Double Circulation

Introduction

How do we divide things into living and nonliving organisms? When we talk about cows, dogs, human beings – how do we know that they are all living beings? As we know, all living organisms have a circulatory system. The bodies of mammals are composed of complex organ systems and tissues, such as the respiratory organ system, excretory organ system, circulatory system, etc. But the major part of the body runs on the circulatory system, without which we can not survive. The key of the circulatory system is the heart, which is situated in the chest cavity between both lungs and is slightly tilted towards the left. Here, we are going to discuss the human heart and more about double circulation.

Blood and the circulatory system

The circulatory system includes the blood, blood vessels, and the structure and process of the heart.

Blood is a fluid that constantly circulates throughout the body, providing all body parts with oxygen and nutrition and removing waste. Blood comprises blood plasma that contains different blood cells.

The blood vessels are of three types: arteries, veins, and capillaries. They are the tubular structures that carry blood to or from different organs and organ systems. Arteries are the blood vessels that carry blood from the heart to the various organs and tissues. Veins carry deoxygenated blood away from the organs and tissues to the heart. Capillaries are minute blood vessels that carry blood between the arteries and veins.

Structure of heart: The heart is a complex organ that is made up of cardiac muscles. Our heart is just the size of our fist. The heart is divided into four chambers, i.e., two atria and two ventricles. The atria are the upper heart chambers that receive blood from the veins and through which the blood enters the ventricles. The ventricles are the two chambers at the bottom of the heart that pump blood to the various organs and tissues. The deoxygenated blood is transported to the lungs, whereas the oxygenated blood has to be transported to the heart.

The heart has a thick muscular wall to pump blood to various organ systems. Some valves ensure that blood does not flow in the backward direction—the different chambers of the heart aid in keeping the oxygenated and deoxygenated blood separated. And because of this separation, the body can derive oxygen from the oxygenated blood. The heart is protected by a double-walled muscular bag called the pericardium.

Process of the heart: The oxygenated blood is transported from the lungs to the thin-walled upper left chamber of the heart called the left atrium. When blood is collected, the left atrium relaxes. It then contracts when the left ventricle expands for the transportation of blood. The blood is pumped out to the body when the muscular left ventricle contracts.

The deoxygenated blood is transported from the body to the upper right chamber of the heart, which is called the right atrium. This right atrium expands when it receives the blood. In the lower chamber, the right ventricle dilates when the right upper atrium contracts. This blood transferred to the right ventricle is then transferred to the lungs for oxygenation.

Circulatory system: It is the main system of the body that circulates the blood and lymph through the body. The whole circulatory system consists of the heart, blood vessels, lymph, and lymphatic vessels. Through this system, an organism can get enough oxygen and nutrients.

As we know, the blood is pumped by the right ventricle, which then enters into the pulmonary artery. The left ventricle pumps the blood into the aorta.

Before delivering blood to this systemic circulation, the hepatic portal vein takes the blood from the intestine to the liver.

Double circulation definition

Let’s discuss more the double circulation of blood.

Double circulation is a type of circulatory system in which blood circulates twice via the heart. The systemic circulation is separated from the pulmonary circulation in this form of circulation. The heart is divided into two halves in this circulation: the right side pumps deoxygenated blood into the pulmonary portion, whereas the left side pumps oxygenated blood into the systemic circulation. Such circulation is found in birds and mammals. In contrast, animals with only one circulatory system, such as fish, have two-chambered hearts. In this circulation, the blood flows in two different paths, one path is for oxygenated blood, and the other path is for deoxygenated blood.

Double circulation classification

Let’s discuss the pulmonary pathway and systematic pathway in detail,

Pulmonary pathway: It is the path that carries the deoxygenated blood from the right atrium on the right side to the lungs for the oxygenation of the blood. It is a system of blood vessels that forms a complete pathway between the heart and the lungs.

Systemic pathway: It carries the oxygenated blood from the left ventricle of the heart to the various organs of the body. It provides the blood supply to all parts of the body. It carries oxygen and nutrients to the cells and takes carbon dioxide and waste products away.

Necessity of double circulation 

• It is necessary as it separates oxygenated and deoxygenated blood
• This systematic manner of double blood circulation helps the body maintain its constant body temperature
• It provides high energy demand for mammals
• It helps to maintain the high blood pressure in birds and mammals
• It also allows the pure blood to transfer to the different tissues and organs of the body
• This circulation supplies oxygen to various organs of the body in high quantities

Conclusion

From the above discussion, we understand that when the blood passes through the heart twice in one complete cycle, it is called double circulation. It is very helpful in mammals and birds. Blood is pumped from the heart to the lungs for its oxygenation and then returns to the heart before it gets distributed to all parts of the body. Also, we learnt the structure of the heart that consists of four chambers, two atria and two ventricles. All the chambers are separated from each other by the thick muscular membrane. The double circulation of blood comprises two separate cycles known as pulmonary circulation and systemic circulation.