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Transport Mechanisms

Transport Mechanisms. Chapter 20. Cardiac Cycle. Pattern of contraction (systole) & relaxation (diastole) in 1 heartbeat Average = 0.8 secs (75/min) Atrial Systole – blood sent into ventricles through AV valves Ventricular Systole – ventricles contract - AV valves close

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Transport Mechanisms

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  1. Transport Mechanisms Chapter 20

  2. Cardiac Cycle • Pattern of contraction (systole) & relaxation (diastole) in 1 heartbeat • Average = 0.8 secs (75/min) • Atrial Systole • – blood sent into ventricles through AV valves • Ventricular Systole • – ventricles contract • - AV valves close • - high pressure opens SL valves • - blood into arteries • Diastole • – Blood from veins enters & fills atria • - pressure differences open AV valve

  3. Valves & Heart Sounds • AV (mitral) valve closure = heart sound (‘lubb’) • SL (aortic) valve closure = second heart sound (‘dubb’) • Irregular sounds = heart murmur • Due to valve problems • Measured by phonocardiogram • Heard using a stethoscope

  4. Heart Conducting System • Pacemaker (Sino-atrial node – SAN): (1) • Found in the right atrium wall • Exhibits spontaneous excitation • Starts electric impulses - heart muscle cells contract • Wave of excitation makes atria contract – (2) • Impulse picked up by atrio-ventricular node (AVN) – (3) • Impulse passed to conducting fibres – (4) • Ventricles stimulated – ventricular systole – (5)

  5. Measuring Electrical Activity • Electrocardiogram (ECG) shows electrical activity of the heart • Abnormal ECG’s - caused by rapid electrical excitation • Atrial Flutter: • Co-ordinated, but very rapid contractions • Fibrillation: • Heart muscle contraction irregular & uncoordinated • Ventricular Tachycardia: • Abnormal ventricular cells act like pacemakers • Ventricle contracts independently of the atrium • All 3 can be relieved by artificial pacemakers

  6. Blood Pressure • Ventricular Systole • – aorta pressure rises to a max (avg.120mmHg) • Ventricular Diastole– pressure is at a min (avg. 80 mm Hg) • Measured using a sphygmomanometer • Aorta elastic walls maintain blood pressure • As blood circulates round the body the pressure gradually decreases • Blood flowing through blood vessels = peripheral resistance

  7. High Blood Pressure • Increased heart contraction rate/force = higher blood pressure • Common causes: stress or high salt intake • Dangers: • Ventricles work much harder • Arterial walls more prone to atherosclerosis • Damage to blood vessels - stroke

  8. Lymphatic System • Lymphatic vessels absorb excess tissue fluid (lymph) • Lymph moved by vessel compression (body movements) • Backflow prevented by valves • Lymph re-enters bloodstream via lymphatic ducts in the arms • Lymph also contains lipids absorbed by lacteals in the intestine

  9. Lymph Nodes • Occur in glands around the body e.g armpit, neck, groin • Consist of lymph nodules, central medulla, & germinal centre • Fibres in between the nodules lined with macrophage cells • As lymph passes, macrophage remove unwanted material by phagocytosis • Lymph drains into medulla & exits by lymphatic vessel • Illness = too many bacteria = nodes swell up

  10. Oedema • Accumulation of tissue fluid in between cells & capillaries • Causes swelling • Caused by: • High blood pressure • Malnutrition • – low plasma protein in blood • - blood and tissue fluid equal conc. • - fluid doesn’t return osmotically • - causes kwashiorkor • Parasites • – invade lymphatic system & block vessels (e.g legs) • - causes elephantiasis

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