ch 14: cardiac output, blood flow, and blood pressure

cardiac output

volume of blood pumped each minute by each ventricle

CO = HR x SV

SV

stroke volume = volume of blood ejected by each ventricle with each beat

sinoatrial node

rhythmically excites at ~ 100 beats/min (pacemaker potential)

HR is lower (70-75 bpm) due to ACh release in PNS

ACh binds to...

muscarinic ACh receptors in cells of SA node, resulting in slower rate of depolarization

during fight or fight, NE in SNS and E from adrenal medulla bind to...

beta-adrenergic receptors in cells of SA node, resulting in faster rate of depolarization and increased HR

other effects include:

increased contractility, faster contraction and relaxation

sympathetic signals are...

NE and E

increase HR

parasympathetic signals are...

ACh

decrease HR

end-diastolic volume (EDV)

volume of blood in ventricles at the end of diastole

greater EDV -> greater SV due to stretch of cardiac muscle

total peripheral resistance (TPR)

resistance: impedance to blood flow

vasoconstriction is main factor that increases restriction

greater TPR = lower SV which leads to heart working harder to eject blood due to resistance

contractility (sympathetic input)

E and NE increase ventricular contractility = greater SV

increasing the amount of stretch of cardiac muscle results in...

stronger contraction (greater tension) due to greater interaction between actin and myosin and increased release of Ca2+ from SR

increased contractility is caused by

sympathetic nerve stimulation

to increase the SV...

fill the heart more fully with blood (EDV). the increased stretch in the ventricle will align its actin and myosin in a more optimal pattern of overlap

AND

deliver sympathetic signals (NE, E) to increase ventricular contractility. the heart will also relax more rapidly, allowing more time to refill

increase EDV and sympathetic signals, decrease TPR

to increase HR

increase sympathetic signals (NE, E) and reduce parasympathetic

extracellular fluid

representing about 1/3 of the total body water, is distributed between ISF (80%) and blood (20%)

water is...

gained via drinking

lost via excretion of urinating, exhalation of air, sweating, and feces

within the body, water is exchanged...

between the intracellular and extracellular compartments

filtratiion

movement of fluid and solutes out of the blood

absorption

movement of fluid and solutes into the blood

starling forces

opposing forces, constantly acting on walls of capillaries

blood pressure causes...

fluid and solute to filter out of the vessels to form ISF (filtration)

solutes: glucose, organic molecules, salts, and ions

osmotic forces

cause water to be absorbed from tissues into vessels (absorption)

blood volume regulated by

mechanisms that affect drinking, urine volume, and distribution of fluid between plasma and ISF

water loss and gain must be balanced (homeostasis)

kidneys

play a role in regulating blood volume

ADH (hypothalamus/posterior pituitary) and aldosterone (adrenal cortex)

act on kidneys to regulate BV by increasing or decreasing urine volume

ANP (atrial natriuretic peptide)

hormone from the heart

causes natriuresis

synthesized in the atria and increases amount of Na+ and water secreted in urine

natriuresis

excretion of sodium in urine

secretion of ANP is stimulated by

stretching of atria, where there is increased BV

results in increased urine volume to reduce blood volume

mean arterial pressure (MAP)

MAP = CO x TPR

MAP = DP + 1/3(pulse pressure)

pulse pressure = systolic - diastolic

what is typically the cause of a change in TPR, regulating MAP

arteriolar resistance

e.g. vasodilation and vasoconstriction

blood flows from

higher pressure region to lower pressure region

determined by pressure difference between the mean pressure of 100 mmHg at the origin of flow and the pressure at the end of the circuit (0 mmHg)

pressure decreases as

distance increases from LV

during moderate, sustained exercise, CO significantly...

increases from its baseline of appx 5.5 L/min

greatly increased flow to skeletal muscle due to increased local metabolism, which results in vasodilation

vasoconstriction in GI system and kidneys due to

sympathetic activity

blood pressure

affected by resistance, SV, HR, CO

resistance greatest in arterioles

increase SV, HR, or CO = increase BP

regulated BP by kidneys regulating BV

baroreceptor reflex maintains BP

why is resistance greatest in arterioles

reduced diameter = increased resistance = reduced blood flow = reduced downstream = blood flow and pressure in capillaries

constriction (arterioles) increases

pressure upstream (arteries) and decreases it downstream (capillaries, veins)

hypotension

low BP: reduces blood flow to brain and cardiac muscle

causes:

CV disease, defect, or even

dehydration, diarrhea, vomiting, large urine loss, severe sweating, burns, hemorrhage

neural, endocrine defects

medication

response is baroreceptor reflex

baroreceptors

stretch receptors in the heart whose AP frequency is directly proportional to MAP

baroreceptors deliver information about MAP to the...

medulla oblongata of the brain (controls heart, lungs)

result is autonomic output to heart and vessels

hypertension

chronic high BP (above 140/90 mmHg)

left ventricle must pump against increased arterial pressure so left ventricular hypertrophy occurs, eventually leading to heart failure

other complications:

damage to blood vessels, heart attack, kidney damage, stroke

causes of hypertension

unknown (genetic, environmental/diet) (primary hypertension)

atherosclerosis of aorta (secondary hypertension)

kidney disease -> decreased urine formation (secondary hypertension)

endocrine disorders (secondary hypertension)

heart failure is when CO is inadequate for maintaining adequate blood flow...

low CO leads to increased fluid retention -> increased BV, SV, and EDV

the failing heart is less able to handle a large EDV

causes:

heart attack

hypertension

damage to heart due to coronary blood flow in coronary arteries

treatments: diuretics, medications to increase contractility, vasodilators, medications that affect renal hormones like aldosterone