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 oecessity 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 oecessity 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 (Iewborns 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?
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Classification of blood pressure for adults |
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Category |
diastolic, mmHg |
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Normal |
≤ 120 |
≤ 80 |
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120 – 139 |
or 80 – 89 |
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Stage 1 Hypertension |
140 – 159 |
or 90 – 99 |
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Stage 2 Hypertension |
160 – 179 |
or 100 – 109 |
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≥ 180 |
or ≥ 110 |
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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.
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No |
Indexes |
I aged group |
II aged group |
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1 |
Source of impulse |
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2 |
Heart rhythm |
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3 |
Heart rate |
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4 |
Voltage of ECG |
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5 |
Electrical power direction |
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6 |
Amplitude and duration of ECG components |
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Sphygmogram – graph registration of arterial pressure
Anacrota – а (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 с 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 draietwork
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)
