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Cardiovascular Physiology Function of cardiovascular system: 1-Transport and distribute essential substance to the tissues. 2-Remove by-product of metabolism. 3-Regulate body temperature. 4-Humoral communication throughout the body. 5-Adjustment of O2 and nutrient supply in different physiology states. The CVS consists of: 1-Pump(heart) pulmonary circulation , systemic circulation 2-Distributing and collecting tubes (arteries and veins). 3-Extensive system of thin vessels which permit rapid exchange between tissues and vascular channels (capillaries). Hemodynamics The arterial blood flow is pulsatile in character (due to cardiac ejection) and become steady in the capillaries because of large surface area so the exchange of diffusible substance occur between blood and tissue. *The heart is an extremely complication pump. *The blood vessels are multi branched elastic tubes of varying diameters. *The blood is not a simple fluid, it is a suspension of cells (RBCs, WBCs, platelets), lipid globules, proteins. Velocity of Blood Stream Velocity The rate of displacement with respect to time (cm/sec.) or (distance per unit time ) . Flow: volume per unit time (cm3/sec.) V=velocity Q= flow A=cross-sectional area Steady flow: is the absence of variation of flow in time (non pulsation flow). Laminar flow: is a gradient of flow rate between the stationary peripheral layer of fluid and the rapidly flowing central layers of fluid. Viscosity: is the friction exerted by the movement of laminae of blood relative to each other. 1 Resistance: hydraulic resistance is the ratio of pressure drop to flow. The Vascular System 1-Blood flow: the amount of blood that passes through a blood vessel in a given time. Factors which control blood flow are: a- differences in pressure between the two ends of the tube. b- resistance of flow which means friction between tube wall and fluid and between the molecules of the fluid. So resistance depend on the nature (property) of the fluid (viscosity) and the geometry of the tube (length and radius). *The flow is directly proportional to the pressure difference and inversely proportional to the resistance. Fraction viscosity resistance flow Length flow (but it is constant in blood vessels). *radius is markedly determine the resistance while the length of blood vessels and viscosity of blood is constant. 2-Arterial Blood pressure: The contraction of the ventricles ejects blood into the systemic and pulmonary arteries during systole. This will distends the arteries by raising arterial blood pressure. The systolic pressure: is the maximum pressure reachen during peak ventricular ejection. The diastolic pressure: is the minimal pressure occur just before ventricular contraction. The blood pressure :is generally recorded as: Systolic / Diastolic=120/80 mm Hg. Plus pressure: can be felt in an artery is due to the difference between systolic and diastolic pressure. Plus pressure= systolic pressure-diastolic pressure = 120-80=40mmHg. Factors which change pulse pressure are: 1- an increased stroke volume will systolic pressure. 2 2-decreased arterial distensibility (as in arteriosclerosis) will systolic pressure. The bood pressure is regulated by: 1-Cardic output (SV and HR) C.O BP. 2-Peripheral resistance R BP. 3-Blood viscosity B.vis. BP. *Polycythemia and plasma proteins viscosity. Mean arterial pressure: Is the most important pressure because it is the average pressure driving blood into the tissues throughout the cardiac cycle. Mean arterial pressure is not the value half way between systolic and diastolic pressure because diastolic usually lasts longer than systole. Mean arterial pressure= 1/3 syst.pr.+2/3 diast.pr. = 1/3x120+2/3x80 = 93 mmHg Hypertension : increased arterial blood pressure than normal. Hypotension: decreased arterial blood pressure than normal. Baroreceptors: are pressure or stretch receptors located in the carotid sinus and aortic arch. They respond to the changes in the arteries induced by changes in arterial blood pressure through either inhibition or stimulation of the vasomotor center in the medulla oblongata. Mareys Law: is the relationship between increased blood pressure and decreased heart rate during regulation of blood pressure. Chemoreceptors: are receptors found in the vasomotor center that sensitive to CO2 and in the aortic are carotid bodies that sensitive to O2. 3 Cerebral Circulation R. external carotid artery supplies right side of thyroid gland , tongue, throat, face , ear , scalp and Dura matter. R. internal carotid artery supplies brain , right eye, and right sides of forehead and nose. L. external and internal carotid arteries are similar to that of right . * Inside the cranium , anastomoses of left and right internal carotids along with basilar artery from a hexagonal arrangement of blood vessels at base of brain near sella turcica called cerebral arterial circle (circle of Willis). From this circle arise arteries supplying most of the brain . The function of the cerebral arterial circle are: 1-to equalize blood pressure to brain 2-provide alternate routes for blood to brain in case of arterial damage. Exchange of gases and material occur in the sinuses of the brain. Right and left internal jugular veins receive blood from face and neck. They arise as continuation of sigmoid sinuses at base of skull. Intracranial vascular sinuses are located between layers of Dura matter and receive blood from brain, Other sinuses that drain into internal jugular include superior sagittal sinus, inferior sagittal sinus, straight sinus and transverse (lateral) sinuses. Internal jugulars descend on either side of neck and join with sub clavian veins in the same side to form right and left brachiocephalic veins. From here blood flows into superior vena cava. Right and left external jugulars. They drain blood from parotid (salivary) glands, facial muscle, scalp and other superficial 4 structures into subclavian veins, then into brachiocephalic veins and then into superior vena cava. Fetal circulation : It is not necessary for the fetal heart to pump much blood through either the lungs or the liver because : 1-the lungs are nonfunctioning during fetal life. 2-the liver is only partially functional. 5