2026 exam 2ex phys bloodflow and stroke vol

exam 2

what are some factors that change resistance in blood flow?

-thickness or viscosity of blood

-length of the tube

-diameter of the blood vessel

blood flow is _____related to the resistance encountered to the flow

inversely

ex.) like a garden hose…open hose = low resistance =lots of water flow

pinched hose= high resistance = less water flow

**how does blood flow change with exercise?

-dilation of blood vessels

-opening dominant capillaries

-shunting of blood from non-active areas

***what is autoregulation?

regulation of mm blood flow by local intrinsic factors

what are some examples of intrinsic control of blood flow?

-decrease in oxygen

-increase in temp

-increase in acidity or decrease in pH

-increase adenosine, magnesium, and potassium ions

what does intrinsic control of blood flow mean?

the blood vessels themself can regulate its diameter w out needing instructions from the brain or hormones

what are the 2 types on intrinsic blood flow?

1. endothelial mechanisms

2. myogenic mechanisms

in regards to intrinsic blood flow, what does the endothelial mechanisms do

the endothelium (a thin layer of cells lining inside of blood vessels) which sense changes in the blood vessel and releases substances to change vascular smooth mm

in regards to intrinsic blood flow, what does the myogenic mechanism do?

built in pressure sensors in the vessels that respond to pressure/stretch

the sympathetic causes dilation or constriction in skeletal mm?

constriction mostly but can cause vasoconstriction

**what is sympatholysis?

when locally produced substances inhibit the vasoconstriction effect of increase sympathetic activity

Activation of the sympathetic nervous system also causes the adrenal gland of the medulla to release Norepinephrine and Epinephrine which causes what?

vasoconstriction in all blood vessels EXCEPT heart and skeletal mm

what are some parasympathetic factors affecting blood flow?

-constricts coronary blood vessels

-constricts blood vessels in skeletal mm and skin

-dilates blood vessels in abdomen and kidneys

during exercise, the sympathetic nervous system cause the veins to do what?

venoconstrict to push more blood back to the heart

in regards to mechanical activity of the heart, the cardiac cycle is divided into two periods or cycles. what are these called?

systole and diastole

systole is when the heart contracts and ejects blood

diastole is when the heart relaxes and fills w blood

ejection fraction is what?

the percentage of the blood within the left ventricle that is pumped per beat

what is a normal ejection fraction percentage?

50-70 % of the blood within the left ventricle is ejected per beat

what is below normal ejection fraction percentage?

40-55%

at what percentage of ejection fraction can you confirm a diagnosis of heart failure?

less than 40%

at what percentage of eejection fraction may a patient be at risk for life-threatening irregular heart beeats?

less than 35%

cardiac output (CO) is defined as what?

the amount of blood ejected each min

how is cardiac output (CO) calculated?

heart rate x stroke volume

what is stroke volume?

the amount of blood in mL pumped by the heart per beat

what is the average stroke volume at rest for males? females?

70-90 mL, trained 100-120 mL

50-70 mL, trained 70-90 mL

how is stroke volume calculated?

end diastolic volume - end systolic volume

what is preload?

the degree of myocardial stretch (length of myocardium) at the initiation of contraction

it is a function of venous return and is represented by end-diastolic volume or pressure

what is starlings law of the heart?

the force of contraction is directly related to myocardial fiber stretch

increasing the ______ or ______ causes more stretch and thus the next contraction will be more forceful and will pump more blood out of the heart which is aka ____

preload or end diastolic volume

aka stroke volume

what is afterload?

the resistance or pressure the ventricles must overcome to eject blood out of the heart during systole

pressure the heart has to push against

why is there an increase in venous return during exercise?

-rhythmical contraction of mm

-respiratory and abdominal pumps (veins of thorax and abdomen are emptied towards heart)

-vasoconstriction of veins

what happens to stoke volume as exercise intensity increases?

it rises from rest to moderate work then plateus around 40-60% of vo2max

Venous return increases during exercise how does this come about?

-skeletal mm pump

-respiratory pump

-venoconstriction

how does the increase in venous return change stroke volume?

sterlings law bc when you exercise, more blood via veins is being pumped back to the heart which makes the filling of the ventricles increase which creates a stronger contraction which increases stoke volume

What are the changes that occur with SV with exercise?

-it plateaus at about 40-60% vo2max

-increase venous return, increase amount of blood in heart, increase ventricle contraction, increase stroke vol

-highly trained athletes, it may never plateau

what are the factors that influence blood flow during exercise?

-which mm are working

-vasodilation in working mm

-sympathetic nervous system

-epithelium + myogenic mechanisms

What are baroreceptors and why are they important during exercise?

they detect changes in blood pressure

they are important bc we dont want bp to change so they regulate it and keep it relatively unchanged as we exercise

How does venous return effect preload?

preload is the amount of blood in the heart before a contraction therefore venous return makes it so that there is more blood in the heart before a contraction so venous return increases preload

how do we get more blood to the mms that are exercising?

-blood vessels in the working mm dialate

-we shunt it from non exercising mms and digestive

what are the general adaptations that result in an increased stroke volume?

-improved venous return (improves bodies ability to return blood to the heart)

-improves ventricular filling

-improves heart as a mm to contract harder