BIOL 2002C 1st Edition Lecture 10 Outline of Current Lecture I Control of Blood Flow in Tissues II Regulation of MAP Current Lecture Describe the exchange of materials across a capillary wall Describe the 4 ways that chemicals can move from the bloodstream across endothelial cell membranes of capillaries and then into interstitial fluids and the reverse See Fig from another text posted on Blackboard Be able to label this Fig both in terms of the structures shown and where each of the 4 ways of moving chemicals is labeled in the figure a Direct Diffusion lipid soluble molecules like oxygen and carbon dioxide diffuse through the lipid bilayers of the endothelial cell membrane non polar hydrophobic substances b Pinocytosis Some larger molecules like proteins are transported by vesicles through pinocytosis it is active transport c Intercellular clefts narrow passageways small water soluble molecules like sugar and amino acids can diffuse through fluid filled capillary clefts d Fenestrations larger pathways windows permeability varies from high liver to low brain 21 4 CONTROL OF BLOOD FLOW IN TISSUES Explain how local mechanisms regulate blood flow How do pre capillarysphincters operate to control blood flow into capillary beds Fig 21 3 and Fig from other text Microcirculation Regulated by precapillary sphincters composed of smooth muscle Fig 21 37 Occurs when precapillary sphincters are open Regulation of precapillary sphincters I by nerve fibers and local chemical conditions Sphincters are found on arterial end These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Metarteriole thoroughfare channel vascular shunt When precapillary sphincters are closed blood does not flow thru capillary bed but proceeds directly to the venule this happens when tissues have low metabolic needs Define the hydrostatic and osmotic pressures that are exerted within capillaries Explain how the interaction of hydrostatic and osmotic pressures between capillaries and interstitial fluids leads to fluid leaving or entering capillaries Fig 21 36 Be able to calculate NFP given HP s and OP s and know how to interpret the NFP in terms of the direction fluids would move into or out of capillaries a Colloid Osmotic Pressure OP force caused by proteins like albumin in water which can t leave capillaries so tend to draw water toward them Constant osmotic pressure along capillary bed of 28 mm Hg in capillaries only 8 mm Hg in interstitial fluids Colloid osmotic pressure tends to draw fluids INTO capillaries b Hydrostatic pressure HP Capillary force exerted by blood against capillary wall o same as capillary BP o higher at arteriole end 30 mm Hg than venous 10 mm Hg Interstitial fluid pressure of fluids outside capillaries o minimal because fluid quickly removed by lymphatics 3 mm Hg HP tends to force fluids OUT of capillaries Net Filtration Pressure NFP HPc HPif OPc OPif outward inward 30 3 28 8 33 20 If NFP is POSITIVE fluid is driven out of the capillary if NFP is NEGATIVE fluid is drawn back into the capillary 13 Define Autoregulation keeping blood pressure constant with priority to brain heart and kidneys Long term can involveangiogenesis for production of new blood vessels and enlargement of existing vessels Short term Metabolic vasodilation of arterioles serving capillary beds of needy tissues caused by decreasing levels of O2 or nutrients increasing waste products NO nitric oxide attaches to Hb in lungs and is released in tissues when O2 is unloaded to cause local vasodilation of capillaries 21 5 REGULATION OF MEAN ARTERIAL PRESSURE Recall the definitions of mean arterial pressure cardiac output and peripheral resistance Know how blood pressure changes when cardiac output peripheral resistance and blood volume change Fig 20 21 goal is to regulate MAP to maintain adequate flow to entire body Since blood flow CO P1 P2 PR BP CO x PR therefore BP is directly proportional to Cardiac output Peripheral resistance Blood volume since CO HR x SV Since Homeostasis strives to keep BP constant a change in one of these factors usually causes a compensatory change in one of the others Describe the general focus of short term controls changing peripheral resistance by changing blood vessel diameter Use nervous neural or hormonal controls Respond very quickly to BP changes Short term mechanoreceptors baroreceptors to adapt to BP within a few days andlong term controls changing blood volume Kidney very important in regulating blood volume close to 5 L Some mechanisms begin to respond within minutes but continue to work for much longer periods of time What is the vasomotor center Fig 21 38 cluster of sympathetic neurons in medulla oblongata vasomotor nerve fibers innervate smooth muscle of small arteries and arterioles these fibers release NE which cause vasoconstriction rising BP In skeletal muscle they release Ach which causes vasodilation to increase blood flow to muscles but not important in overall BP regulation What is vasomotor tone arteriole smooth muscle is always somewhat constricted because of steady signals from vasomotor Sympathetic fibers Describe in detail the mechanisms for controlling blood pressure Short term a Baroreceptors Figs 21 39 21 40 Mechanorecptors respond to changes in arterial BP and arterial stretch Found in carotid sinuses aortic arch and elastic arteries of neck and thorax brachiocephalic and subclavian Rise in arterial BP more impulses to vasomotor center which inhibits Sympathetic neurons vasodilation of arterioles and veins so BP falls ALSO Rise in arterial BP more impulses to cardiac center which stimulates parasympathetic activity and inhibits sympathetic decreased heart rate and contractile force Falling BP causes opposite effects b Chemoreceptors Figs 21 42 21 43 Sensitive to levels of Oxygen Carbon Dioxide pH in blood Usually act under emergency conditions when blood levels change dramatically found in aortic and carotid bodiesandmedulla oblongata aortic arch medulla oblongata Falling oxygen pH or rising CO2 increased AP frequency to stimulate vasomotor center vasoconstriction raises BP rate of blood return to heart and lungs send impulses to cardioaccelleratory center which increases cardiac output c CNS IschemicResponse Due to rare emergency conditions such as severe restriction of blood flow to brain or BP 50mmHg severe hypotension Reduced O2 ischemia increased CO2 and decreased pH