Level: JHS, Basic 9 | Subject: Integrated Science | Strand: Systems | Topic: The Heart, Blood Vessels and Circulation
Curriculum reference: B9.3.1.1 Understand the circulatory and excretory systems in humans. Indicator B9.3.1.1.1: Describe the structure and function of the human heart and blood vessels. All the exemplars are merged into one set of notes.
1. The Circulatory System
The circulatory system carries blood around the body. It has the heart (the pump), the blood vessels (the pipes) and the blood. It transports oxygen, digested food, hormones, water and heat to cells, and carries away carbon dioxide and wastes.
2. Structure of the Heart
The heart is a muscular organ about the size of a fist, found in the chest between the lungs, slightly to the left.
- Four chambers: two upper atria (right atrium and left atrium) receive blood, and two lower ventricles (right ventricle and left ventricle) pump blood out.
- The left ventricle has the thickest wall because it pumps blood to the whole body.
- The septum is a wall that separates the left and right sides, so oxygen-rich and oxygen-poor blood do not mix.
- Valves make blood flow in one direction only. The tricuspid valve (right side) and bicuspid valve (left side) lie between atria and ventricles. The semilunar valves lie at the exits to the arteries.
| Vessel at the heart | Carries |
|---|---|
| Vena cava | Oxygen-poor blood from the body to the right atrium |
| Pulmonary artery | Oxygen-poor blood from the right ventricle to the lungs |
| Pulmonary vein | Oxygen-rich blood from the lungs to the left atrium |
| Aorta | Oxygen-rich blood from the left ventricle to the body |
3. Blood Vessels
| Vessel | Structure | Function |
|---|---|---|
| Artery | Thick, strong, elastic wall; narrow space; carries blood under high pressure; pulse can be felt | Carries blood away from the heart (mostly oxygen-rich, except the pulmonary artery) |
| Vein | Thinner wall; wide space; has valves | Carries blood back to the heart (mostly oxygen-poor, except the pulmonary vein) |
| Capillary | Very thin wall, one cell thick | Exchange of oxygen, food and wastes between blood and cells |
4. Pathway of Blood (Double Circulation)
Pulmonary circulation (heart to lungs and back): Right ventricle, pulmonary artery, lungs (blood gets oxygen and gives out carbon dioxide), pulmonary vein, left atrium.
Systemic circulation (heart to body and back): Left atrium, left ventricle, aorta, body organs (oxygen is delivered), vena cava, right atrium, right ventricle.
Blood passes through the heart twice in one full round of the body, so it is a double circulation.
5. Heart Beat and Pulse
A resting adult heart beats about 70 times a minute. The pulse is the beat felt in an artery, for example at the wrist. Exercise, fear and fever make the heart beat faster.
6. Keeping the Heart Healthy
- Exercise regularly.
- Eat less salt, fat and sugar. Eat plenty of fruits and vegetables.
- Avoid smoking and too much alcohol.
- Keep a healthy weight and check blood pressure.
Remember: Arteries go away from the heart, veins return to the heart, and capillaries do the exchange.
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Education Always (education.inspiringalways.com). Original notes written to follow the NaCCA Basic 9 Integrated Science curriculum.