CARDIOVASCULAR SYSTEM PHYSIOLOGY

Pulmonary circulation: Path of blood from right ventricle through the lungs and back to the heart. Systemic circulation: Oxygen-rich blood pumped to all organ systems to supply nutrients. Rate of blood flow through systemic circulation = flow rate through pulmonary circulation. Fig P. 379

Fig b P. 380

Atrioventricular and Semilunar Valves Atria and ventricles are separated by AV (atrioventricular) valves. –One way valves. At the origin of the pulmonary artery and aorta are semilunar valves. –One way valves. –Open during ventricular contraction. Opening and closing of valves occur as a result of pressure differences. Fig a P. 380

Cardiac Cycle Refers to the repeating pattern of contraction and relaxation of the heart. –Systole: Phase of contraction. –Diastole: Phase of relaxation.

Fig P. 381

End-diastolic volume - Amount of blood in the ventricles before they contract - also known as preload. Ave = ml. Stroke volume - Amount of blood ejected from the heart in a single beat. Ave = ml. End-systolic volume - Amount of blood remaining in the ventricles after they contract. Ave = ml.

Closing of the AV and semilunar valves. Lub (first sound): Produced by closing of the AV valves during isovolumetric contraction. Dub (second sound): Produced by closing of the semilunar valves when pressure in the ventricles falls below pressure in the arteries. Heart Sounds Murmur - Abnormal heart sounds produced by abnormal patterns of blood flow in the heart. Fig P. 383

Fig P. 382

Electrical Activity of the Heart Autorhythmic cardiac muscle cells: –Demonstrates automaticity: Sinoatrial node functions as the pacemaker. –Spontaneous depolarization (pacemaker potential): Caused by diffusion of Ca 2+ through slow Ca 2+ channels. –Cells do not maintain a stable RMP.

Fig P. 385

Electrical Activity of the Heart Myocardial cells: – have a RMP of –90 mV. SA node spreads APs to myocardial cells. –When myocardial cell reaches threshold, these cells depolarize.

Fig P. 385

Fig P. 386

Electrical Activity of the Heart Sinus rhythm - SA node is the pacemaker. Heart rate of bpm Ectopic focus: –Pacemaker other than SA node: If APs from SA node are prevented from reaching these areas, these cells will generate pacemaker potentials. –Junctional rhythm - AV node is the pacemaker. Results in heart rate of bpm.

Fig P. 386

Excitation-Contraction Coupling in Heart Muscle Depolarization of myocardial cell stimulates opening of VG Ca 2+ channels in sarcolemma. –Ca 2+ diffuses down gradient into cell. Stimulates opening of Ca 2+ -release channels in SR. –Ca 2+ binds to troponin and stimulates contraction (same mechanisms as in skeletal muscle). During repolarization Ca 2+ actively transported out of the cell via a Na + -Ca 2+ - exchanger.

Electrocardiogram (ECG/EKG) The body is a good conductor of electricity. –Tissue fluids have a high [ions] that move in response to potential differences. Electrocardiogram: –Measure of the electrical activity of the heart per unit time. Potential differences generated by heart are conducted to body surface where they can be recorded on electrodes on the skin.

Electrocardiogram (ECG/EKG) The ECG helps the physician gain insight into: –The anatomical orientation of the heart –Relative sizes of its chambers –Disturbances of rhythm and conduction –The extent, location, and progress of ischemic damage to the myocardium –The effects of altered electrolyte concentrations –The influence of certain drugs ( i.e. digitalis, calcium channel blockers, and antiarrhythmic agents)

Fig P. 388

Electrocardiogram (ECG/EKG) P wave: –Atrial depolarization. QRS complex: –Ventricular depolarization. –Atrial repolarization. T wave: –Ventricular repolarization. Fig P. 389

P-R interval - Length of time between the P wave and the beginning of the QRS complex. Normal range = sec. Fig P. 387

QRS complex - Normal range = sec. Fig P. 387

S-T segment - Length of time during which the entire ventricular myocardium is depolarized. About 0.12 sec. Myocardial ischemia may be detected by changes in this segment. Fig P. 387

Fig P. 397

Q-T interval - From the beginning of ventricular depolarization through their repolarization. Ave. = sec; varies inversely with heart rate. Fig P. 387

SINUS RHYTHM

JUNCTIONAL RHYTHM

SECOND DEGREE HEART BLOCK

Cardiac Rate Imbalances Tachycardia - Abnormally fast heart rate (>100 bpm). Bradycardia - Abnormally slow heart rate (<60 bpm).

Fig P. 398

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Discontinuous

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Atherosclerosis The narrowing of the blood vessel lumen. Responsible (indirectly) for half the deaths in the Western world. Often begins with a tear in the tunica interna - and progressively builds up fatty plaque. - It usually ends in arteriosclerosis: the death of the tunica media and deterioration of elastic fibers. Fig a P. 395

LYMPHATIC SYSTEM Fig P. 400

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