Blood is a heterogeneous, viscous, and red connective tissue.
Structure of Blood
The blood in human body comprises of two major components: Plasma and Blood corpuscles (cells).
Plasma
Plasma is a hay-colored fluid that constitutes around 55% of the total composition of the blood. The blood corpuscles are free to float on the plasma. It is responsible for the transmission of digested food, waste materials, hormones, and other important or harmful chemicals from the site of production to the site of consumption or excretion. It regulates the body temperature, amount of water, chemical compositions, and pH value of the blood. It contains fibrinogen that helps in blood clotting.
Blood Corpuscles
These are the blood cells present in the blood. They constitute around 45% of the blood.
Red Blood Cells (RBCs)or Erythrocytes
- RBCs are red colored, biconcave, and enucleated(lack the presence of a nucleus)disc like structure present in the plasma.
- They contain hemoglobin that provides them the red-color.
- In the body of a healthy man, number of RBCs ranges from 5 - 5.5 million per cubic mm and in the body of a healthy woman, it ranges from 4.5 - 5 million per cubic mm.
- The life span of RBCs is around 120 days. They are destroyed in the liver.
- The major function of RBCs is to help in the exchange of gases, and maintain the viscosity of blood and ion-balance.
White Blood Cells (WBCs)or Leucocytes
- WBCs are irregular in shape and have a nucleus.
- In the body of a healthy human being, number of WBCs ranges from 4000 to 11000 per cubic mm.
- Their life span is very short, i.e., few days only. They are destroyed in the liver, spleen and at the site of infection.
- Its major function is to protect the human body from foreign bodies. It produces antibodies that functions to kill and/or neutralize the germs, viruses, and bacteria that enter our body and destroy the damaged cells by phagocytosis. It keeps the human body healthy.
Platelets or Thrombocytes
- Platelets are colorless, oval, or round, blood corpuscles that do not have a nucleus.
- In the body of a healthy human being, number of platelets varies from 2.5 lakhs to 4.5 lakhs.
- Their life span is around 5 to 10 days.
- They are destroyed in the spleen.
- Its important function is to help in the coagulation or clotting of blood by releasing a chemical called thromboplastin.
Functions of Blood
We have studied the specific functions of the Blood Cells in this chapter above. Below, we discuss the major functions of the blood in the human body:
- Transportation: Blood transports essential materials like water, nutrients, hormones, and oxygen to the tissues. It also transports waste substances like urea, carbon dioxide, etc. to the site of excretion.
- Protection: It protects the body by fighting against germs and toxic materials. Fibrinogen and prothrombin proteins present in platelets and plasma help in blood clotting.
- Regulation: It maintains body temperature and balances the amount of water to a constant level. It also regulates different chemicals like salt, sodium, potassium, calcium, acidity, alkalinity, etc.