Question

1. What are the physiological factors that affect blood pressure?

Answer 1

Physiological factors affecting blood pressure

​​​​​​1.Peripheral resistance

The resistance of arteries to blood flow is called peripheral resistance.It is determined by the factors: blood vessel diameter, total vessel length and blood viscosity.

More pressure is needed to keep blood moving through a vessel with high resistance. Hence blood pressure increases​ with increase in peripheral resistance

2.Vessel elasticity

Elasticity of vessel wall refers to the ability to resume its normal shape after stretching and compressing. If vessel walls are not able to expand and recoil, their resistance to blood flow would increase, which in turn leads to rise in blood pressure.

3.Cardiac output.

Cardiac output is the volume of blood pumped from the heart through the ventricles. It is measured in litres/minute. Any factor that causes cardiac output to increase will elevate the blood pressure. This include sympathetic stimulation, catecholamines, thyroid hormones and increased calcium levels. Also, any factor that decreases cardiac output, such as parasympathetic stimulation, alteration in potassium levels and decreased calcium levels decreases the blood pressure.

4.Volume of circulating blood

It is the amount of blood moving through the body. When there is an increased venous return, it stretches the walls of atria where specialised baroreceptors are present. These are pressure sensing receptors and it stimulates cardiac center. Cardiac center responds by increasing sympathetic stimulation and inhibiting parasympathetic stimulation​, which ultimately increase the blood pressure. The converse is also true

5.Viscosity of blood.

It is a measure of thickness of blood. It is influenced by the presence of plasma proteins and formed elements. Higher the viscosity, higher the resistance to flow, and higher is the blood pressure.