Double Circulation In Humans: Definition, Diagram, Flow Chart

What Is Double Circulation?

Double circulation is the main characteristic by which the human circulatory system favours the efficient transport of oxygen and nutrients. In the double circulatory system, blood flows through the heart twice for each complete circuit: once in the pulmonary circuit (between the heart and lungs), to facilitate oxygenation, and secondly, within the systemic circuit (between the heart and body), to provide oxygen and nutrients.

By comparing the difference between single and double circulation, we can see that the double circulation of blood prevents the mixing of oxygenated and deoxygenated blood, which enhances metabolic efficiency.

The Circulatory System Overview

The circulatory system consists of the heart, blood vessels, and blood, which provide the various tissues with all the necessary nutrients and oxygen and get rid of carbon dioxide and metabolic waste products.

Role in Respiration & Purification

The circulatory system supplies food and gases to all parts of the body and removes metabolic waste from it. In respiration, the circulatory system is directly related to the heart and lungs concerning the circulation and purification of blood. But does the heart have a lone role in purification? Let us look in detail at double circulation and the relative organs.

Types of Circulatory Systems

There are two types of circulatory systems found in animals: the open circulatory system and the closed circulatory system.

Open Circulatory System

Many invertebrates have an open circulation in which there are no small blood vessels or capillaries interfacing with cells or connecting arteries with veins. In insects and other arthropods, in most molluscs, and in many smaller invertebrate groups blood sinuses, called a hemocoel, replace capillary beds found in animals with closed systems.

Closed Circulatory System

In closed circulation the circulating fluid, blood, is confined to vessels throughout its journey through the vascular system. The closed circulatory system is further divided according to the number of circulations blood goes through in the heart.

Single Circulation

Blood passes through the heart once for every complete circuit through the body in a single circulatory system. Blood flows from the heart to the gills for purification and is then distributed to various body parts. Only one cardiac cycle is completed, hence the name single circulation. Single circulation is mainly seen in fish, amphibians, and some reptiles.

Double Circulation in Humans

Double circulation is a pattern in which blood circulation involves two routes—one for oxygenated blood and another for deoxygenated blood. The key organ standing behind double circulation in human beings is the human heart, which is divided into four chambers: left atrium, right atrium, left ventricle, and right ventricle. The heart only connects to the lungs through the pulmonary artery and vein. It is the dual blood pathways, namely pulmonary and systemic:

Systemic Circulation (Step-by-Step)

Systemic circulation refers to the flow of oxygenated blood supplied by the left ventricle to the capillaries of tissues. The process is stated below:

• The oxygen-rich blood flows into the aorta, and it in turn distributes them throughout the body. Veins and venules collect the deoxygenated blood having carbon dioxide back from various parts of the body.

• The deoxygenated blood gets pumped again to the superior vena cava.

• From the superior vena cava, deoxygenated blood again goes back to the right atrium.

• The right atrium supplies the deoxygenated blood to the right ventricle. This blood will be used in the pulmonary circulation.

Pulmonary Circulation (Step-by-Step)

The blood circulation comes in between the right atrium to the left atrium. Following is the process:

• The pulmonary artery picks up blood from the right ventricle and carries it into the lungs for oxygenation.

• From here, following purification, the oxygenated blood is pumped back through the pulmonary vein to reach the left atrium and thereby enter the left ventricle.

• The oxygenated blood thereafter gets pumped into the aorta to complete its course around the body.

Advantages of Double Circulation

The advantages of double circulation are:

• Double circulation ensures that oxygenated blood does not interfere with deoxygenated blood.

• The body at any given time is assured of a supply of oxygen and efficiency would be improved.

• This also allows mammals to maintain their body temperatures.

Common Disorders Related To Double Circulation

Some of the common disorders related to double circulation are:

• Congenital Heart Defects: Structural defects of the heart which are present at birth, can directly influence double circulation.

• Cardiovascular Diseases: A fusion of the defects in the heart and circulatory systems, for instance, coronary artery disease—a disease linked with a heart that can directly influence the performance of circulation.

Double Circulation NEET MCQs (With Answers & Explanations)

Types of questions asked from this topic are:

• Components of an ECG waveform

• Normal ECG values

Practice Questions for NEET

Q1. A part of circulatory system that transports deoxygenated blood from heart to the lungs and brings oxygenated blood back to the heart is referred to as

1. Pulmonary circulation

2. Coronary circulation

3. Systemic circulation

4. Single circulatory system

Correct answer: 1) Pulmonary circulation

Explanation:

The heart ---------> Lungs ---------> The heart
Deoxygenated blood travels from the right ventricle to the lungs as part of pulmonary circulation, whereas oxygenated blood returns to the left atrium from the lungs.
After emerging from the right ventricle, the pulmonary trunk splits into the left and right pulmonary arteries.
The left and right lungs get deoxygenated blood from the left and right pulmonary arteries, respectively. The lungs are where the gas exchange takes place.
Likewise, each lung's two pulmonary veins deliver oxygen-rich blood to the left atrium.

The chambers of the heart related to the lungs through pulmonary vessels together form pulmonary circulation.

Hence, the correct answer is 1) Pulmonary circulation.

Q2. Incomplete double circuit circulation is not observed in

1. Fishes

2. Frog

3. Crocodiles

4. Turtle

Correct answer: 3) Crocodile

Explanation:

The incomplete or mixed double circuit in reptiles

• The mixed or incomplete circuit of reptiles is much more complicated than that of amphibians as they have a three-chambered heart with incompletely divided ventricle

• Sinus venosus is present in reptiles but is less functional

• The conus arteriosus is divided into right systemic, left systemic and pulmonary arches

• The left and right systemic arches are connected through a connection tube called the foramen of the pizza

• The SA node is present in the right auricle.

Hence, the correct answer is option 3) Crocodiles.

Q3. Choose the incorrect statement

1. The mixed or incomplete circuit of reptiles is much more complicated than that of amphibians

2. Sinus venosus is present in reptiles but is less functional

3. The conus arteriosus in reptiles is divided into right systemic, left systemic and pulmonary arches

4. The SA node is present in the left auricle in reptiles

Correct answer: 4) The SA node is present in the left auricle in reptiles

Explanation:

The mixed or incomplete circuit of reptiles is much more complicated than that of amphibians as they have a three-chambered heart with incompletely divided ventricle. Sinus venosus is present in reptiles but is less functional. The conus arteriosus is divided into right systemic, left systemic and pulmonary arches. The left and right systemic arches are connected through a connection tube called foramen of panizzae. The SA node is present in the right auricle.

Hence, the correct answer is option 4) The SA node is present in the left auricle in reptiles.

Also Read:

• MCQs on Double Circulation in Humans

• Cardiac Output

• Coronary Circulation

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