The Circulatory System Blood vessels

Each human being has approximately 5 litres of blood in his/her body Each human being has approximately 5 litres of blood in his/her body. Each time the heart beats about 150 millilitres of blood is pumped out of it and carried to different parts of the body by means of blood vessels.

3 different types of blood vessels Arteries Veins Capillaries

Arteries and veins The walls of the arteries and veins are made up of the same three layers An outer fibrous connective tissue layer A middle smooth muscle layer An inner endothelium layer

Differences between arteries and veins Carries blood away from the arteries Carries blood towards the heart Thick-walled because middle smooth muscle layer is thick Thin-walled because middle smooth muscle is thinner Blood is under pressure Blood not under pressure No valves within the arteries (except those within the heart) Have semi-lunar valves to prevent back-flow of blood

The circulatory system Blood circulation

Double circulation Pulmonary circulation – Blood flows from the heart to the lungs and back to the heart. Systemic circulation – Blood flows from the heart to all parts of the body and back to the heart.

Blood tissue Blood is salty Slightly sticky and reddish fluid. pH of little more than 7 Composition of blood 55% is plasma 45% blood corpuscles

3 types of blood corpuscles Red blood cells (erythrocytes) White blood cells (leucocytes) Blood platelets

The main function is to transport oxygen. erythrocytes Disc-shaped No nuclei Haemoglobin – gives blood its red colour Function The main function is to transport oxygen. The oxygen dissolves in the haemoglobin and forms oxyhaemoglobin before being transported

Leucocytes Irregularly shaped No nuclei Function The leucocytes protects the body in the following ways: They may engulf the microbes They may form a barrier against the microbes They may produce antibodies which destroy the microbes

The blood platelets play an important role in the clotting of blood Fragments of cells No nuclei Function The blood platelets play an important role in the clotting of blood

Blood plasma Blood plasma acts as a transport medium for the following: Digested food substances such as glucose and amino acid Excretory products such as urea and uric acid Plasma proteins such as fibrinogen which play an important part in the clotting of blood Salts Gasses such as oxygen and carbon dioxide Hormones and enzymes

Functions of the blood system It absorbs digested food from the alimentary canal and transports it to all parts of the body. It absorbs oxygen in the lungs and transports it to all parts of the body. It transports excretory wastes to the excretory organs (kidneys, lungs, and sweat glands in skin)