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The Cardiovascular System: Blood Vessels and Hemodynamics

A. Anatomy of blood vessels 1. Arteries a. Elastic (conducting) arteries b. Muscular (distributing) arteries c. Anastomoses 2. Arterioles 3. Capillaries 4. Venules 5. Veins 6. Blood distribution

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The Cardiovascular System: Blood Vessels and Hemodynamics

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  1. A. Anatomy of blood vessels 1. Arteries a. Elastic (conducting) arteries b. Muscular (distributing) arteries c. Anastomoses 2. Arterioles 3. Capillaries 4. Venules 5. Veins 6. Blood distribution B. Capillary exchange a. Diffusion b. Vesicular transport c. Bulk flow (filtration and reabsorption) C. Hemodynamics: physiology of circulation 1. Velocity of blood flow 2. Volume of blood flow a. Blood pressure b. Peripheral resistance 3. Venous return D. Control of blood pressure and blood flow 1. Cardiovascular center a. Input to cardiovascular center b. Output from cardiovascular center 2. Neural regulation a. Baroreceptors b. Chemoreceptors 3. Hormonal regulation 4. Autoregulation (local control) E. Blood vessel routes The Cardiovascular System: Blood Vessels and Hemodynamics

  2. Arteries • 1. lumen • 2. tunica intima a. endothelium b. internal elastic lamina • 3. tunica media • 4. tunica adventitia

  3. Arterial Properties • 1. elasticity • 2. contractility a. vasoconstriction b. vasodilation

  4. Arterial Types Muscular Arteries • 1. elastic (conducting) a. elastin b. pressure reservoirs • 2. muscular (distributing) a. great contractility b. blood shunting c. anastomoses d. collateral circulation Elastic arteries Muscular Arteries

  5. Arterioles • 1. highest contractility • 2. blood shunting

  6. Routing of Blood Flow

  7. Capillaries • 1. microscopic • 2. distribution • 3. exchange • 4. simple squamous • 5. precapillary sphincters • 6. vasomotion Endothelium basement membrane

  8. Capillary Types • 1. continuous • 2. fenestrated • 3. sinusoids

  9. Venules and Veins • 1. same basic tunics • 2. larger lumen • 3. thinner tunica media • 4. very distensible • 5. valves Valve

  10. Blood Reservoirs Skin, liver, and spleen

  11. Capillary Exchange • 1. diffusion • 2. vesicular transport • 3. bulk flow a. filtration b. reabsorption c. Starling's law of the capillaries • What is vasomotion?

  12. Bulk Flow is Dependent On Four Pressures • 1. blood hydrostatic pressure (BHP = 30 mm Hg-arterial) (outward force) = 10 mm Hg-venous • 2. interstitial fluid hydrostatic pressure (IFHP = 0 to -3(suction) mm Hg) (inward force) • 3. blood colloid osmotic pressure (BCOP = 28 mm Hg) (inward force) • 4. interstitital fluid osmotic pressure (IFOP = 8 mm Hg) (outward force)

  13. Net Filtration Pressure (Arterial End) • NFP = outward forces - inward forces = (BHP + IFOP) - (BCOP + IFHP) = (30 + 8) - (28 + 0) = (38) - (28) = +10 mm Hg • If IFHP was (-3) then NFP = 13 mm Hg • net flow of fluid is? out of the capillary (filtration)

  14. Net Filtration Pressure- Venous End • NFP = outward forces - inward forces = (BHP + IFOP) - (BCOP + IFHP) = (10 + 8) - (28 + 0) = (18) - (28) = -10 mm Hg • If IFHP was (-3) then NFP = -7 mm Hg • net flow of fluid is? into of the capillary (reabsorption)

  15. The Forces of Capillary Filtration and Absorption

  16. Capillary Exchange

  17. Hemodynamics Blood flow(ml/min) Perfusion (ml/min/g) Blood flow velocity (mm/sec) Cross-sectional area (cm2) capillaries (2500 cm2) venules (250 cm2) 1200 mm/sec total cross sectional area 15mm/sec Flow α∆Pressure Resistance veins (80 cm2) If total cross-sectional area then velocity (aorta to capillaries) aorta (2.5 cm2) velocity 5 mm/sec arterioles (40 cm2) arteries (20 cm2) 0.4 mm/sec 80 mm/sec (IVC) If total cross-sectional area then velocity (capillaries to venae cavae) venae cavae(8 cm2) Relationship between blood flow velocity and total cross-sectional area of the vascular tree

  18. Blood Pressure • 1. What is blood pressure? • 2. direct determinants of BP a. cardiac output b. blood volume c. peripheral resistance

  19. Volume of Blood Flow • CO = SV x HR = 5.25 L/min (the volume of blood circulating through systemic or pulmonary vessels each minute) • Two other factors influence cardiac output: 1) blood pressure 2) resistance (opposition) • CO = mean arterial blood pressure (MABP) resistance (R)

  20. Resistance (Opposition to Flow) • 1. blood viscosity • 2. total blood vessel length • 3. blood vessel radius

  21. Systemic vascular resistance (SVR)(total peripheral resistance (TPR) • 1. major function of arterioles • 2. vasodilation vs vasocontriction a. Blood flow is proportional to the fourth power of vessel radius. r = 1 mm r4 = 14 = 1 flow = 1 mm/sec r = 2 mm r4 = 24 = 16 flow = 16 mm/sec r = 3 mm r4 = 34 = 81 flow = 81 mm/sec b. Therefore, a 3-fold change in resistance exerts an 81-fold change in velocity.

  22. Mechanisms of Venous Return • 1. decreasing x-sec area • 2. venous valves • 3. muscle pumps • 4. respiratory pump

  23. Control of Blood Pressure and Blood Flow • The cardiovascular center (CVC) consists of three groups of neurons: • 1. cardioacceleratory neurons • 2. cardioinhibitory neurons • 3. vasomotor neurons

  24. 1. input a. higher brain centers b. baroreceptors c. chemoreceptors Nervous Input to Medullary Cardiovascular Center CVC Input higher brain cerebral cortex limbic system hypothalamus baroreceptors (blood pressure) chemoreceptors (O2, H+, CO2) medulla oblongata

  25. 2. output a. vagus (X) nerve b. sympathetic neurons (1) heart (2) arterioles Nervous Output From Medullary Cardiovascular Center CVC Output Medulla oblongata vagus nerve (X) heart (decrease rate) cardiac accelerator nerves (sympathetic) heart (increase rate and contractility) vasomotor nerves (sympathetic) blood vessels (vasoconstriction and vasodilation)

  26. Neural Control of the Heart Reflexes Reflexes activate the Vasomotor center – results in vasoconstriction/vasodilation of arterioles Baroreflexes and chemoreflexes carotid sinus and aortic sinus reflexes right atrial (Bainbridge) reflex Medullary ischemic reflex sensory fibers in c.n. IX carotid sinus baroreceptors cerebrum aortic sinus baroreceptors hypothalamus SA node cardiovascular center in medulla AV node spinal cord parasympathetic fibers in c.n. X sympathetic fibers in spinal nerves

  27. Baroreceptor Reflex

  28. Chemoreceptor Reflex

  29. Negative Feedback of Neural Control CONTROLLED CONDITION a stimulus or stress disrupts homeostasis by causing a decrease in blood pressure RETURN TO HOMEOSTASIS increased blood pressure RECEPTOR baroreceptors in carotid and aortic sinuses are stretched less, resulting in decreased rate of nerve impulses to the cardiovascular center EFFECTORS • contractility = stroke volume • heart rate • therefore cardiac output • 3. vasoconstriction = resistance CONTROL CENTER 1. increased sympathetic output via cardioacceleratory center 2. decreased parasympathetic output from cardioinhibitory center

  30. Hormonal Regulation • 1. epinephrine and norepinephrine potent vasoconstrictor  increased resistance  increased BP increased HR + increased SV = increased CO  increased BP • 2. antidiuretic hormone increases water retention by kidneys  increased blood volume  increased BP • 3. angiotensin II potent vasoconstrictor  increased resistance  increased BP • 4. aldosterone promotes sodium retention by kidneys increased water retention  increased blood volume  increased BP • 5. atrial natriuretic peptide decreases sodium retention by kidneys decreased water retention  decreased blood volume  decreased BP

  31. Autoregulation • Ability of tissues to regulate their own blood supply • Metabolic theory of autoregulation Inadequate perfusion = A. Decreased O2  vasodilation B. Increased wastes (CO2, H+, K+, adenosine)  vasodilation Adequate perfusion again = vasoconstriction • Vasoactive Chemicals - secreted by platelets, endothelial cells, perivascular tissues with trauma - Examples include Histamine, prostaglandins, bradykinin stimulate vasodilation • Reactive hyperemia

  32. Summary of Blood Pressure Control decreased blood pressure leads to decreased activity of baroreceptors in carotid and aortic sinuses increased activity leads to decreased nervous input to cardioinhibitory center increased activity leads to • increased activity of the: • cardioacceleratory center • vasomotor center decreased activity leads to increased sympathetic output from spinal cord norepinephrine secretion causes increased heart rate increased stroke volume increased vasoconstriction leads to leads to leads to increased cardiac output increased resistance leads to leads to increased blood pressure negative feedback

  33. Blood Vessel Routes (see Handout)

  34. Beginning of the Aorta

  35. Arterial Supply Head and Neck

  36. Arterial Circle of the Brain- Circle of Willis

  37. Arterial Supply to the Upper Arm

  38. Arterial Supply to the Thorax

  39. Arterial Supply to the Abdomen

  40. Arterial Supply to the Pelvic Region and Lower Limb

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