Question

Describe the structure of the human heart with a neat labelled diagram.

Answer 1

Hint: The human heart is a mesodermally derived hollow, muscular organ. It is situated in the thoracic cavity, in between the lungs, slightly tilted to the left. It is a four-chambered muscular organ, protected by a double walled membranous sac, pericardium. The size of the heart is about the clenched fist. It is made of a special type of muscle called the cardiac muscle. 

Complete Answer:

- The human heart is divided into four chambers, two relatively small upper chambers called atria and two larger lower chambers called ventricles. 

- The ventricles are the chambers that pump blood and the chambers that receive blood are the atrium chambers. Both the right atrium and the ventricle make up the "right heart," and the "left heart" is made up of the left atrium and ventricle. The heart structure also houses the largest artery in the body, the aorta.

- The heart's right and left regions are separated by a muscle wall called the septum. 

- For re-oxygenation, the right ventricle pumps blood through the pulmonary arteries to the lungs.

Then, through the pulmonary veins, the oxygenated blood is obtained from the lungs by the left atrium.

- The pericardium is one of the very first structures which can be observed when viewing the external structure of the heart.

(I) Pericardium: Pericardium is a two layered sac consisting of outer parietal and inner visceral pericardium, enclosing the pericardial fluid in between both the layers. The pericardial cavity is present in between both the layers, which contains pericardial fluid. The fluid protects the heart from shock, and mechanical injuries and also provides lubrication between the two layers, and allows the heart to expand and contract.

Two exclusive layers of the pericardium are

1. Visceral Layer: It lines the outer surface of the heart.

2. Parietal Layer: It forms a sac which contains the fluid in the pericardial cavity around the outer region of the heart.

(II) Heart Wall Structure: The wall of the heart consists of 3 layers, namely:

-Epicardium - It is the outermost layer of the heart, composed of a thin-layered membrane that lubricates and protects the outer section.

- Myocardium- This is a layer of muscle tissue that constitutes the middle wall of the heart. It provides thickness to the wall and is also responsible for pumping action of the heart.

- Endocardium- It is the innermost layer that lines the inner chambers and covers the valves of the heart. In addition, it stops the blood from sticking to the inner walls, thus avoiding potentially fatal blood clots.

- The blood flows within vessels of varying sizes in organisms with closed circulatory systems. 

- All vertebrates possess this form of circulation, including humans.

The vessels in the blood typically consist of the following:

- Veins supply the heart with deoxygenated blood via the lower and upper vena cava, which eventually drains into the right atrium.

- Arteries are the blood vessels which are responsible for supplying oxygenated blood away from the heart to other parts of the body. Aorta is the largest artery and it branches off into various smaller arteries and is responsible for transporting oxygen rich blood from the heart to the rest parts of the body.

- Capillaries are small, tube-like vessels that form a network between veins and arteries.

Note: Valves are flaps of fibrous tissues located between the veins in the cardiac chambers. These valves provide one-way passage and permit the flow of blood from atrium to ventricle and and from the ventricles to the pulmonary artery or aorta. The right and the left atria are separated by a thin, muscular interatrial septum, whereas the left and the right ventricles are separated by a thick-walled interventricular septum. 

- The atrio-ventricular septum separates the atrium and the ventricle of the same side of the heart. There is an opening present in between each of these septa through which the two chambers of the same side are connected. 

- The opening present between the right atrium and the right ventricle is guarded by the tricuspid valve, whereas a bicuspid or mitral valve guards the opening between the left atrium and the left ventricle. The openings of the right and the left ventricles into the pulmonary artery and the aorta respectively are provided with the semilunar valves.