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Transport Mechanisms

This chapter discusses the cardiac cycle, detailing the pattern of contraction (systole) and relaxation (diastole) during a heartbeat, typically lasting 0.8 seconds. It explains the roles of atrial and ventricular systole in blood movement through AV valves and into arteries. The heart’s conducting system, including the sinoatrial node's function as a pacemaker, is highlighted alongside measuring electrical activity with an ECG. The section also covers blood pressure dynamics, causes of high blood pressure, and the lymphatic system's role in fluid balance and immune response.

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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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