Lecture 7

Question 2

How is mean arterial pressure regulated?

Answer 2

By regulating cardiac output and total peripheral resistance

Question 3

What is Darcy’s law?

Answer 3

Pressure difference = flow x resistance

Question 4

What is mean arterial pressure formula?

Answer 4

CO x TPR

Question 5

Why must MAP be maintained?

Answer 5

Too high is risk for stroke, kidney damage, heart failure
Too low is risk for insufficient blood flow

Question 6

How does the Frank-Starling mechanism work?

Answer 6

Increase in venous return leads to an increase in filling pressure of the left atria
Leads to increase in blood entering the ventricle which stretches the ventricle muscle and increases sarcomere length and increases sensitivity to calcium
Heart contracts harder and so pumps a larger volume
The left side now matches the right

Question 7

What is orthostasis?

Answer 7

Standing for too long, causing gravity to pull blood into the lower body

Question 8

How does orthostasis affect stroke volume

Answer 8

• Reduces pressure difference in venous system
• Reduces flow back to heart so reduces venous return
• Therefore stroke volume is reduced

Question 9

How does exercise affect stroke volume

Answer 9

• Active constriction of large veins push blood back to the heart
• Muscle and respiratory pumps push blood back to the heart
• Increased venous return
• Increased stroke volume

Question 10

What is the effect of the sympathetic nerves in the kidneys?

Answer 10

Leads to increased renin secretion which leads to an increase in angiotensin ii
Angiotensin II is a vasoconstrictor which increases TPR
Also, sympathetic nerves constrict renal afferent arterioles which leads to a lower GFR
This can restore blood volume and pressure

Question 11

What does Atrial natriuretic peptide do?

Answer 11

Opposes the actions of Angiotensin II and aldosterone to reduce Na+ reabsorption

Question 12

What does angiotensin ii do to increase plasma volume?

Answer 12

-Angiotensin II also stimulates the release of aldosterone from the adrenal gland
- Aldosterone is a steroid hormone and so alters expression of sodium channels and pumps
- It increases the reabsorption of sodium ions in the kidneys
- More sodium is absorbed
- More water absorbed
- Blood volume is restored