Classwork Series and Exercises { Basic Science – JSS2}: Circulatory System

Basic Science JSS 2 Week 3

Topic: Circulatory System

Introduction

Higher organisms e.g. man, require blood to carry materials to and from different parts of their body. There is need for organisms to transport oxygen from the lungs to other living cells within the organisms and also, dissolved food materials absorbed in the villi to other parts of the body which need them. Circulation is the process by which absorbed food materials are carried through arteries, capillaries and veins to all parts of the body where they are utilized for body functioning. Materials which are transported by blood in human body are water, salts, hormones, oxygen, digested food, etc. waste materials also removed from the body through blood circulation.

Parts of the Circulatory System

The organs that are responsible for blood circulation in the body are together called the circulatory system. The circulatory system consists of the blood vessels and the heart.

The Heart

The heart pumps blood to all part of the body through the circulatory system. The heart is a muscular organ that lies in the chest cavity and is almost conical in shape. It is made up of four chambers. These four chambers include two upper chambers which are the right auricle and left auricle; and two lower chambers, the right ventricle and left ventricle. Blood enters the heart at the auricles and leaves from the ventricles. The heart is constantly beating, contracting and relaxing. There are about 70-75 beats per minute although this beating rate may vary with individuals. Beating rate is faster in children than in adults.

Blood Vessels

These are channels or routes through which blood passes to different parts of the body. There are three types of blood vessels; the arteries, veins and capillaries.

1. Arteries: These are the blood vessel that carry blood away from the heart to all parts of the body except the pulmonary artery.
2. Veins: These are blood vessels that carry blood to the heart from all parts of the body except the pulmonary vein.
3. Capillaries: These are tiny networks of blood vessels that connect arteries to veins. Blood flows out from the heart through arteries to all parts of the body, through capillaries and then into the veins, and back to the heart where circulation continues.

Characteristics of Capillaries

1. They are small, very thin walled vessels which lie between the cells of human organs.
2. They connect the arteries with the veins
3. They allow food and oxygen to pass from the blood to the body cells
4. They also collect waste materials from cells
5. They allow the exchange of materials between the blood and cells.

Importance of Circulatory system

1. Helps in excretion of waste products from the body
2. Digested food materials like glucose, amino acids, fatty acids and glycerol are carried from the intestine to the tissues where they are stored or used up, water and oxygen are also carried by the blood.
3. Protection of the body against diseases e.g. white blood cells
4. Regulation of the body temperature: the blood helps in the distribution of heat produced in muscles and organs like liver, to other parts of the body.
5. Helps in blood clotting in wounds e.g. blood platelets
6. Sustains life by supplying nutrients to cells

Blood defects and Diseases

Blood is made up of the blood particles and plasma. The blood particles are the:

1. Red blood cells (erythrocytes)
2. White blood cells (leucocytes)
3. Platelets (thrombocytes)

While plasma is the liquid part of the blood which consists of water, proteins, dissolved food materials, mineral salts, waste products, etc.

Blood defects are those imperfections associated with the normal state of the blood, for example, high blood pressure and low blood pressure. Blood diseases are illnesses associated with the blood such as anaemia.

There are several defects and diseases of the blood, but we shall consider defects and diseases such as anaemia, hemophilia, sickle cells and leukaemia.

Anaemia: This is a blood disease resulting from shortage of red blood cells in the blood. As a result of this, less oxygen is supplied to the cells and to the entire body system. There is usually general tiredness for the sufferer because the body requires more energy which it does not get for proper body functioning.

Sickle cells: This is a kind of anaemia caused by abnormally shaped (sickle shaped) red blood cells. These red cells cannot carry oxygen, hence the patient faints occasionally. The disease is inherited.

Leukaemia: This is another disease of the blood that occurs as a result of over production of the white blood cells. Hence, the balance of the blood components is altered so that there is imbalance of red and white blood cells. Intensive radiation exposure or moderately intense exposure for long periods increases the risk of acute and chronic lymphocytic leukaemia.

The Movement of Blood through the Left and Right Ventricles and Auricles

From the left side of the heart, blood flows from the pulmonary veins to the left auricle, to the left ventricle to the aorta and to all parts of the body. The blood here is oxygen-rich (re-oxygenated).

On the right side of the heart, blood flows from the vena cavae to the right auricle, to the right ventricle and then to the pulmonary artery.

The blood from two sides of the heart does not mix because of the presence of a dividing structure called septum.