Cardiac Output Ch 14 Lecture 1 Volume of blood pumped each minute by each ventricle Cardiac output Stroke volume x heart rate o Stroke volume Amount of blood squirted out every contraction mL beat o Heart rate Beats min o Avg heart rate 70 bpm o Avg Stroke volume 70 80 o Avg Cardiac output 5500mL min Pretty much entire volume of blood Regulation of cardiac rate o Spontaneouds depolarization occurs at SA node HCN channels open allowing Na in o Sympathetic Norepinepherine and epinephrine produce cAMP which targets the CN part of the HCN channels cAMP increases the rate of depolarization increasing heartrate Anything that increases epinephrine norepinephrine will raise HR Called a Chronotropic effect o Parasynpathetic acetylcholine will open K Channels Slows heart rate Regulation of Stroke Volume o 3 Variables o End diastolic volume Volume of blood in the ventricles at the end of diastole Sometimes called preload Stroke volume increases with increased EDV Affected by total peripheral resistance Frictional resistance in the arteries Strength of ventricular contraction Stroke volume increases along with contractility o Arterial blood pressure Afterload o Contractility o Ejection Fraction SV EDV Normally about 60 o Frank Starling Law Increased EDV results in an increased contractility and thus increased stroke volume The increased stretch of the ventricles increases the stroke volume Intrinsic Control of Contraction Strength o Intrinsic to the muscles o Due to myocardial stretch Extrinsic Control Venous Return o Effects end diastolic volume o Factors that affect venous return o Regulated by the sympathetic nervous system Increases in contraction due to making more Ca2 available to sarcomeres Total blood volume Venous pressure Veins are compliant Streetch at a given pressure They hold more blood than arteries but maintain lower pressure o More factors in venous return Highest pressure in venules vs lowest pressure in veins closest to heart Sympathetic nerve activity to stimulate smooth muscles and lower compliance Skeletal muscle pumps Pressure difference between abdominal and thoracic cavities Blood volume Ch 14 Lecture 2 Blood Volume Body Water Distribution o 2 3 of our body water is found in cells o Of the remaining third 80 is in interstial fluid and 20 in plasma o Controlled by osmotic forces and hydrostatic pressure o Water intake and urine formation also play role in regulation of blood volume o Water loss Urine formation Lungs Skin sweat glands Feces Tissue Capillary Fluid exchange o Filtration Has to do with blood pressure hydrostatic pressure in capillaries that dictates whether fluid will move in out of capillaries interstitial space Pressure is higher on arterial side than on veinous side 36mmHg at arteriole end vs 16 at veinous o Colloid osmotic pressure Due to proteins dissolved in fluid Colloid stuff that is not totally dissolved undissolved like milk Blood plasma has a higher colloid osmotic pressure than interstitial fluid Difference is known as oncotic pressure Oncotic pressure 25mmHg Fluid would preferably move into the capillaries o Starling Forces Combination of hydrostatic pressure and oncotic pressure which will predict movement of fluids across capillary membranes Movement is proportional to fluid out fluid in Hydrostatic pressure in capillary Colloid osmotic pressure in IF Hydrostatic pressure of IF Colloid pressure in capillary Colloid osmotic pressure is usually constant so the hydrostatic pressure is what is changing Example 37 26 11mmHg which means 11mmHg pushing fluids out of the capillaries arteriol On venule side it was negative 9 means that 9mmHg pushing into vein The fact that it s 2mmHg different means that a little fluid gets pushed out of the capillaries to be absorbed by the cells and or picked up by the lymphatic system o Edema Excessive accumulations of interstitial fluids swelling Result of Venous obstruction Leakage of plasma proteins into Interstitial space High arterial blood pressure Decreased plasma protein concentration Obstruction of lymphatic drainage Then he showed us a scary example Elephantitis Regulation of blood Volume o Kidneys Formation of urine begins with filtration of fluid through capillaries in the kidneys known as glomeruli 180L of Filtrate is filtered through them daily but only 1 5L is taken out for urine Remainder is reabsorbed into the blood Controlled by several hormones ADH Aldosterone Anti diuretic hormone Produced by hypothalamus and released by posterior pituitary when osmoreceptors there detect increased plasma osmolarity Stimulates water reabsorption Increase in plasma osmolarity increases thirst as well Increase in blood volume causes blood to become dilute and ADH is no longer released Also influenced by stretch receptors in L Atrium carotic sinus and aortic arch These inhibit ADH Secreted by the adrenal cortex indirectly when blood volume and pressure are reduced Stimulates reabsorption of salt and water in kidneys Water will follow by osmosis automatically and blood volume increases Regulated by renin angiotensin aldosterone system o Specialized set of cells juxtaglomurular apparatus that secrete the enzyme renin when blood pressure is low o Converts angiotensinogen to angiotensin I which is then converted to angiotensin II by ACE enzyme o Angiotensin II effects Vasoconstriction Stimulates thirst Stimulates production of aldosterone see above Produced by the atria of the heart when stretch is detected o Promotes salt and water excretion in urine in response to increase in blood volume o Inhibits ADH secretion o Instead of holding salt in you get excretion and a drop in blood volume Atrial Natriuretic Peptide Vascular Resistance to Blood Flow Cardiac output is distributed unequally to different organs o Regulated by unequal resistance to blood flow in each of the organ system Physical Laws Regulating blood flow o High pressure to low pressure o Rate is proportional to differences in pressures o More weight given to diastolic than systolic So 120 80 is not 100 more like 93 o Rate of blood flow is inversely proportional to the frictional resistance to blood flow within the vessels Blood flow current Change in Pressure Resistance Change in pressure is the difference from each end of the tube Resistance length of the blood vessel x viscosity of the blood radius to the fourth power Poiseuille s law Adds in physical constraits Blood flow Change in pressure x radius 4 x pi viscosity x Length of the vessel Biggest
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