Blood: Every animal has a circulatory system, hence blood is present in them. Blood is the crimson fluid that comes out of our bodies when we are wounded or harmed. Blood is a type of liquid connective tissue that assists in the transmission of oxygen and nutrients to cells as well as the removal of carbon dioxide and other waste items. We will learn more about the components, kinds, and functions of blood in this article. Continue reading to learn more interesting details.

What is Blood?

Blood is a fluid connective tissue that consists of blood cells, plasma and platelets. It circulating through blood vessels delivers oxygen and nutrients to various cells and tissues. It forms about \(8\) to \(10\% \) of our body weight.

Composition of Blood

Blood consists of two major parts:

1. Plasma, which is nearly \(55\) to \(58\% \).
2. Formed (cellular) elements or blood corpuscles which are nearly \(42\) to \(45\% \).

Plasma is the liquid portion of blood. Plasma is a straw-coloured fluid part of the blood that forms \(55 – 58\% \) of total blood. It is slightly heavier than water.

This has the following composition:

1. \(90\% \) of the plasma is water.
2. \(7\) to \(8\% \) of proteins are present, which includes Albumin, Globulin, Antibodies, Fibrinogen, Prothrombin, etc.
3. \(1\% \) salts are present which include \(N{a^ + },{\rm{ }}{K^ + },{\rm{ }}HC{O_3}^ – ,{\rm{ }}C{l^ – },\) etc.
4. There are soluble gases, like oxygen and carbon dioxide.
5. There is glucose, hormones, amino acids, etc.

Types of Blood

1. Formed (cellular) elements, i.e., shaped structures visible under the microscope, are cells and cell-like structures present in the blood. They form \(42 – 45\% \)of blood.

These are of three types, i.e.,

1. Red Blood Cells or RBCs
2. White Blood Cells
3. Blood Platelets

Red Blood Cells

1. Red Blood Cells (RBCs) are also known as erythrocytes. They contain a complex chemical compound called haemoglobin which has iron.
2. Haemoglobin combines with an oxygen molecule to form oxyhaemoglobin, and it delivers the bound oxygen to cells.
3. The red colour of erythrocytes is because of this iron-containing compound haemoglobin.
4. The mature red blood cells are minute, biconcave and disc-shaped. It is the haemoglobin in the RBCs which makes it possible for the blood to act as a carrier of oxygen from the lungs to the tissues.
5. Mature RBCs in human beings do not have a nucleus. They lose their nuclei to increase the space for haemoglobin and thus oxygen.
6. They are made inside the bone marrow and are destroyed by the liver when they die. They have a lifespan of \(100 – 120\) days.
7. They are disc-shaped and can fold and bend when forced through the smallest blood vessels.

White Blood Cells

1. White Blood Cells (WBCs) are also known as leukocytes. These blood cells fight against pathogens and other foreign bodies and thus protect our bodies from diseases.
2. White blood cells are colourless, and they have a nucleus. They are larger than RBCs but are fewer in number.
3. There are about \(5000\) to \(7000\) WBCs present in \(1\) cubic millimetres of blood. Many of the WBCs are made in the bone marrow.
4. Depending on the type, they live from a few hours to many days.
5. When they travel along in the blood, they are spherical, but they flatten and continuously change their shape along the inner walls of the blood vessels.
6. They show amoeboid movements, which help them squeeze out of capillaries into tissues, and the process is known as diapedesis.

Based on the presence and absence of granular structure in the cytoplasm, WBCs are classified into two types, i.e., Agranulocytes and Granulocytes.

Agranulocytes

These WBCs have no granules in the cytoplasm and are produced in the bone marrow. These are of two types:

1. Lymphocytes – which have a round or oval-shaped nucleus.
2. Monocytes – which have a bean-shaped or kidney-shaped nucleus.

Granulocytes

These WBCs have larger granules in the cytoplasm and have a lobed nucleus.

These are of three types:

1. Neutrophils – \(3\) to \(5\) lobes of the nucleus.
2. Basophils – the nucleus is coiled or S-shaped.
3. Eosinophiles – \(2\) lobed, i.e., bilobed.

Blood Platelets

1. Platelets are also known as Thrombocytes. These platelets help in preventing the loss of blood from our body as they cause clotting of blood at the site of injury.
2. They are also made in the bone marrow and have a lifespan of \(8\) to \(14\)days. There are about \(2.5\) lakh blood platelets in \(1\) cubic millimetres of blood.

Blood Vessels

Blood vessels are the channels through which blood is distributed to body tissues. Blood flow in the blood vessels which are of the following three types:

1. Arteries
2. Veins
3. Capillaries

Arteries

1. Arteries are vessels that carry blood away from the heart, i.e., these blood vessels carry oxygen-rich blood from the heart to all the tissues of the body. All arteries except pulmonary arteries carry pure blood.
2. They are elastic with a narrow lumen. Arteries branch into small arteries called arterioles and end in capillaries.

Veins

1. Veins bring blood back to the heart, i.e., which carry deoxygenated blood from all body parts to the heart. All veins except pulmonary veins carry impure blood.
2. Veins are less elastic with the wider lumen and are superficially situated, which can be seen from the skin’s surface.
3. The small veins are called venules formed from capillaries and join to form veins. The veins have pocket shaped valves to prevent the backflow of blood, and the blood flows smoothly through the veins.

Capillaries

1. Capillaries are fine vessels that connect the arteries and veins.
2. Arteries branch to form arterioles. Arterioles further branch to form capillaries. Capillaries reunite to form the venules and unite to form the vein.
3. The wall of capillaries is formed of a single layer of endothelial cells, which lies in close contact with the body tissues.

Functions of Blood

Blood is a liquid connective tissue. The main functions of the blood in our body can be treated under the following types, i.e., Transport and Protection.

A. Transport by Blood

1. Transport of oxygen from lungs to the tissues. It occurs through red blood cells in combination with haemoglobin in the form of unstable compound oxyhaemoglobin, which breaks up to deliver oxygen on reaching the tissues.
2. Transport of digested food from the alimentary canal to the tissues. These substances are simple sugars like glucose, vitamins, mineral salts, amino acids, etc.
3. Transport of carbon dioxide from the tissues to the lungs. It occurs partly in combination with haemoglobin and partly as a solution in blood plasma.
4. Distribution of hormones- Blood carries hormones secreted by the endocrine glands to different body organs.
5. Transport of excretory –Blood carries a waste product called urea from the liver to the kidneys for excretion in urine.
6. Distribution of heat- Blood helps regulate the body temperature by absorbing or releasing heat, known as homeostasis.

B. Protection by Blood

1. Blood contains WBCs, which protect the body from many infectious diseases by engulfing bacteria that may have entered the body.
2. Blood also produces antitoxins and antibodies, which neutralise the poisonous substances or kill the germs which enter the body.
3. Blood contains platelets that form a clot around any injuries or wounds, thus preventing blood loss and entring disease-causing germs.

Blood Groups

The genetically determined system by which blood can be classified into different groups according to the presence or absence of agglutinogen, i.e., antigens on the surface of RBCs and the antibody in the blood plasma, is called the blood grouping system.

The blood groups are classified into two types, i.e., ABO blood groups and Rh blood group systems.

Blood Clotting

Blood clotting, which also refers to hemostasis, is the formation of a gel-like or clot-like structure, preventing bleeding or loss of blood, i.e., haemorrhage in cases of injured blood vessels. It also occured in a blood sample drawn from the body and kept in a plain test tube or a vial.

The straw-coloured liquid, called serum, refers to plasma minus blood coagulation factors. The gel or a clot consists of a network of insoluble protein fibres called fibrin, in which the formed elements of blood get entrapped. Blood clotting, coagulation, or the process of gel formation, consists of a series of chemical reactions to result in the formation of a fibrin network.

Related Topics to study

1. Blood Groups 2. Clotting of Blood 3. Blood Vessels 4. Structure of Blood Vessels

Summary

Blood is a bodily function that transports life-sustaining elements to the body’s cells in humans and other animals. Because it comprises numerous types of cells that conduct intricate roles for the human body, it is frequently referred to as a fluid “tissue.”

Through this article, we understand that Blood is very important for us as it plays an important role in the transportation and helps confer immunity. Blood carries oxygen and glucose, and it takes away carbon dioxide. Plasma and formed elements are the two components of blood. Several blood cells help in the body’s protection.  Blood is required for survival and to stay healthy and strong.

FAQs on Blood

Q.3: What are the 4 components of blood?
Ans: The 4 major components of blood are plasma, red blood cells, white blood cells, and platelets.

Q.4: What does healthy blood look like?
Ans: In normal healthy blood, if a smear is taken, red blood cells will appear as regular and round cells with a pale centre.

Q.5: What is inside the blood?
Ans: The blood is made up of plasma and formed elements like RBCs, WBCs, and platelets.

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