The heart and circulation

1. The heart and circulation Structure of the heart Regulation of heart activity The circulatory system- cardiovascular and lymphatic

2. Structure of the heart Two atria, two ventricles Atria receive blood from venous system Ventricles pump blood into arterial system Septum separates right from left side

3. A double pump: pulmonary and systemic circulation

4. Valves embedded in fibrous skeleton AV valve between right atrium and ventricle- tricuspid valve AV valve between left atrium and ventricle bicuspid (mitral) valve Semilunar valves at base of pulmonary artery and aorta

7. Cardiac cycle and heart sounds Contraction- systole Relaxation- diastole Atria contract simultaneously Then ventricles contract- with a little overlap Stroke volume- amount of blood ejected from ventricles during systole end-systolic volume- what’s left

9. Electrical activity of the heart Myocardial cells beat automatically Action potential is usually originated in sinoatrial node Spontaneous depolarization (pacemaker potential) diffusion of calcium through slow channels threshold- fast calcium channels open, voltage regulated sodium channels open repolarization produced through diffusion of potassium

10. Other parts of the heart can produce pacemaker potentials Depolarize more slowly than SA node; usually stimulated by action potentials from SA node before they could start their own pacemaker potentials “ectopic pacemakers” can set a rhythm if SA node conduction is blocked; pace will be slower

12. Heart muscle cannot sustain contraction Long refractory periods- heart cannot be stimulated until it has relaxed from previous contraction Arrhythmias- something affects the cardiac cycle; treatment depends on what it is Fast Na channel blockers Slow Ca channel blockers -adrenergic receptor blockers

13. What does the ECG measure?

14. The ECG and heart sounds

15. Blood vessels- arteries and veins Arteries, arterioles, capillaries Veins and venules Arteries are more muscular Veins have valves

17. Capillaries deliver blood to cells Specialized types of capillaries in different organs Fenestrated- kidneys, endocrine glands, intestines Discontinuous- bone marrow, liver and spleen Continuous- everywhere else

18. Veins Veins can expand to accommodate increasing amounts of blood; arteries can’t Venous pressure is low compared to arterial pressure Blood flow through veins is facilitated by: contraction of skeletal muscles valves that prevent backflow

20. Atherosclerosis • Plaques block blood vessels • Macrophages accumulate (“fatty streaks”) • Inflammatory mechanism that accumulates damage • Vasodilation function can be disrupted

21. LDL, HDL, and cholesterol • Cholesterol is carried to liver by LDL • Recycled via LDL receptors on liver cells • LDL (and cholesterol) can accumulate in blood • HDL carries cholesterol away from arterial walls • High HDL levels are beneficial

22. Heart disease and EGC analysis

23. Arrhythmias Bradycardia- slow rate (less than 60 bpm) Tachycardia- fast rate (more than 100 bpm) Can occur normally; is abnormal if rate increases during rest (ectopic pacemakers) Flutters- extremely rapid contractions Fibrillation- different groups of fibers are activated so coordinated pumping of chambers is not possible

24. Lymphatic system Fluid transport from tissues Fat transport from intestines Immune response

27. Summary • “Double pump” enables heart to deliver oxygenated blood to the body- and recirculate it • Valves regulate blood movement through the heart • Electrical activity can be measured and monitored • Arterial system delivers blood to the body, and the venous system returns it to the heart • Lymphatic system helps regulate fluid levels among the body compartments