Circulatory System – Grade 9 Natural Sciences
Function of the Circulatory System
The circulatory system transports oxygen, nutrients, hormones, and other essential substances
throughout the body. It removes waste products such as carbon dioxide and helps regulate body
temperature. It also plays a role in immunity.
Main Components
The circulatory system consists of the heart, blood, and blood vessels.
The Heart
The heart is a muscular organ that pumps blood. It has four chambers: right atrium, right ventricle,
left atrium, and left ventricle. The right side handles deoxygenated blood, and the left side handles
oxygenated blood. Valves prevent backflow of blood.
Path of Blood Through the Heart
Body → Vena cava → Right atrium → Right ventricle → Pulmonary artery → Lungs → Pulmonary
veins → Left atrium → Left ventricle → Aorta → Body.
Blood Vessels
Arteries carry blood away from the heart and have thick elastic walls. Veins carry blood toward the
heart and contain valves. Capillaries are tiny vessels where gas and nutrient exchange occurs.
Blood Components
Red blood cells carry oxygen using haemoglobin. White blood cells defend against pathogens.
Platelets help blood clot. Plasma is the liquid that transports dissolved substances.
Double Circulation
Humans have double circulation: pulmonary circulation (heart ↔ lungs) and systemic circulation
(heart ↔ body).
Gas Exchange
Gas exchange occurs in capillaries. Oxygen diffuses into cells, and carbon dioxide diffuses into the
blood.
Function of the Circulatory System
The circulatory system transports oxygen, nutrients, hormones, and other essential substances
throughout the body. It removes waste products such as carbon dioxide and helps regulate body
temperature. It also plays a role in immunity.
Main Components
The circulatory system consists of the heart, blood, and blood vessels.
The Heart
The heart is a muscular organ that pumps blood. It has four chambers: right atrium, right ventricle,
left atrium, and left ventricle. The right side handles deoxygenated blood, and the left side handles
oxygenated blood. Valves prevent backflow of blood.
Path of Blood Through the Heart
Body → Vena cava → Right atrium → Right ventricle → Pulmonary artery → Lungs → Pulmonary
veins → Left atrium → Left ventricle → Aorta → Body.
Blood Vessels
Arteries carry blood away from the heart and have thick elastic walls. Veins carry blood toward the
heart and contain valves. Capillaries are tiny vessels where gas and nutrient exchange occurs.
Blood Components
Red blood cells carry oxygen using haemoglobin. White blood cells defend against pathogens.
Platelets help blood clot. Plasma is the liquid that transports dissolved substances.
Double Circulation
Humans have double circulation: pulmonary circulation (heart ↔ lungs) and systemic circulation
(heart ↔ body).
Gas Exchange
Gas exchange occurs in capillaries. Oxygen diffuses into cells, and carbon dioxide diffuses into the
blood.
