Connective Tissues and its Type

The cells of connective tissue are loosely spaced and embedded into a noncellular matrix. The matrix may be solid (as in bone), soft (as in loose connective tissue), or liquid (as in blood).

The most abundant tissue in our body is connective tissue. 

On the basis of nature of matrix, major types of connective tissue are: 

(i) Loose/areolar connective tissue

(ii) Adipose tissue

(iii) Fluid/vascular connective tissue

(iv) Fibrous / Dense regular connective tissue

(v) Skeletal connective tissue

1.0Loose Connective Tissue

The simplest and most widely distributed connective tissue is Areolar Loose connective tissue. Loose connective tissue is a mass of widely scattered cells whose matrix is a loose weave of fibres. 

Many of the fibres are strong protein fibres called collagen. Loose connective tissue is found beneath the skin and between organs. It is a binding and packing material whose main purpose is to provide support to hold other tissues and organs in place.

2.0Adipose Tissue

It consists of adipose cells (Adipocytes) filled with fat globules in loose connective tissue. Each adipose cell stores a large droplet of fat that swells when fat is stored and shrinks when fat is used to provide energy. Adipose tissue pads and insulates the animal body. The layer of adipose tissue found in whale is known as blubber. The hump of camel is also rich in adipose tissue.

3.0Fluid/Vascular Connective Tissue

It is a special type of connective tissue which maintains link among different parts of the body. It receives materials from certain parts of the body and transports them to the other parts. It constitutes the transport system of animals. It consists of two basic components – blood and lymph.

Blood

Blood is a connective tissue of cells separated by liquid matrix called plasma. It lacks fibres in its matrix.  Blood constitutes 55 percent of plasma and 45 percent blood corpuscles. Plasma contains water, salts, sugars, lipids, amino acids etc.

Blood corpuscles are of 3 types :

(i) Red blood cells or erythrocytes.

(ii) White blood cells or leucocytes.

(iii) Platelets or thrombocytes. 

Blood Cells

Components	Erythrocytes (RBCs)	Leucocytes (WBCs)	Platelets
Number per mm3 of blood	5-6 million	5,000-10,000	2,50,000-4,00,000
Function	Transport oxygen and carbon dioxide	Destroy foreign cells, produce antibodies, roles in allergic responses	Blood clotting

Functions of blood

(i) It transports nutrients, hormones and vitamins to the tissues and carries excretory products from the tissues to the excretory organs.

(ii) The RBCs of blood helps in the transport of respiratory gases, oxygen & CO₂.

(iii) The WBCs fight with diseases by producing antibodies and engulfing the germs (antigens). Neutrophils are polynuclear leucocytes.

(iv) Blood platelets helps in the clotting of blood.

(v) Blood helps in thermoregulation, water balance and maintenance of pH of body.

In human, RBCs are small, circular, biconcave & disc shaped and lack nuclei when mature.

Heparin is a natural anti-coagulant in our blood that prevents the blood from clotting inside the blood vessels.

Lymph

Lymph is actually filtered blood which is similar to blood in composition except that it is devoid of RBC, platelets and some blood protein. WBCs are present in abundance in lymph. Due to the absence of haemoglobin, lymph is colourless. 

Functions of lymph

(i) Helps in the transport of nutrients. Nutrients that filter out from blood capillaries into lymph are transported back by lymph into blood through heart.

(ii) Helps in the transportation of fat absorbed from intestine to the blood.

(iii) Keeps the tissues and organs of the body moist.

(iv) Lymphatic organs (lymph nodes, spleen) produce lymphocytes which in turn produce antibodies to strengthen the immune system of the body.

4.0Fibrous/Dense Regular Connective Tissue

This tissue consists mainly of fibres. The fibres are of two types:

Collagen white fibres

The dominance of the (white inelastic) collagen fibres contribute to the considerable mechanical strength of white fibrous tissue.

Elastin yellow fibres

It can stretch upto one and a half times their length then snaps back to its original length when relaxed. 

Dense regular connective tissue occurs in two forms.

(a) Tendons

These are cords of dense (white fibres) connective tissue that attach skeletal muscles to bones. They have great strength, but its flexibility is limited.

(b) Ligaments

These are cords of yellow fibrous connective tissue containing elastin and collagen fibres having little matrix that connect one bone to the another.

Excessive pulling or overstretching of ligaments produces sprain.

5.0Skeletal Connective Tissue

It mainly consists of bones and cartilages, that provide a strong supportive framework for the body. In this connective tissue, the matrix contains numerous fibres and in some cases deposits of insoluble calcium salts.

Bone

It is a rigid connective tissue that has a matrix of collagen fibres and salt of calcium and phosphorous compounds, giving it greater rigidity and strength. Most of the skeletal system is comprised of bone. Bone is the hardest tissue of our body but the hardest substance in our body is enamel, found as covering on teeth. Haversian system are the structural units of mammalian bone. It consists of Haversian canals, Haversian lamellae and osteocyte. 

Functions of bones

(i) It provides support for muscle attachment.

(ii) It protects the internal organs from mechanical injury.

(iii) It serves as a reservoir for calcium.

Immature bone cells are called osteoblast, mature bone cells are called osteocytes, immature cartilage cells are called chondroblast, mature cartilage cells are called chondrocytes. Bone destroying cells are called osteoclast, cartilage destroying cells are called chondroclast.

Cartilage

It is a connective tissue with an abundant number of collagen fibres in a rubbery matrix. The matrix is made up of proteins and sugars. It is both strong and flexible but softer than bone. It forms the embryonic skeleton of vertebrates and the adult skeleton of sharks and rays. It also occurs in the human body in the ear pinna, tip of the nose, trachea, larynx and surrounding ends of joints such as knees.

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