Thursday, 12 September 2019

Structure Of Heart

Structure of Heart

Structure Of Heart

Fig. Structure of Heart

The heart is the most important organs of the human body. It is a muscular organ responsible for pumping blood through the blood vessels by repeated, rhythmic contractions. The term cardiac means related to the heart and comes from the Greek word Kardia, for “heart.” The heart pumps the blood, which carries all the vital materials that help in various body functions. like, the brain requires oxygen and glucose, which, if not received continuously, will cause it to loose consciousness. Muscles need O2, C6H12O6, and amino acids, as well as the proper ratio of sodium, calcium and potassium salts in order to contract normally. The glands need a sufficient supply of raw materials from which they manufacture the specific secretions. If the heart ever ceases to pump blood, the body begins to shut down and after a very short period of time, death occurs. All vertebrates including humans have a single heart.

LOCATION OF HEART


In the body of a human, the heart is generally situated in the middle of the thorax with the largest part of the heart slightly offset to the left (although sometimes it is on the right, underneath the breastbone). The heart is generally felt to be on the left side because the ventricle of left heart is stronger (it pumps to all body parts).
The heart is located in the mediastinum which is the space between two lungs, i.e., the central subdivision of the thoracic cavity. The heart apex of the human body is the blunt point situated in an inferior (pointing down and left) direction. A stethoscope can be placed directly over the apex of the human heart so that the beats can be counted. It is located posterior to the 5th intercostal space just median of the left mid-clavicular line.

STRUCTURE OF HEART


The human Structure Of Heart is a muscular organ of a somewhat conical or pyramidal form with the upper broad part, the base and lower narrow, the apex. The apex is slightly directed to the left. The human heart has two separate pumps: a right one that pumps blood through the lungs and a left one that pumps blood through the peripheral organs.
Primer pump is weak of each atrium or the ventricle, helping to move blood into the ventricle. The ventricles then supply the main pumping force that propels the blood to the whole body. The average an adult human heart is about 12 cm in length, 9 cm in width and 6 cm in thickness. Its heart weight varies in males from 280-340 g (average 300 g) and in females from 230-280 g (average 250 g). The heart width is said to be about 0.45% of body weight in males and 0.40% in females.
The heart is closely present in a fibrous sac known as the pericardium and is surrounded by the lungs. The pericardium is made up of two layers: parietal and visceral pericardium. In between these two layers, a space called pericardial cavity is present which is filled with pericardial fluid. The pericardium protects the heart from shocks and mechanical injuries and also allows free movements of the heart.

External Structure


The human heart is 4 chambered, consisting of two atria and two ventricles. 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 also present coronary sulcus, anterior interventricular sulcus, and posterior interventricular sulcus. These have coronary arteries, through which the heart receives blood.
The left atrium is smaller than the right atrium. Each atrium has an appendage called an auricle which increases its surface area. The superior vena cava, inferior vena cava, and coronary sinus open into the right atrium. The left atrium receives four openings of pulmonary veins. Ventricles are thick-walled and the left ventricle is longer and narrower than the right ventricle. Its walls 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.

Internal Structure


Atrium


The two thin-walled atria are separated by the interatrial septum. The right atrium receives blood through superior vena cava, inferior vena cava, and coronary sinus. The superior vena cava carries blood from the upper body and the inferior vena cava carries blood from the lower body region. Coronary sinus carries blood from the heart itself. The right atrium receives deoxygenated blood while the left atrium receives oxygenated blood from the lungs through two pairs of pulmonary veins. An oval depression known as fossa ovalis is present in the right atrium near the interatrial septum. It marks the position of an opening between two atria in the fetus, i.e., foramen ovale but in the adult, it persists only as a depression.

Ventricle

both ventricles are separated from each other by a thick, curved partition, the interventricular septum. Muscular ridge or trabeculae carnage, and a few large, conical, muscular elevations termed the papillary muscles. The moderator band extends from the interventricular septum to the anterior papillary muscle in the right ventricle.
The left and right pulmonary arteries carry deoxygenated blood to the lungs. The aorta arising from the left ventricle is divisible into the ascending aorta, arch of the aorta and descending aorta. The left and right 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 and aorta between connected through ligamentum arteriosum that represents the remnant of an embryonic connection between the pulmonary trunk and aorta. In the embryo, the ligamentum arteriosum is called ductus arteriosus. Blood supply to the heart by Coronary arteries and its arise from the ascending aorta and arteries exit from behind the aortic valve cusps in the very first part of the aorta. Lead to a branching network of small arterioles, arteries, venules,  capillaries, and veins similar to those in other organs.

Heart valves

Location and functions of heart valves have been summarised in the given table

Structure of Heart

Fig.Valves of the heart

There are no valves at the entrances of the superior and inferior venae cavae (plural of vena cava) into the right atrium and of the pulmonary veins into the left atrium. However, little blood back into the veins through atrial contraction pumping because atrial contraction constricts their sites of entry into the atria, greatly increasing the resistance to backflow. Actually, Into the veins a little blood is ejected back and this accounts for the venous pulse that can often be seen in the neck veins when the atria are contracting.

Functioning of valves

The closing and opening of the AV valves are passive processes resulting from pressure differences across the valves. When the blood pressure in an atrium is greater than in the corresponding ventricle, the valve is pushed open and blood flows from atrium to ventricle. Achieves an internal pressure greater than that in its connected atrium when contracting ventricle, the AV valve between them is forced closed. Therefore, blood does not normally move back into the atria and is forced into the pulmonary trunk from the right ventricle and into the aorta from the left ventricle.
To prevent the Atrioventricular valves from being pushed up into the atria when the ventricles are contracting (a condition called prolapse), the valves are fastened to muscular projections (papillary muscles) of the V walls by fibrous strands chordae tendineae. The papillary muscles do not close or open the valves. They act only to limit the valves’ prevent & movement the backward flow of blood. The aortic and pulmonary artery semilunar valves function quite differently from the AV valves. The high pressure in the arteries at the end of systole causes the semilunar valves to snap to the closed position, in contrast to the much softer closure of the AV valves. Because of smaller openings, the velocity of blood ejection from the aortic and pulmonary valves is far greater than that through the much larger Atrioventricular valves.

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