Human Heart

 The heart is cone shaped hollow muscular organ having the base above and apexx below. The apexx incline toward the left side. The heart weighs about 300grams.

Position of the heart 

The heart lies in the throax,between the lungs and behind sternum and directed more to the left than ride side.

Structure of the Heart:

The heart is about the size of a shut clench hand.The adult heart weighs about 20-260grams. It is divided by a septum into two side ,right and left. There is typically no correspondence between these different sides after birth.

Each side of the heart is further subdivided into two Chambers,an upper chamber called atrium, and lower Chamber ventricle. There are two atria right and left and two ventricles. The atria and ventricles of each side communicate with one another by means of the atrioventricular opening,which a guarded by valves, one the right side by the tricuspid valve and an left side mitral valve. The atrioventricular valves permit of the passage of blood in one direction i.e from atrium to ventricle;and they prevent the blood flowing backwards from ventricle to atrium.

The tricuspid valve is composed of three flaps or cups and the mitral of two flaps.

Layers of Heart

1. The pericardium ; out covering

2. The myocardium ; the middle muscular layer.

3. The endocardium: the inner lining.

The muscular walls of the heart vary in thickness,the ventricles have the thickest wall. The wall of the heart left-thicker than those of right-ventricle, because the force of contraction of the left-ventricle is much greater. The wall of atria are composed of thinner muscli.

The interior of each of the ventricular wall is marked by thickened colums of muscle. Some of these project as papillae. The papillary muscles and to the apices are attached their tendious cords, the chardac tendineae. These cords have a second attachment to the lower borders of the atrioventricular valves, and this attachment prevent the flaps of the valves from being forced up into the atria when the ventricles contract.

Blood vessels attached to the heart

The predominant and second rate vena cava void their blood into the right chamber. The opening of the latter is guarded by the semilunar valve of Eustachius.The aspiratory supply route diverts blood from the right ventricle,the four pneumonic veins carry blood from the lungs to the left chamber. The aorta diverts blood from the left ventricle.

The opening of the aorta and the pulmonary artery are guarded by semilunar valves. The valve between the left ventricle and aorta is called aortic valve and prevent blood flowing backwards from the aorta to the left ventricle. The valve between the right ventricle and pulmonary artery is called the pulmonary valve and prevent blood flowing backwards the pulmonary artery into the right ventricle.

Blood supply

The right anf left coronary corridors are quick to leave the aorta.These then divide into smaller arteries which encircle the heart and supply blood to all parts of the organ.The return blood from the heart is gathered chiefly by coronary sinus and returned straightforwardly into the right chamber.

Nerve supply

Although the action of the heart is rhythmic in character, its rate of contraction is modified by impulses reachinf it from the vagus and sympathetic nerves.

THE CIRCULATION OF THE BLOOD

The heart is the chief of the circulation of the blod. The course of the blood from the lift-ventricle. through arteries, arterioles ,veterning in to the right atrium by vein is called the greatee or systemic circulation. The course from the right ventricle, through the lungs to the left chamber is the lesser or pneumonic flow.

The systemic circulation:

The blood leaves the left ventricle of the heart by the aorta the largest artery in the body . This breaksup into smaller arteries which Carry the blood to the different parts of the body . These divide and Subdivide untill the arterioles are reached. These have exceptionally strong walls which thin their channels and oppose the progression of blood

This has two functions. It maintained the arterial blood pressure and by varying the size of the Channel - It-regulater the flow of blood in to the cappillaries have very thin walls so that trade can occur between the plasma and the interstitial liquid.These Capillaries then unite and form Larger vessels called venules which in turn become veins, and carry the blood back to the hearts The veins unite and unite again untill Finally two Large venous trunks are formed, the inferior vena cava which collects the blood from the trunk also, lower limits and the Predominant vena cava which gathers blood from the head and furthest points - Both these Vessel emply their items into the right-chamber of the heart .

PULMONARY CIRCULATION:-

The blood then passes into the right ventricle which contracts and pumps it into the pulmonary artery - This divides to Carry the blood to right and Left Lungs. The Lungs offer next to no protection from the blood in the vessels moving through them. In the Lunge each artery breaks up into numerous smaller arteries, then into arterioles and finally into Pulmonary capillaries which surround the alveoli in the Lungs tissue where the blood takes up oxygen and emits carbon dioxide.

The pulmonary capillaries then unite untill Vein are formed and the blood is returned to the heart by four pulmonary veins which empty into the left atrium This blood the passes into the left-Ventricle which agreements and siphons it into the aorta to start the Foundational flow

 PORTAL CIRCULATION:-

Blood from the stomach digestion tracts, pancreas and Spleen is gathered by the Entryway vein.

 In the liver this vein breaks down into a capillary system and uniting with capillaries of the hepatic artery, which brings blood from the aorta to the Livers traverses the substance of this organ. This dual blood Supply is collected System of veins which unite to form the hepatic vein conveying the blood to the inferior vena cava and thence to the heart- Portal Obstruction may occur when a branch Or branches or the portal vein are obstructed may occur to severe injury to the liver and in some instestine in hepatitis. When severe, such an obstruction is complicated by ascities, a collection of excess flind in the peritoneal cavity.

CORONARY CIRCULATION:

The Superior and Inferior Vena cave empty y their blood into the right atrium .The opening of the latter is guarded by the semi- Lunar valve of Eustaclius. The pulmonary artery Carries blood away from the right- · ventricle .The four pulmmary Veins bring blood from the Lungs to the Left-artium. The aorta Carries blood away from the Left-ventricle.The Openings of the aorta and the aspiratory course are watched by the semilunar valves. The Valve between the Left- ventricle and the aortă- is called the aortic valve and prevents blood flowing back wards from the aorta to the left- Ventrcle. The valve between right- the ventricle and the pulmonary artery is called the pulmonary valve and prevents blond flowing back wards from the pulmonary artery into the right- ventricles.

The right and left-cornary. arteries are the first to leave the aorta, these then divide into smallar arteries which encircle the heart and supply blood to all parts of organ .The return blood from the heart is gathered chiefly by the, Cornary sinus and returned straightforwardly into the right chamber.