Human Circulatory System - The Blood and Blood Vessels

Human Circulatory System: Introduction

- The circulatory system is composed of the main parts namely:
- The heart acts as a pump. It pumps blood to all parts of the body.
- The blood is used to transport various substances within the body.
- The blood vessels are tubes or channels that the blood flows through. The blood vessels include: arteries, veins and capillaries.

The Heart

Study the parts of the heart shown below:
- The heart has two chambers: the upper and lower chambers.
- The upper chamber is called auricle while the lower chamber is called ventricle.
- Each chamber is divided into two parts.
(i) Right auricle/atrium
(ii)Left auricle/atrium
(iii)Right ventricle
(iv)Left ventricle

Functions Of Parts Of The Heart

Auricles / Atria

- These are the upper chambers.
- Auricles receive blood from different parts.
- Right auricle receives blood without oxygen from all parts of the body.
- Left auricle receives blood with oxygen from the lungs.
- Auricles have thin muscles.

Ventricles

- These are the lower chambers.
- They receive blood from the auricles and pump it outside the heart.
- Right ventricle receives deoxygenated blood from right auricle and pumps it into the lungs for oxygenation through pulmonary artery.
- Left ventricle receives oxygenated blood from the left auricle and pumps it to all parts of the body through the aorta.
- The heart is connected to other body parts through the blood vessels.

Note:

• The left ventricle has stronger muscles than right ventricle.
• The heart has valves to prevent backflow of blood.
• The left auricle is also called the left atrium while the right auricle is also called the right atrium

Examples Of Blood Vessels In The Heart And Their Functions

Pulmonary artery: - Carries blood without oxygen (deoxygenated) from the heart to the lungs.
Aorta: - It is the main artery. It carries blood with oxygen (oxygenated) to the rest of the body.
Vena cava: - It is the main vein that receives blood that has no oxygen (deoxygenated blood) from the rest of the body and carries it to the heart.
Pulmonary vein: - It carries blood with oxygen from the lungs to the heart.

Types of blood vessels and their functions

- The blood vessels are used to transport blood in the body.
- There are three main types of blood vessels.
- They include: arteries, veins and capillaries.

Arteries

1. They carry blood away from the heart.
2. They are located deep in the skin.
3. They have thick walls and narrow lumen where the blood flows under very high pressure.
4. All arteries carry oxygenated blood except pulmonary artery.
5. They have no valves.

Veins

1. They carry blood to the heart.
2. They are located near the skin.
3. They have thin walls and wide lumen where blood flows under low pressure.
4. All veins carry deoxygenated blood except the pulmonary vein that carries blood with oxygen.

Capillaries

1. They are spread all over the body.
2. They have thin walls and have no valves.

The Blood

- The blood is made up of four components:

1. Plasma
2. White Blood Cells
3. Red Blood Cells
4. Platelets

Functions of Plasma

- It is the liquid part of blood.
- It is used in transportation of:

• Other blood cells.
• Waste materials.
• Digested food.
• Heat and hormones.

Functions of White blood cells

- They protect the body from diseases.

Functions of Red blood cells

- They contain haemoglobin which is a red colouring matter.
- Haemoglobin combines with oxygen for transportation.

Functions of Platelets

- They help in clotting of blood.
- Clotting of blood prevents excess loss of blood after an injury.

Importance Of Blood Circulation In The Body

- The movement of the blood from the heart to the other parts and back to the heart is called blood circulation.
- The blood circulation is important since it helps in transportation of:

• Digested food from the ileum to other body parts.
• Oxygen from the lungs to other body parts.
• Carbon dioxide from the body parts to the lungs for removal.
• Excretory wastes from the body cells to the excretory organs.
• Heart from the body cells to all body parts.

Blood Groups

- A human being has four main blood groups. These blood groups are:

1. Blood group A
2. Blood group B
3. Blood group AB
4. Blood group O

Importance of blood groups during blood transfusion

- Blood transfusion is the process in which blood from one person is given to another person.
- Blood transfusion involves the giver and the receiver.
- The person who gives blood during transfusion is known as the donor.
- The person who receives blood during transfusion is known as the recipient.
- During blood transfusion, it is important to know the blood group of the donor and the recipient.
- A donor can only give certain blood groups and a recipient can also receive blood from some specific donors.
- The table below shows the blood groups, the donors and the recipients.

Blood Group	Donates 2	Receives From
Group A	A and AB	A and O
Group B	B and AB	B and O
Group AB	AB only	All Groups
Group AO	All Groups	O only