2.7 Transportation of Material Through Blood

Introduction

Blood is the body's transport system. It carries essential substances to cells and removes waste products from them. Without blood, cells would not receive oxygen and nutrients, and harmful waste would accumulate. This topic explains the materials transported by blood and the functions of blood in transportation.

Definition

Transportation through blood is the process by which blood carries digested food, oxygen, carbon dioxide, excretory waste, hormones, and heat to and from different parts of the body.

Main Idea

One of the main functions of blood is transport. The materials that are transported through blood are:

• Digested food
• Oxygen
• Carbon dioxide
• Excretory waste
• Hormones
• Heat

Core Concept

Materials Transported by Blood

Detailed Explanation

1. Transport of Digested Food

The digested substances transported from the alimentary canal to tissues are:

• Simple sugars (like glucose)
• Amino acids
• Vitamins
• Mineral salts

How they are transported:

• Amino acids and simple sugars are absorbed into the blood through the blood capillaries.
• Fatty acids are absorbed by the lacteals.

Simple explanation: Blood carries nutrients from the intestine to all body cells.

Pathway:

Intestine → Blood capillaries → Hepatic portal vein → Liver → General circulation

2. Transport of Oxygen

Oxygen is transported by red blood cells.

How it is transported:

• The red blood cells contain a pigment called haemoglobin.
• Each molecule of haemoglobin binds four oxygen molecules forming oxyhaemoglobin.
• The oxygen molecules are carried to the cells in the body tissue.
• The oxyhaemoglobin releases the oxygen to the tissues.

Equation:

Haemoglobin + Oxygen → Oxyhaemoglobin

Simple explanation: Red blood cells pick up oxygen in the lungs and carry it to all body cells. Haemoglobin is the molecule that holds the oxygen.

Why this is important:

• Oxygen is needed for cellular respiration.
• Without oxygen, cells cannot produce ATP (energy).

3. Transport of Carbon Dioxide

There are three means by which carbon dioxide is transported in the bloodstream from tissues and back to the lungs:

Simple explanation: Carbon dioxide is carried in three ways: as bicarbonate ions, bound to haemoglobin, and dissolved in plasma.

Why this is important:

• Carbon dioxide is a waste product of cellular respiration.
• It must be removed from the body to maintain proper pH.

4. Transport of Excretory Materials

Wastes are excreted from cells. They get dissolved in the blood.

How they are transported:

• The blood carries them to kidneys through blood capillaries.
• The waste materials get filtered out of the blood.
• Useful substances and excess water are reabsorbed into the blood.

Simple explanation: Blood carries waste products like urea from cells to the kidneys, where they are filtered out and excreted in urine.

Examples of excretory materials:

• Urea
• Uric acid
• Creatinine
• Excess salts

5. Transport of Hormones

Hormones are transported through the blood from the place of origin to the target cells.

How they are transported:

• Each hormone acts upon only those cells which have specific receptors.
• The cells which are acted upon by hormones are called target cells.

Simple explanation: Hormones are chemical messengers. Blood carries them from endocrine glands to target cells, where they deliver their message.

Why this is important:

• Hormones regulate many body functions (growth, metabolism, reproduction).
• Without blood transport, hormones could not reach their target cells.

6. Distribution of Heat

The blood plays a role in temperature regulation.

How it works:

• Blood distributes heat throughout the body.
• By changing the blood flow to the skin, the body can control heat exchange at its surface with its surroundings.

Simple explanation: Blood carries heat from active tissues (like muscles) to other parts of the body. It also helps release heat through the skin.

Why this is important:

• Maintains normal body temperature (about 37°C).
• Prevents overheating during exercise.
• Helps conserve heat in cold conditions.

Intermediate Level

Blood transports the following materials:

Key points:

• Oxygen is carried by haemoglobin in red blood cells.
• Carbon dioxide is carried in three forms.
• Hormones act only on target cells with specific receptors.
• Blood helps regulate body temperature.

Important Points

• - One of the main functions of blood is transport.
• - The materials that are transported through blood are digested food, oxygen, carbon dioxide, excretory waste, hormones, and heat.
• - The digested substances transported from the alimentary canal to tissues are simple sugars, amino acids, vitamins, and mineral salts.
• - Amino acids and simple sugars are absorbed into the blood through the blood capillaries.
• - Fatty acids are absorbed by the lacteals.
• - Oxygen is transported by red blood cells.
• - The red blood cells contain haemoglobin.
• - Each molecule of haemoglobin binds four oxygen molecules forming oxyhaemoglobin.
• - The oxyhaemoglobin releases the oxygen to the tissues.
• - Carbon dioxide is transported in three ways: (a) as bicarbonate ions, (b) as carboxyhaemoglobin, (c) dissolved in plasma.
• - Wastes are excreted from cells and get dissolved in the blood.
• - The blood carries wastes to kidneys through blood capillaries.
• - Hormones are transported through the blood from the place of origin to the target cells.
• - Each hormone acts upon only those cells which have specific receptors.
• - The cells which are acted upon by hormones are called target cells.
• - The blood plays a role in temperature regulation.
• - It distributes heat throughout the body.
• - By changing the blood flow to the skin, the body can control heat exchange.

Remember

• - Blood transports: digested food, oxygen, carbon dioxide, excretory waste, hormones, heat
• - Oxygen = carried by haemoglobin in RBCs
• - Carbon dioxide = carried in 3 ways (bicarbonate ions, carboxyhaemoglobin, dissolved in plasma)
• - Digested food = sugars and amino acids via blood capillaries; fats via lacteals
• - Excretory waste = carried to kidneys
• - Hormones = carried from glands to target cells
• - Heat = distributed throughout body

Common Mistakes

• 1. Thinking oxygen is dissolved in plasma.
• - Most oxygen is carried by haemoglobin in red blood cells. A small amount is dissolved in plasma.
• 2. Forgetting that carbon dioxide is transported in three ways.
• - Bicarbonate ions, carboxyhaemoglobin, and dissolved in plasma.
• 3. Confusing the transport of sugars and fats.
• - Sugars and amino acids are absorbed into blood capillaries.
• - Fats (fatty acids and glycerol) are absorbed into lacteals.
• 4. Believing hormones act on all cells.
• - Hormones act only on target cells that have specific receptors.
• 5. Thinking blood only transports oxygen.
• - Blood transports many materials: nutrients, wastes, hormones, heat.
• 6. Mixing up the direction of carbon dioxide transport.
• - Carbon dioxide is carried from tissues to lungs.
• 7. Forgetting the role of blood in temperature regulation.
• - Blood distributes heat and helps control body temperature.

Quick Revision

60-Second Revision

• Blood transports = digested food, oxygen, carbon dioxide, excretory waste, hormones, heat
• Oxygen = carried by haemoglobin in RBCs (oxyhaemoglobin)
• Carbon dioxide = carried in 3 ways (bicarbonate ions, carboxyhaemoglobin, dissolved in plasma)
• Digested food = sugars and amino acids via blood capillaries; fats via lacteals
• Excretory waste = carried to kidneys
• Hormones = carried from glands to target cells
• Heat = distributed throughout body
• Warning: Do not confuse the transport of sugars (blood capillaries) with fats (lacteals).