Chapter 14: Cardiac Output, Blood Flow, Blood Pressure

major physiological regulators of blood flow through an organ

1. MAP: mean arterial pressure = an average, driving force 2. vascular resistance = arterioles provide greatest resistance due to capacity to vasoconstrict and vasodilate (blood vessel radius)

basoreceptor reflex function

1. blood pressure drops 2. baroreceptors detect this change and send information to the medulla 3. the medulla then increases our sympathetic NS and represses our parasympathetic NS 4. we then have vasoconstriction of our arterioles that increases total peripheral resistance 5. and we have in increase in cardiac rate which increases cardiac output 6. thus increasing blood pressure

3 most important things affecting blood pressure

1. cardiac output 2. stroke volume (determined by blood volume) 3. total peripheral resistance (vasoconstriction) BP = CO x total PR if you have an increase in any of these variables without a compensatory decrease in another will lead to an increase in blood pressure therefore, blood pressure can be regulated by (1) kidneys, which regulate blood volume & thus stroke volume, and (2) sympathoadrenal system, which increase vasoconstriction leading to an increase in total peripheral resistance

nitric oxide as a paracrine regulator of blood flow

1. parasympathetic stimulation activates eNOS (endothelial nitric oxide synthase) in the tunica interna 2. eNOS produces nitric oxide 3. nitric oxide flows into the tunica media and activates guanylyl cyclase 4. guanylyl cyclase converts GTP to cGMP which causes a decrease in intracellular calcium 5. this causes vasodilation of the smooth muscle cells in the tunica media

endocrine regulators of blood flow

AII (angiotensen II) = vasoconstrictor of smooth muscles and vessels ADH = can serve as a vasoconstrictor but not really effective

blood pressure shit

BP and flow further reduced in capillaries due to total cross-sectional area is greater as compared to arteries & arterioles -large numbers -although smaller in diameter, capillary bed presents less resistance than arterioles variations in arteriole diameter, VC or VD, thus affect capillary bld flow but also simultaneously impact arterial BP upstream, therefore, an increase in total PR due to arteriole VC can raise arterial BP BP can also be elevated by an increase in cardiac output, which is influenced by other factors

pulse pressure (PP)

PP = systolic pressure - diastolic pressure

Summary Slide

Slide 35

according to Frank-Starling law of the heart, outputs of the right and left ventricles are matched. Explain why this is important and how this matching is accomplished.

The Frank-Starling intrinsic law of the heart demonstrates that the strength of ventricular contraction varies directly with the end-diastolic volume return of venous blood to RIGHT ventricles varies considerably throughout the day, due to Frank-Starling law RIGHT ventricular contraction strength and thus, the stroke volume will adjust instantly to these preload variations NET RESULT = ventricle raises its stroke volume output when venous return is increased and lowers its stroke volume when venous return is lowered Now, LEFT ventricle subsequently receives altered volume of blood, it too will adjust its stroke volume to match that of the right ventricle THUS, -heart can intrinsically compensate for the moment-to-moment fluctuations in the return of blood to the heart - if the stroke volumes were not matched, one ventricle or the other would soon be depleted of blood and the pump would fail

parasympathetic regulation of blood flow

always cholinergic and always promote vasodilation in the arterioles limited in its distribution so it has less of an effect

baroreceptor

baroreceptors are stretch receptors found in vessels close to the heart (aortic arch and carotid sinuses) that monitor pressure they function to counteract blood pressure changes so fluctuations in pressure are minimized they maintain blood pressure on a beat to beat basis = short term response

vascular smooth muscle tone

basically a basal level of vasoconstriction throughout the body obtained via adrenergic sympathetic fibers this is the state of our vascular smooth muscle at rest in a position where we have the option to either vasoconstrict or vasodilate

blood flow distribution during rest and exercise

blood flow to heart and skeletal muscles are regulated by both extrinsic and intrinsic mechanisms brain is mainly intrinsic and requires constant flow cutaneous is mainly extrinsic and has the most variation in blood flow (sympathetic and parasympathetic mechanisms)

cholinergic sympathetic fibers

cause arteriole skeletal muscle to vasodilate during fight or flight reaction epinephrine is also released from the adrenal medulla and binds to beta adrenergic receptors that causes vasodilation therefore the blood flow to skeletal muscle increases - this provides an advantage to help our muscles react

Poiseuille's Law

change in pressure x radius/blood viscosity, length of blood vessel blood flow is directly impacted by vasoconstriction or vasodilatation blood vessel length and blood viscosity do not significantly change in a normal individual

effect of vasodilatation in a large organ

decrease total peripheral resistance and thus the mean arterial pressure compensatory mechanisms to counteract: we will have vasoconstriction in other areas and increased cardiac output this is what happens when we workout

paracrine regulators that cause smooth muscle contraction (vasoconstriction)

endothelin-1 Table 14.4

which type of exercise, isotonic or isometric contractions, puts more "strain" on the heart? explain.

exercise using isometric muscle contractions would put a greater "strain" on the heart to accomplish heavy lifts, people often employ the Valsalva's manoeuvre in which a deep breath is taken with an expiratory effort against a closed glottis; performance of this manoeuvre transiently increases the intrathoracic pressure that, in turn, reduces venous return, lowers stroke volume, decreases cardiac output, and lowers arterial blood pressure also during this breath holding interval, there is a drop in blood pressure stimulates the baroreceptor reflex, resulting in tachycardia and decreased total peripheral resistance when the glottis finally opens, intrathroacic pressure and cardiac output return to normal. However, the decrease in peripheral resistance is still in effect causing a transient, explosive, flow of blood to dilated capillaries, possibly causing rupture (haemorrhage) or a stroke, if in the brain although the baroreceptor reflex will eventually respond and compensate for the blood pressure changes, the fluctuations that occur during isometric muscular exercise can be dangerous in people predisposed to cardiovascular disease and/or weakened blood vessels isotonic exercise is usually not associated with breath holding

paracrine regulation of blood flow

extrinsic regulation blood vessels are particularly subject to paracrine regulation, especially the endothelium (tunica interna) the endothelium produces several paracrine regulators that impact smooth muscle in the tunica media

hyperemia

increased blood flow

pressure vs size in blood vessels

large arterioles = constant pressure small arterioles = greatest degree of change, blood flow slows down, pressure decreases, increase in resistance capillaries = slow blood flow, lower pressure so that exchange can happen venules and veins = blood can actually "hangout" here and not be constantly moving

paracrine regulators that cause smooth muscle relaxation (vasodilation)

nitric oxide, bradykinin and prostacyclin

atrial stretch reflex

receptors present in atria respond to increase in venous return to the heart which causes an increase in sympathetic nerve activity and stimulates a reflex tachycardia (increases heart rate) ADH release is inhibited so that we increase urine excretion and decrease blood volume also see an increase secretion of ANP (atrial natriuretic peptide) = lowers blood pressure by lowering blood volume via increasing urinary salt and water excretion

intrinsic regulation of blood flow

regulation that occurs inside the organs represents a built in mechanism within individual organs to provide localised regulation of vascular resistance and blood flow used to maintain relatively constant blood flow rates within organ despite wide fluctuations in blood pressure = autoregulation two mechanisms: myogenic and metabolic

extrinsic regulation of blood flow

regulation that occurs outside of the organ autonomic nervous system and endocrine control

total peripheral resistance

represent the sum of all vascular resistance within systemic circulation blood flows through only one set of resistance vessels (arterioles) before returning to the heart arteries arranged in parallel = organs are not "down stream" from one another

mean arterial pressure (MAP)

represents average arterial pressure during cardiac cycle the difference between MAP and venous pressure is what drives blood through capillary beds of organs hard to estimate since heart doesn't spend equal time in diastole and systole MAP = diastolic pressure + 1/3PP a rise in total peripheral resistance and heart rate increases diastolic pressure more than systolic pressure, however, increase in cardiac output raises systolic pressure more than diastolic pressure (WHY??) -because as we increase total PR we decrease stroke volume so we are pumping less blood out at a time and therefore are increasing our blood pressure in between pumps, vs an increase in cardiac output we are increasing the amount of blood pumped out so our systolic pressure (or blood pressure during ventricular contraction) will be increased

blood pressure

resistance to flow within arterial system is greatest in arterioles due to their smaller diameter flow through the arterioles must be equal to flow through larger vessel that give rise to them, flow is reduced according to Poiseuille's law, therefore, pressure and blood flow are reduced in capillaries downstream with pressure increase upstream in larger vessels 1 aorta and many vessels downstream to assist with blood flow, but will reduce due to P's law THUS, pressure and flow reduced downstream in capillaries with increase pressure in vessels upstream this is important to slow velocity of blood flow in capillaries to allow exchange sets up a pressure gradient that ensures blood flows

importance of organs being arranged in parallel

resistance within a blood vessel will only affect blood flow in the organ that it goes to instead of affecting any other organ

metabolic regulation

result of chemical environment created by organs metabolism Localized chemical conditions that promote vasodilation 1. decreasing oxygen 2. increasing CO2 3. decrease tissue pH 4. release of adenosine or K from tissues (paracrine regulators) these chemical changes promote vasodilation to bring blood into this area to flush these things out or replenish

sympathetic regulation of blood flow

stimulation by the sympathoadrenal system causes an increase in cardiac output and total peripheral resistance total peripheral resistance is increased by the sympathetic nervous system releasing norepinephrine. The smooth muscle in the tunica media of vessels contains alpha adrenergic receptors that norepinephrine can bind to. These are also found in the arterioles of the skin and viscera. This binding produces vasoconstriction of the arterioles which increases total PR

myogenic regulation

the response of vascular smooth muscle to keep tissues perfused as well as protection against high blood pressure 1. blood pressure increase and vascular smooth muscle stretched = responds by contracting or vasoconstricting - this protects vessels downstream from elevated pressure 2. blood pressure decrease = vessels dilate to retain adequate blood flow

baroreceptor reflex general definition

tonically (constantly) active, as blood pressure increases the frequency of action potentials increases information is sent via cranial nerves to the medulla which houses the vasomotor control centers (regulates vasoconstriction and vasodilation in blood vessels and assists with total peripheral resistance) it also houses the cardiac control centers (modifies heart rate) more sensitive to decrease changes than increase and sudden changes rather than gradual changes

reaction of smooth muscle from the activation of fight or flight reaction

when activated the digestive tract, kidneys, and skin all vasoconstrict because of the release of epinephrine and norepinephrine binding to the alpha adrenergic receptor

you're participating in a 75 mile cycling benefit race and its a summer day in SC - hot and humid. You've consumed your water supply and in the last miles of the race you are thirsty. Should you accept water or a sports drink from a race support member? explain.

you are thirsty because you are dehydrated and your blood plasma osmolality is elevated during endurance race, blood sodium and total blood volume have been lowered by the increased need to sweat while racing due to evaporative heat loss -result = low blood pressure drinking pure water may not be the answer in this extreme case, because blood sodium is lost in sweat, so that a lesser amount of water is required to dilute the blood osmolality back to normal when the blood osmolality is normal, the urge to drink is extinguished. Therefore, on prolonged endurance races such as this one, you should accept the sports drink offered providing it contains only a weak solution of sodium and carbohydrate concentrations and providing you drink it following a predetermined schedule (rather than waiting until thirsty)