CIRCULATORY SYSTEM IN MAMMALS

CIRCULATORY SYSTEM IN MAMMALS, Meaning: circulatory system refers to the continuous movement or flow of the blood around the body involving the heart and the blood vessels.  

The circulatory system, also known as the cardiovascular system, is a vital organ system responsible for transporting blood, nutrients, gases, hormones, and waste products throughout the body. It consists of the heart, blood vessels (arteries, veins, and capillaries), and blood.

The heart acts as the central pumping organ of the circulatory system. It receives deoxygenated blood from the body through the veins and pumps it to the lungs for oxygenation. Oxygenated blood then returns to the heart and is pumped out to the rest of the body through arteries, providing oxygen and nutrients to the body\’s tissues and organs.

Arteries are the blood vessels that carry oxygenated blood away from the heart. They have thick, elastic walls that help maintain blood pressure and withstand the force generated by the heart\’s contractions. As arteries branch out into smaller vessels called arterioles, they eventually lead to the smallest blood vessels called capillaries.

Capillaries are thin-walled vessels where the exchange of oxygen, nutrients, and waste products occurs between the blood and surrounding tissues. Oxygen and nutrients are released into the tissues, while waste products such as carbon dioxide and metabolic byproducts are collected by the capillaries to be transported away.

After passing through the capillaries, blood enters the venous system. Veins are the blood vessels that carry deoxygenated blood back to the heart. They have thinner walls than arteries and rely on valves and the contraction of surrounding muscles to prevent blood from flowing backward.

Types of circulatory system

Circulatory systems in animals can grouped into three major categories:
(a) Closed and opened circulatory systems,
(b) Single and double circulatory systems
(c) Pulmonary and systemic circulatory systems.

closed and opened circulatory systems

Closed and opened circulatory system: the closed circulatory systems are made up of blood vessels called arteries from the heart which branch many times into small units called capillaries but eventually join up with other vessels called veins that are connected to the heart.

By this design, blood is therefore always confined within the cell of the body. Some invertebrates like annelids and all vertebrates have closed circulatory systems.

In mammals, for example, there is no mixing of oxygenated and deoxygenated blood in the heart. While oxygenated blood is confined to the left part of the heart, deoxygenated blood is confined to the right side.

Open circulatory system:

in this system, the blood vessels lead out of the heart but end in blood spaces called haemocoel within the body cavity. In these spaces, the blood comes into direct contact with the cells after which it is returned to the heart. Arthropods and some Molluscs have open circulatory systems.

The single and double circulatory systems in mammals

(i) Single circulatory system: in a double circulatory system, the blood only passes through the heart twice every time it makes one complete movement around the body.

Each time the blood passes through the heart, it goes through a separate pathway. This system is common in fish which has only two-chambered heart–one auricle and one ventricle. read more about fishery here

(ii) Double circulatory system:

in a double circulatory system, the blood passes through the heart twice every time it makes one complete movement around the body. Each time the blood passes through the heart, it goes through a separate pathway.

This is found in mammals. The double circulation gives rise to the two pathways involved in a double circulatory system called pulmonary and systemic circulation.

differences between diffusion and circulatory system

Diffusion
1. It occurs mainly in small organisms
2. It takes place at a slow rate.
3. It is less efficient.
4. It does not require the expenditure of energy

Circulatory system

1. It occurs in multicellular organisms.
2. It takes place at a faster rate.
3. It is more efficient.
4. It requires the expenditure of more energy.

differences between open system and close system of blood circulation

Open system
1. Blood bathes the major organ

and tissues directly  

1. There are no small vessels or capillaries connecting arteries with veins
2. It is found in some Molluscs arthropods and lower
3. Blood returns directly to the heart
4. The blood ends up in blood spaces (haemocoels) within the body
   Closed system  what-is-poikilothermic-animal-and-homoiothermic-animals
5. Fluids with nutrients get to the body tissues from the capillaries as tissue fluids and lymph
6. Smaller blood capillaries unite the small arteries with the veins
7. It is found in annelids, vertebrates and some invertebrates
8. Blood returns to the heart through the veins.
9. Blood flows via the arteries, veins and capillaries

Pulmonary and systemic circulation

1. Pulmonary circulation: the pulmonary circulation involves the movement of blood between the heart and the lungs. In other words, it involves the movement of blood from the heart to the lungs for oxygenation.

Systemic circulation in mammals

: the systemic circulation involves the movement of blood between the heart and all other part of the body besides the lungs.

In one complete circulation, blood from any part of the body enters the heart for the first time, it is then sent to the lungs for oxygenation.

From the lungs, it is brought back to the heart for the second time before it can be redistributed to all parts of the body. This is the sequence involve in double circulation

Pulmonary and systemic circulation can be represented mathematically by linear equation as: pulmonary circulation= heart + lungs    

Systemic circulation= heart + body

The appearance of the heart twice in the two equations represents the double circulation of blood in animals.
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