BLOOD FLOW IN THE ARTERIAL SYSTEM. PHYSIOLOGY OF MICROCIRCULATION. PHYSIOLOGY OF VENOUS AND LYMPH SYSTEM

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.

Kinds of blood movements:

laminar

Turbulence

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 110-125 mm Hg, at the end of diastole - 70-80 mm Hg. In pulmonary trunk during systole the blood pressure is 20-25 mm Hg, in diastole - 10-15 mm Hg. In large arteries blood flow velocity is 0.1-0.2 m/s. In large veins returning blood flow to the heart is caused by lowest blood pressure - 0 mm Hg.

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.

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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 - 0.15 in vena cava.

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.

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):

P_t=F/r, where

P_t – 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).

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

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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.

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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.

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.

lymphatic system

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.

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).

a) 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.)

b) 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.)

c) Venous pressure (Venous pressure is pressure of blood, which are circulated in veins. Venous pressure in healthy person is from 50 to 100 mm H₂O. Increase of venous pressure in physiological condition may be in the action of physical activity. Determine of venous pressure is called phlebotonometry and give for doctors information about activity of right atrium.)

d) 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.)

e) 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.)

Lymph and lymphatic circulation (Lymph vessels are present in all tissues, except bones, nervous and superficial layers of skin.)

a) 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.)

b) 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.)

c) 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 2-4 L. Appreciable quantities of protein enter the interstitial fluid in the liver and intestine, and smaller quantities enter from the blood in other tissues. The walls of the lymphatic are permeable to macromolecules, and the proteins are returned to the bloodstream via the lymphatic. The amount of protein returned in this fashion in 1 day is equal to 25-50 % of the total circulating plasma protein. In the kidneys, formation of a maximally concentrated urine depends upon an intact lymphatic circulation; removal of reabsorbed water from the medullar pyramids is essential for the efficient operation of the countercurrent mechanism and water enters the vasa recta only if an appreciable osmotic gradient is maintained between the medullar interstitial and the vasa recta blood by drainage of protein-containing interstitial fluid into the renal lymphatic. Some large enzymes – notably histaminases and lipase – may reach the circulation largely or even exclusively via the lymphatic vessels after their secretion from cells into the interstitial fluid. The transport of absorbed long-chain fatty, for example, cholesterol from the intestine via the lymphatic vessels.)

d) 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.)

Local regulation of blood flow

a) 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.

b) 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.

Neuro-humoral regulation of systemic circulation

a) 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.

b) 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.

c) 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.

d) 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.

e) 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.

Haemodinamic in special body conditions

a) 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 0,5 l of blood. After this impulsations from baroreceptors is activated and resistive vessels are contracted, mainly in skin and muscles. At the same time rate of heartbeat increases, which permit make up for cardiac output. In insufficient reflex regulation orthostatic unconsciousness may occur.

b) 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.

c) 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.

Coronary circulation

a) 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 %.

b)

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.)

b) 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.)

c) 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.)

d) 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.)

Anatomic and physiological properties of blood circulation system in fetus and children

a) 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 %.)

b) 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 -50 mm Hg) during the gasps contributes to the expansion of the lungs, but other poorly understood factors are also involved. The sucking action of the first breath plus constriction of the umbilical veins squeezes as much as 100 mL of blood from the placenta (the "placental transfusion"). Once the lungs are expanded, the pulmonary vascular resistance falls to less than 20 % of the in uteri value, and pulmonary blood flow increases markedly. Blood returning from the lungs raises the pressure in the left atrium, closing the foramen oval by pushing the valve that guards it against the between atriums septum. The duct arteries constrict within a few minutes after birth but at least in sheep, do not close completely for 24-48 hours. Eventually, the foramen oval and the ducts arteries both fuse shut in normal infants, and by the end of the first few days of life the adult circulatory pattern is established. The mechanism responsible for obliteration of the ducts arteries, like that responsible for expansion of the lungs, is incompletely understood, although there is evidence that a rise in arterial PO₂ add asphyxia are both capable of making the ducts constrict. Bradykinin has been shown to constrict the umbilical vessels and the ducts arteries while dilating the pulmonary vascular bed. Prostacyclin appears to have a role in maintaining the potency of the ducts arteries before birth, and rectal administration of one or 2 small doses of indomethacin, a drug that inhibits prostaglandin synthesis, closes the ducts in many infants who would otherwise require surgical closure.)

c) Blood pressure in children (In newborns systolic arterial pressure is 65-80 mm Hg, diastolic – 30-46 mm Hg; in 7-9 years systolic arterial pressure is 80-100 mm Hg, diastolic – 41-59 mm Hg; in 10-13 years systolic arterial pressure is 82-120 mm Hg, diastolic – 40-65 mm Hg; in 14-15 years systolic arterial pressure is 90-120 mm Hg, diastolic – 50-70 mm Hg; in 16-17 years systolic arterial pressure is 100-125 mm Hg, diastolic – 50-75 mm Hg; in adults systolic arterial pressure is not more than 139 mm Hg, diastolic – not more than 89 mm Hg. Venous pressure is higher in children than in adult. Volume of heart is increase more than diameter of arteries. Heart beat rate in children more than in adult and it decrease with ages. In teenagers arterial pressure is higher.)

d) 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.)

Classification of hypertension (1999)

Index	Level of arterial pressure
	Systolic, mm Hg	Diastolic, mm Hg
Optimal AP	< 120	< 80
Normal AP	< 130	<85
Higher-normal АP	130-139	85-89
Hypertension І degree Measure hypertension	140-159	90-99
	140-149	90-94
Hypertension ІI degree	160-179	100-109
Hypertension of IIІ degree	>180	>110
Isolated systolic hypertension   Measure hypertension	>140	<90
	140-149	<90

Classification of hypertension (NHLBI, 2003).

Index	Level of arterial pressure
	Systolic, mm Hg	Diastolic, mm Hg
Normal AP	< 120	< 80
Prehypertension	120-139	or 80-89
Hypertension І degree	140-159	or 90-99
Hypertension ІІ degree	>160	or >100

e) 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.)

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.)

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 30 mm Hg over the point of loosing pulsation on radial artery or to 200 mm Hg. Put stethoscope in elbow hole over the brachial artery. Than blow off ear slow and muck the level of systolic pressure in the moment of appearance Korotkov’s sounds. Muck diastolic pressure in the moment of disappearance Korotkov’s sounds.

Auscultatory method

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	systolic, mmHg	diastolic, mmHg
Normal	≤ 120	≤ 80
Prehypertension	120 – 139	or 80 – 89
Stage 1 Hypertension	140 – 159	or 90 – 99
Stage 2 Hypertension	160 - 179	or 100 - 109
Hypertensive Crisis	≥ 180	or ≥ 110

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.

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.

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.

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 (2/3^rd)

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

(“Resistance is inversely proportional to

the radius of the vessel to the 4^th power”)

Blood Vessel Diameter

Changes in vessel radius significantly alter peripheral resistance

Resistance varies inversely with the fourth power of vessel radius (one-half the diameter)

Poiseuille’s Law:

             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 1/16^ththe 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

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 120 mm Hg

Diastolic pressure

Minimum pressure in arteries when blood is draining off into vessels downstream

Averages 80 mm Hg

Blood Pressure Measurement

Critical closing pressure:

Pressure at which a blood vessel collapses and blood flow stops

Laplace’s Law:

Force acting on blood vessel wall is proportional to diameter of the vessel times blood pressure

Measurement of BP

Blood pressure cuff is inflated above systolic pressure, occluding the artery

As cuff pressure is lowered, the blood will flow only when systolic pressure is above cuff pressure, producing the sounds of Korotkoff

Named after Dr. Nikolai Korotkoff, a Russian physician who described them in 1905

Korotkoff sounds will be heard until cuff pressure equals diastolic pressure, causing the sounds to disappear

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 20 mm Hg

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

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

7,200 L blood pumped per day    (5 L/min  x  60 min  x  24 hrs)

20 L of plasma leave arteries

17 L of plasma return to veins

3 L carried away as lymph

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 Flow

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.

Extrinsic – nervous and endocrine (non-local forces)

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.

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].

Intrinsic Regulation of Blood Flow (Autoregulation)

Blood flow can increase 7-8 times as a result of vasodilation of metarterioles and precapillary sphincters

Vasodilator substances are produced as metabolism increases

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:

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

If ↑ Pressure, then ↑ Stretch.  Response:  Vasoconstriction

If↓ Pressure, then↓ Stretch.  Response:   Vasodilation

Intrinsic Regulation of Blood Flow (Autoregulation)

Extrinsic Regulation of Blood Flow

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

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

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

Baroreceptor Reflex Control

Chemoreceptor Reflex Control

Baroreceptor Effects

Long-Term Regulation of Blood Pressure

Renin-angiotensin-aldosterone mechanism

Vasopressin (ADH) mechanism

Atrial natriuretic mechanism

Fluid shift mechanism

Stress-relaxation response

Renin-Angiotensin-Aldosterone System (RAAS)

Vasopressin (ADH) Mechanism

Atrial Natriuretic Peptide (ANP)

Produced by the atria of the heart

Stretch of atria stimulates production of ANP

Antagonistic to Aldosterone and Angiotensin II

Promotes Na⁺ and H₂O excretion in the urine by the kidney

Promotes vasodilation, lowering TPR

“Atrial”     = atria of the heart

“natri-”    = sodium

“-uretic”  = urination

“Peptide” = small protein

Atrial Natriuretic Peptide (ANP)

Cerebral Circulation

Cerebral blood flow (CBF) is notnormally influenced by sympathetic nerve activity

Cerebral blood flow regulated almost exclusively by intrinsic mechanisms:

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

Metabolic Mechanism:

Areas of brain with high metabolic activityreceive most blood

Cerebral arteries dilate due to increased [K⁺] [CO₂] [H⁺] and [Adenosine] in CSF