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Ch 15: Blood Flow and the Control of Blood Pressure, Part 2

Keypoints. Blood pressure (BP) and Regulation Exchange at capillaries Lymphatic system Cardio-vascular diseases. Ch 15: Blood Flow and the Control of Blood Pressure, Part 2. 8 L . R =.  r 4. Review:. R = Resistance L = Length of “pipe” = viscosity r = radius.

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Ch 15: Blood Flow and the Control of Blood Pressure, Part 2

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  1. Keypoints Blood pressure (BP) and Regulation Exchange at capillaries Lymphatic system Cardio-vascular diseases Ch 15: Blood Flow and the Control of Blood Pressure, Part 2

  2. 8L  R = r4 Review: • R = Resistance • L = Length of “pipe” • = viscosity • r = radius

  3. Control of Blood Flow 1. Local control: • By paracrines • O2 CO2 NO (in erection) • In the heart, adenosine serves as a paracrine to dilate coronary arteries • Others: histamine, • ↓ O2 and ↑ CO2 arteriolar dilation • The ↑ flow is hyperemia

  4. Control of blood flow, cont’d 2. Endocrine: • ANP and Angiotensin II (Chapt 20) 3. ANS (mostly sympathetic): • NE on α receptors  vasoconstriction • E on β2 receptors  vasodilation (F or F)

  5. Distribution of Blood

  6. Exchange at the Capillaries • Capillaries are anatomically designed for exchange • Continuous (leaky junctions) • Fenestrated (kidney and intestine) • Sinusoids in liver, bone marrow and kidney • Capillaries in the brain are less leaky and are surrounded by astrocytes and pericytes BBB Fig 15-16

  7. Exchange at the Capillaries • Capillary blood flow: Greatest total cross sectional area  Lowest Velocity • Most cells within 0.1mm of capillary – why? • Direct correlation between # of caps and metabolic needs of tissue • Three types of exchange of molecules across the barrier:

  8. Paracellular diffusion – between the cells Leaky cell-cell junctions Transendothelial transport (transcytosis) through the cells Endo- and exocytosis, diffusion through the endothelial cell Bulk flow: mass movement of H2O and dissolved solutesas result of hydrostatic or osmotic pressure Filtration – flow direction out of capillaries Absorption – flow direction into capillaries Methods of Capillary Exchange

  9. Two Forces Regulate Capillary Bulk Flow • Hydrostatic P: lateral component of fluid flow • Colloid Osmotic P: due to solute difference (main solute difference due to proteins inside the capillary) Mostly: • Net filtration at arterial end • Net re-absorption at venous end Fig 15-18

  10. Lymphatic System Close functional association with three other systems • Cardiovascular • Digestive • Immune

  11. Lymphatic System Functions • Return filtered fluid & proteins to circulatory system (anatomical design!) • Transfer fat from small intestine to circulatory system (lacteals) • Trap and deal with pathogens

  12. Edema Due to disruption of capillary exchange 2 major causes: • Blockage of lymph drainage • Cancer & fibrotic growth • Pathogens • Pregnancy • Capillary filtration > absorption • Venous pressure  due to right / left heart failure, backs up in to capillaries • Plasma protein concentration  due to liver failure or severe malnutrition (Kwashiorkor) reduces colloid osmotic pressure •  in interstitial protein

  13. Regulation of Blood Pressure • Reflex control: Baroreceptor Reflex = 1o homeostatic control for BP; adjustments for standing • Medullary cerebrovascular control center (CVCC) integrates neural control (fig 15-23) • Baroreceptors = stretch sensitive receptors in aorta and carotid artery Fig 15-21 Cardiovascular System: Blood Pressure Regulation

  14. Regulation of Blood Pressure, cont’d • Arterial chemoreceptors activated by O2 • Cerebral cortex • emotional responses such as blushing & fainting  vasovagal response • Integration with Kidney function Orthostatichypotension normally triggers Baroreceptor reflex

  15. Cardiovascular Diseases • Account for ~ 1/2 of deaths in US – most common: CAD • Uncontrollable & controllable risk factors • Gender, age, genetics • Cigarette smoking, obesity, high BP, high cholesterol, DM

  16. Cigarette Smoking: • Nicotinic cholinergic receptors stimulate sympathetic neurons at precapillary sphincters • Vasoconstriction & BP  • Risk for atherosclerosis  • Carbon monoxide (myocardium extracts most of O2 brought to it under resting conditions)

  17. Atherosclerosis • Common to several cardiovascular diseases • Changes in artery walls start with extracellular lipid deposits • Macrophages ingest the EC LDL-cholesterol • Called foam cells • Fatty streaks just under endothelial lining of larger arteries • Macrophageparacrines ↑ smooth muscle cells • Smooth muscle cells proliferate  stable plaques vs. vulnerable (easy to rupture) plaques  platelet activation  thrombus • Cerebral and coronary thrombi and emboli  Stroke or MI Fig 15-24

  18. Role of Hypertension • Essential HT = idiopathic and/or hereditary • Creates damage to endothelium • Plaques form and occlude lumina • ↑ BP  ↑ afterload (R)  cardiac hypertrophy • CHF • Ca2+ channel blockers hyperpolarize smooth muscle cells  less likely to contract • ACE inhibitors block ACE-I → ACE II • Vasodilation • Diuretics  blood volume • β-blockers  catecholamine effects

  19. Running Problem: Essential Hypertension

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