Question

Inernal and external structure of human heart notes in hindi on biological discussion

Answer 1

Answer:

External Structure:

The left and right atria are separated externally by a shallow vertical interatrial groove. The atria are demarcated externally from the ventricles by an oblique groove called atrioventricular sulcus. There are present coronary sulcus, anterior inter ­ventricular sulcus and posterior inter ventricular sulcus. These have coronary arteries, through which the heart receives blood.

As stated earlier, there are left and right atria which have thin walls. The left atrium is smaller than the right atrium. The right atrium is a roughly quadran­gular chamber. Each atrium has an appendage called an auricle (L auris- ear), so named because its shape resembles a dog’s ear. The auricle increases the atrium’s surface area. The superior vena cava, inferior vena cava and coronary sinus open into the right atrium.

Human Heart in Front View

(a) The superior vena cava carries blood from the body’s upper region,

(b) The inferior vena cava is larger than the superior and carries blood from the lower body’s region,

(c) The coronary sinus carries the majority of blood from the heart itself. The coronary veins open into the coronary sinus. The right atrium receives deoxygenated blood. The left atrium is less in volume than that of right atrium but it has thicker walls. The left atrium is roughly cuboidal. It projects as the left auricle towards the left side.

(d) The left atrium receives oxygenated blood from the lungs through two pairs of pulmonary veins.

There are present left and right ventricles with thick walls. The wall of the right ventricle is thinner than that of the left ventricle. The left ventricle is longer and narrower than the right ventricle. The walls of the left ventricle are about three times thicker than the right ventricle.

The pulmonary trunk arises from the right ventricle. It divides into left and right pulmonary arteries that carry deoxygenated blood to the lungs. The aorta arises from the left ventricle. It is divisible into the ascending aorta, arch of aorta and descending aorta.

The right and left coronary arteries arise from the ascending aorta. The arch of the aorta (also called aortic arch) gives rise to the brachiocephalic artery (Innominate artery), left common carotid artery and left subclavian artery. The descend­ing aorta runs through the thorax and abdomen and hence it is divisible into thoracic and abdominal parts.

The pulmonary trunk is connected with the aorta by the ligamentum arteriosum that represents the remnant of an embryonic connection between the pulmonary trunk and aorta. In embryo the ligamentum arteriosum is called ductus arteriosus. Coronary arteries arise from the ascending aorta and supply blood to the heart.

Internal Structure:

The two thin walled atria are separated from each other by the interatrial septum. The right atrium receives the openings of superior vena cava, inferior vena cava and coronary sinus. The opening of inferior vena cava is guarded by Eustachian valve.

The opening of the coronary sinus has coronary or Thebasian valve. In the right atrium adjoin­ing the interatrial septum, an oval depression, the fossa ovalis is present. It marks the position of an opening, the foramen ovale, between the two atria in the foetus, but in the adult it persists only as a depression. The left artrium receives four openings of pulmonary veins.

The artrioventricular opening between the left atrium and the left ventricle is guarded by the bicuspid valve, also called mitral valve (having two flaps). The right atrio-ventricular opening is guarded by the tricuspid valve, as it has three flaps.

Attached to the flaps of the bicuspid and tricuspid valves are special fibrous cords, the chordae tendineae, which are joined to the other ends with the special muscles of the ventricular wall, the papillary muscles. The chordae tendineae prevent the bicuspid and tricuspid valves from collapsing back into the atria during powerful ventricular contractions.

The chordae tendineae can be seen extending from the valves to the columnae carneae, which are the muscular ridges or projections on the walls of the ventricles. The columnae carneae divide the cavity of the ventricles into smaller spaces, known as fissures. The walls of the ventricles are thicker than the atria. The thickest portion of the human heart is the wall of the left ventricle.  

As stated in the external structure, the pulmonary trunk and aorta arise from the right and left ventricles respectively. At the base of the pulmonary trunk and aorta are located three half-moon shaped pockets known as pulmonary semilunar valves and aortic semilunar valves respectively. These valves allow the free and forward flow of blood, but prevent any backward flow. Thus the valves of the heart are:

(a) Bicuspid valve,

(b) Tricuspid valve,

(c) Aortic semilunar valves and

(d) Pulmonary semilunar valves.