Composition of Blood

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Composition of Blood

Blood is a vital connective tissue that circulates throughout the body, delivering oxygen and nutrients to cells and removing waste products. It plays a key role in transport, regulation, and protection within the human body. Understanding the composition of blood helps explain how it supports vital functions like respiration, immunity, and temperature regulation.

1.0What Is Blood?

Blood is a fluid connective tissue that circulates continuously through the heart and blood vessels. It consists of two major components:

Plasma – the liquid part of blood.
Formed elements – the cellular components suspended in plasma.

An average adult has about 5–6 liters of blood, constituting roughly 8% of total body weight.

2.0Average Composition of Blood Percentages

Component	Percentage	Description
Plasma	~55%	Liquid portion containing water, proteins, nutrients, and hormones.
Formed Elements	~45%	Includes red blood cells (RBCs), white blood cells (WBCs), and platelets.

3.0Components of Blood

Plasma

Plasma is the straw-colored fluid that makes up about 55% of total blood volume. It serves as the transport medium for nutrients, hormones, gases, and metabolic waste.

Composition of Plasma

Constituent	Percentage/Function
Water	~90–92%; acts as a solvent and temperature regulator
Plasma Proteins	~7–8%; includes albumin, globulins, and fibrinogen
Inorganic Salts	Maintain osmotic balance and pH (Na⁺, K⁺, Ca²⁺, Cl⁻, HCO₃⁻)
Nutrients	Glucose, amino acids, lipids, vitamins
Waste Products	Urea, uric acid, creatinine
Hormones and Enzymes	Regulate physiological processes
Gases	Oxygen, carbon dioxide, and nitrogen in dissolved form

Major Plasma Proteins

Albumin: Maintains osmotic pressure and regulates fluid balance.
Globulins: Function in immunity (antibodies) and transport.
Fibrinogen: Essential for blood clotting.

Formed Elements

Formed elements constitute about 45% of the blood and include red blood cells (RBCs), white blood cells (WBCs), and platelets.

Red Blood Cells (Erythrocytes)

Shape: Biconcave, circular, and non-nucleated (in mammals).
Function: Transport oxygen from lungs to tissues and carbon dioxide from tissues to lungs.
Count: About 5–5.5 million per µL of blood.
Pigment: Contain hemoglobin (Hb), which binds oxygen.
Lifespan: Around 120 days; destroyed in the spleen (graveyard of RBCs).
Formation: Produced in the bone marrow (erythropoiesis).
Significance: RBCs determine the oxygen-carrying capacity of blood.

White Blood Cells (Leukocytes)

Function: Defend the body against infections and foreign substances.
Count: About 6,000–8,000 per µL of blood.
Types: Divided into granulocytes and agranulocytes based on the presence or absence of cytoplasmic granules.

a. Granulocytes

Type	Percentage	Function
Neutrophils	~60–65%	Engulf and destroy microbes (phagocytosis).
Eosinophils	~2–3%	Combat allergies and parasitic infections.
Basophils	~0.5–1%	Release histamine and heparin during inflammation.

b. Agranulocytes

Type	Percentage	Function
Lymphocytes	~25–30%	Produce antibodies and maintain immunity.
Monocytes	~5–6%	Act as macrophages; engulf pathogens and debris.

c. Platelets (Thrombocytes)

Shape: Small, irregular cell fragments without nuclei.
Count: About 1.5–3.5 lakh per µL of blood.
Origin: Produced in bone marrow from megakaryocytes.
Function: Play a critical role in blood clotting by releasing clotting factors.
Lifespan: Around 7–10 days.

Also Read: Functions of Blood

4.0Functions of Blood

Transport Function: Blood transports oxygen from lungs to tissues and CO₂ from tissues to lungs and nutrients, hormones, and waste materials throughout the body
Regulation: Maintains body temperature, pH, and osmotic pressure
Protection: WBCs defend against infections. Platelets and clotting factors prevent excessive bleeding
Homeostasis: Keeps internal conditions stable despite external changes

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Composition of Blood

Blood is a vital connective tissue that circulates throughout the body, delivering oxygen and nutrients to cells and removing waste products. It plays a key role in transport, regulation, and protection within the human body. Understanding the composition of blood helps explain how it supports vital functions like respiration, immunity, and temperature regulation.

1.0What Is Blood?

Blood is a fluid connective tissue that circulates continuously through the heart and blood vessels. It consists of two major components:

Plasma – the liquid part of blood.
Formed elements – the cellular components suspended in plasma.

An average adult has about 5–6 liters of blood, constituting roughly 8% of total body weight.

2.0Average Composition of Blood Percentages

Component	Percentage	Description
Plasma	~55%	Liquid portion containing water, proteins, nutrients, and hormones.
Formed Elements	~45%	Includes red blood cells (RBCs), white blood cells (WBCs), and platelets.

3.0Components of Blood

Plasma

Plasma is the straw-colored fluid that makes up about 55% of total blood volume. It serves as the transport medium for nutrients, hormones, gases, and metabolic waste.

Composition of Plasma

Constituent	Percentage/Function
Water	~90–92%; acts as a solvent and temperature regulator
Plasma Proteins	~7–8%; includes albumin, globulins, and fibrinogen
Inorganic Salts	Maintain osmotic balance and pH (Na⁺, K⁺, Ca²⁺, Cl⁻, HCO₃⁻)
Nutrients	Glucose, amino acids, lipids, vitamins
Waste Products	Urea, uric acid, creatinine
Hormones and Enzymes	Regulate physiological processes
Gases	Oxygen, carbon dioxide, and nitrogen in dissolved form

Major Plasma Proteins

Albumin: Maintains osmotic pressure and regulates fluid balance.
Globulins: Function in immunity (antibodies) and transport.
Fibrinogen: Essential for blood clotting.

Formed Elements

Formed elements constitute about 45% of the blood and include red blood cells (RBCs), white blood cells (WBCs), and platelets.

Red Blood Cells (Erythrocytes)

Shape: Biconcave, circular, and non-nucleated (in mammals).
Function: Transport oxygen from lungs to tissues and carbon dioxide from tissues to lungs.
Count: About 5–5.5 million per µL of blood.
Pigment: Contain hemoglobin (Hb), which binds oxygen.
Lifespan: Around 120 days; destroyed in the spleen (graveyard of RBCs).
Formation: Produced in the bone marrow (erythropoiesis).
Significance: RBCs determine the oxygen-carrying capacity of blood.

White Blood Cells (Leukocytes)

Function: Defend the body against infections and foreign substances.
Count: About 6,000–8,000 per µL of blood.
Types: Divided into granulocytes and agranulocytes based on the presence or absence of cytoplasmic granules.

a. Granulocytes

Type	Percentage	Function
Neutrophils	~60–65%	Engulf and destroy microbes (phagocytosis).
Eosinophils	~2–3%	Combat allergies and parasitic infections.
Basophils	~0.5–1%	Release histamine and heparin during inflammation.

b. Agranulocytes

Type	Percentage	Function
Lymphocytes	~25–30%	Produce antibodies and maintain immunity.
Monocytes	~5–6%	Act as macrophages; engulf pathogens and debris.

c. Platelets (Thrombocytes)

Shape: Small, irregular cell fragments without nuclei.
Count: About 1.5–3.5 lakh per µL of blood.
Origin: Produced in bone marrow from megakaryocytes.
Function: Play a critical role in blood clotting by releasing clotting factors.
Lifespan: Around 7–10 days.

Also Read: Functions of Blood

4.0Functions of Blood

Transport Function: Blood transports oxygen from lungs to tissues and CO₂ from tissues to lungs and nutrients, hormones, and waste materials throughout the body
Regulation: Maintains body temperature, pH, and osmotic pressure
Protection: WBCs defend against infections. Platelets and clotting factors prevent excessive bleeding
Homeostasis: Keeps internal conditions stable despite external changes

Frequently Asked Questions

What are the two main components of blood?

What is the function of plasma proteins?

What are the normal counts of RBCs, WBCs, and platelets?

Why are red blood cells biconcave in shape?

What is the lifespan of red blood cells?

Frequently Asked Questions

What are the two main components of blood?

What is the function of plasma proteins?

What are the normal counts of RBCs, WBCs, and platelets?

Why are red blood cells biconcave in shape?

What is the lifespan of red blood cells?

Join ALLEN!

Composition of Blood

1.0What Is Blood?

2.0Average Composition of Blood Percentages

3.0Components of Blood

Plasma

Major Plasma Proteins

Formed Elements

a. Granulocytes

b. Agranulocytes

c. Platelets (Thrombocytes)

4.0Functions of Blood

Table of Contents

Join ALLEN!

Composition of Blood

1.0What Is Blood?

2.0Average Composition of Blood Percentages

3.0Components of Blood

Plasma

Major Plasma Proteins

Formed Elements

a. Granulocytes

b. Agranulocytes

c. Platelets (Thrombocytes)

4.0Functions of Blood

Table of Contents