Transport Mechanisms Chapter 20

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

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

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)

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

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

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

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

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

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