1. The Heart  Part of the Cardiovascular System  The transport system that keeps blood circulating

2. Structure and Function  250-350 grams  Within the thorax, in the mediastinum  2/3 lies to the left of midsternal line  Base – broad flat posterior surface is directed toward right shoulder  Apex–points inferiorly toward left hip

3. Homeostatic Imbalance  Pericarditis – inflammation of the pericardium  Hinders production of serous fluid and roughens serous membrane surfaces  “Creaking sound” when heart rubs against pericardial sac, pain deep to sternum  Severe cases – cardiac tamponade “heart plug” caused by fluid compressing the heart

4. Conduction System of Heart  Rhythmical electrical activity causes continuous beating  Autorhythmic cells are self-excitable and repeatedly generate action potentials that trigger contractions (heart continues to beat after nerves cut)  Pacemaker that forms conduction system

5. Pacemaker  Cardiac chambers stimulated in coordinated manner to pump blood  Autonomic nervous system and hormones modify but don’t establish the rhythm

6. Conduction of Impulse  Cardiac excitation begins in the sinoatrial (SA) node in right atrial wall inferior to opening of sup. vena cava  Action potential propagates throughout both atria and atria contract  Action potential reaches atrioventricular (AV) node → bundle of His (connection between atria and ventricles)

7. Conduction  → right and left bundle branches toward the apex → Purkinje fibers → throughout ventricles  About 200 milliseconds after the atria contract, the ventricles contract

8. Homeostatic Imbalance  Angina pectoris or “choked chest”  Thoracic pain caused by fleeting deficiency in blood delivery to myocardium  Serious, prolonged blockage can lead to heart attack or coronary (myocardial infarction MI) because blockage results in noncontractile scar tissue

9. Homeostatic Imbalance  Valve deformities  Incompetent valve – forces heart to repump same blood; improper closure and blood back flows  Valvular stenosis – valve flap becomes stiff and constricts the opening (scar tissue after endocarditis or Ca 2+ salt deposit) ‏  Both increase work load and weaken heart  Faulty valve is usually the mitral (bicuspid) ‏

10. Homeostatic Imbalance  Heart region deprived of blood becomes ischemic  Cells begin to metabolize anaerobically producing lactic acid  Increased acidity inhibits cardiac cells’ ability to produce ATP (ATP needed to pump Ca 2+ into extracellular space) ‏  Increased H + and Ca 2+ inside cell causes gap junctions to close  Forces action potentials to find alternate routes (if area is large leads to heart attack) ‏

11. Homeostatic Imbalance  Defect in intrinsic conduction system  Irregular heart rhythms (arrhythmias) ‏  Uncoordinated atrial and ventricular contractions  Fibrillation: rapid and irregular or out of phase contractions  Heart rhythm taken away from the SA node (pacemaker) by rapid activity in other heart regions  Defibrillation – electrically shocking the heart which stops the chaotic twitching by depolarizing the entire myocardium

12. Homeostatic Imbalance  Defective SA node (Sinoatrial node) ‏  Ectopic focus – abnormal pacemaker takes over pacing of heart  AV node may take over (atrioventricular) ‏  Only route for impulse transmission from atria to ventricles is through AV node  Damage to AV node = heart block and interferes with the ability of ventricles to receive pacing impulses

13. Homeostatic Imbalance  Heart murmurs are abnormal heart sounds  Healthy blood flow is silent in adults  Sounds may indicate valve problems  Incompetent valve = swishy sound with backflow through the partially open valve after the valve has closed  Stenotic valve = “narrowed” high-pitch sound or click when valve should be wide open during systole

14. Homeostatic Imbalance  Reduced Ca 2+ blood levels (hypocalcemia) depress the heart  Hypercalcemia prolongs the plateau phase of the action potential that can lead to spastic heart  Excess Na + (hypernatremia) inhibits transport of Ca 2+ into cardiac cells and blocks heart contractions  Excess K + (hyperkalemia) interferes with depolarization by lowering resting potential –may lead to heart block and cardiac arrest  Hypokalemia is also life threatening because heart beats feebly

15. Homeostatic Imbalance  Tachycardia “heart hurry” – abnormally fast heartbeat – more than 100 beats/min  Elevated body temperature  Stress  Drugs  Heart disease  Promotes fibrillation and is pathological  Bradycardia – less than 60 beats/min  Low body temperature  Drugs  Parasympathetic nervous activation  Warning of brain edema after head trauma

16. Homeostatic Imbalance  Congestive heart failure (CHF) ‏  Pumping efficiency (CO) is so low that blood circulation is inadequate  Progressively worsens, reflects weakening of myocardium caused by  Coronary artherosclerosis (clogging of vessels with fatty buildup)  Increasing hypoxia due to insufficient O 2  Persistent high blood pressure  The myocardium must exert more force to open the aortic valve and pump out the same amount of blood (becomes weaker) ‏

17. Homeostatic Imbalance  CHF (continued) ‏  Multiple myocardial infarcts  MI’s depress pumping efficiency because dead heart cells are replaced by scar tissue  Dilated cardiomyopathy (DCM) ‏  Ventricles stretch and become flabby and myocardium deteriorates  Cause often unknown  Contractility is impaired, CO is poor and condition progressively worsens

18. Homeostatic Imbalance  Pulmonary congestion  Left side of heart fails  Lungs become engorged with blood  Leads to pulmonary edema  Can cause suffocation  Peripheral congestion  Right side of heart fails  Blood stagnates in organs  Inadequate oxygen and nutrients  Edema pronounced in extremities

19. Homeostatic Imbalance  Seriously weakened heart is irreparable  Treatment involves:  Conserving heart energy with digitalis which reduces heart rate  Removing excess fluids with diuretics  Use drugs to lower blood pressure and reduce afterload  Transplants