The Heart

Four chambered muscular pump.

Two sides: right - pulmonary and left - systemic

Housed within pericardial sac; Pericardial cavity with pericardial fluid

Chambers and Valves

Atria

Ventricles

Atria and ventricles are separated by a fibrous skeleton

Atrioventricular Valves

Tricuspid (right side)

Bicuspid (Mitral -- left side)

Semilunar Valves (pulmonary and aortic)

Pulmonary, Systemic, and Coronary Circulations

Cardiac Cycle

Systole (contraction) & Diastole (relaxing, filling)

Heart Sounds

1st (lub)--closing of A.V. valves. 2nd (dub)--closing of semilunar valves.

Electrical Activity

Pacemaker: Sinoatrial node has cells with fast, rhythmic discharge.

Ectopic pacemakers: Other areas in the heart may discharge independently of normal pacemaker (SA node). "Ectopic" = "out of place"

Action potentials of cardiac cells differ from nerve action potential -- Calcium influx prolongs depolarization.

Conducting system of Heart

SA Node --> Atrioventricular Node --> A.V. bundle (bundle of His) --> left and right bundle branches --> Purkinje fibers.

Conducting system allows for synchronous contraction of myocardial cells.

Electrocardiogram (ECG) Represents electrical activity of the heart.

Pop Quiz: Where is the repolarization phase of the atria?
A) it doesn't occur. B) within the QRS complex. C) Within the T wave.

Cardiac Output: quantity of blood pumped by either ventricle in one minute.

C.O = stroke volume X heart rate

Stroke volume = volume of blood expelled by ventricle in one beat (stroke).Stroke volume can vary.

Cardiac reserve is the difference between actual volume of blood pumped and the volume the heart is capable of pumping.

Larger ventricles and more efficient pumping increases stroke volume.

Cardioregulatory center in medulla oblongata regulates heart rate. Has both accelerative and inhibitory areas. Works via autonomic nervous system.

Reflexes:

Baroreceptors are pressure receptors in aorta and carotid arteries. Increased blood pressure stimulates receptors --> results in parasympathetic output --> decreases heart rate and dilates blood vessels. Low blood pressure results in opposite effect.

Chemoreceptors are present in carotid and aortic sinuses. These respond to levels of oxygen and carbon dioxide and blood pH.

Exercise increases carbon dioxide, lowers pH and oxygen in blood. This is detected and heart rate increases via reflex.

Control of stroke volume

Frank-Starling law of the heart: "Within physiological limits, the more the ventricles are filled during ventricular diastole, the more blood they will eject upon systole." Due to effect of stretch on cardiac muscle. Increase in venous return to heart, the greater the stretch on heart muscle, the heart muscle increases its force of contraction to expel the blood.

Clinical Conditions:

Myocardial infarction (heart attack):

Angina Pectoris: Chest Pain associated with heart attacks

Congestive heart failure

Septal defects: congenital. Allows mixing of blood.

Valvular heart diseases:

Inflammatory diseases:

Arrhythmias: