Ch. 14 Lecture 1Cardiac Output• Volume of blood pumped each minute by each ventricle• Cardiac output=Stroke volume x heart rateo Stroke volume: Amount of blood squirted out every contraction mL/beato Heart rate Beats/mino Avg heart rate=70 bpmo Avg Stroke volume= 70-80o Avg Cardiac output = 5500mL/min Pretty much entire volume of blood• Regulation of cardiac rateo Spontaneouds depolarization occurs at SA node HCN channels open allowing Na+ ino 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 effecto Parasynpathetic acetylcholine will open K+ Channels Slows heart rate • Regulation of Stroke Volumeo 3 Variableso End diastolic volume Volume of blood in the ventricles at the end of diastole Sometimes called preload Stroke volume increases with increased EDVo Arterial blood pressure Afterload Affected by total peripheral resistance: Frictional resistance in the arterieso Contractility Strength of ventricular contraction Stroke volume increases along with 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 Controlo Regulated by the sympathetic nervous system Increases in contraction due to making more Ca2+ available to sarcomeres• Venous Returno Effects end diastolic volumeo Factors that affect venous return Total blood volume Venous pressure Veins are compliant. Streetch at a given pressure. They hold more blood than arteries but maintain lower pressureo 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 2Blood Volume• Body Water Distributiono 2/3 of our body water is found in cellso Of the remaining third, 80% is in interstial fluid and 20% in plasmao Controlled by osmotic forces and hydrostatic pressureo Water intake and urine formation also play role in regulation of blood volumeo Water loss: Urine formation Lungs Skin (sweat glands) Feces• Tissue/Capillary Fluid exchangeo 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 veinouso 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 capillarieso 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 systemo Edema Excessive accumulations of interstitial fluids “swelling” Result of• High arterial blood pressure• Venous obstruction• Leakage of plasma proteins into Interstitial space• Decreased plasma protein concentration• Obstruction of lymphatic drainage Then he showed us a scary example: Elephantitis. • Regulation of blood Volumeo 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• 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. Aldosterone• 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 systemo Specialized set of cells: juxtaglomurular apparatus- that secrete the enzyme renin when blood pressure is lowo Converts angiotensinogen to angiotensin I, which is then converted to angiotensin II by ACE enzymeo Angiotensin II effects Vasoconstriction Stimulates thirst Stimulates production of aldosterone (see above) Atrial Natriuretic Peptide• Produced by the atria of the heart when stretch is detectedo Promotes salt and water excretion in urine in response to increase in blood volumeo Inhibits ADH secretion. o Instead of holding salt in, you get excretion and a drop in blood volume. Vascular Resistance to Blood Flow• Cardiac output is distributed unequally to different organso Regulated by unequal resistance to blood flow in each of the organ system• Physical Laws Regulating blood flowo High pressure to low pressureo 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
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