2.2 Components of Blood

Introduction

Blood is a vital fluid that circulates throughout the body, transporting oxygen, nutrients, hormones, and waste products. It is a specialized connective tissue made up of cells suspended in a liquid medium. This topic explains the composition of blood, including plasma and blood cells, and the functions of each component.

Definition

Blood is a type of special connective tissue with cells suspended in a fluid medium. It circulates in the blood vessels. Almost all the substances to be transported are present either dissolved or suspended in the blood.

• Plasma — the liquid part
• Blood cells — red blood cells, white blood cells, and platelets

Main Idea

Blood is a complex mixture of plasma and blood cells. Plasma is the liquid part (about 55% of blood), and blood cells form about 45% of blood. Each component has specific functions essential for life.

Core Concept

Composition of Blood

Simple explanation: Blood is like a river (plasma) carrying different types of boats (blood cells) that do different jobs.

Detailed Explanation

1. Plasma

The liquid part of the blood is called plasma. It constitutes about 55% by volume of blood in a normal person.

Composition of Plasma:

Plasma contains 90% water and 10% dissolved substances.

Simple explanation: Plasma is mostly water. It carries dissolved substances like proteins, salts, nutrients, hormones, and waste products.

Functions of Plasma:

• Transport — carries nutrients, hormones, and waste products.
• Maintains osmotic pressure — due to plasma proteins like albumin.
• Clotting — due to fibrinogen.
• Defence — due to immunoglobulins (antibodies).

2. Plasma Proteins

Plasma proteins make up 7–9% of plasma.

Simple explanation: Plasma proteins are like tools in the blood. Fibrinogen helps in clotting, antibodies fight germs, and albumin keeps the right amount of water in the blood.

3. Mineral Ions

Dissolved mineral salts e.g., chlorides, bicarbonates, sodium, potassium, and calcium.

Function: Help maintain electrolyte balance, pH balance, and osmotic pressure.

Simple explanation: Mineral ions are like tiny charged particles that help the body maintain proper balance of fluids and chemicals.

4. Metabolites and Wastes

Metabolites: Amino acids, glucose, vitamins, lipids. Metabolic wastes: Urea, uric acid.

Function: Transport of nutrients to cells and waste products to excretory organs.

Simple explanation: Metabolites are useful substances being carried to cells. Wastes are harmful substances being carried away from cells.

5. Hormones

All the hormones present in the plasma are to be carried by the blood.

Function: Hormones are chemical messengers that travel through the blood to target organs.

Simple explanation: Hormones are like messages in the blood that tell different organs what to do.

6. Dissolved Gases

Carbon dioxide and oxygen are dissolved in the plasma.

Function: Transport of respiratory gases.

Simple explanation: Oxygen and carbon dioxide dissolve in plasma and are carried between the lungs and tissues.

7. How to Separate Plasma from Blood

Centrifugation:

You can centrifuge blood which separates the components of blood according to their density. Centrifuge machines spin blood samples very fast to separate out:

• Top layer: Plasma (yellow)
• Middle layer: Buffy coat (leukocytes and platelets)
• Bottom layer: Red blood cells

Simple explanation: When blood is spun very fast in a machine, it separates into layers. The lightest part (plasma) goes to the top, and the heaviest part (RBCs) goes to the bottom.

8. Blood Cells

Blood cells form about 45% by volume of the blood. These include:

• Red blood cells (erythrocytes)
• White blood cells (leukocytes)
• Platelets (thrombocytes)

9. Serum

Serum is the clear liquid part of the blood that remains after blood cells and clotting proteins have been removed.

Simple explanation: Serum is plasma without the clotting proteins. It is the liquid that remains after blood clots.

Intermediate Level

Blood is composed of plasma and blood cells:

Plasma (55%):

Blood cells (45%):

Key points:

• Plasma is the liquid part of blood.
• Plasma proteins include fibrinogen, immunoglobulins, and albumin.
• Blood cells are suspended in plasma.
• Centrifugation separates blood into plasma, buffy coat, and RBCs.
• Serum is plasma without clotting proteins.

Important Points

• - Blood is a type of special connective tissue with cells suspended in a fluid medium.
• - Blood consists of plasma and blood cells.
• - Plasma constitutes about 55% by volume of blood.
• - Plasma contains 90% water and 10% dissolved substances.
• - Plasma proteins make up 7–9% of plasma.
• - Fibrinogen takes part in blood clotting.
• - Immunoglobulins (antibodies) defend against diseases.
• - Albumin maintains osmotic pressure.
• - Mineral ions include chlorides, bicarbonates, sodium, potassium, and calcium.
• - Metabolites include amino acids, glucose, vitamins, and lipids.
• - Metabolic wastes include urea and uric acid.
• - Hormones are carried by the blood.
• - Dissolved gases include carbon dioxide and oxygen.
• - Blood cells form about 45% by volume of blood.
• - Blood cells include red blood cells, white blood cells, and platelets.
• - Serum is the clear liquid part of the blood that remains after blood cells and clotting proteins have been removed.

Remember

• - Blood = plasma + blood cells
• - Plasma = 55% of blood
• - Plasma = 90% water + 10% dissolved substances
• - Plasma proteins = fibrinogen, immunoglobulins, albumin
• - Blood cells = RBCs, WBCs, platelets
• - RBCs = oxygen transport
• - WBCs = defence
• - Platelets = clotting
• - Serum = plasma without clotting proteins
• - Centrifugation separates blood into layers

Common Mistakes

• 1. Thinking plasma and serum are the same.
• - Plasma contains clotting proteins. Serum does not.
• 2. Confusing plasma proteins.
• - Fibrinogen = clotting.
• - Immunoglobulins = defence.
• - Albumin = osmotic pressure.
• 3. Forgetting that plasma is mostly water.
• - Plasma is 90% water.
• 4. Thinking blood cells are the largest component of blood.
• - Plasma (55%) is larger than blood cells (45%).
• 5. Mixing up the layers after centrifugation.
• - Top = plasma.
• - Middle = buffy coat (leukocytes and platelets).
• - Bottom = red blood cells.
• 6. Believing hormones are not in plasma.
• - All hormones are carried in the plasma.
• 7. Thinking oxygen is only carried by red blood cells.
• - A small amount of oxygen is dissolved in plasma. Most oxygen is carried by haemoglobin in RBCs.

Quick Revision

60-Second Revision

• Blood = plasma + blood cells
• Plasma = 55% of blood; 90% water + 10% dissolved substances
• Plasma proteins = fibrinogen (clotting), immunoglobulins (defence), albumin (osmotic pressure)
• Blood cells = RBCs (oxygen transport), WBCs (defence), platelets (clotting)
• Serum = plasma without clotting proteins
• Centrifugation = separates blood into plasma (top), buffy coat (middle), RBCs (bottom)
• Warning: Do not confuse plasma (with clotting proteins) with serum (without clotting proteins).