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Peripheral Circulation and Regulation

Peripheral Circulation and Regulation. Peripheral Circulatory System. Systemic vessels Transport blood through most all body parts from left ventricle and back to right atrium Pulmonary vessels Transport blood from right ventricle through lungs and back to left atrium

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Peripheral Circulation and Regulation

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  1. Peripheral Circulation and Regulation

  2. Peripheral Circulatory System • Systemic vessels • Transport blood through most all body parts from left ventricle and back to right atrium • Pulmonary vessels • Transport blood from right ventricle through lungs and back to left atrium • Blood vessels and heart regulated to ensure blood pressure is high enough for blood flow to meet metabolic needs of tissues

  3. Blood Vessel Structure • Arteries • Elastic, muscular, arterioles • Capillaries • Blood flows from arterioles to capillaries • Most of exchange between blood and interstitial spaces occurs across the walls • Blood flows from capillaries to venous system • Veins • Venules, small veins, medium or large veins

  4. Capillaries • Capillary wall consists mostly of endothelial cells • Types classified by diameter/permeability • Continuous • Do not have fenestrae • Fenestrated • Have pores • Sinusoidal • Large diameter with large fenestrae

  5. 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

  6. Structure of Arteries and Veins • Three layers except for capillaries and venules • Tunica intima • Endothelium • Tunica media • Vasoconstriction • Vasodilation • Tunica adventitia • Merges with connective tissue surrounding blood vessels

  7. Structure of Arteries • Elastic or conducting arteries • Largest diameters, pressure high and fluctuates • Muscular or medium arteries • Smooth muscle allows vessels to regulate blood supply by constricting or dilating • Arterioles • Transport blood from small arteries to capillaries

  8. Structure of Veins • Venules and small veins • Tubes of endothelium on delicate basement membrane • Medium and large veins • Valves • Allow blood to flow toward heart but not in opposite direction • Atriovenous anastomoses • Allow blood to flow from arterioles to small veins without passing through capillaries

  9. Blood Vessel Comparison

  10. Aging of the Arteries • Arteriosclerosis • General term for degeneration changes in arteries making them less elastic • Atherosclerosis • Deposition of plaque on walls

  11. Pulmonary Circulation • Moves blood to and from the lungs • Pulmonary trunk • Arises from right ventricle • Pulmonary arteries • Branches of pulmonary trunk which project to lungs • Pulmonary veins • Exit each lung and enter left atrium

  12. Systemic Circulation: Arteries • Aorta • From which all arteries are derived either directly or indirectly • Parts • Ascending, descending, thoracic, abdominal • Coronary arteries • Supply the heart

  13. Branches of the Aorta

  14. Systemic Circulation: Veins • Return blood from body to right atrium • Major veins • Coronary sinus (heart) • Superior vena cava (head, neck, thorax, upper limbs) • Inferior vena cava (abdomen, pelvis, lower limbs) • Types of veins • Superficial, deep, sinuses

  15. Major Veins

  16. Veins of Thorax

  17. Hepatic Portal System

  18. Dynamics of Blood Circulation • Interrelationships between • Pressure • Flow • Resistance • Control mechanisms that regulate blood pressure • Blood flow through vessels

  19. Laminar and Turbulent Flow • Laminar flow • Streamlined • Outermost layer moving slowest and center moving fastest • Turbulent flow • Interrupted • Rate of flow exceeds critical velocity • Fluid passes a constriction, sharp turn, rough surface

  20. Blood Pressure • Measure of force exerted by blood against the wall • Blood moves through vessels because of blood pressure • Measured by listening for Korotkoff sounds produced by turbulent flow in arteries as pressure released from blood pressure cuff

  21. Blood Pressure Measurement

  22. Blood flow Amount of blood moving through a vessel in a given time period Directly proportional to pressure differences, inversely proportional to resistance Poiseuille’s Law Flow decreases when resistance increases Flow resistance decreases when vessel diameter increases Viscosity Measure of resistance of liquid to flow As viscosity increases, pressure required to flow increases Blood Flow, Poiseuille’s Lawand Viscosity

  23. 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 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 Critical Closing Pressure, Laplace’s Law and Compliance

  24. Physiology of Systemic Circulation • Determined by • Anatomy of circulatory system • Dynamics of blood flow • Regulatory mechanisms that control heart and blood vessels • Blood volume • Most in the veins • Smaller volumes in arteries and capillaries

  25. Cross-Sectional Area • As diameter of vessels decreases, the total cross-sectional area increases and velocity of blood flow decreases • Much like a stream that flows rapidly through a narrow gorge but flows slowly through a broad plane

  26. Pressure and Resistance • Blood pressure averages 100 mm Hg in aorta and drops to 0 mm Hg in the right atrium • Greatest drop in pressure occurs in arterioles which regulate blood flow through tissues • No large fluctuations in capillaries and veins

  27. 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

  28. Capillary Exchange andInterstitial Fluid Volume Regulation • Blood pressure, capillary permeability, and osmosis affect movement of fluid from capillaries • A net movement of fluid occurs from blood into tissues. Fluid gained by tissues is removed by lymphatic system.

  29. Fluid Exchange Across Capillary Walls

  30. Vein Characteristics Venous return to heart increases due to increase in blood volume, venous tone, and arteriole dilation Effect of Gravity In a standing position, hydrostatic pressure caused by gravity increases blood pressure below the heart and decreases pressure above the heart Vein Characteristics andEffect of Gravity on Blood Pressure

  31. Control of Blood Flow by Tissues • Local control • In most tissues, blood flow is proportional to metabolic needs of tissues • Nervous System • Responsible for routing blood flow and maintaining blood pressure • Hormonal Control • Sympathetic action potentials stimulate epinephrine and norepinephrine

  32. Local Control of Blood Flow by Tissues • Blood flow can increase 7-8 times as a result of vasodilation of metarterioles and precapillary sphincters in response to increased rate of metabolism • Vasodilator substances produced as metabolism increases • Vasomotion is periodic contraction and relaxation of precapillary sphincters

  33. Nervous Regulation of Blood Vessels

  34. Short-Term Regulation ofBlood Pressure • Baroreceptor reflexes • Change peripheral resistance, heart rate, and stroke volume in response to changes in blood pressure • Chemoreceptor reflexes • Sensory receptors sensitive to oxygen, carbon dioxide, and pH levels of blood • Central nervous system ischemic response • Results from high carbon dioxide or low pH levels in medulla and increases peripheral resistance

  35. Baroreceptor Reflex Control

  36. Baroreceptor Effects

  37. Chemoreceptor Reflex Control

  38. Effects of pH and Gases

  39. Long-Term Regulation of Blood Pressure • Renin-angiotensin-aldosterone mechanism • Vasopressin (ADH) mechanism • Atrial natriuretic mechanism • Fluid shift mechanism • Stress-relaxation response

  40. Renin-Angiotensin-AldosteroneMechanism

  41. Vasopressin (ADH) Mechanism

  42. Atrial natriuretic Hormone released from cardiac muscle cells when atrial blood pressure increases, simulating an increase in urinary production, causing a decrease in blood volume and blood pressure Fluid shift Movement of fluid from interstitial spaces into capillaries in response to decrease in blood pressure to maintain blood volume Stress-relaxation Adjustment of blood vessel smooth muscle to respond to change in blood volume Long Term Mechanisms

  43. Shock • Inadequate blood flow throughout body • Three stages • Compensated: Blood pressure decreases only a moderate amount and mechanisms able to reestablish normal blood pressure and flow • Progressive: Compensatory mechanisms inadequate and positive feedback cycle develops; cycle proceeds to next stage or medical treatment reestablishes adequate blood flow to tissues • Irreversible: Leads to death, regardless of medical treatment

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