ardiac C Output : volume of blood pumped/ min by each ventricle SV: blood pumped/ beat by each ventricle HR: # beats/ min CO= SV x HR *sympathetic nervous system has large control on
Blood Volume -2/3 int racellular compartment (nerve, muscle) -1/3 extracellular *80% of this is interstit ial f luid *20% of this is blood plasma Exchange of Fluid between Capillar ies and T issues -distribution of ECF between blood and interstitial compartments is in state of equilibrium -movement out of capillaries is driven by hydrostatic pressure exerted against capillary wall -the oncotic pressure w ithin the capillary causes f luid to move back i n Overall Fluid Movement -determined by net fil t ration pressure and forces opposing it (Starling forces) [fluid out] [fluid in] (Pc+ I)(Pi+ p) Pc = Hydrostatic pressure in capillary
i= Colloid osmotic pressure of interstitial fluid (proteins, electrolytes= want to move it toward) Pi= Hydrostatic pressure in interstitial fluid p= Colloid osmotic pressure of blood plasma *normally filtration, osmotic reuptake, and lymphatic drainage maintain proper ECF levels
-higher hydrostatic pressure at the arteriole (move out) -higher osmotic pressure at the venule (move in) *not all fluid reabsorbed, just what you need *usually the equilibrium is maintained by filtration, reuptake, and lymphatic drainage Edema = excessive accumulation of f luid resulting from: -venous obstruction (won't let you pull the water back in) *veins cannot return blood to the heart, so f luid goes somewhere else= swollen feet -leakage of plasma proteins into interstitial f luid or excess production of glycoproteins -low plasma protein levels *alcoholism (protein not in those calories) -obstruction of lymphatic drainage *cancer Regulation of Blood Volume by Kidney -urine formation begins with fil t ration of plasma in g lomerulus *capillar ies are pourus and a lot of f luid can come in -filt rate passes through and is modified in the renal t ubles
-volume of urine excreted can be varied by changes in reabsorpt ion of filt rate according to needs of body as detected by the k idney as well as by the act ion of hormones *helps maintain volume of the system and what is in the sytem Vascular resistance to blood flow -determines how much blood f lows through a tissue or organ -vasodilation: decreases resistance (increases blood f low) -vasoconstriction: increases resistance (decreases blood f low) Physical Laws Describing Blood Flow -Poiseuille's Law : describes the factors affecting vascular resistance Resistance = L(8)/r4() = viscosity L = the length of a blood vessel r = radius of the blood vessel *change the radius= controls the minute-to-minute levels of vascular resistance * mean arterial pressure and vascular resistance are the determinants of blood f low to any organ
Total Peripheral Resistance (what heart pumps against) -total peripheral resistance: sum of vascular resistance within the systemic circulation -arteries supply t issues and organs in parallel circuits *change in resistance in these circuits relative determines blood f low
eat big meal: increase f low to GI (less to skeletel)
r un: increase f low to skeletal (less to GI) *blood f low sent to organs based on need * kidney usually stays about the same Ext r insic Regulation of Blood Flow -sympathet ic nervous system -act ivat ion causes increased CO and increased resistance in the circulat ion -parasympathet ic nervous system -act ivat ion causes vasodilatat ion *only innervates digest ive t ract, genitalia, and salivary glands * not as important as sympathet ic nervous system in blood pressure I n t r insic Regulation of Blood Flow (Autoregulation) -myogenic control mechanisms= occur in some tissues because vascular smooth muscle contracts when stretched and relaxes when not stretched -metabolic control mechanisms: match blood f low to local t issue needs ex: low O2 or pH or high CO2 or K from increased metabolism cause vasodilatation w hich i ncreases blood f low * in some cases the f unction of the organ d ictates i ts blood f low as well I n t r insic Regulation of Blood Flow - the endothelium of blood vessels produces several compounds that promote relaxation and constriction: 1) N it r ic oxide (NO), bradykinin, and p rostacyclin = all potent vasodilators 2) endothelin and angiotensin I I = vasoconstrictors produced by endothelium Blood P ressure (BP) BP= CO (cardiac output) x total peripheral resistance if CO= HR x SV then, BP = (HR x SV) x TPR *an increase in any of these can result in increased BP Measurement of Blood P ressure -via auscultation (examine by listening) -no sound is heard during l aminar f low (normal, quiet, smooth, blood f low) -korokoff sounds can be heard when sphygmomanometer cuff pressure is greater than d iastolic but lower than systolic pressure
*cuff constricts artery creating turbulent flow and noise as blood passes constriction during systole and is blocked during diastole * 1st korotkoff sound is heard at pressure that blood is 1st able to pass thru cuff (systolic) *last occurs when one can no longer hear systole because cuff pressure= diastolic pressure The indirect, or ausculatory, method of blood pressure measurement:
The arterial blood pressure is then: 120/ 80 *pump it up to higher than systole (so assume they have hypertension: 200)
H ypertension = BP in excess or normal range for age and gender (> 140/90 mm Hg-male) -affects about 20% of adults -prim ary or essent ial hypertension : caused by complex and poorly understood p rocesses *most common type -secondary hypertension : caused by known d isease p rocesses Dangers of H ype rtension -patients are often asymptomatic until substantial vascular damage occurs *contribute to atherosclerosis *increases workload of the heart (afterload) leading to ventricular hypert rophy and congestive heart failure *often damages cerebreal blood vessels, leading to stroke * "silent killer" T reatment of H ypertension -lifestyle changes: *stop smoking
*moderation of alcohol *weight reduction *reduce Na intake *increase K intake -drug treatments