Cardiovascular Physiology 31 Flashcards
What pressure drives blood flow to all the organs and tissues (except the lungs) in the average cardiac cycle?
The mean arterial pressure (MAP)
What is the prerequisite for ensuring adequate blood flow to all organs and tissues?
Maintaining MAP
What would happen if blood pressure were to decrease significantly?
The tissues of the body would quickly die as the would not receive significant oxygen and metabolites would build up
What are the consequences of chronically high blood pressure?
Damage to the arteries, heart and kidneys
How can MAP be calculated in relation to CO and TPR?
MAP = CO x TPR
What does MAP depend on?
The cardiac output (CO) and the total peripheral resistance (TPR)
What alters MAP?
Cardiac output and total peripheral resistance
What is total peripheral resistance?
The combined resistance to flow of all the systemic blood vessels
Why doesn’t the pulmonary circulation provide a lot of resistance to flow?
Because the vessels are very short, do not contain much smooth muscle and are not as numerous compared to those in the systemic circulation
What produces resistance in blood vessels?
Friction between the blood and the walls of the blood vessels
Where is the major site of resistance in the system circulation?
The arterioles
What are changes in TPR due mostly to?
Changes in the resistance of the arterioles. ex contraction of the smooth muscle in the walls of the arterioles
What is TPR primarily determined by?
Total arteriolar resistance
What allows arterioles to change their diameter?
The smooth muscle in their vessel walls
Why is the pressure drop through arterioles great?
Because blood experiences a lot of resistance to flow in them
What are the types of controls that can affect TPR?
- Local controls
- Neural controls
- Hormonal controls
What do the controls that affect TPR do?
Cause vasodilation or vasoconstriction
What will any change in arterial pressure elicit?
Homeostatic mechanisms
What two types of mechanisms are used to regulate the MAP?
- Short-term regulation
* Long-term regulation
How long do short term adjustments of MAP last?
Seconds to hours
What are short-term regulation of MAP brought about by?
Baroreceptor reflexes
What do Baroreceptor Reflexes do?
Modify the activity of autonomic nerves supplying the heart and blood vessels and changes in the secretion of hormones like epinephrine
What are the long-term regulations of MAP?
Adjusts in blood volume and normal salt and water balance through mechanisms that require urine output and thirst
What kind of receptors are Arterial Baroreceptors?
Mechanoreceptors
What do Arterial Baroreceptors detect?
Changes in the blood pressure
Where are the Baroreceptors found?
In the carotid sinus and the aortic arch
What is the wall of the artery like a baroreceptors?
Thinner than usual and has a large number of branching sensory neuronal processes
What changes do the Arterial Baroreceptors response to?
Changes in MAP and changes in pulse pressure
When do the Arterial Baroreceptors respond to changes in pressure?
When the walls of the vessel stretch and relax
What is the degree of wall stretching proportional to?
The pressure within the artery
What is the Pulse pressure?
The difference between the systolic and diastolic pressures
What is the rate of discharge of a baroreceptor proportional to?
The MAP
How is the rate of discharge of the baroreceptor affected by an increase in MAP?
The baroreceptor increases the frequency with which it fires
What does the rate of the Baroreceptor action potential flucuate with?
Changes in pressure
How is the firing rate of baroreceptors affected by a decrease in pressure?
The baroreceptor has a decreased firing rate
What is the primary integrating center for the baroreceptor reflexes?
The medullary cardiovascular center in the medulla oblongata
What do the inputs that the medullary cardiovascular center receives from baroreceptors determine?
The frequency of action potential sent from the center to neural pathways that terminate on the cell bodies of neurons of the vagus or parasympathetic neurons to the heart or sympathetic neurons to the heart, arterioles and veins
What does an increase in firing by the arterial baroreceptors signal the medullary cardiovascular center to do?
Decrease the sympathetic activity to the heart, arterioles and veins and increase parasympathetic activity to the heart decreases arterial pressure
What do Baroreceptors adapt to?
Sustained changes in arterial pressure
Why are Baroreceptors only used in short term regulation of blood pressure?
Because they adapt to sustained changes in blood pressure
What mechanisms does the long term regulation of arterial blood pressure require?
Hormonal and Renal mechanisms
