Theory:

What are the main characteristics of connective tissue?
  • It arises from the mesoderm of the embryo.
  • It has elements such as matrix, fibres and cells.
There is a connective tissue that is in the form of fluid and has the above-mentioned characteristics.
  • It also arises from the mesoderm of the embryo.
  • It has a non-living fluid matrix called plasma.
  • It has soluble protein molecules as fibres.
  • It also has different types of cells.
Hence this tissue is called fluid connective tissue. We call it "blood".
Blood - a liquid connective tissue:
 It is a fluid connective tissue that connects various parts of the body. It helps to maintain the continuity of the body. It contains a liquid matrix called plasma, blood cells like RBCs (Red blood corpuscles), WBCs (White blood corpuscles) and platelets suspended in it. Plasma is a pale yellow colour fluid. It contains proteins, water, salt and enzymes.
  • It transports nutritive materials, gases, vitamins and hormones to tissues present all around the body.
  • It carries waste products from tissues to excretory organs like the liver and kidney.
  • It also conducts heat and maintains the body temperature.
Blood has mainly two components,
  1. Blood plasma
  2. Blood corpuscles
Screenshot 2021-04-27 140817.jpg
Blood and its components
Blood plasma:
  • It is a transparent, clear fluid with pale yellow colour.
  • It contributes \(55-60%\) of blood and has \(90-92%\) of water.
  • Apart from water, it has inorganic salts such as sodium, potassium, magnesium and calcium.
Blood corpuscles:
Blood cells or corpuscles are one of the elements of the blood. It contributes \(40-45%\) of blood and is heavier than plasma.
It is of three types.
  1. Red blood corpuscles or erythrocytes
  2. White blood corpuscles or leukocytes
  3. Blood platelets or thrombocytes
shutterstock_741666913.jpg
Types of blood cells
1. Red blood corpuscles:
The red blood cell contains a pigment called haemoglobin, and due to that, blood is red.
  • The life span of RBC is \(120\) days.
  • Mature RBC do not contain a nucleus.
  • Most of the cell organelles like mitochondria and lysosomes are absent in these cells.
  • The shape of the RBC is known to be a biconcave disc.
  • Red blood cells, also termed erythrocytes, play a critical role in transporting gases such as oxygen from the lungs. They also aid in carbon dioxide transport from tissues to the lungs.
Important!
Note:
  • In humans, RBCs are smaller than WBCs. RBCs are \(7.2 µm\) in diameter.
  • Per cubic mm of blood contains about \(5.5\) and \(4.5 million\) RBCs for a normal adult man and woman, respectively.
  • A decrease in RBC count results in a condition called anaemia.
  • An increase in RBC count results in a condition called polycythemia.
2. White blood corpuscles:
  • It is colourless.
  • It is irregular in shape.
  • The life span of WBC is \(13\) to \(20\) days.
  • WBCs are also called leucocytes.
  • WBC contain nucleus and cell organelles like ER, golgi apparatus and mitochondria.
  • WBCs are larger than RBCs but smaller in number.
  • Per cubic mm of blood contains \(5000\) to \(9000\) WBCs are present in human.
  • There are five different types of cells (WBC) are there. i.e. monocytes, lymphocytes, neutrophils, basophils and eosinophils.
shutterstock_387954859.jpg
Different types of white blood cells
 
Leucocytes are of two types: 

A. Granulocytes (with granules in the cytoplasm)
B. Agranulocytes (without granules in the cytoplasm)
A. Granulocytes:
They have irregularly shaped nuclei and small cytoplasmic granules. The specific types of granulocytes are basophils, neutrophils and eosinophils.

a. Eosinophils:
  • It makes \(1-2%\) of total leucocytes count, i.e., \(70-300 cells per cubic mm\) of blood.
  • It has a bi-lobed nucleus.
  • Granules of these cells are the largest among all components of leucocytes.
Function: It plays an essential role in immunity, allergy and hypersensitive reactions.
b. Basophils:
  • It makes \(0.5-2.7%\) of leucocytes count. i.e., \(35-150 cells per cubic mm\) of blood.
  • It has an S-shaped nucleus with two or three lobes.
  • It constitutes the mast cells which consists of heparin and histamine.
  • It is the least component present in leucocytes based on count.
c. Neutrophils:
  • It makes \(60 - 70%\) of total leucocytes. i.e., \(4000-5000 cells per cubic mm\) of blood.
  • It has two to five-lobed nucleus.
  • Granules of these cells are the smallest among all components of leucocytes.
  • It is the highest component present in leucocytes based on count.
B. Agranulocytes:
 They do not have distinct cytoplasmic granules. The specific types of agranulocytes are lymphocytes and monocytes. 
 
a. Lymphocytes: It has a spherical cell and less motile.
 
Function: Responsible for the production of antibodies.
b. Monocytes: It is the largest white blood cell and has a large nucleus indented on one side (horse-shoe shaped). Cells are actively motile and phagocytic.
Function: White blood cells are a major part of the immune system, helping the body fight against disease-causing pathogens by producing antibodies.
Important!
Do you know!
  • A decrease in WBC count in the blood creates a condition called leukopenia.
  • An increase in WBC count in the blood creates a condition called leukaemia (cancer of the blood).
  • Monocytes are the largest cell of white blood cell, while lymphocytes are the smallest.