Question

4. List the mechanisms that can affect blood pressure in the short term and long term. Illustrate and explain how the Baroreceptor reflex responds to (i) a sudden increase in mean arterial pressure and (ii) a when standing up from a prone position.

Answer 1

# Blood pressure is regulated by two basic mechanisms:

1) Short term

Short term mechanisms acts immediately on target and controls blood pressure quickly. This regulate blood vessel diameter,heart rate and contractility.

- Baroreceptors reflex

- Chemoreceptors reflex

- CNS ischemic response

- Hormonal release(which includes Anti diuretic hormone and Angiotensin II)

2) Long term

Long term mechanisms takes long time for blood pressure regulation. This mechanism controls BP by adjusting volume of extracellular fluid and blood. This mechanism mainly associated with Kidney.

- Pressure diuresis

- Pressure natrauresis

- Renin-angiotensin-aldosterone system.

# Effect of baroreceptors:

1) When increased in mean arterial blood pressure

Baroreceptors are located in walls of systemic arteries, when there is increase in mean arterial blood pressure it stretches baroreceptors which results in transmiting signals to vasomotor centre in brain( tractus solitarius). Then secondary signals generated which inhibits vasocontrictor center of medulla and excite the vagal parasympathetic center. which effects in vasodilatation of arteries and veins,also decreased heart rate and strength of heart contraction. This ultimately reduces arterial blood pressure as there is decreased in peripheral resistance annd cardiac output.

2) When standing up from prone position

There is decreased in central blood volume which decreases cardiac output and decreases arterial pressure too. which is sensed by baroreceptors and signals send to vasomotor center and activation of sympathetic nervous system. and increase in sympathetic outflow increases heart rate,contractility and cardiac output also constriction of arterioles and veins seen and aretrial pressure maintains towords normal.