Composition of blood

The composition of blood includes two main components plasma and blood cells. Plasma, the light-yellowish coloured liquid part of blood, makes up the majority of its volume. In a healthy adult, the body contains about 5 to 6 liters of blood. Blood has a slightly alkaline pH of 7.4, which helps maintain a stable internal environment of body.

Plasma

Plasma constitutes 55% of blood volume. It is composed of approximately 90% water, along with other components such as blood clotting factors, plasma proteins, immunoglobulins, electrolytes, and various organic and inorganic substances. Among these, three key plasma proteins are particularly important.

• Albumins
• Globulins
• Fibrinogen

Capillary membranes are impermeable to plasma proteins, enabling these proteins to generate a colloidal osmotic pressure of approximately 25 mmHg. This pressure is essential for maintaining fluid balance within the body.

Difference between plasma and serum

Plasma is the liquid component of blood that contains clotting factors, such as fibrinogen, whereas serum is plasma without these clotting factors.

• Plasma= (Whole Blood – Blood cells)
• Serum = (Plasma – Fibrinogen)

Blood cells

Blood cells fall into three main categories: –

• Erythrocytes or Red blood cells
• Leukocytes or or White blood cells
• Thrombocytes or Platelets

Erythrocytes or Red blood cells

Red blood cells (RBCs) have a biconcave shape and contain hemoglobin, the pigment that gives them their red color. These cells play an important role in transporting oxygen from the lungs to body tissues and carrying carbon dioxide back to the lungs for exhalation. Additionally, RBCs are key to determining blood groups, as their membranes carry specific antigens, such as A, B, and Rh factors. These antigens define whether an individual has blood type A, B, AB, or O, and whether they are Rh-positive or Rh-negative.

Leukocytes or White blood cells

White blood cells (WBCs) are unique because they have a nucleus, unlike red blood cells (RBCs), which lack nucleus. WBCs are further divided into two types based on the presence or absence of granules in their cytoplasm: –

• Granulocytes (presence of granules)
• Agranulocytes (absence of granules)

Granulocytes

The granules in the cytoplasm of granulocytes (a type of white blood cell) have unique staining properties. Based on how they react to stains, granulocytes are further divided into three categories:

• Neutrophils, which take up both acidic and basic stains
• Eosinophils, which only absorb acidic stains
• Basophils, which take up basic stains

Agranulocytes

Agranulocytes, which lack granules, are divided into two types: 

• Monocytes 
• Lymphocytes.

Lymphocytes are divided into two types based on their functions:

• T lymphocytes
• B lymphocytes

T lymphocytes are responsible for cellular immunity, where they directly attack and destroy invading organisms.

B lymphocytes play a key role in humoral immunity by producing antibodies that specifically target and neutralize harmful invaders, helping the body fight infections.

Function of WBCs

White blood cells (WBCs) play an important role in maintaining our health. Their key functions include destroying harmful microorganisms, fighting infections, and eliminating bacteria, parasites, and even tumor cells. Additionally, WBCs target and neutralize invading pathogens while aiding in the breakdown of tumor tissue, serving as the body’s primary defense system.

Thrombocytes or Platelets

Platelets play a crucial role in blood clotting, thanks to their three key properties: 

• Adhesiveness (sticking to damaged surfaces)
• Aggregation (clumping together)
• Agglutination (binding to form clots).

These actions help stop bleeding and promote healing.

Conclusion

Blood is a fluid connective tissue that acts as the body’s transportation system, carrying essential substances like oxygen, nutrients, and waste products from one part of the body to another. Blood plays a vital role in transporting oxygen from the lungs to every part of the body and carrying carbon dioxide back to the lungs for removal. It also delivers nutrients from the digestive system and hormones from endocrine glands to tissues, ensuring the body functions smoothly.

FAQs

Q. Why don’t red blood cells (RBCs) perform aerobic respiration?

Ans- Mitochondria, a cell organelle, are responsible for aerobic respiration. However, red blood cells do not contain mitochondria, so they cannot perform aerobic respiration.

Q. Which blood cell is essential for blood coagulation?

Ans- Platelets

Q. Who discovered blood groups?

Ans- Blood groups were discovered by the Austrian scientist Karl Landsteiner in 1901. He identified the A, B, and O blood types, a discovery that earned him the Nobel Prize in Physiology or Medicine in 1930.

Q. Who discovered blood circulation?

Ans-The discovery of blood circulation is credited to William Harvey, an English physician, in the early 17th century. 

Q. Which vitamin is essential for blood clotting?

Ans- Vitamin K

Q. How is oxygen transported in the blood?

Ans- Oxygen is transported in the blood with the help of hemoglobin, a protein found in red blood cells.

Q. Which organ is known as the graveyard of red blood cells (RBCs)?

Ans- The spleen is called the ‘graveyard of RBCs’ because it filters out and breaks down old or damaged red blood cells.