Double Circulation 

Double circulation is a type of blood circulation system in which blood passes through the heart twice during one complete cycle — once for oxygenation and once for supplying oxygenated blood to the body. It ensures efficient separation of oxygenated and deoxygenated blood, which is essential for warm-blooded animals like mammals and birds.

1.0Types of Circulation in Double Circulation

In humans, double circulation allows proper oxygen supply to tissues and efficient removal of carbon dioxide, maintaining high metabolic rates.

The human circulatory system includes two major circuits:

1. Pulmonary Circulation
2. Systemic Circulation

These two circuits work together to ensure continuous oxygen delivery and waste removal.

Pulmonary Circulation

Pulmonary circulation carries deoxygenated blood from the heart to the lungs and returns oxygenated blood back to the heart.

Pathway:

1. The right ventricle pumps deoxygenated blood into the pulmonary artery.
2. The pulmonary artery transports it to both lungs.
3. In the lungs, gas exchange occurs — carbon dioxide is released, and oxygen is absorbed.
4. The pulmonary veins then carry the oxygenated blood back to the left atrium of the heart.

Systemic Circulation

Systemic circulation carries oxygenated blood from the heart to body tissues and returns deoxygenated blood back to the heart.

Pathway:

1. The left ventricle pumps oxygen-rich blood into the aorta.
2. The aorta branches into arteries that deliver blood to all body organs and tissues.
3. After oxygen delivery and nutrient exchange, blood becomes deoxygenated.
4. Deoxygenated blood returns through the vena cavae (superior and inferior) to the right atrium of the heart.

2.0Diagrammatic Overview of Double Circulation

(For webpage optimization, include a labeled image showing both pulmonary and systemic circulation with arrows indicating blood flow.)

Representation:

• Blue arrows → Deoxygenated blood
• Red arrows → Oxygenated blood
• Arrows connecting the lungs and heart show pulmonary circulation
• Arrows connecting the heart and body organs show systemic circulation

3.0Significance of Double Circulation

Double circulation offers several physiological advantages:

• Complete separation of oxygenated and deoxygenated blood: Prevents mixing, ensuring maximum oxygen supply to tissues.
• Efficient gas exchange: Blood passing through lungs each time ensures continuous oxygenation.
• Stable body temperature: Supports high metabolic activity in warm-blooded animals.
• Efficient waste removal: Carbon dioxide and other metabolic wastes are continuously expelled.
• Increased oxygen delivery: Allows higher energy output necessary for active lifestyles and complex organ systems.

Comparison Between Pulmonary and Systemic Circulation

4.0Double Circulation Examples

Double circulation is observed mainly in birds and mammals, where oxygenated and deoxygenated blood are completely separated by a four-chambered heart. This adaptation supports their high energy requirements and constant body temperature.

Here are some prime examples:

1. Humans:

• Exhibit complete double circulation.
• The right side of the heart pumps deoxygenated blood to the lungs (pulmonary circuit), while the left side pumps oxygenated blood to the rest of the body (systemic circuit).

2. Birds (e.g., Pigeon, Crow, Sparrow):

• Possess a four-chambered heart similar to humans.
• Efficient separation of blood helps maintain body heat and supports flight metabolism.

3. Mammals (e.g., Dog, Cow, Elephant, Whale):

• All mammals exhibit double circulation.
• Oxygen-rich and oxygen-poor blood never mix, ensuring maximum oxygen delivery for energy-intensive activities.

4. Crocodiles:

• Though reptiles generally have incomplete double circulation, crocodiles are an exception.
• They possess a four-chambered heart, providing complete double circulation similar to birds and mammals.

These examples highlight how evolution of a four-chambered heart ensures efficient oxygen transport — a key factor in sustaining higher metabolic activity and warm-blooded physiology.

5.0Double Circulation in Other Vertebrates

• Fish: Have single circulation — blood passes through the heart only once in one cycle.
• Amphibians and reptiles: Show incomplete double circulation as their heart has partial separation between oxygenated and deoxygenated blood.
• Birds and mammals: Show complete double circulation with a four-chambered heart ensuring total separation of both blood types.

This evolution of complete double circulation marks an adaptation for higher metabolic rates and endothermic (warm-blooded) living.

6.0Relation Between Heartbeat and Double Circulation

Each heartbeat represents a complete cycle of:

• Blood entering the heart
• Pumping through pulmonary circulation
• Returning and being pumped again through systemic circulation

Thus, each cardiac cycle supports double circulation, sustaining the continuous flow of blood through both circuits.