General Plan Of Circulation In Vertebrates

General Plan of Circulation in Vertebrates

Overview of the Circulatory System

The circulatory system in vertebrates consists of the heart, arteries, veins, capillaries, blood vascular system, and the lymphatic system, which includes lymph channels and lymph. This system allows blood to circulate and transport oxygen, carbon dioxide, nutrients, hormones, and other essential substances. Additionally, it removes waste products of metabolism by transporting them to excretory organs and protects the body against infection and disease.

Components of the Circulatory System

In vertebrates, the circulatory system is a closed type, meaning blood flows through a network of closed blood vessels, such as arteries and veins. The primary components of the circulatory system are:

1. Arteries

- Function: Carry blood away from the heart.

- Structure: Have thick walls due to muscles and elastic tissue, maintaining high pressure.

2. Veins

- Function: Carry blood towards the heart.

- Structure: Have thinner walls with less muscle and elastic tissue, facilitating lower pressure.

3. Capillaries

- Function: Carry blood from arteries to veins, facilitating exchange between blood and tissues.

- Structure: Consist of a single layer of epithelial cells, allowing efficient exchange.

Portal System

Typically, arteries divide into arterioles, which further divide into fine capillaries that supply blood to tissues. Capillaries then merge to form veins that return blood to the heart. However, in vertebrates, there is an arrangement where a vein, before reaching the heart, divides into a set of capillaries in certain organs and supplies blood. This blood is then collected by another set of capillaries, forming venules and finally veins. This arrangement is known as the portal system.

Types of Circulatory Systems

Single Circulation

In a single circulation system, blood travels only once through the heart in one complete cycle of the body. This means blood makes a single circuit where it is pumped, oxygenated, distributed, and finally returned to the heart.

Example of Single Circulation in Fish:

In fish, the heart has two main chambers: one atrium and one ventricle.

The process of single circulation includes the following steps:

1. Heart to Gills: Deoxygenated blood is pumped from the heart to the gills through the ventral aorta.

2. Oxygenation: In the gills, blood picks up oxygen and releases carbon dioxide through the gill filaments.

3. Gills to Body: Oxygenated blood flows from the gills to the rest of the body via the dorsal aorta.

4. Oxygen Delivery: As blood travels through the body, it delivers oxygen to tissues and organs, becoming deoxygenated in the process.

5. Return to Heart: The deoxygenated blood returns to the heart through a series of veins, completing the circuit.

In this system, all the blood in the heart is deoxygenated, leading to the heart being called a venous heart.

Double Circulation

In a double circulation system, blood flows twice through the heart during one complete cycle of the body. This ensures more efficient oxygen supply and separation of oxygenated and deoxygenated blood.

Example of Double Circulation in Mammals:

In mammals, the heart is four-chambered, consisting of two atria and two ventricles. The double circulation process includes these steps:

1. Pulmonary Circuit:

- Heart to Lungs: Deoxygenated blood is pumped from the right ventricle to the lungs via the pulmonary artery.

- Oxygenation: In the lungs, blood releases carbon dioxide and picks up oxygen.

- Lungs to Heart: Oxygenated blood returns to the left atrium through the pulmonary veins.

2. Systemic Circuit:

- Heart to Body: Oxygenated blood is pumped from the left ventricle to the rest of the body through the aorta.

- Oxygen Delivery: As blood circulates through the body, it delivers oxygen to tissues and organs, becoming deoxygenated.

- Body to Heart: Deoxygenated blood returns to the right atrium through the superior and inferior venae cavae, completing the circuit.

This double circulation system allows for higher blood pressure and more efficient oxygen delivery to tissues, supporting the higher metabolic demands of mammals and birds. In this system, there is no mixing of oxygenated and deoxygenated blood, making the heart a pulmonary heart.

Conclusion

Understanding the circulatory system in vertebrates highlights the complexity and efficiency of biological processes that sustain life. The differences between single and double circulation systems illustrate the evolutionary adaptations that enable various species to thrive in their environments. By studying these systems, we gain insight into the intricate mechanisms that support vital functions and the diversity of life on Earth.

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