BiologyHuman biology

What is Blood?

Plasma, blood cells, and platelets make up blood, which is a fluid connective tissue.

It transports oxygen and nutrients to many cells and tissues throughout our bodies. It accounts for about 8% of our body weight. A typical adult has about 5-6 litres of blood.

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What is Plasma?

Plasma is a sticky, straw-colored fluid that makes up roughly 55% of the blood.

Water makes about 90-92% of the plasma, with proteins accounting for 6-8%.

The primary proteins are as follows −

  • Fibrinogen

  • Globulins

  • Albumins.

Fibrinogens are required for blood clotting and coagulation. Globulins are primarily engaged in the body's defensive systems, whereas albumins aid in osmotic equilibrium.

Plasma contains glucose, amino acids, lipids, and other substances that are constantly in transit throughout the body. Factors that aid in blood coagulation or clotting are also present in plasma in an inactive state. The serum is plasma lacking the clotting factors.

Types of Blood Cells

Blood is made up of cells known as created constituents of blood. In the body, these cells have their own jobs and duties to play.

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Following are the blood cells that circulate throughout the body −

Erythrocytes (Red Blood Cells or RBC)

These are the most numerous of all the blood cells. A healthy adult male contains 5 million to 5.5 million RBCs per millilitre of blood. In adults, RBCs are generated in the red bone marrow. Most animals' RBCs lack a nucleus and are biconcave in form. These cells carry a red-colored, iron-containing complex protein called haemoglobin, which gives them their colour and name. In every 100 ml of blood, a healthy person contains 12-16 gms of haemoglobin. These molecules are important in the transportation of respiratory gases. RBCs have a lifespan of around 120 days before being destroyed in the spleen (the graveyard of RBCs).

Leukocytes (White Blood Cells or WBC)

Leukocytes are known as white blood cells (WBC) as they lack haemoglobin, and are hence colourless. They are nucleated and very few in number, with an average blood volume of 6000-8000 mm–3. Leucocytes have a limited lifespan.

Granulocytes and Agranulocytes are the two primary types of WBCs.

Granulocytes include neutrophils, eosinophils, and basophils.

  • Neutrophils make up the majority of total WBCs (60-65%), whereas basophils make up the smallest percentage (0.5-1%). Neutrophils and monocytes (6–8%) are phagocytic cells that kill foreign organisms that enter the body.

  • Basophils (0.5-1%) are inflammatory cells that release histamine, serotonin, heparin, and other substances.

  • Eosinophils (2-3%) are immune cells that fight infections and are linked to allergic responses.

Agranulocytes include lymphocytes and monocytes.

  • Lymphocytes are divided into two types: B and T lymphocytes. The immunological responses of the organism are controlled by both B and T cells.

  • Monocytes, which are the largest cells, are capable of ingesting infectious agents.

What are Platelets?

Platelets, also known as thrombocytes, are megakaryocyte cell fragments (special cells in the bone marrow). Normally, blood contains 1,500,00-3,500,00 platelets per milliliter. Platelets may emit a range of chemicals, the majority of which are involved in blood coagulation and clotting.

A decrease in their number might lead to clotting problems, which can result in excessive blood loss.

Blood Grouping

During the blood transfusion, the two most important group systems examined are the following two −

  • ABO Blood Group System

  • Rhesus Blood Group System.

ABO Blood Group System

ABO Blood Group System classification is based on the antigens Antigen A and Antigen B. Based on the presence or absence of antigens on the surface of red blood cells and plasma antibodies, the ABO grouping system is divided into four categories.

They are as follows −

  • Antigen A and antibody B are found in Group A.

  • Antigen B and antibody A are found in Group B.

  • A and B antigens are present in Group AB, but no antibodies are present (neither A nor B).

  • Group O has neither A nor B antigens, but both A and B antibodies.

Mismatching of blood groups can cause clumping of red blood cells, which can cause a variety of illnesses. The ABO group system is vital during blood donation or blood transfusion.

While transfusing, the blood cells must match, i.e. donor-recipient compatibility. Because there are no antibodies for A and O in blood group A, a person of blood group A can receive blood from either group A or O.

Rh Blood Group System

The Rh blood grouping system is a popular alternative to the ABO blood grouping system. About two-thirds of the population has the third antigen, known as Rh factor or Rh antigen, on the surface of their red blood cells, which determines whether the blood group is positive or negative.

An individual is rhesus positive (Rh+ve) if the Rh factor is present; if the Rh factor is lacking, the individual is rhesus negative (Rh-ve) as they develop Rh antibodies. As a result, donor-individual compatibility is also critical in this scenario.

Coagulation of Blood

In the event of an accident or trauma, blood coagulates or clots. This is a process that prevents the body from losing too much blood. Over time, you would have seen a dark reddish-brown scum forming at the site of a cut or damage. It is a clot or coagulates made up mostly of a network of fibrin threads in which dead and damaged blood components are trapped.

Fibrins are made when the enzyme thrombin converts inert fibrinogens into the blood. Thrombins, in turn, are made from prothrombin, an inactive molecule found in the blood. The above process requires the enzyme complex thrombokinase. This complex is produced by a sequence of interconnected enzymic processes (cascade process) involving a variety of components that are inactive in the plasma.

Trauma or injury causes platelets in the blood to release particular substances that activate the coagulation process. Coagulation can also be triggered by substances secreted by tissues around the injury site. The involvement of calcium ions in clotting is critical.


Q1. What exactly is blood?

Ans. Plasma, various kinds of blood cells, and platelets make up blood, which is a fluid connective tissue. Blood's primary purpose is to transport oxygen and nutrients to the body's cells and tissues.

Q2. Name the various components of blood.

Ans. Blood is primarily broken down into the following components −

  • Plasma,

  • RBC,

  • WBC,

  • Platelets.

Q3. What are granulocytes, and what do they do?

Ans. Granulocytes are leukocytes having granule-like features that carry microorganismdigesting enzymes. Eosinophils, basophils, and neutrophils are the three types of granulocytes.

Q4. What are Agranulocytes?

Ans. Agranulocytes are white blood cells with no discernible granules in their cytoplasm. They do, however, play a crucial role in the body's immune system. Monocytes and lymphocytes are two types of monocytes.

Updated on 13-Oct-2022 11:19:47