Blood is a body fluid in the circulatory system of human beings and other organisms that delivers necessary substances such as nutrients and oxygen to the cells and transfers metabolic waste products away from those cells. Another body fluid, lymph, also helps transport certain substances. Blood is a special connective tissue consisting of a fluid matrix, plasma, and formed elements. It can be called the lifeline of many living organisms since it is responsible for the most vital functions in the body. There are many important functions performed by blood in the body, which are discussed below.

Functions of Blood

Blood is utilised for various vital activities in the body, which are listed below:

• It is responsible for the supply of oxygen to tissues and organs of the body and the transfer of carbon dioxide from tissues and organs back to the heart. These gases are bound to haemoglobin present in the body. Deprivation of oxygen in the blood and its reduced supply to the brain can cause unconsciousness and eventually death
• It is responsible for supplying nutrients such as glucose, amino acids, fatty acids, minerals, salts, vitamins, and other substances. These nutrients are bound to the blood plasma and get distributed to different body parts
• It maintains immunity in the body by circulating white blood cells and detecting foreign material by antibodies. These antibodies fight and destroy infectious foreign materials
• Removal of waste such as carbon dioxide, urea, and lactic acid takes place by blood. It takes these waste products to their respective excreting organs. For example, it takes carbon dioxide to the lungs and excessive water to the kidneys
• The platelets present in the blood are responsible for coagulation, i.e., converting blood from a liquid to a semisolid gel to stop bleeding in case a vessel is damaged
• Blood also transports hormones secreted by endocrine system glands to target organs and tissues in the body. It also transfers signals regarding tissue damage. These are called messenger functions
• It maintains and regulates the body temperature. It absorbs and distributes heat throughout the body. It helps to maintain homeostasis by the release or conservation of warmth

Constituents of Blood

Blood consists of two main elements: the plasma and the blood cells. These are explained below.

Plasma

Plasma is a clear yellow coloured liquid, a little sticky in nature, containing dissolved proteins, mineral ions, glucose, hormones, and carbon dioxide, including the blood cells. Around 90% of the plasma constitutes water, and around 6 % of it constitutes proteins. The main protein in the plasma is albumin, which regulates osmotic blood pressure. 55% of the blood fluid is plasma. In an average human, the blood plasma volume totals 2.7–3.0 litres.

Blood Cells

These constitute around 45% of the blood fluid. There are three types of cells: Erythrocytes or Red Blood cells (RBC), Leukocytes and White Blood Cells (WBC), Thrombocytes or Platelets.

Red Blood Cells

RBCs form around 40%-45% of the blood cell volume. They are produced in the bone marrow at a rate of four to five billion cells per hour. The lifespan of red blood cells is about 120 days. They are destroyed in the spleen organ, which is also known as the graveyard of RBC. RBCs are red in colour due to the presence of haemoglobin, an iron-containing complex protein that carries oxygen. These are also responsible for defining different blood types. The red blood cells are made up of haemoglobin and the membrane which contains proteins and lipids.

White Blood Cells

WBCs or Leukocytes account for only 1 % of the total blood cell volume, but they play a very important role in the body. The white blood cells are made up of granulocytes, monocytes and lymphocytes; sometimes mast cells are also observed in the white blood cells. The granulocytes present in the blood are made up of neutrophils, eosinophils and basophils. They are a part of the immune system of the body. They help fight diseases and attack the foreign disease-causing bodies in the blood. WBCs also remove old cells and cellular debris from the blood. These cells are colourless as they do not have haemoglobin. They are also constantly generated from the bone marrow.

Platelets

Platelets or Thrombocytes are cell fragments that are produced from the specialised cells of the bone marrow and they contain dense granules, alpha granules and lambda granules as their components. They control bleeding and help in the clotting of blood. There are 2 to 5 lakhs platelets in the human body.

Conclusion

Blood is a body fluid in the circulatory system of human beings and other organisms that delivers necessary substances such as nutrients and oxygen to the cells and transfers metabolic waste products away from those cells. It performs many vital functions in the body, such as respiration, supply of nutrients, removal of waste, immunological functions, coagulation, messenger functions, and body temperature regulation. Blood consists of two main elements: the plasma and the blood cells. Plasma is a clear yellow coloured liquid, a little sticky in nature, containing dissolved proteins, mineral ions, glucose, hormones, and carbon dioxide, including the blood cells. Blood cells are further divided into red blood cells, white blood cells, and platelets.