Blood: Definition, Composition, Types of cells, Vessels and Sample Questions

Blood is a vital component of living organisms. It is a connective tissue consisting of blood cells, platelets, and plasma. Any organism having a circulatory system has blood which aids in various life process. It has two types of cells known as red blood cells and white blood cells. In this article, we will explore the types of blood cells, the composition of blood, and blood vessels.

Composition of Blood

Blood is composed of the below-mentioned parts:

• Plasma
• Blood Cells
• Platelets

Plasma

Plasma is the liquid part of the blood that contains 90% of water. For the existence of every living cell, water is necessary. It also makes the exchange of fluids and other extracellular fluids easier, so that all tissues remain hydrated.

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Blood Cells

Blood consists of various blood cells. Each cell has its own functions in the body. 

Platelets

Platelets are tiny cells that are disc-shaped. They help in the regulation of blood flow when a body part is damaged. It aids fast recovery of any part of the body where the loss of blood is happening.

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Types of Blood Cells

The two types of blood cells present in the body are:

1. RBC (Red Blood Cells)

These are also known as Erythrocytes. RBC’s are biconcave and they are present without a nucleus in human beings. RBCs contain Haemoglobin which is an iron-rich protein due to which the color of blood is red. RBC’s are produced in the bone marrow which is mainly responsible for the transportation of oxygen to and from various tissues and organs present in the human body.

2. WBC(White Blood Cells)

These are also known as Leucocytes and they are colorless blood cells due to the absence of hemoglobin. WBC’s are further divided into two categories: granulocytes and agranulocytes. They are mainly responsible for providing immunity and maintaining defense mechanisms in the human body.

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Types of WBC’s

WBC’s are further divided into 2 categories which are classified on the presence and absence of granules.

1. Granulocytes
2. Agranulocytes

1. Granulocytes

These are the type of WBC’s that have granules in their cytoplasm. The granulated cells include below:

• Eosinophils

1.  These leucocytes are present in the immune system.
2.  These cells help to fight infections and allergies.
3. These cells are produced in the bone marrow which constitutes 2 to 3% of WBC’s. Maximum cells are present in the food pipe.

• Basophils 

1.  These are present in less number and constitute only 0.5 to 1% of WBC’s.
2. They release anti-allergic enzymes like histamine, serotonin, and heparin and helps in fighting parasites.
3. They play a vital role in fighting Asthma.

• Neutrophils 

1. They are present in the bloodstream and are cells that are predominantly present in pus.
2. These constitute about 60 to 65% of the whole WBC’s present in the human body.
3. They act as oxidants which helps in the destruction of bacteria.
4. These are the first cells to respond to any pathogens.
5. They have a lifespan of up to 8 hours and are produced every day in the bone marrow.

2. Agranulocytes

These are the type of WBC’s which do not have granules in their cytoplasm. Agranulocytes are further classified into below:-

• Monocytes

1. These have a single bean shared nucleus.
2. They help in removing dead cells and help in destroying pathogens that can cause blood-related infections. That’s they are also known as garbage trucks of the immune system.

• Lymphocytes

1. They are known as natural killer cells because they play a major role in producing antibodies.
2. Two types of lymphocytes exist in the human body

- B- Lymphocytes

- T- Lymphocytes

Types of Blood Cells

Platelets 

1. These are also known as thrombocytes
2. They help when there is bleeding in any part of the human body and loss of blood is more.
3. They play a major role in the coagulation of blood.

Blood Vessels

Blood vessels are responsible for carrying out the circulation process in all parts of the human body.

The three types of blood vessels that exist in our human body are as follows:

1. Arteries: These are responsible for carrying oxygen-rich blood from the heart and circulating the same to all parts of the human body.
2. Veins: These are responsible for carrying out deoxygenated blood from all parts of the body to the heart.
3. Capillaries: For transporting blood in tissues, blood vessels are further divided into thin tubes which are called capillaries.

 

Layers of Blood Vessels

There are three types of layers present in both arteries and veins.

• Tunica Intima – These are the thinnest and innermost layers present in arteries and veins which are in direct contact with blood.
• Tunica Media – This is the second layer in arteries and veins which is made up of smooth muscles.
• Tunica Externa- This layer surrounds tunica media which is made up of collagen.

Blood Vessels

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Things to Remember

• Blood is a fluid-like structure that is responsible for transporting oxygen and other nutrients to all the cells of the body.
• Blood is composed of plasma, blood cells, and platelets.
• There are two types of blood cells: white blood cells and red blood cells.
• Plasma is the liquid part of the blood that contains 90% of water.
• Platelets help in the regulation of blood flow when a body part is damaged.
• RBCs contain Haemoglobin which is an iron-rich protein due to which the color of blood is red.
• WBCs are mainly responsible for providing immunity and maintaining defense mechanisms in the human body.
• Blood vessels are responsible for carrying out the circulation process in all parts of the human body.

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Sample Questions 

Ques. How many types of blood groups exist in the human body? (1 mark)

Ans. There are four types of blood groups present in the blood of the human body.

• A
• B
• AB
• O

Ques. Which blood group is known as universal donor and universal acceptor? (2 marks)

Ans. Blood O is known as a universal donor which means a person having blood group O can give blood to persons possessing any blood group.

Blood group AB is a universal acceptor which can take blood from any person possessing any of the mentioned blood groups like A, B, AB, O.

Ques. Why do arteries have a thick and elastic-natured wall? (2 marks)  

Ans. Arteries are having very thick and elastic walls because they need to carry blood that is flowing with high pressure due to the heart-pumping action.

Ques. What are red and white blood cells? (2 marks)

Ans. Red Blood Cells: RBCs are biconcave. They contain Haemoglobin. RBC’s are produced in the bone marrow and are mainly responsible for the transportation of oxygen to and from various tissues and organs present in the human body.

White Blood Cells: These are colorless blood cells due to the absence of hemoglobin. WBC’s are further divided into two categories: granulocytes and agranulocytes. They are responsible for providing immunity and maintaining defense mechanisms in the human body.

Ques. What are the three types of blood vessels present in the human body? (3 marks)

Ans. 1) Arteries: They carry oxygen-rich blood from the heart and circulate it to all parts of the human body.

2) Veins: They carry out deoxygenated blood from all parts of the body to the heart.

3) Capillaries: For transporting blood in tissues, blood vessels are further divided into thin tubes which are called capillaries.