Difference between Single and Double Circulation

What Is Circulation? (Overview)

Blood is circulated throughout the animal body, a process through which nutrients, gases, and waste products are delivered to their respective sites of consumption as well as production. The type of closed circulatory systems depend on the number of circuits, which include single circulation and double circulation. This system, within which the blood flows, is a system of the blood vessels, either the arteries or the veins, and it is called the closed circulatory system.

In single circulation, the blood will flow to and from the heart in one single path. In double circulation, the circulation of the blood is carried in two circuits that are connected by the heart with blood that is oxygenated and deoxygenated. The following article brings out the differences between the single and the double circulation in a detailed study.

What Is Single Circulation?

Single circulation is the original type of circulatory system present and is associated with most fishes. These organisms have a two-chambered heart representation made out of one atrium and one ventricle.

Structure of Heart in Fishes

• The circulatory system of fish involves the flow of deoxygenated blood away from the body tissues.

• It pumps deoxygenated blood to the gills so that it can get oxygenated there.

• Fully oxygenated blood coming from the gills- flows directly to all the different body tissues.

• The blood that had left the heart returns deoxygenated from tissues.

Efficiency And Adaptation

• Blood flows through a single circulatory pathway.

• It is inefficient in that blood flows at a considerably low pressure.

• Suitable to the metabolic requirements of fishes.

What Is Double Circulation?

Double circulation is one of the circulatory systems of birds and mammals. The animals have a four-chambered heart, which comprises two atria and two ventricles.

Structure of Heart in Birds & Mammals

• The heart is divided into two separate circuits: systemic and pulmonary circulation.

• The left atrium receives oxygenated blood from the lungs and sends it to the left ventricle.

• The right atrium receives deoxygenated blood coming from the body tissues and sends it to the right ventricle.

Two Circuits

Systemic Circulation

• Oxygenated blood is ejected out of the left ventricle into the aorta and pumped to various body tissues.

• Once the oxygen and nutrients have been supplied, the deoxygenated blood returns to the right atrium.

Pulmonary Circulation

• From the right ventricle, circulation sends deoxygenated blood to the lungs through the pulmonary artery.

• The now oxygenated blood returning to the left atrium again from the lungs enters there by the pulmonary vein.

Efficiency And Adaptation

• Blood passes through two different pathways, which allows for an effective oxygenation of blood and nutrient delivery.

• This system has a higher pressure flow of blood.

• It supports the higher metabolic demands that exist in birds and mammals.

Single vs Double Circulation – Comparison Table

The difference between single and double circulation is included in the table:

Significance In Evolution & Biology

One of the most significant things to learn is the difference between single and double circulation. This difference can help us see how various animals in nature have evolved differently. As species evolved, their hearts became complex, allowing more efficient separation of oxygenated and deoxygenated blood. This complexity relates with rising energy demands, supporting active lifestyles and higher metabolic rates. Together, these evolutionary adaptations highlight the deep link between habitat, cardiac structure, and overall biological efficiency.

Double Circulation NEET MCQs (With Answers & Explanations)

Types of questions asked from this topic are:

• Two circuits: systemic & pulmonary

• Single vs double circulation

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