Cardiac Physiology

General organization of heart

located in mediastinum, enclosed in pericardium, functions as a double pump

What are the three circulatory divisions?

systemic, pulmonary, and coronary

What is systemic circulation?

oxygenated blood from the left ventricle to body, returns deoxygenated blood to the right atrium

What is pulmonary circulation?

deoxygenated blood from the right ventricle to lungs, return oxygenated blood to the left atrium

what is coronary crcualtion?

supplies blood to the heart itself

How does blood move through the heart?

systemic circulation (venous blood) → superior vena cava / inferior vena cava → right atrium → right ventricle → pulmonary arteries (L/R) → pulmonary circulation → pulmonary veins (4) → left atrium → left ventricle → aorta → systemic circulation (arterial blood)

What are the four parts of heart wall?

pericardium, epicardium, myocardium, and endocardium

What is the pericardium?

fibrous and serous layers of heart

What is the epicardium?

outer visceral layer of heart

What is the myocardium?

contractile muscle tissue of heart

What is the endocardium?

inner layer of heart, contains connective and elastic fibers

What is the difference between cardiac and skeletal muscles?

cardiac muscles: single nucleus, intercalated discs, gap junctions, and syncytium

skeletal muscles: multinucleated, and no gap junctions

What is the resting membrane potential of cardiac muscles?

-85 to -95 mV for cardiac cells

-90 to -100 mV for conductive fibers

What are the five action potential phases?

1. depolarization (Na+ influx)

2. early repolarization (Na+ channels inactive)

3. plateau (Ca2+ influx)

4. repolarization (K+ efflux)

5. ion distribution restored (Na+/K+ pump)

What is excitation-contraction coupling?

1. action potential triggers Ca2+ influx

2. Ca2+ binds to troponin and removes tropomyosin inhibition

3. cross-bridge formation leads to contraction

What are the 5 steps of the cardiac cycle?

1. Atrial contraction and ventricular filling

2. Isovolumetric contraction

3. Ventricular ejection

4. Isovolumetric relaxation

5. Atrial relaxation and passive ventricular filling

How long is systole and what cardiac cycle steps does it include?

250 to 300 ms, steps 1-3

How long is diastole and what cardiac cycle steps does it include?

500 to 550 ms, steps 4-5

What are the four heart sounds?

S1 "Lub", S2 "Dub", S3, and Murmurs

What causes S1 "Lub"?

AV valves closing (beginning of systole)

What causes S2 "Dub"?

closure of aortic and pulmonary valves (end of systole, begin of diastole)

What is S3?

an occasional weak sound

What are heart murmurs?

abnormal heart sounds due to valve issues

What are the effects of the sympathetic nervous system?

increased heart rate and contractility

What are the effects of the parasympathetic nervous system?

decreased heart rate

What are the basics of electrocardiogram (ECG)?

P wave, QRS complex, and T wave

What is P wave?

atrial depolarization

What is QRS complex?

ventricular depolarization

What is T wave?

ventricular repolarization

What is arterial supply?

The left and right coronary arteries originate from the aorta at the sinuses of Valsalva

What is venous return?

the flow of blood back to the heart

What is myocardial oxygen consumption?

high oxygen demand, most flow occurs during diastole

What causes myocardial ischemia?

atherosclerosis and thrombosis

What are the effects of myocardial ischemia?

reduced circulation, contractility, stroke volume and cardiac output

What are metabolic markers of myocardial ischemia?

decreased oxygen, ATP, Na+/K+ ATPase

increased hydrogen, lactate and intracellular Ca2+

What are the two types of humoral regulation

vasoconstrictors and vasodilators

What are types of vasoconstrictors?

epinephrine, norepinephrine, angiotensin, endothelin and vasopressin

What are types of vasodilators?

epinephrine, bradykinin, serotonin, histamine, prostaglandins, and nitric oxide

What is nervous regulation?

Direct: sympathetic and vagal effects

Indirect: myocardial contractility