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Structure of blood vessels carrying blood

There are three sorts of blood vessels in our body – arteries, capillaries, and veins. Blood vessels perform their function and are allowed specific functions in different parts.

Example – Very fine branches of capillary specifically perform the function of exchange of gases. Similarly, arteries which are flexible and tough allows the body to cope with the high blood pressure. Also, the veins are accompanied with valves to prevent the blood from going back when the pressure is low. All kinds of blood vessels vary in size of its lumen which is a hollow opening inside the blood vessels.


 Blood performs the function of transportation of nutrients and oxygen from the heart to cells and vice-versa. Blood comprises of four components.

  • Red blood cells – Transportation of oxygen in the body.
    • Red blood cells contain haemoglobin which in combination with oxygen gives it the red colour. Also, these cells are important in providing energy when you are doing some vigorous exercise or playing sports as haemoglobin combines oxygen with it which is used during respiration.
    • These are disc-shaped.
    • These have no nucleus.
    • These are small and concave look give it a large surface area and enables rapid diffusion of gases.
  • White blood cells – These provide immunity by fighting infections
  • Plasma – It is the fluid minus blood cells or simply the component that gives fluidity to blood.

Functions of the cardiovascular system

It has three major functions:

  • Transport of carbon dioxide, oxygen, and nutrients
  • Clotting of blood in injuries.
  • Maintenance of body temperature

How blood regulate our body temperature?

Blood vessels tend to enlarge when the body is near a high-temperature environment. This process is known as vasodilation. This enables the body to release heat to the temperature and prevents overheating.

You must have observed that often people turn pink in colour when they are sitting outside on a hot day for too long. This is due to the vasodilation of blood vessels.

Similarly, in a cold environment, the blood vessels near the surface of the skin contracts. This is called vasoconstriction and takes the blood away from the skin to prevent the loss of heat.

Blood pressure

The contraction of the heart pushes the blood towards the blood vessels and creates pressure. Blood pressure consists of two values

  • Systolic – Constriction of heart
  • Diastolic – relaxation of the heart

Blood pressure can be identified with cardiac output, denoted as Q and the resistance of the blood flow, denoted as R. The diameter and thickness of the blood vessels cause resistance to the flow of blood.

Heart rate

It is the number of times our heart beat in a minute, or you can say the number of times the ventricles pumps out blood. The average rate of heartbeat is 70 per minute.

Stroke Volume

It is the amount of blood our heart pumps out of the ventricles every time it contracts. Stroke volume is 70 ml when you are resting.

Cardiac quotients

Cardiac output is the measure of the amount of blood pumped from the heart in one minute and is calculated multiplying the stroke volume with the heart rate

Q = HR x SV

Where SV ranges between 70 to 90 millilitres at rest. Fit people tend to have a larger stroke volume. We can calculate cardiac output in different situations –

Q (when resting) = SV x HR

= 70 x 70

 = 4900 ml/min

Q (when exercising) = SV x HR

= 120 x 180

 = 21600 ml/min

Changes in heart rate during exercise

Heart rate is calculated in beats per minute. When we are exercising, the heart rate jumps up so that enough blood is taken to the muscles that are working vigorously to provide oxygen and nutrients. Also, an increase in heart rate enables the body to remove waste products through blood.

Maximal heart rate can be calculated by using following equation:

Maximal Heart Rate = 200 – age of the person.

Changes in stroke volume during exercise

During exercise, the blood is pumped out of heart at a faster rate that signifies the increased stroke volume.

Changes in the cardiac output during exercise

In resting situation, 5 litres per minute is the optimal cardiac output while during active exercise situation, 30 litres per minute of cardiac output is observed as both the stroke volume and heart rate increase.

Changes in blood pressure during exercise

An increase in cardiac output has a direct effect on blood pressure. Since exercise results in increased cardiac output, the blood pressure also increases.

The blood pressure reading at the beginning of the exercise should be around 160/85 mmHg.