Circulatory System PDF

Circulatory system 1  Haemodynamics Study of physical laws of blood circulation and properties of both blood and blood vessels. Systemic circulation (84%) (Peripheral circulation). – Supplies blood flow to all tissues of body except lungs....

Circulatory system 1  Haemodynamics Study of physical laws of blood circulation and properties of both blood and blood vessels. Systemic circulation (84%) (Peripheral circulation). – Supplies blood flow to all tissues of body except lungs. – 64 % in veins, – 13 % in arteries, – 7 % in systemic arterioles and capillaries. Pulmonary circulation (16%) – Supplies blood flow to lungs. – 9 % in Pulmonary vessels – 7% in heart. 2  Vascular system Arteries Arterioles control – Large elastic arteries carry blood from blood flow and pressure heart divide into muscular artery that branch to various organs in body. Arterioles – Deliver blood to capillaries, regulate blood flow and blood pressure. Capillaries. – Arterioles enter a tissue, they branch into numerous tiny vessels. – Exchange of nutrient and waste between blood and interstitial fluid. Venules – Groups of capillaries within a tissue reunite to form small veins. Veins – Convey blood from tissues back to heart with provided with valves. Vasa vasorum 3 – blood vessels in larger blood vessels. Veins: large compliant and low Resistance. Arterioles and Metarterioles  Microcirculation of capillary exchange The movement of substances between blood and interstitial fluid. Substances enter and leave capillaries by three basic mechanisms: 1. Diffusion – Movement of O2, CO2, Glucose and wastes form high con to low con. Con of O2 in capillary blood is normally greater than in interstitial fluid. Large quantities of O2 normally move from blood toward tissues. 2. Transcytosis – For transport of hormone like insulin and antibodies. – Packed as pinocytic vesicles and move by exocytosis and endocytosis. 3. Bulk flow – Movement of fluid and solute between blood and interstitial fluid. – Movement from blood capillaries into interstitial fluid is called filtration – Reverse movement is called reabsorption. 5  Fluid Filtration Across Capillaries Four primary forces determine whether fluid will move out of blood into interstitial fluid, or in opposite direction. – 1. Capillary pressure (Pc) ,force fluid outward capillary membrane. – 2. Interstitial fluid pressure (Pif), force fluid inward capillary membrane, when Pif is positive but outward when Pif is negative. – 3. Capillary plasma colloid osmotic pressure (Πp), to cause osmosis of fluid inward the capillary membrane. – 4. The interstitial fluid colloid osmotic pressure (Πif), to cause osmosis of fluid outward the capillary membrane. 6  Capillary Exchange: Net filtration pressure 7  Blood pressure Force per unit area exerted on the wall of blood vessel by its contained blood. Normal blood pressure is 120/80 mm Hg. Differences in BP provide driving force to move blood from high pressure area to low pressure area. – BP raises to 120 mmHg during systole called systole blood pressure. – BP drops to 80 mmHg during diastole called diastolic blood pressure. BP is determined by – 1. Cardiac output 2. Blood volume 3. Vascular resistance. 8  Hypertension and Hypotension Increased systemic arterial BP is hypertension. Primary hypertension or Essential hypertension. – Absence of any underlying diseases – Benign hypertension (BP of 200/100 mmHg). During resting BP comes to normal. Leads to persistent increase in BP leads to vascular, cardiac and renal disorders. – Malignant hypertension (250/150 mm Hg) Severe symptoms of renal diseases and retinal hemorrhage. Secondary hypertension. – Cardiovascular, endocrine, renal and neurogenic. Hypotension – Decreased systemic arterial BP is hypotension. – Systolic BP decreased to 90 mm Hg. 9 Normal blood pressure 120 mm Hg 80 mm Hg 25 mm Hg 25 mm Hg 10 mm Hg 8 mm Hg 10  Blood pressure Systolic blood pressure (120 mm Hg). Directly proportional to CO. Diastolic blood pressure (80 mm Hg) Directly proportional to TPR. – When vasoconstriction administered, TPR also increased. – When vasodilation administered, TPR will decreased. MAP - Mean arterial pressure. (average of arterial pressures measured ms) – MAP = 60% of Diastolic BP + 40% of Systolic BP. – Drives the blood from heart to tissues. MSP – Mean systemic pressure. – Maintain the flow to wards back to heart (venous return). – Pressure maintained in systemic circulation (when heart stop working). – Mean pressure of arterial + capillary + venous = 6.5 mm Hg. 11 Factors Regulating Blood Pressure Inhalation decrease venous pressure EDV Preload Contractility After load TPR – Total Peripheral Resistance Systole BP Diastole BP 12  Regulation of blood pressure Short term or fast regulation (Rapid regulation) – Neurological regulation. Long term or slow regulation. (RAAS) – Renin – Angiotensin – Aldosterone 13 Neurological Regulation 14  Neurological regulation Nucleus of Tractus solitaries Mechanoreceptors Cardio inhibitory center Cardio accelerator center Inhibit vasomotor center 1. Venodilation 2. Artereodilation 3. Inhibit adrenal glands Baroreceptors in carotid sinus sensitive to decreased arterial pressure 15 Baroreceptors in arch of aorta sensitive to increased arterial pressure, not for 16  Chemoreceptors Two types of chemoreceptor's – Central chemoreceptor's (medulla near 4th ventricle). pCO2 > pH > pO2. – Stimulate by high H+ – Regulate sympathetic and parasympathetic outflow. – Peripheral chemoreceptor's Carotid bodies and Arotic bodies (out side the vessel). IX, X afferent nerve stimulate CNS (Tractus solitarius) pO2 > pCO2> pH. – Stimulate by low O2 (Hypoxemia) – Regulate sympathetic outflow. 17 18  Auscultatory method – To measure systolic and diastolic pressure. Stethoscope is placed over antecubital artery and BP cuff is inflated around upper arm. Inflated cuff compress the artery no sound heard by stethoscope, when released slowly a sound heard with each pulsation. – These sounds are called Korotkoff sounds. – Sound due to blood jetting through partly occluded vessel. The jet causes turbulence in vessel beyond the cuff and this sets up vibrations heard through the stethoscope. Pressure in cuff falls below systolic pressure, blood begins to slip through artery beneath the cuff during peak of systolic pressure, and begins to hear tapping sounds is systolic pressure. – When the cuff is fully deflated, no more sound is heard. When pressure in the cuff falls to equal diastolic pressure, the artery no longer closes during diastole. At this point it is diastolic pressure. sounds no longer present. 19 Auscultatory method Size of the cuff. 1. Under 1 year of age =2.5cm. 2. 1-3 yrs =5- 6cm 3. 4-8 yrs- 9- 10cm 4. Average adults =12.5cm 5. Obese adults20  Pulse pressure The difference between diastolic and systolic pressures – Two major factors affect the pulse pressure: 1. The stroke volume output of heart – Greater the stroke volume, pulse pressure also increased. 2. The compliance (total distensibility) of arterial tree. – less compliance of arterial system, greater the rise in pressure. – Decrease in compliance with ageing process, increase pulse pressure. Pulse pressure is determined by ratio of stroke volume output to compliance of arterial tree. 21  Amount of blood that moves to a particular organ in a given time. Blood flow (expressed in ml/min or L/minute). – Total blood flow is equal to CO = 5 - 6 L /min. Two types of blood flow. – 1. Laminar flow or streamline flow or Pulsatile flow BF at a steady rate through a long, smooth blood vessel, central portion of blood stays in center of vessel. When laminar flow occurs, velocity of flow in center of vessel is far greater than that toward outer edges (arteries). – Non pulsatile flow. In stable blood flow, there is no variation of flow in time. i.e. flow is non-pulsatile (veins). – 2. Turbulent flow Velocity of blood flow above the critical level. Blood flowing in all directions in 22 vessel and continually mixing within  Volume of blood flow Factors determining volume of blood flow – 1. Pressure gradient. – 2. Resistance to blood flow. – 3. Diameter of blood vessels. – 4. Velocity and viscosity of blood flow. 23  Blood flow Two major factors determine BF. 1. Pressure difference between two ends of vessel. – i.e., the force that pushes blood through vessels. 2. Resistance of flow, hindrance to flow through vessels. According to Ohms Law Blood flow is determined by = Q = ΔP/R. Where Q = Blood flow. ΔP = Difference in pressure. R = Resistance. 24  Blood Flow Vs Pressure and Resistance Blood flow (Q) is directly proportional to the difference in blood pressure (P) between two points in the circulation. – If P increases, blood flow speeds up. – if P decreases, blood flow declines. Blood flow is inversely proportional to resistance (R). – If R increases, blood flow decreases. R is more important than P in influencing local blood pressure. – Pressure difference b/w two ends of aorta = 20 mm Hg. – Pressure difference b/w arteries and arterioles =70 mm Hg. 25  Resistance to Vascular Flow Blood pumped by heart flows from high pressure systemic circulation (aorta) to low pressure side ( vena cava) through many miles of blood vessels arranged in series and in parallel. Vascular flow may be arranged in series or parallel. – When blood vessels are arranged in series, flow through each blood vessel is same and total resistance to blood flow (R total) is equal to the sum of the resistances of each vessel: – Blood flows through series, pressure decreases. Blood vessels branch extensively to form parallel circuits that supply blood to many organs and tissues of body. – This parallel arrangement permits each tissue to regulate its own blood flow. – The total resistance is far less than the resistance of any single blood vessel. – In each parallel artery pressure is the same. 26 Vascular Resistance Vascular resistances may be in series or parallel. If in series (like in renal vasculature, where peritubular capillaries are in series with glomerular capillaries), resistances are additive. when in parallel (like in pulmonary and systemic circulations) they are additive as reciprocals. – 1/RT= 1/R1+1/R2+1/R3, etc. – RT is less than any of the individual R terms 27 28  Resistance The three important sources of resistance are 1. Blood viscosity. When viscosity increases resistance also increases. Blood flow is inversely proportional to viscosity of blood. – In polycythemia (hematocrit raises to 60 – 70). Viscosity increases leads to decrease in blood flow. – In anemia. Viscosity decreases leads to increase in blood flow. 2. Total blood vessel length. – Longer the vessel, the greater the resistance. Obese persons have long blood vessel. 3. Blood vessel diameter. – Resistance inversely proportional with diameter. Atherosclerosis decrease the diameter of blood vessels. 29  Velocity of blood flow The rate of blood flow through a particular region Velocity of blood flow = Q/TCA Three factors determine the velocity of blood flow. – 1. Cardiac output The velocity is directly proportional with CO. – 2. Cross sectional area of the blood vessel (TCA) The velocity of blood flow is inversely proportional to vascular cross- sectional area. – 3. Viscosity of blood flow (minor factor). Mean volume of blood is directly proportional with viscosity of blood flow. Greater the viscosity, less the flow in vessel if all other factors are constant. Under resting conditions, velocity of aorta is 33 cm/sec 30 but only 1/1000 as in capillaries, about 0.3 mm/sec.  Conductance of Vessel Poiseuille’s Law. Integrating velocities of all concentric rings of flowing blood and multiplying them by areas of rings. F is rate of blood flow, ∆P is pressure difference b/w the ends of vessel, r4 is 4th power of radius of vessel, l is length of the vessel, η is viscosity of the blood. Thus, fourth power law makes it possible for arterioles, responding with only small changes in diameter to nervous signals or local tissue chemical signals, either to turn off almost completely the blood flow to the tissue or at the31 other extreme to cause a vast increase in flow.  Vascular Distensibility When pressure in blood vessels is increased, it dilates blood vessels and decreases their resistance. Distensible nature of arteries allows them to accommodate the pulsatile output of heart. Provides smooth, continuous flow of blood through the very small blood vessels of the tissues. – Most distensible vessels are veins. – Slight increases in venous pressure cause veins to store 0.5 to 1.0 liter of extra blood. Arteries, are eight times less distensible than veins. 32  Vascular Compliance or Capacitance Total quantity of blood that can be stored in a given portion of circulation for each mm of Hg. – Describes the distensibility of blood vessels times volume. – It is inversely related to elastance or stiffness. – Greater the amount of elastic tissue in vessel have higher the elastance but lesser the compliance. Compliance is equal to distensibility times volume. – Compliance of a systemic vein is 24 times that of its corresponding artery. – 8 times distensible and has a volume about 3 times as great. 33  Venous system serves as blood reservoir Venous system serves as a blood reservoir for the circulation hold 60% of blood. When body lost blood, arterial pressure begins to fall, nervous signals are elicited from carotid sinuses. Stimulate brain and sympathetic nerves to veins, causing them to constrict for normal work of circulatory system. The other blood reservoir are – The spleen – decrease in size release 100 ml of blood. – The liver – release several 100 ml of blood. – The large abdominal veins – contribute 300 ml of blood. – The venous plexus beneath the skin – contribute several 100 ml. Heart and lungs also contribute to 100 – 200 ml respectively. 34  Factors regulate blood flow to tissues – 1. Delivery of O2 to tissues. – 2. Delivery of other nutrients, such as glucose, AA and fatty acids. – 3. Removal of CO2 from the tissues. – 4. Removal of H+ ions from tissues. – 5. Maintenance of proper concentrations of other ions in tissues. – 6. Transport of hormones and other substances to tissues. 35  Hormonal vasoconstrictors – Norepinephrine and Epinephrine. Stimulated by sympathetic nervous system during stress and exercise. – Angiotensin II. Constrict powerfully small arterioles, Acts on many arterioles of body at same time to increase the TPR. Plays an integral role in regulation of arterial pressure. – Vasopressin. Concentration of circulating blood vasopressin after severe hemorrhage can rise high enough to increase the arterial pressure as much as 60 mm Hg. – Endothelin Severe blood vessel damage, release of endothelin and cause vasoconstriction helps to prevent extensive 36 bleeding from arteries as large as 5 mm in diameter.  Hormonal vasodilators – Bradykinin. Regulating blood flow and capillary leakage of fluids in inflamed tissues. Regulate blood flow in skin, salivary and GI glands. – Histamine Released by mast cells and basophils in the blood. During allergic condition, cause vasodilation and increased permeability of capillaries. 37  Vascular Control by Ions Vasoconstrictors Increase Ca2+ ion con causes vasoconstriction. Vasodilators Increase in K+ and Mg2+ ion cons. Increase in H+ ion con causes dilation of arterioles. Anions like acetate and citrate, cause mild degree. Increase in CO2 causes moderate vasodilation in most tissues, but marked vasodilation in the brain. 38 THE END 39