Human heart:

Human heart is divided into different chambers internally. 1 or 2 auricles and 1 or 2 ventricles, these are called true chambers. Study of heart is called cardiology.

(1) Fishes have a heart with 2 chambers (1 auricles, 1 ventricle). It handles only deoxygenated blood. This type of heart is called venous heart.

(2) Amphibians have heart which receives both oxygenated blood & deoxygenated blood, called arterio-venous heart & is 3 – chambered with 2 auricles and a ventricle. Lung fish has 3 chambered Heart.

(3) Reptiles receives both type of blood called arterio-venous heart. They have 4 – chambered heart with 2 auricles & partly divided ventricle.

(4) Mammals & birds have a heart with 4 chambers & receives both – type of oxygenated & deoxygenated blood.

Human Heart:

 Human heart is about 300 gram in males & 250 grams in females.

• It is present in the middle of thoracic cavity between the lungs, above the diaphragm. Cavity is called mediastinal cavity or mediastinum.
• It has a tough covering called pericardium. It has 2 layers inner visceral pericardium and outer parietal pericardium.  Space between them is called pericardial cavity. This cavity has a fluid that keeps the heart moist.
• Pericardium, protects the heart from injury, keeps the heart in place and also from overfilling with blood. Fluid is called pericardial fluid.

(1) Upper smaller two auricles/atrium (left & right auricles)

(2) Lower larger two ventricles (left & right ventricles)

(3) Auricles form a small part of Heart and ventricles form a large part of heart.

(4) Inter – ventricular groove is that place which separates left & right ventricles.

Explanation of different parts of human heart:

(1) Superior vena cava: Collects deoxygenated blood from upper body parts & pump it to heart.

(2) Inferior vena cava: Collects deoxygenated blood from lower body part & pump it to heart.

(3) Semi lunar valves: Lies below aorta and prevent backflow of blood into ventricles so that blood flows only in one direction towards aorta.

(4) Sino – atrial nodes (S – A node): Lies in the walls of right auricles below the opening of superior vena cava. It has a property of self excitation, so it acts as a pacemaker of heart. It starts a wave of contraction in left & right auricles to start heart cycle. After contraction, auricles push the blood into ventricles.

(5) Atrio – ventricular node (A – V node): Lies in wall between right auricles & right ventricle. It also starts ventricular contraction by the contraction started by S – A node.

(6) Atrium (auricles): These act a blood collecting chamber for blood returning to heart. Right atrium collects deoxygenated blood from superior & inferior vena cava and left atrium collects oxygenated blood coming from lungs after oxygenation. Atrium have thin walls to push the blood into ventricles.

(7) Ventricles: Ventricles are distributing chambers for blood coming from auricles. Right ventricle collects deoxygenated blood coming from right auricles & passes it to lungs left ventricle collects blood coming from left auricle & passes it to aorta for distribution in the body.

(8) Pulmonary artery: Arteries always carry oxygenated blood away from heart but in case of pulmonary artery it carries deoxygenated blood away from heart to lungs. It takes blood from right ventricles. Left pulmonary artery to left lung & right pulmonary artery to right lung.

(9) Pulmonary vein: Veins always carry deoxygenated blood to heart but in case of pulmonary vein, it carries oxygenated blood to heart coming from lungs.

(10) Tricuspid valve: Between right atrium & right ventricle their lies an aperture called atrio-ventricular aperture. Tricuspid valve, lies at this aperture. It allows the passage of blood from right atrium to right ventricle in one direction by checking out the backflow of blood. This valve contains three flaps, so called Tricuspid valve.

(11) Bicuspid valve: Between left auricle & left ventricle their lies an aperture called atrio-ventricular aperture. Bicuspid valve lies at this aperture. It allows the passage of blood from left atrium to left ventricles by checking out backflow of blood. It has 2 flaps, so called bicuspid.

(12) Aorta: It is the longest blood vessels (artery). It takes oxygenated blood from left ventricle and transfers it to body parts for distribution to all tissues of body.

(13) Inter ventricular septum: It is a space between left & right ventricles. It keeps the blood free from mixing.

(14) Buddle of this and purkinge fibers: It starts from atrio-ventricular node (A – V node) & downwards to inter auricular & inner ventricular septa. Here it divided into right & left bundle branches. One branch goes into the wall of left ventricle & other branch goes into the wall of right ventricle. Here these branches break into large number of purkinge fibers. Heart beat travels in these fibers as electric wave. Purkinge fibre is heart of heart.

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