Vascular capacity Flashcards
What is the vascular capacity?
The volume of blood that can fit into blood vessels
What 2 things regulate vascular capacity?
Cardiac output and vascular diameter
What is cardiac output?
The volume of blood that the heart pumps per unit time. Determined by heart rate x stroke volume
What is the stroke volume?
The volume of blood that the heart pumps with each beat
What regulates stroke volume?
Venous return (preload, filling of right atrium) Arterial pressure (afterload) Contractility (rate and strength of contractions)
How is stroke volume controlled intrinsically?
Venous return (ΔEDV) and arterial pressure
How is stroke volume controlled extrinsically?
Contractility has regulated by the nervous system and endocrine system
What is the EDV (end diastolic volume)?
Maximum amount of blood in the ventricles
What happens to the stroke volume if blood volume is increased? What is the series of events that leads to that?
Increased blood volume means increased EDV, which increases stretching of the ventricles, which increases the strength of contraction and increases SV
Does the end diastolic volume stay constant?
Changes with the amount of blood returning to the heart
What is the Frank Starling Law of the Heart?
The heart pumps out all the blood that enters the ventricles
What happens to the ventricle muscles when the end diastolic volume increases?
The muscles get stretched and contract stronger in response, which increases the stroke volume
How does the sympathetic nervous system affect the stroke volume?
Causes it to increase, which causes more blood to be pumped around the body and circulate stress hormones
What is the mean arterial pressure?
The pressure gradient across the circulatory system
What is the total peripheral resistance?
The sum of the resistance of all blood vessels in the circulatory system
Between the cardiac output, mean arterial pressure, and total peripheral resistance, which one does stays constant?
Mean arterial pressure. Bulk flow of the entire system depends on the pressure gradient
How is total peripheral resistance changed?
Vasoconstriction and vasodilation
How does the body redirect blood flow away from certain organs?
Arteriolar-venular shunts
Which blood vessels determine which organs get access to blood flow?
Arterioles
How is a capillary bed closed off or opened?
Sphincters composed of rings of smooth muscle cells. They contract to close off a capillary bed like a valve
Why would blood be shunted away from an area?
Low metabolic needs
What happens in the capillary beds of organs with high metabolic needs?
Pre-capillary sphincters relax and the arterioles dilate, which decreases the resistance and increases the amount of blood received by that region
What are baroreceptors?
Pressure sensors found in the arterial system that sense artery stretching due to increased cardiac output
What do baroreceptors do when they sense an increase in artery pressure?
Send a signal to the medulla oblongata which causes a reflex reduction of the cardiac output and peripheral vascular resistance to maintain the MAP
