Circulatory System And Composition of Blood

Introduction of Circulatory System

It is very important for every living organism to get food and oxygen to survive, as well as remove excretory substances like carbon dioxide, ammonia, etc., as a result of metabolism. In large organisms, this work is done by a special type of transport system. This transport system works by transporting nutrients, gases, hormones, excretory substances, etc. from one place to another within the body. Apart from this, it is also helpful in regulating temperature in different parts of the body. Through this, the physical and chemical conditions of all the tissues of the body remain in a balanced state. This action is called homeostasis. Open in some animals and closed circulatory system is found in some. The liquid connective tissue in animals with an open circulatory system moves freely in the body cavity without any duct, but in animals with a closed circulatory system, fluid connective tissue like blood and lymph moves in different types of vessels in the body. A closed circulatory system is found in humans.

human circulatory system

The blood circulation system in humans was discovered by William Harvey. It is also called the cardiovascular system because the heart works by pumping blood into the blood vessels. There are 3 major parts of the human circulatory system-

a) Liquid connective tissue- Blood and Lymph

b) Vessels- Blood and Lymph vessels

c) Heart


Liquid connective tissue blood originates from the mesoderm of the fetus. It is heavier than water (density 1.04-1.04), viscous, salty in taste, mildly alkaline, and opaque. About 7 to 8% of the total weight of blood is found in the human body.


Composition of Blood in Human Circulatory System

It has two main components – 1: Plasma, 2: Blood cells

1: Plasma

Plasma forms about 55% of the total blood in it with 90% water and 10% complex organic (eg antibodies, glucose, amino acids, fatty acids, hormones, enzymes, vitamins, heparin, fibrinogen, prothrombin, albumin, Globulin, etc.) and inorganic substances (salts of sodium, potassium, calcium, phosphorus, iron, etc. and some gases such as oxygen, carbon dioxide, ammonia, etc.).

2: Blood cells

Blood corpuscles make up about 45% of the entire blood. It is mainly of three types:

types of blood cells

a: Red Blood Corpuscles (RBC):

These are red-colored, without a nucleus, and amphoteric corpuscles. Their quantity in the blood is about 45 to 55 lakhs per cubic millimeter. Their red color is due to the respiratory pigment called hemoglobin present in them. They act as transport of oxygen and carbon dioxide gases. Their normal life span is 120 days.

b) White Blood Corpuscles (WBC) or Leukocytes

These are irregular, nucleated, colorless corpuscles. Their lifespan is only 1 to 2 days. The number of these per cubic millimeter of blood is 5000 to 9000. They can come through the walls of blood capillaries. These are mainly of two types:

I: Granulated White Blood Corpuscles

Their cytoplasm is granular and the nucleus usually appears divided into two or more parts. Depending on the different types of stains, they are of the following three types:

I a: Acidophils or Eosinophils

It is about 2 to 4% of the total white blood cells and can be stained by acidic dyes (eg eosin). Their nucleus is divided into two lobes. At the time of infection of parasitic microbes, their number increases, causing a disease called Eosinophilia. They are helpful in providing immunity to the body and perform important functions in allergies and hypersensitivity.

I b: Basophils

These are 0.2% -0.5% of the total white blood particles. It accepts alkaline dyes (eg, methylene blue). Their nucleus is divided into two to three lobes and appears ‘S’ shaped. They secrete heparin, histamine, and serotonin substances which cause allergic reactions. They increase inflammation in tissues also.

I c: Neutrophils

They contain 60 to 70% of the white blood particles, they take all types of stainers. Their nucleus is divided into three to five lobes. They provide protection to the body by phagocytosis by eating germs.

II: Non-granulated White Blood Corpuscles

No granules are found in their cytoplasm. Their nucleus is round and does not divide into lobes. These are of two types:

II a: Lymphocytes:

They comprise 20 to 30% of the total white blood particles. These are the smallest white blood corpuscles in size with a large nucleus and deflated on one side. Their main function is to provide protection to the body by producing antibodies that destroy germs.

II b: Monocytes

They comprise 2 to 10% of the total white blood particles. Their nucleus is large and circular in shape. Their main function is to provide protection to the body by eating germs.

c: Blood Platelets

Their number varies from 2 to 5 lakhs per cubic millimeter of blood in humans. It is superfine centerless, oval, and flamboyant. It helps in clotting blood in case of injury.

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