• The heart is a cone-shaped, muscular organ located between the lungs behind the sternum.
• The heart muscle forms the myocardium,
• the inner lining of the myocardium is called Endocardium and the outer layer cells is called the Epicardium.
• The pericardium (visceral) is the outer membranous sac with lubricating fluid.
• The heart has four chambers: two upper, thin-walled atria, and two lower, thick-walled ventricles.
• The ventricle are, the chambers that eject blood in to arteries. The functions of the atrium are to receive the incoming blood from the vein.
• The septum is a wall dividing the right and left sides.
• Coronary arteries: the vessels that supply blood to the heart muscle.
Cardiac valves permit blood to flow in only one directions through
• Atrioventricular Valves:
1] Tricuspid valve: separates the Rt atrium from the
2] Bicuspid valve [Mitral valve]: lies Lt atrium and
• Semilunar valves:
1] Pulmonic valve: the valve between the Rt ventricle
and the pulmonary artery.
2] Aortic valve: the valve between the Lt ventricle and
Internal view of the heart
• Each heartbeat is called a cardiac cycle.
• When the heart beats occur, the two atria contract together, then the two ventricles contract; then the whole heart relaxes.
• Systole is the contraction of heart chambers; diastole is their relaxation.
• The heart sounds, lub-dup, are due to the closing of the atrioventricular valves, followed by the closing of the semilunar valves.
Conducting system of the heart
Intrinsic Control of Heartbeat
• The SA (sinoatrial) node, or pacemaker, initiates the heartbeat approximately 60-100 impulses / min.
• The AV (atrioventricular) node conveys the stimulus and initiates contraction of the ventricles, located right Atrial wall, similar to S.A node but with impulses about 40-60/ min..
• The signal for the ventricles to contract travels from the AV node through the atrioventricular bundle to the smaller Purkinje fibers.
Extrinsic Control of Heartbeat
• A cardiac control center in the medulla oblongata speeds up or slows down the heart rate by way of the autonomic nervous system branches: parasympathetic system (slows heart rate) and the sympathetic system (increases heart rate).
• Hormones epinephrine and norepinephrine from the adrenal medulla also stimulate faster heart rate.
The Vascular Pathways
• The cardiovascular system includes two circuits:
• Pulmonary circuit which circulates blood through the lungs, and
• Systemic circuit which circulates blood to the rest of the body.
• Both circuits are vital to homeostasis.
The Pulmonary Circuit
• The pulmonary circuit begins with the pulmonary trunk from the right ventricle which branches into two pulmonary arteries that take oxygen-poor blood to the lungs.
• In the lungs, oxygen diffuses into the blood, and carbon dioxide diffuses out of the blood to be expelled by the lungs.
• Four pulmonary veins return oxygen-rich blood to the left atrium.
The Systemic Circuit
• The systemic circuit starts with the aorta carrying O2-rich blood from the left ventricle.
• The aorta branches with an artery going to each specific organ.
• The vein that takes blood to the vena cava often has the same name as the artery that delivered blood to the organ.
• Stroke volume: the amount of blood ejected per heart beat. (Cardiac output) CO = SV X HR
Passage of Blood Through the Heart
• Blood follows this sequence through the heart: superior and inferior vena cava → right atrium → tricuspid valve → right ventricle → pulmonary semilunar valve → pulmonary trunk and arteries to the lungs → pulmonary veins leaving the lungs → left atrium → bicuspid valve → left ventricle → aortic semilunar valve → aorta → to the body.
External heart anatomy
1] Cardiac enzyme:
– CPK : creatinine phosphate kinase. 50-350
– LDH: lactic dehydrogenase 100-135
– SGOT: 0-40
– Blood level rise in 2 to 3 days.
2] Total cholesterol, Triglycerides and lipoproteins to evaluate atherosclerotic diease.
3] Serum electrolyte:
– Na : ↓ Na : hyponatremia. ↑ Na : hypernatremia.
– Ca: ↑ Ca : causes ECG changes or dysrhythmias
– K: ↓ K cause cardiac irritability.
– Glucose: many cardiac patients also have serum glucose level will ↑ with stress.
4] Chest x-ray:
Usually used to determine size and position of the heart. E.g CHF, placement of cardiac catheters.
5] Cardiac catheterization:
Invasive diagnostic procedure in which one or more catheters are introduced into the heart, used to assess the patency of the patient coronary arteries.
x-ray examination of blood vessels.
7] Rt heart catheterization:
Involve passing a catheter from femoral vein- Rt atrium → Rt .ventricular → tricuspid valve.
8] Lt heart catheterization:
The same but passing a catheter through femoral artery.