Leaving Certificate Agricultural Science

1. Leaving Certificate Agricultural Science The Circulatory System

2. Functions of the Circulatory System • To carry digested food from the small intestine to all areas in the body which need it. • To carry oxygen from the lungs to the rest of the body. • To aid in the disposal of all wastes from the body. • To distribute heat. • To fight diseases by using white blood cells to fight off infection.

4. Composition of Blood • The blood is made up of different types of cells and a liquid medium for which they are transported. • The cells in the blood are Red Blood Cell (Corpuscles), White Blood Cells and Platelets. • Plasma is the liquid medium of blood. • Red Blood Corpuscles are technically not cells at all, as they do not contain a nucleus. • Their red colour is from a substance known as haemoglobin. • Haemoglobin binds with oxygen so it is the red blood corpuscles that carry oxygen in the body.

6. Blood Cells (Video)

7. Composition of Blood 2 • White Blood Cells are largest and not as plentiful in the blood as corpuscles. • These cells are used to fight infection. • Foreign bodies are either devoured by the cells or the cells produces antibodies, which in turn attack the infection. • Platelets are small fragments of cells, and are responsible for blood clotting. • A Haemophiliac (someone who cannot clot) doesn’t have any platelets. • Plasma is the medium in which all the cells are maintained. • It contain water, proteins (fibrinogen), food, wastes (e.g. CO2), Antibodies and Hormones.

8. The Heart • The heart is a four-chambered hollow muscle, used to pump blood all over our bodies. • It is divided into four compartments, the left and right ventricles and the left and right atria (atrium in singular). • The right side of the heart pumps blood low in oxygen (de – oxygenated) to the lungs. • The left side of the heart pumps blood rich in O2 (oxygenated blood) all over the body.

10. The Heart Beat • Blood enters the heart through the superior and inferior Vena Cava and into the right atrium. • The tricuspid valve opens and the blood is moved into the right ventricle. • The walls of the right ventricle contract and the blood is pumped up to the lungs (through the pulmonary artery) where oxygen replaces CO2 in the blood. • The oxygenated blood enters the heart from the lungs through the left atrium (via the pulmonary vein). • Again a valve opens and the blood moved into the left ventricle. • The walls of the ventricle contract and the blood is pumped all over the body via the Aorta. • The rate of beat is controlled by the pace maker in the septum.

11. Arteries and Veins Arteries: • Carry blood away from the heart always. • Have thick muscular walls • Have a pulse • Deep under the skin • Have no valves Veins: • Carry blood to the heart. • Have thin walls • Do not have a pulse • Near surface of the skin • Have valves to stop back-flow of blood. • Capillaries are small blood vessels acting as veins and arteries. • The walls of capillaries are only one cell thick so substances (Food or cells) can easily get through them and into the blood or out.

12. Hepatic Portal Vein • The Hepatic portal system is a transport system between the small intestine, the liver and the heart. • It consists of the hepatic portal vein, the hepatic artery and the hepatic vein. • The hepatic artery carries oxygenated blood to the liver for use and the collection of wastes. • The hepatic vein carries the used blood back to the heart. • The Hepatic Portal Vein carries blood from the small intestine to the liver. • This blood is low in O2 but rich in Glucose and other food types. • The Glucose is converted to Glycogen in the Liver and stored there.

13. Hypertension • Hypertension (or high blood pressure) is caused by the blood vessels becoming narrow because of the build up of fat or from stress. • The heart therefore needs to pump harder to get the blood through the narrow vessels. • This can cause the left ventricle to grow, and can lead to the heart not functioning properly.

14. Heart Attack & Stroke • The heart also needs a supply of blood and gets from the coronary arteries. • If these arteries get blocked, a heart attack occurs. • A stroke is caused by a blockage or leak of blood vessels in the brain. • Every year in Ireland, 10,000 people die of heart attack or stroke.

15. Risk Factors of Heart Disease • The risks factors of heart attack and stroke are: • Smoking – nicotine can also block the arteries. • Obesity – more fat deposits in the blood vessels • Regular exercise can reduce the risk of heart disease. • Stress increases the risk of heart attacks.