3.5.1 Mammalian Circulation

Key Features of the Mammalian Circulatory System:

1. Suitable Transport Medium:

• Blood acts as the transport medium in mammals.
• It is water-based, allowing substances like oxygen, nutrients, and waste to dissolve and be transported easily.

2. Pump for Movement:

• The heart maintains a pressure gradient to ensure blood flows to all parts of the body.
• This ensures continuous and efficient delivery of substances.

3. Flow Regulation:

• Valves in veins prevent backflow of blood, maintaining one-way movement throughout the system.

4. Closed and Branched System:

• The circulatory system is closed, meaning blood flows through a network of vessels (arteries, veins, and capillaries) without leaving them.
• It is highly branched, ensuring all tissues receive adequate blood supply.

Double Circulatory System:

1. Two Circuits:

• Pulmonary Circuit:
• Blood is pumped from the heart to the lungs to pick up oxygen and remove carbon dioxide.
• Systemic Circuit:
• Oxygenated blood is pumped from the heart to the rest of the body to supply organs and tissues.

2. Advantages:

• Blood flows through the heart twice per complete cycle, ensuring it maintains high pressure for faster delivery to tissues.
• This system meets the high metabolic demands of mammals.

The Heart in Circulation:

1. Two Pumps:

• Right Side:
• Pumps deoxygenated blood to the lungs for oxygenation (pulmonary circuit).
• Left Side:
• Pumps oxygenated blood to the rest of the body (systemic circuit).
• The left side is larger and stronger to handle the higher pressure needed for systemic circulation.

2. Structure:

• Atria: Thin-walled chambers that receive blood.
• Ventricles: Thick-walled chambers that pump blood out of the heart.
• Valves: Prevent backflow, ensuring one-way blood flow.

Comparison with Single Circulatory Systems:

Feature	Double Circulation	Single Circulation
Number of Circuits	Two (pulmonary and systemic)	One (e.g., fish)
Blood Pressure	Maintains high pressure in body	Blood pressure drops after passing through gills.
Efficiency	Meets high metabolic demands	Sufficient for organisms with lower metabolic rates.

Summary of Blood Flow in Mammals:

1. Deoxygenated blood enters the right atrium from the body via the vena cava.
2. It is pumped into the right ventricle and then to the lungs via the pulmonary artery.
3. Oxygenated blood returns to the left atrium via the pulmonary vein.
4. It is pumped into the left ventricle and out to the body via the aorta.

Key Terms:

• Closed System: Blood remains within vessels, preventing leakage.
• Double Circulation: Blood passes through the heart twice per complete cycle.
• Pulmonary Circuit: Transports blood to and from the lungs.
• Systemic Circuit: Transports blood to and from the body.