AS Biology – Revision Notes Unit 3 – Physiology And Transport

AS Biology – Revision Notes Unit 3 – Physiology And Transport

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questionbase.50megs.com AS-Level Revision Notes AS Biology – Revision Notes Unit 3 – Physiology And Transport The Heart And Circulation 1. Multicellular organisms cannot rely on their surface area to get oxygen and nutrients to all the cells. Instead they have a specialised circulatory system. 2. Double circulation gives a more efficient supply of oxygen to the cells – as one lot of red blood cells are dropping off O 2 , another lot is becoming more oxygenated. The two systems are: a. Pulmonary – from the heart to the lungs and back. b. Systemic – from the heart to the rest of the body and back. 3. The cardiac cycle takes place as follows: a. Atria receive blood. b. Auriculoventricular valves (bicuspid and tricuspid) open. c. Auricular systole – atria contract, forcing blood into ventricles. d. Ventricular systole – ventricles contract, forcing blood through the semilunar valves into the aorta and pulmonary artery. e. Auricular and ventricular diastole – all chambers relax. 4. Cardiac muscle cells beat autonomously. Groups of cells beat in a coordinated manner. The heart beat is myogenic (originating in the heart), as opposed to neurogenic (originating outside the heart). 5. The cardiac cycle is controlled by electrical impulses: a. The electrical impulse originates at the sino-atrial node (SAN). This stimulates atrial systole (lasts about 0.1s). b. The electrical impulse reaches the atrio-ventricular node (AVN), then travels down the bundle of His and along the Purkinje fibres to the base of the ventricles. This stimulates ventricular systole (lasts about 0.3s). c. The impulse ends, and diastole takes place (lasts about 0.4s). 6. In an electrocardiogram (ECG), the electrical activity is shown by peaks. The small P wave shows the contraction of atrial muscles. The very large R wave shows the contraction of ventricle muscles. The T wave shows the relaxation of ventricle muscles. 7. The pressures in the heart change during the cardiac cycle: a. The atria passively fill with blood from the pulmonary vein and vena cava, and so the pressure increases. b. As the atrial systole takes place, the pressure increases and the blood is forced into the ventricles causing the pressure there to increase. c.
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This note was uploaded on 09/19/2011 for the course BIOL 126-001B taught by Professor Hulbert during the Spring '10 term at Camosun College.

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AS Biology – Revision Notes Unit 3 – Physiology And Transport

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