Cardiac physiology part 3

describe blood flow in the heart

• deoxygenated blood enters the right atrium through superior vena cava

• travels to right ventricle

• sent towards lungs via pulmonary artery

• travels back through pulmonary vein into left atrium

• is then sent down toward left ventricle and then sent back out via aorta towards rest of bodies tissue as oxygenated blood

How does blood flow based on pressure gradient?

blood flows from areas of high to low pressure

what is the function of the valves?

structures that prevent backflow of blood; ensure unilateral blood flow

open and close due to pressure gradients within the heart

where are the atrioventricular valves located?

tricuspid valve: controls flow of blood from right atrium to right ventricle

bicuspid valve: controls flow of blood from left atrium to left ventricle

where are the semilunar valves located?

pulmonary valve: controls flow of blood from right ventricle to pulmonary artery/lungs

aortic valve: control blood flow from left ventricle to aorta/body tissues

If the pressure in the atrium is greater than the pressure in the ventricle, what will happen to the AV valve?

Atrioventricular valve will open and allow blood flow from atrium to ventricle

If pressure in the ventricle in greater than the pressure in the atrium what will happen to the AV valve?

Atrioventricular valve will close to prevent backwards flow of blood

If the pressure in the ventricle is greater than the pressure in the blood vessel, what will happen to the valve?

semilunar valves will open and allow blood flow from ventricles to blood vessels

If pressure in the blood vessel is greater than blood flow in the ventricle, what will happen to the valves?

The semilunar valves will close to prevent backwards flow of blood

define cardiac output

• amount of blood pumped by each ventricle in one minute

• volume from left ventricle and right ventricle are identical or nearly

what’s the equation for cardiac output?

Cardiac output = heart rate x stroke volume

define heart rate

amount of beats per minute; average = 75 bpm

define stroke volume

amount of blood pumped per each contraction; average 70mL/beat

what are the units for cardiac output, heart rate, and stroke volume?

CO: mL/min

HR: beats/min

SV: mL/beat

How does PNS influence HR? Describe the mechanism in which it does this

• PNS will decrease cardiac output

• PNS releases acetylcholine which increases permeability of pacemaker cells to K+ (slows closure of K+ channels)

• this increase amount of K+ that exits pacemaker cells which leads to hyperpolarization

• hyperpolarization makes it harder to reach threshold = less AP

• leads to pacemaker cells firing less frequently and myocardial cells being activated less

How does the SNS impact heart rate? describe the mechanism in which it does this

• Increases HR

• SNS will release norepinephrine which decreases permeability of K+ in pacemakers

• quicker closure of K+ channels creates decrease in K+ efflux

• this causes depolarizing effect and threshold can be reached faster

• leads to more AP and increase in pacemaker cell activity

explain stroke volume regulation intrinsically

• Frank-sterling law: increase stretch will lead to increase amount of contraction force

• the more blood that enters equals higher amount of stretch which causes increased contraction and increase in SV and CO

How does blood vessel health impact stroke volume?

reduction in elasticity in blood vessels will lead to increased pressure/resistance and if blood can’t flow right there is decrease in CO

Explain stroke volume regulation extrinsically, which division of the ANS impacts myocardial cells? what is its impact on stroke volume?

• myocardial cells only have sympathetic innervation

• increased SNS activity there is increased contractility of cells which leads to increase in SV and increase in CO

which hormone can impact stroke volume?

• hormones on myocardial cells

• T3 and epinephrine will increase contractility and increase SV and CO