Question

Mammals are said to have double circulation. It means (a) Blood vessels are paired. (b) There are two types of blood vessels attached to every organ. (c) There are two systems, one from the heart to the lungs and back to the rest of the body. (d) Blood circulates twice through the heart.

Short answer

The correct answer is (c). There are two systems in mammals: one from the heart to the lungs and back, and the other from the heart to the rest of the body and back.

Step-by-step solution

Understanding Double Circulation

In the context of mammals, double circulation refers to the process where the blood passes twice through the heart during one complete circuit around the body. This is divided into two circuits- the pulmonary circuit (from the heart to the lungs and back) and the systemic circuit (from the heart to the rest of the body and back).

Option Analysis

Analyze each of the provided options based on the explanation of double circulation. (a) refers to paired blood vessels, which is not part of double circulation. (b) suggests two types of blood vessels attached to every organ, which is also not an accurate description of double circulation. (c) suggests two systems: one from the heart to the lungs, and another from the heart to the rest of the body. This matches the definition given above. (d) suggests blood circulates twice through the heart. This is technically correct but does not fully capture the meaning of double circulation since it doesn't include the circulation through the body and lungs.

Choose the Correct Answer

Based on the analysis of the definitions and the options provided, the correct answer is (c) since this is the most accurate and complete definition of double circulation.

Key concepts

Pulmonary Circuit

The pulmonary circuit is a crucial component of double circulation in mammals. It involves the movement of blood between the heart and the lungs. Here's how it works:

• Deoxygenated blood, which means it has low oxygen content, is pumped from the heart to the lungs.
• In the lungs, carbon dioxide (a waste product) is exchanged for oxygen.
• This newly oxygen-rich blood then returns to the heart.

This circulation process allows mammals to efficiently exchange gases, crucial for breathing and energy production. Every time your heart beats, it pushes blood along this path to ensure your body has the oxygen it needs.

Systemic Circuit

After blood gains oxygen in the lungs, it enters the systemic circuit. This path carries oxygenated blood from the heart to the rest of the body. Here's how the systemic circuit operates:

• Oxygen-rich blood leaves the heart and travels through arteries to various tissues and organs.
• The tissues use the oxygen in metabolic processes to produce energy, releasing carbon dioxide as a by-product.
• Now deoxygenated, the blood returns to the heart through veins.

This process is vital as it distributes essential oxygen and nutrients, maintaining cellular activity and overall health.

Heart

The heart is the powerhouse that drives both the pulmonary and systemic circuits. It consists of four chambers:

• Two atria: These upper chambers receive blood. The right atrium collects deoxygenated blood returning from the body, while the left atrium holds oxygenated blood arriving from the lungs.
• Two ventricles: These lower chambers pump blood out of the heart. The right ventricle sends blood to the lungs, and the left ventricle pushes oxygen-rich blood to the body.

The heart's rhythmic contractions ensure continuous blood flow. Each complete heartbeat involves a full cycle through both circuits, highlighting the double nature of mammalian circulation.

Lungs

Lungs play a pivotal role in the pulmonary circuit of double circulation. They are the site where gas exchange occurs, facilitating the oxygenation of blood. Here's what happens in the lungs:

• Blood loaded with carbon dioxide arrives at the lungs.
• In tiny air sacs called alveoli, oxygen is absorbed while carbon dioxide is released from the blood.
• The fresh, oxygenated blood then prepares to journey back to the heart and subsequently to the rest of the body.

Lungs not only support respiration but are integral in keeping the blood supply refreshed, underscoring their importance in the circulatory system.