Anatomy And Physiology Of Heart

HEART CIRCULATORY SYSTEM is the cardiovascular system consisting of heart and blood vessels, arteries, arterioles, capillaries, venules, veins, sinuses and lymphatics). The circulatory system transports respiratory gases, nutrients and waste products to various parts of the body.

LOCATION Heart is a pumping organ of blood vascular system. It is located in the thorax between the lungs and abdomen behind the sternum and its apex rests on the diaphragm. STRUCTURE The structure of heart resembles the closed fist. It is hollow, muscular , contractile organ. The walls of heart possess three layers. 1. The outer layer known as epicardium composed of serous layer 2. The middle layer known as myocardium composed of cardiac muscle. 3. The inner layer known as endocardium which lines the four chambers of the heart and also covers the valves.

The heart is also enclosed in a fibrous sac called as pericardium. The space between pericardium and epicardium is known as pericardial cavity. This contains serous fluid that has lubricating action and thus helps in free movement of the heart. A septum divides the heart into right and left valves. These are further subdivided into four chambers viz. Right auricle, right ventricle, left auricle and left ventricle. The auricle (atria) is thin walled and serves as a receiving chamber for blood and are low pressure pumps. The ventricles are thick walled and serve as high pressure pump. The two atria open into the respective ventricles. These are guarded by an atrioventricular (AV) valve. Right AV

valve is called as tricuspid valve (three cusps) where as left AV valve is called as bicuspid valve (two cusps) or mitral valve. The atria and ventricle are completely separated from each other in order to prevent the mixing of impure (deoxygenated blood) and pure (oxygenated) blood. Superior and inferior vena cava brings deoxygenated blood from the upper and lower part of the body to the right atrium. This blood then enters the right ventricle through right AV valve. The AV valve allows the blood to flow from the atria to respective ventricles but prevents the back flow of blood. The walls of right ventricle are thinner then that of left ventricle. This is due to the fact that right ventricle has to pump deoxygenated blood to lungs only (which are very near) whereas, left ventricle has to pump oxygenated blood all over the body. The deoxygenated blood from right ventricle then goes to lungs for oxygenation through pulmonary artery. Pulmonary vein brings the oxygenated blood from the lungs to the left atrium. This pure blood is then forced from the left atrium to left ventricle through the left AV valve. The left ventricle opens in to aorta, which supply blood to all other tissues and organs. The opening of ventricles into these great arteries (pulmonary and aorta) is guarded by semilunar valves. These valves allow blood to enter the great artery from the ventricle but prevent its back flow.

SYSTEMIC CIRCULATION Systemic circulation is the flow of blood from the left ventricle through the aorta to all parts of the body (except lungs) and back to the right atrium. The functions of systemic circulation are to supply oxygen and nutrients to body tissues and to remove carbon dioxide, heat and other waste material from the tissue. All systemic arteries branch from the aorta, which arises from the left ventricle of the heart.

PULMONARY CIRCULATION The flow of blood (impure) from the right ventricle of the heart to the lungs for purification and return of the pure blood from the lungs to the left atrium is called as pulmonary circulation. It is short circulation. The pulmonary trunk arises from the left ventricle and divides into four pulmonary arteries which carries blood in lungs (It is only this part of

circulation where an artery carries deoxygenated blood). Pulmonary veins bring back the oxygenated blood from the lungs to the left atrium. (It is only this part of circulation where a vein carries oxygenated blood). CONDUCTING SYSTEM OF THE HEART Heart has its own system to stimulate contraction without any nerve supply. The heart has specialized tissues which generates and conduct the cardiac impulse all over the heart. These tissues are z Sinoatrial node (SA node) z Atrioventricular node (AV node) z Atrioventricular bundle (Bundle of His) z Bundle branches (Left and right) z Purkinje fibers (Conducting myofibres)

1. Sinoatrial node (SA node) : Sinoatrial node is also known as pace maker. It is situated in the right atrium near opening of superior vena cava. This is a region where the heart beat or contraction origins. 2. Atrioventricular node(AV node) : It is a bundle of cardiac muscle fibers situated on the interatrial septum near the coronary sinus, which receives impulses from SA node and conducts it to the ventricle. 3. Atrioventricular bundle (Bundle of His) It is tract of conducting fiber which runs from AV node to the top of inter ventricular septum. The impulses from the AV node are conducted to the ventricles through the bundle of His. 4. Bundle branches (Left and right) At inter ventricular septum, bundle of His divides into two branches and enters into left and right ventricle known as left and right bundle branches respectively. These bundles branches carry impulses from bundle of His to the ventricles. 5. Conduction myofibers (Purkinje fibers) A typical muscle fibers that emerge from the bundle branches and passes into the fibers of the myocardium of the ventricles .The impulses from the bundle branches to the ventricle muscle fibers is carried through the Purkinje fibers .Purkinje fibers form the electrical impulse conducting system of the heart