Ch 15: Blood Flow and the Control of Blood Pressure

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

Fig 15-2

Angiogenesis • Growth of new blood vessels– occurs during • Normal body maturation and growth • Monthly re-growth of functional endometrium • Wound healing • Endurance training • Cancer growth • Clinical implications:Promote or inhibit angiogenesis with relevant cytokines

Fig 15-4 Blood Pressure Pressure created by ventricular contraction is driving force for blood flow Pulsatile blood flow in arteries  Elastic arteries expand and recoil for continuous blood flow Pulse wave disappears past arterioles

Blood Pressure (BP) Measurements • Ventricular pressure difficult to measure  measure arterial BP • BP highest in the arteries – falls continuously throughout systemic circulation • Read as “Systolic over diastolic”– normal value  120 / 80 mm Hg • 2003: New range for blood pressure readings between 120/80 and 139/89 “Prehypertension” • Diastolic pressure in ventricle: ? mm Hg

BP Estimated by Sphygmomanometry Auscultation of brachial artery with stethoscope in cubital fossa Based on effects oflaminar flow vs. turbulent flow

Principles ofSphygmomanometry Cuff inflated until brachial artery compressed and blood flow stopped kind of sound? Compare to Fig 15-7

Slowly release pressure in cuff: turbulent flow

Pressures at which . . . . . . sound (= blood flow) first heard: . . . sound disappeared: CDAnimation Cardiovascular System: Measuring Blood Pressure

Mean Arterial Pressure • Sometimes useful to have single value for driving pressure: Mean Arterial Pressure MAP = Diastolic P + 1/3 Pulse Pressure(for 60 -80 bpm) • MAP for 120/80 = ? • MAP closer to diastolic pressure – why?

MAP influenced by • Cardiac output • Peripheral resistance (role of arterioles  see Ch14)most common cause of hypertension • Total blood volume • Blood distribution Figs 15-8 & 10

BP too low: • Driving force for blood flow unable to overcome gravity • O2 supply to brain  • Symptoms?

Shock = generalized circulatory failure • Hypovolemic shock  volume loss (dehydration, blood loss, burns) • Distributive shock  loss of vascular tone (anaphylactic, septic, toxic) • Cardiogenic shock  pump failure • Dissociative shock  inability of RBC to deliver O2 (CO poisoning) Cell damage due to inadequate perfusion Signs and symptoms? Management ?

BP too high: • Weakening of arterial walls lead to Aneurysms Risk of rupture & hemorrhage • Cerebral hemorrhage • Rupture of major artery

Exchange at the Capillaries • Capillaries are anatomically designed for exchange • Capillary blood flow: Greatest total cross sectional area  Velocity ? • Most cells within ____ µm of capillary – why? • Direct correlation between # of caps and metabolic needs of tissue • Three types of exchange of molecules across the barrier Fig 15-16

Paracellular diffusion Transendothelial transport (transcytosis) – some diffusion Bulk flow: mass movement of H2O and dissolved solutesas result of hydrostatic or osmotic pressure Filtration – flow direction out of caps Absorption – flow direction into caps Methods of Capillary Exchange

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

= Pcap + cap Fluid Exchange cap = 25 mmHg     Fig 15-18

3) Lymphatic System Close functional association with three other systems

Lymphatic System Functions • Return filtered fluid & proteins to circulatory system (anatomical design!) – Fig 15-18 • Transfer fat from small intestine to circulatory system • Trap and deal with pathogens

Edema Due to disruption of capillary exchange 2 major causes: • Blockage of lymph drainage • Cancer & fibrotic growth • Pathogens • Capillary filtration > absorption • Venous pressure  due to right / left heart failure • Plasma protein concentration  due to liver failure or severe malnutrition (Kwashiorkor)

Right or Left Heart Failure? Alveolar Flooding

Sweden Kroniskt invalidiserande lymfödem (2,1 liter) i höger arm sedan 8 år.

Kwashiorkor

Regulation of Blood Pressure • Reflex control:Baroreceptor Reflex = 1o homeostatic control for BP • Baroreceptors = stretch sensitive ______receptors in aorta and carotid artery • Medullary CVCC integrates neural control Cardiovascular System: Blood Pressure Regulation CD Animation Fig 15-22

Additional Control of BP • Arterial chemoreceptors activated by O2 • Cerebral cortex • emotional responses such as blushing & fainting  vasovagal response • Integration with Kidney function Orthostatichypotension normally triggers Baroreceptor reflex

Cardiovascular Disease (CVD) • Account for ~ 1/2 of deaths in US – most common: CAD or CHD • Uncontrollable & controllable risk factors • Gender, age, genetics • Cigarette smoking, obesity, high BP, high cholesterol, DM

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

Atherosclerosis Changes in artery walls start with lipid deposits Macrophage ingests LDL-cholesterol Fatty streaks just under endothelial lining of larger arteries Macrophageparacrines attract smooth muscle cells Smooth muscle cells proliferate  stable plaques vs. vulnerable plaques Cerebral and coronary thrombi and emboli  ? Fig 15-24

Role of Elevated Cholesterol in Development of Atherosclerosis • Lipids insoluble in plasma  lipoproteins • Chylomicronto muscle & adipose cells,VLDLto adipose cells • 2 main types of cholesterol carriers:HDLto livervs.LDL to body cells

the end Essential Hypertension

Ch 15: Blood Flow and the Control of Blood Pressure