Human Heart: How the Heart Works 

1.0Heart

Size – 5 inches length × 3.5 inches wide × 2.5 inches thickness

Colour – Reddish brown 

Shape – Conical

Weight – 250 – 300 gm.

The heart is a muscular cone-shaped organ about the size of a clenched fist of the same person.

It is located in the upper body (chest area) between the lungs and with its broad base facing upward and backward and narrow apex directed downwards, forwards and slightly towards the left.

Structure of Heart

The heart is enclosed in a tough, two layered sac, the pericardium. It is divided into separate right and left sections by the septum or “septa”. Each of these (right and left) sections is also divided into upper and lower compartments known as atrium or auricle and ventricle respectively.

The four main chambers of the heart are:

(i) Right Atrium

(ii) Right Ventricle

(iii) Left Atrium

(iv) Left Ventricle 

It is essential that blood flows in the correct direction through the heart so that the structure of the heart includes a series of valves which ensures that blood does not flow backwards when the atria or ventricles contract. 

The Tricuspid valve (Atrioventricular valve) separates the right atrium from the right ventricle.

The Pulmonary valve (Semilunar valve) separates the right ventricle from the pulmonary artery.

The Mitral (also known as the Bicuspid) valve is the atrioventricular valve which separates the left atrium from the left ventricle. 

The Aortic valve (Semilunar valve) separates the left ventricle from the aorta.

• Coronary circulation is the circulation of blood in the blood vessels that supply the heart muscles. The food and oxygen requirements of the heart wall are high in view of its constant beating.

Note:- The aorta is the largest artery and the vena cava is the largest vein.

‘Atrium’ is a Latin word meaning “Entrance hall” and ‘Ventricle’ is a Latin word that stands for “Little belly”.

Working of Heart

The heart functions as a pump in the circulatory system. The right atrium collects deoxygenated blood from two large veins, superior and inferior vena cava. When the atrium contracts, the blood is pumped through the tricuspid valve into the right ventricle.  As the right ventricle contracts, the tricuspid valve closes and the blood is pumped into the pulmonary artery through the pulmonary valve.

Pulmonary artery carries the blood to the lungs where carbon dioxide is exchanged for oxygen. The left atrium receives oxygenated blood via pulmonary vein. 

When left atrium contract, blood enters into the left ventricle through bicuspid (mitral) valve. Then left ventricle contracts and blood is pumped into aorta through aortic valve. During contraction of left ventricles, mitral valve get closed to prevent backward flow into atrium.  Valves ensure that blood does not flow backwards when the ventricles contract.

2.0Open and Closed circulatory system

The blood vascular system is of two types - open and closed.

Open Circulatory System

The blood comes in direct contact with the tissue cells. Blood vessels arising from the heart pour the blood into tissue spaces called sinuses. e.g. Arthropods and molluscs.

Closed Circulatory System

The blood remains in blood vessels during its entire trip in the body and never comes in direct contact with the tissue cells. E.g. Annelids, All vertebrates.

3.0Systemic and Pulmonary Circulation

The right portion of heart is known as pulmonary heart and it has deoxygenated blood. The left portion of heart is known as systemic heart and it has oxygenated blood.

Systemic Circulation

In this, blood completes its circulation from left ventricle to right auricle through the body organs. It is in between heart and remaining parts of the body except lungs.

Oxygenated blood from lungs → heart → Systemic arteries → Body parts → Systemic veins → heart

Pulmonary Circulation

In this, blood completes its circulation from right ventricle to left auricle through the lungs.

It is in between heart and lungs.

Deoxygenated blood from body → heart → Pulmonary arteries → lungs → Pulmonary veins → heart

Differences between pulmonary and systemic circulation

Single Circulation and Double Circulation

In single circulation, Blood moves through heart only once during completion of whole circuit in the body. In double circulation, blood passes twice through heart during completion of full circuit.

Double circulation is an improvement over single circulation. The heart pumps both the types of blood (oxygenated and deoxygenated) forcefully through the body. 

Differences between single and double circulation:

4.0Also Read