Human Circulation A closer look

Contents Cardiac cycle Maintenance of heartbeat Principles governing blood circulation Cardiovascular disease Lymphatic system Blood composition and function

Cardiac cycle complete sequence of pumping and filling

Electrical activity of the heart Influenced by nerves (vagus nerve – acetylcholine, epinephrine), hormones, and body temp. 1 - Sinoatrial node (Pacemaker) 2 - Atrioventricular node 3 - Atrioventricular Bundle (Bundle of His) 4 - Left & Right Bundle branches 5 - Bundle Branches 6 - Purkinje fibers AV valves SL valves

Cardiac output Total volume of blood pumped by the left ventricle per minute Heart rate (HR)  # beats per minute Stroke volume (SV)  mL Product gives the cardiac output (Q) Average adult Q = HR x SV = 70 beats/min x 75 mL/beat = 5.25 L/min Maximum HR = 200-your age Training heart rate is 75% MHR e.g. 200-15 = 185 * 0.75 = 139 beats/min 20 minutes, 3x a week

Pulse Stretching of arteries as an effect of heartbeat Pressure waves moving the artery walls when blood moves into aorta Usually accurate measure of heart rate Normal resting pulse is 60-100 bpm Common pulse points 1. Temporal artery 3. Carotid artery 4. Brachial artery 5. Radial artery

Blood vessel structure

Physical principles governing blood circulation Blood flow velocity Aorta (30 cm/s) Capillaries (0.026 cm/s) Law of continuity Volume of flow per second must be constant through the entire pipe Total cross-sectional area of the capillaries determines flow rate Blood flow slows down in capillary beds Nerves, muscle, hormone control

Osmotic pressure – amount of pressure required to prevent diffusion of water

Blood pressure Force exerted by blood on walls of vessels Determined by cardiac output and peripheral resistance by arterioles Arterial pressure measured by a sphygmomanometer Systolic/Diastolic (mmHg) Factors Heart rate Blood volume Resistance of vessels Viscosity

Blood composition and function

Negative feedback mechanism Erythropoietin produced in liver (low O2) stimulates marrow cells

Lymphatic System Functions Anatomy Returns excess body fluid to blood Transports fats from intestines to blood Defense Anatomy Lymph nodes scattered throughout body (thymus, spleen) Vessels

Cardiovascular disease Cardiovascular disease (>50% of all deaths) Heart attack- death of cardiac tissue due to coronary blockage Stroke- death of nervous tissue in brain due to arterial blockage Atherosclerosis: arterial plaques deposit Arteriosclerosis: plaque hardening by calcium deposits Hypertension: high blood pressure Hypercholesterolemia: LDL, HDL