UNIT 11 TRANSPORT SYSTEM IN HUMAN BEINGS 2013

Transcription

1 Students should be able to: identify the main parts of the heart and the main blood vessels: i) the four chambers: ventricles, atrium. ii) pulmonary artery, pulmonary vein, aorta, vena cava. iii) valves. state the function of the heart. briefly describe the transport (circulatory) system in human beings with reference to the heart and blood vessel. identify the components of blood i.e. white blood cells, red blood cells, platelets and plasma. state that the main function of blood is to transport food (nutrients) and oxygen to all parts of the body and to remove carbon dioxide and waste products from the body. identify the three main types of blood vessels as arteries, veins and capillaries. describe the functions of arteries, veins and capillaries. show an awareness of the heartbeat, pulse and blood pressure. 1. The body of a mammal is made up of millions of cells which require oxygen and nutrients. 2. They also produce carbon dioxide and other waste products which must be removed. 3. Thus, in mammals including humans, the transport system carries oxygen and food substances to the cells and removes waste products from the cells. 4. The transport system in humans is known as the blood circulatory system. 5. It consists of the heart, blood vessels and blood. The Heart 1. The human heart is about the size of our fist. 2. It lies in the chest between the two lungs. 3. It is a muscular organ and its main function is to pump blood around the body. It pumps blood continuously from birth to death. How does the heart work? Heart works by contraction and relaxation of the heart muscles as shown below: When the heart muscles contract, blood is forced out from the heart to other parts of the body. When the heart muscles relax, blood fills the heart as it flows from the other parts of the body into the heart. The four chambers of heart 1. The heart consists of four chambers as follows: a) The upper chambers are called the right and left atria (singular: atrium). b) The lower chambers are called the right and left ventricles. The left ventricle wall is the thickest because this part needs to pump oxygenated blood (blood rich in oxygen) throughout the body while the right ventricle only pumps blood to the lungs. MSPSBS/Year / Lower Secondary Science Page 1 of 6

2 2. The table below shows the comparison between the atria and the ventricles. ATRIA CHARACTERISTIC VENTRICLES Receive blood (where blood enters the heart) FUNCTION Thinner WALL Thicker Smaller SPACE Bigger Pump blood from the heart (where blood leaves the heart) Valves in the heart 1. There are four valves in the heart. 2. A valve ensures that blood flows in one direction only and to prevent blood from flowing back. Blood Vessels 1. There are three types of blood vessels in the human body. They are the arteries, veins and capillaries. 2. The table below shows the differences between the artery, vein and capillary. Characteristics Arteries Veins Capillaries Cross section Function Carry blood away from the heart Carry blood into the heart Lumen size Small Large Very small Thickness of the wall Type of blood Presence of valve Rate of blood flow Thick, elastic and muscular to withstand the high pressure Oxygenated except pulmonary artery Thin, not elastic and muscular Deoxygenated except pulmonary vein Absent Present Absent Fast and at high pressure Slow and at low pressure 3. The relation between artery, capillaries and vein: The artery and vein are joined by capillaries. The direction of the flow of blood is from an artery through the capillaries then to the vein. (Heart Artery Capillaries Vein Heart) Connect the arteries to the veins Allow the exchange of materials in and out of the cells Very thin (One-cell thick) Oxygenated and deoxygenated Slow and at a low pressure Flow of blood MSPSBS/Year / Lower Secondary Science Page 2 of 6

3 Blood Vessels in the heart Each chamber of the heart is connected with a big blood vessel as shown in the table below. Heart chamber Blood vessel connected to it (a) Right atrium Vena cava (b) Left atrium Pulmonary vein (c) Right ventricle Pulmonary artery (d) Left ventricle Aorta Blood Circulation The flow of blood 1. The diagram shows the paths of blood flows in the heart. 2. On the left side of the heart as shown in the diagram carries the oxygenated blood while on the right side carries the deoxygenated blood. 3. Differences between oxygenated and deoxygenated blood: Oxygenated blood Rich in oxygen Poor in carbon dioxide Deoxygenated blood Poor in oxygen Rich in carbon dioxide MSPSBS/Year / Lower Secondary Science Page 3 of 6

4 4. The diagram shows the circulation (movement) of blood around the human body. 5. The diagram shows that the blood circulates in two paths: (a) From the heart to the lungs and back to the heart again, [Pulmonary circulation] (b) From the heart to the rest of the body and back to the heart again. [Systematic circulation] 6. As the blood circulates around the body, it passes through the heart twice. This is called double circulation. It takes about one minute for blood to circulate around the body once. 7. In the lungs, blood collects oxygen and loses carbon dioxide. The oxygen is carried by the red blood cells. 8. As the blood moves around the body, it supplies oxygen to the cells and collects carbon dioxide from the cells. 9. The exchange of gases takes place in the lungs. Oxygen from the air sacs diffuses into the blood. At the same time, carbon dioxide diffuses out of the blood into the air sacs. The blood becomes oxygenated. 10. As the oxygenated blood moves around the body, oxygen diffuses from the blood into the cells. 11. Carbon dioxide, which is produced in the cells diffuses out from the cells into the blood. The blood now becomes deoxygenated. 12. The deoxygenated blood moves back to the lungs where the carbon dioxide is removed and more oxygen is taken into the blood system. 13. The diagram shows the exchange of substances between blood and the surrounding cells. The process by which these substances go in and out is called diffusion. MSPSBS/Year / Lower Secondary Science Page 4 of 6

5 Human Blood 1. One important function of blood is to act as a transport medium. 2. The functions of blood are: (a) It carries nutrients from the small intestines and oxygen from the lungs to every cell in the body. (b) It removes carbon dioxide produced in the cells and carries it back to the lungs. (c) It carries other waste products such as urea to the kidneys to be removed from the body. (d) It helps to ingest bacteria or to fight diseases and to produce antibodies. (e) It helps in blood clotting process Additional Information 1. Human blood consists of four components: a) plasma (55%) b) blood cells (45%) [red blood cells, white blood cells and platelets]. 2. The four components of blood: Plasma Red Blood Cells White Blood Cells Platelets Structure Pale yellow liquid Function transport nutrients into the cells and waste products out of the cell Tiny, biconcave discs in shape carry oxygen from the lungs to all the cells in the body Colourless and irregular in shape ingest bacteria or to fight diseases and to produce antibodies. Colourless and irregular in shape to help in blood clotting process HEARTBEAT, PULSE & BLOOD PRESSURE The heart beats about 70 times a minute. This is called the heartbeat rate. MSPSBS/Year / Lower Secondary Science Page 5 of 6

6 1. During each heartbeat, the muscles of the heart contract causing a wave of pressure which forces blood through the arteries. 2. This wave of pressure that expands the artery a little is known as a pulse. There is one pulsation for each heartbeat. 3. The pulse can be felt at various points on the body where the arteries are just under the skin, such as the temples, neck, crook of the elbow, wrist, back of the knee, and the inside back of the ankle. The number of pulses per minute is called the pulse rate. 4. With exercise or physical activity, the heart rate increases to supply the muscles and cells with more nutrients and oxygen to produce extra energy. 5. A baby may have a pulse rate of more than 100 beats per minute. 6. The heart beats faster so that more nutrients and oxygen can reach the cells. Therefore, the heart beats faster or pulse rate increases. 7. The heart can beat up to 200 times per minute with extreme exercise. Therefore the heart or pulse rate increases. 8. Heart beat can be heard using a stethoscope BLOOD PRESSURE 1. As blood flows along the arteries, it pushes on the walls of the arteries. This push exerts a force called the blood pressure. Blood pressure is the force of the blood against the walls of the arteries. 2. Blood pressure results from two forces. (a) It is created by the heart as it pumps blood into the arteries and through the circulatory system. (b) The other is the force of the arteries as they resist the blood flow. 3. During exercise, the heart pumps with more force and hence the blood pressure also increases. 4. The blood pressure is increased by certain factors such as: overeating, diet, stress. 5. In overweight people, the heart has to pump harder. So the blood pressure is often too high. Long-term high blood pressure can cause damage to the heart, blood vessels, the brain and kidneys. 6. Blood pressures can be measured in the artery of the arm by an instrument called the sphygmomanometer. MSPSBS/Year / Lower Secondary Science Page 6 of 6