Physio- Reg. Of Vascular Sys & Cardio Changes

Question 1

Explain the Bayliss’ effect.

Answer 1

— Known as a myogenic autoregulatory response.
— the vascular muscle constricts when the vascular smooth muscle is stretched by an elevated pressure.
Vs.
— the vascular muscle relaxed when the vascular smooth muscle is slightly stretched by reduced pressure.

Question 2

Explain the baroreceptor reflex when blood pressure is elevated.

Answer 2

The following attempts are made to decrease blood pressure:
— increase of firing of baroreceptor reflex
— increase in vagus nerve
— decrease in sympathetic outflow
— decrease in heart rate
— decrease in cardiac contractility
— decrease in cardiac output or
— vasodilation
— decrease in vascular resistance.

These all decrease blood pressure levels back to normal.
Called: the depressor baroreflex.

Question 3

Explain the baroreceptor reflex when blood pressure has dropped.

Answer 3

The effects are made to increase blood pressure back to normal:
— decrease in reflux of baroreceptor
— decrease in vagus nerve
— increase in sympathetic outflow
— increase heart rate
— increase contractility
— increase in cardiac output
— vasoconstriction
— increase in vascular resistance

All these effect increase blood flow back to normal.

Question 4

Explain the renin- angiotensin- aldosterone system.

Answer 4

1. A decrease in the renal perfusion pressure caused the juxtaglomerular cells to secrete renin
2. Renin, enzyme that converts angiostensinogen to angiostensin I
3. ACE converts angiostensin I to angiostensin II
   — ACE inhibitors block the conversion on AI to AII and decrease blood pressure.
   — ACE receptors block the function of AII and decreases blood pressure
4. Angiostensin II produces its effects to bring the systemic pressure back to normal.

Question 5

What effects does angiostensin II have on the regulation of blood pressure back to normal.

Answer 5

1. It stimulates and secretes aldosterone from the adrenal cortex.
   — it increases Na+ reabsorption and increase ECF, blood volume and arterial pressure.
2. Increases the Na+-H+ exchange
3. It increases thirst and water intake
4. It increases vasoconstriction > increases resistance and pressure.

Question 6

Explain how Cerebral ischemia (central chemoreflex) regulates blood pressure back to normal.

Answer 6

1. When the brain becomes ischemic, there is an increase is partial pressure of carbon dioxide.
2. Chemoreceptors increase sympathetic outflow which leads to constriction of the arterioles to cause peripheral constriction (increase TPR)
3. Results in increase in pressure being directed to the brain to be saved.

Note: The crushing effect is an example of the response.

Question 7

Explain how Peripheral chemoreceptors regulates blood pressure back to normal.

Answer 7

— These chemorecptors are found in the common carotid sinus and along the arch of the aorta.
— Very sensitive to decrease in blood O2, CO2 and pH.
— when there is a decrease in blood O2, the vasomotor causes vasoconstriction > increase in TPR and arterial pressure.

Question 8

Explain how the cardiopulmonary reflexes reduce blood levels backs to normal.

Answer 8

1. Increases ANP secretion
2. Decrease ADH secretion in hypothalamus.
3. Renal vasodilation
4. Increase heart rate via bainbridge reflex.

Question 9

Explain how an increase in ANP in the atria reduces blood volume back to normal.

Answer 9

— Inhibits renin secretion
— increases excretion of Na+ and water to reduce blood volume and to decrease the arterial blood pressure.
— relaxes vascular smooth muscles > dilation of arterioles > decrease in TPR.

Question 10

State the mechanisms for an increase in cardiac output in exercise.

Answer 10

1. Increases sympathetic activity
2. Increased venous return (explain)
3. Reduced cardiac afterload - due to metabolic vasodilation in skeletal muscles and reducing the vascular resistance.

Question 11

State the causes for increased blood flow to the muscle during exercise.

Answer 11

1. Increased cardiac output
2. Metabolic vasodilation in the muscle
3. Diversion of blood away from visceral organs

Question 12

Discuss how vasodilation in the skeletal muscle increases blood flow during excerise.

Answer 12

1. Vasodilator metabolites (lactate, K+ and adenosine) causes dilation in the skeletal muscle thus increases blood flow to the muscle. The increase in blood flow > increase O2 delivery to the muscle > increases perfused capillaries pressure. Thus causes a decrease in TPR.
2. Andrenaline increases blood flow during exercise due to the dilation of the blood vessels via the activation of beta2-AR in vascular smooth muscle.

Question 13

Discuss how diversion of blood away from the viceral organs increases blood flow to skeletal muscles during excerise.

Answer 13

The cardiac output increases from 20% to 80% due exercise. Therefore, the visceral blood flow to the kidney and visceral organs decreases from 20% to 5% as blood is diverted towards the skeletal muscle.

Question 14

State the differences in blood pressure,HR, VR, SV and CO in static exercise.

Answer 14

BP- greater increase
HR- smaller increase
SV- smaller increase
CO- smaller increase
VR- small increase

NOTE: In dynamic exercise, there would be a greater increase in BP, HR, VR, SV, and CO.