F α ΔP (“Flow is directly
proportional to change in pressure”)
If ΔP ↑, then F ↑
If ΔP ↓, then F ↓
Blood Flow: Pressure
Changes
Flows down a pressure gradient
Varies with force of ventricular contraction
Highest at the left ventricle (driving P),
decreases over distance
Capillary beds virtually diminish pressure
Compliance (distensibility) on venous side
maintains low pressure
Greatest drop in pressure occurs in
arterioles
Decreases 90% from aorta to vena cava
Blood Flow
Flow rate (F) through a vessel (volume
of blood passing through per unit of time) is directly proportional to the
pressure gradient (ΔP) and inversely
proportional to vascular resistance (R)
F = flow
rate of blood through a vessel
ΔP = pressure gradient
R =
resistance of blood vessels
(“Flow is directly proportional to Change in Pressure
and inversely proportional to Resistance.”)
Meaning:
If ΔP↑ and/or
R↓, then F↑
if ΔP↓ and/or
R↑, then F↓
Blood Flow
Pressure gradient is pressure
difference between beginning and end of a vessel
Blood flows from area of higher pressure to
area of lower pressure
Resistance (R) – opposition to flow
Measure of the amount of friction blood
encounters as it passes through vessels
Referred to as peripheral resistance (PR)
Blood flow is inversely proportional to
resistance (R)
As one goes up, the other goes down
R is more important than DP in influencing
local blood pressure
(“Flow is inversely proportional to Resistance”)
Resistance Factors
Resistance factors:
Viscosity of blood– thickness or
“stickiness” of the blood
Hematocrit
[Plasma Proteins]
Length of blood vessel– the longer the
vessel, the greater the resistance encountered
Radius of blood vessel – the wider the
vessel, the lower the resistance
Slight change in radius (vasoconstriction or
vasodilation) produces significant change in blood flow
Resistance is
inversely proportional to radius4
As one goes up, the other goes down
R = Lh
r4
L = length of the
vessel
h = viscosity of
blood (Greek letter “eta”)
r = radius of the
vessel
Vessel length and blood viscosity do not vary
significantly and are considered CONSTANT = 1
Therefore: R = 1
r4
If the radius is doubled, the
new resistance is 1/16ththe original resistance
If the radius is halved, the
new resistance is 16 times the original resistance
Note: α means “proportional to”
Blood Flow, Vessel
Diameter and Velocity
As diameter of vessels increases, the total
cross-sectional area increases and velocity of blood flow decreases
Blood Flow &
Cross-Sectional Area
At the capillary bed:
Vessel diameter decreases, but number of
vessels increase
Therefore, total cross-sectional area
increases
Therefore, velocity slows, giving capillaries
time to unload O2 and nutrients
Vascular Tree
Closed system of vessels consists of:
Arteries
carry blood away from heart to tissues
Arterioles
smaller branches of arteries
Capillaries
smaller branches of arterioles
smallest of vessels across which all exchanges
are made with surrounding cells
Venules
formed when capillaries rejoin
return blood to veins
Veins
formed when venules merge
return blood to heart
Structure
of Blood Vessels
Arteries
have thickerwallsand narrower lumensthan those that
of veins
Arterial walls must withstand high pressures
Thick layer of smooth muscle in tunica media
controls flow and pressure
Arteries and arterioles have
more elastic and collagen fibers
Remain open and can spring back in shape
Pressure in the arteries fluctuates due to
cardiac systole and diastole
Veins have larger lumens.
Vein walls are thinner than arteries and have valves
Thin walls provide compliance -
blood volume reservoir
Blood pressure is much lower in veins than in
arteries
Valves prevent backflow of blood
Capillaries have verysmall
diameters (many are only large enough for only one RBC to pass through
at a time)
Composed only of basal lamina and endothelium
Thin walls allow for gas, nutrient, waste
exchange between blood and tissue cells.
Role of Arteries
Elastic or conducting arteries
Largest diameters, pressure high and
fluctuates
Pressure Reservoir
Elastic recoil propels blood after systole
Muscular or medium arteries
Smooth muscle allows vessels to regulate blood
supply by constricting or dilating
Role of Arterioles
Transport blood from small arteries to
capillaries
Controls the amount of resistance
Greatest drop in pressureoccurs
in arterioles, which regulate blood flow through tissues
No large fluctuations in capillaries and
veins
Blood
Pressure
Force exerted by blood
against a vessel wall. It depends on:
Volume of blood forced into the vessel
Compliance (distensibility) of vessel walls
Systolic pressure
Peak pressure exerted by ejected blood against
vessel walls during cardiac systole
Averages
Diastolic pressure
Minimum pressure in arteries when blood is
draining off into vessels downstream
Averages
Measurement of Blood
Pressure
Different phases in measurement of blood
pressure are identified on the basis of the quality of the Korotkoff sounds
Average arterial BP is 120/80 mm Hg
Average pulmonary BP is 22/8 mm Hg
Pulse Pressure
Pulse Pressure - Difference between
systolic and diastolic pressures
Increases when stroke volume increases or
vascular compliance decreases
Pulse pressure can be used to take a pulse to
determine heart rate and rhythmicity
Example:
120 mmHg (SP) – 80 mmHg (DP) = 40
mmHg (PP)
Arterial Blood
Pressure
Blood pressure in elastic arteries near the
heart is pulsatile (BP rises and falls)
Pulse pressure – the difference
between systolic and diastolic pressure
Mean arterial pressure (MAP) –
pressure that propels the blood to the tissues
MAP = diastolic pressure + 1/3 pulse
pressure
Effect of Gravity on
Blood Pressure
Effect of Gravity: In a
standing position, hydrostatic pressure caused by gravity increases
blood pressure below the heart and decreases pressure above the heart
Role of Veins
Veins have much lower blood pressure and
thinner walls than arteries
To return blood to the heart, veins have
special adaptations
Large-diameter lumens, which offer little
resistance to flow
Valves (resembling semilunar heart valves),
which prevent backflow of blood
Venous Blood
Pressure
Venous BP is steady and changes little during
the cardiac cycle
The pressure gradient in the venous system is
only about
Veins have thinner walls, thus higher
compliance.
Vascular compliance:
Tendency for blood vessel volume to increase
as blood pressure increases
More easily the vessel wall stretches, the
greater its compliance
Venous system has a large compliance and acts
as a blood reservoir
Capacitance vessels –2/3 blood volume is in
veins
Venous Return
Venous pressure is driving force for return
of blood to the heart.
EDV, SV, and CO are controlled by factors
which affect venous return
Factors Aiding
Venous Return
Venous BP alone is too low to promote
adequate blood return and is aided by the:
Respiratory “pump” – pressure changes
created during breathing squeeze local veins
Muscular “pump” – contraction of
skeletal muscles push blood toward the heart
Valves prevent backflow during venous return
Capillary
Network
Blood flows from arterioles through
metarterioles, then through capillary network
Venules drain network
Smooth muscle in arterioles, metarterioles,
precapillary sphincters regulates blood flow
Organization of a
Capillary Bed
True capillaries – exchange vessels
Oxygen and nutrients cross to cells
Carbon dioxide and metabolic waste products
cross into blood
Atriovenous anastomosis – vascular
shunt, directly connects an arteriole to a venule
Capillaries
Capillary wall
consists mostly of endothelial cells
Types classified by diameter/permeability
Continuous capillary –
Least permeable
Do not have pores
Only small molecules (water, ions) diffuse
through tight junctions
Seen in skin, muscle where small ions and
molecules must enter/exit vessels
Fenestrated capillary –
Large fenestrations (pores)
Small molecules and limited proteins diffuse
Seen in kidney, small intestine where large
molecules must enter/exit vessels
Sinusoidal capillary –
Most permeable
Discontinuous basement
Allow proteins and cells as necessary
Seen in liver, bone marrow, spleen, where
whole cells, proteins must enter/exit vessels
Capillary Exchange
and Interstitial Fluid Volume Regulation
Blood pressure, capillary permeability, and
osmosis affect movement of fluid from capillaries
A net movement of fluid occurs from blood
plasma into tissues – bulk flow
Fluid gained by tissues is removed by lymphatic
system
Diffusion at
Capillary Beds
Distribution of ECF between plasma and
interstitial compartments
Is in state of dynamic equilibrium
Balance between tissue fluid and blood plasma
Hydrostatic pressure:
Exerted against the inner capillary wall
Generated primarily by gravity
and blood pressure
Promotes formation of tissue fluid
Source of Net Filtration Pressure (NFP)
Colloid osmotic pressure:
Exerted against the outer capillary wall
Generated by [plasma proteins]
Promotes fluid reabsorption into
circulatory system
Lymphatic
System
Extensive network of one-way
vessels. It provides accessory route by which fluid can be returned
from interstitial spaces to the blood
Initial lymphatics
Small, blind-ended terminal lymph vessels
Permeate almost every tissue of the body
Lymph vessels
Formed from convergence of initial lymphatics
Eventually empty into venous system near where
blood enters right atrium
One way valves spaced at intervals direct flow
of lymph toward venous outlet in chest
Lymph
Interstitial fluid that enters a lymphatic
vessel
Lymphatic System
Lymphatic System Functions:
Return of excess filtered fluid (3 L/day) back
to heart
Defense against disease
Lymph nodes contain phagocytes which destroy
bacteria filtered from interstitial fluid
Transport of absorbed fat from GI tract to
liver (chylomicrons)
Return of filtered protein
Regulation of blood circulation
Blood Pressure (BP)
Regulation
Pressure of arterial blood is regulated by
blood volume, TPR, and cardiac rate.
MAP = CO ´ TPR
Arteriole resistance is greatest because they
have the smallest diameter
Capillary BP is reduced because of the total cross-sectional
area
3 most important variables are HR, SV, and
TPR
Increase in each of these will result in an
increase in BP
BP can be regulated by:
Kidney and sympathoadrenal system
1. Short-Term Regulation of Blood Pressure
Baroreceptor
reflexes
Change peripheral resistance, heart rate, and
stroke volume in response to changes in blood pressure
Chemoreceptor
reflexes
Sensory receptors sensitive to O2,
CO2, and pH levels of blood
Central nervous system ischemic response
Results from high CO2 or low pH
levels in medulla and increases peripheral resistance
2. Long-Term Regulation of Blood Pressure
1). Renin-angiotensin-aldosterone
mechanism
2). Vasopressin (ADH) mechanism
3). Atrial natriuretic mechanism
4). Fluid shift mechanism
5). Stress-relaxation response
Cerebral
Circulation
● Cerebral blood flow
(CBF) is notnormally influenced by sympathetic nerve activity
● Cerebral blood flow
regulated almost exclusively by intrinsic mechanisms:
1). Myogenic Mechanism:
Dilate in response to decreased pressure
Cerebral Perfusion Pressure (CPP) is
the blood pressure within the brain. CPP is maintained within very narrow
limits
Too low = cerebral ischemia
Too high = intracranial hematoma, cerebral edema
2). Metabolic Mechanism:
Areas of brain with high
metabolic activityreceive most blood
Cerebral arteries dilate due to increased [K+]
[CO2] [H+] and [Adenosine] in CSF
Regulation
of Blood Flow
1. Extrinsic
2. Intrinsic
1. Extrinsic – nervous and endocrine (non-local forces)
Extrinsic Regulation
of Blood Flow
a). Nervous System –CNS sends (or ceases) action potentials to smooth
muscle in walls of blood vessels, stimulating vasoconstriction, or allowing
vasodilation.
Sympathetic neuron axon
terminals at smooth muscle in blood vessels release NE, which stimulates
vasoconstriction, decreasing blood flow. If release of NE from axon
terminal decreases, blood vessels dilate, increasing blood flow.
Sympathetic neuron axon
terminals at cardiac muscle in the heart release NE, which increases cardiac
output, increasing BP.
Nervous system is
immediately responsible for routing blood flow and maintaining blood pressure.
Sympathoadrenal
Increase cardiac output
Increase TPR: α-adrenergic
stimulation - vasoconstriction of arteries in skin and viscera
Parasympathetic
Parasympathetic innervation limited, less
important than sympathetic nervous system in control of TPR
Parasympathetic endings in
arterioles promote vasodilation to the digestive tract, external genitalia, and
salivary glands.
b). Hormonal Control –Sympathetic action potentials to medulla of adrenal
gland stimulate release of epinephrine and norepinephrinewhich reinforce
systemic vasoconstriction, but cause vasodilation at skeletal muscle.
Norepinephrine is primarily
released from sympathetic neuron axon terminals directly onto end target
organs. Epinephrine is primarily released from the adrenal medulla (80% Epi,
20% NE).
Epi from the adrenal medulla
travels through the blood and is able to bind with α1-receptors
on blood vessels, reinforcing vasoconstriction. However, α1-receptors
have a lower affinity for Epi and do not respond as strongly to it as they do
to NE.
Epinephrine also binds to
β2-receptors, found on vascular smooth muscle of heart, liver,
and skeletal muscle arterioles. These receptors are not innervated and
therefore respond primarily to circulating epinephrine. Activation of vascular
β2-receptors in the heart, liver, and skeletal muscle by
epinephrine causes vasodilation, increasing blood flow to these tissues [p.
524].
2. Intrinsic–local autoregulation (‘”self-regulation”)
Autoregulation– In most tissues, blood
flow is proportional to metabolic needs of tissues. If tissue metabolic
processes increase, blood flow to tissue increases.
Intrinsic Regulation
of Blood Flow (Autoregulation)
Blood flow can increase 7-8
times as a result of vasodilation of metarterioles and precapillary sphincters
a). Vasodilator substances are produced as metabolism increases
b). Intrinsic receptors sense chemical changes in environment
Decreased O2
Increased CO2
Decreased pH (Lactic acid)
Increased adenosine
Increased K+
Intrinsic Regulation
of Blood Flow (Autoregulation)
Myogenic Control
Mechanism:
a). Contraction that originates within the vascular smooth
muscle fiber as a result of stretch
Anincrease in systemic arterial
pressure causes vessels to contract
A decrease in systemic arterial
pressure causes vessels to dilate
b). If ↑ Pressure, then ↑ Stretch. Response:
Vasoconstriction
c). If↓ Pressure, then↓ Stretch. Response:
Vasodilation
Intrinsic Regulation of Blood Flow (Autoregulation)
