chambers in the human heart: The human heart consists of four chambers.

Left and right atria: The upper thin-walled chambers are called the left and right atria (singular 'atrium').

Left and right ventricles:

The lower thick-walled chambers are called the left and right ventricles. The left ventricle is the largest and strongest chamber in the heart.

Blood flow through the chambers:

The human heart works as a double pump i.e., it receives deoxygenated (with less oxygen) blood from the body and pumps it to the lungs and, at the same time, it receives oxygenated (with more oxygen) blood from the lungs and pumps it to all the body. Inside heart chambers, the deoxygenated and oxygenated blood are kept separated. Here is a brief description of the circulation of blood inside the heart to show its double-pump mechanism.

Function of the right atrium:

The right atrium receives deoxygenated blood from the body via the main veins i.e., superior and inferior vena cava. When the right atrium contracts it passes the deoxygenated blood to the right ventricle.

The opening between the right atrium and the right ventricle is guarded by a valve known as the Tricuspid valve

Tricuspid valve:

Tricuspid valve (because it has 3 flaps). When the right ventricle contracts, the blood is passed to the pulmonary trunk, which carries blood to the lungs. The tricuspid valve prevents the backflow of blood from the right ventricle to the right atrium.

Semilunar valve:

At the base of the pulmonary trunk, the pulmonary semilunar valve is present which prevents the backflow of blood from the pulmonary trunk to the right ventricle.

The function of the left atrium:

The oxygenated blood from the lungs is brought by pulmonary veins to the left atrium. The left atrium contracts and pumps this blood to the left ventricle.

Bicuspid valve:

The opening between the left atrium and the left ventricle is guarded by a valve known as a bicuspid valve (because it has two flaps). When the left ventricle contracts, it pumps the oxygenated blood into the aorta, which carries the blood to all parts of the body (except the lungs). The bicuspid valve prevents the backflow of blood from the left ventricle to the left atrium. At the base of the aorta, the aortic semilunar valve is present which prevents the backflow of blood from the aorta to the left ventricle.

Collection of deoxygenated blood:

We see the right side of the heart collects the deoxygenated blood from the body and distributes it to the lungs.

Collection of oxygenated blood:

while the left side collects the oxygenated blood from the lungs and distributes it to the body.

Pulmonary circulation or circuit:

The pathway on which deoxygenated blood is carried from the heart to the lungs and in return oxygenated blood is carried from the lungs to the heart is called pulmonary circulation or circuit.

Systemic circulation or circuit:

Similarly, the pathway on which oxygenated blood is carried from the heart to the body tissues and in return deoxygenated blood is carried from the body tissues to the heart is called systemic circulation or circuit.