10. Animal Tissue - part 03 -Connective tissue

 

10. Animal Tissue - part 03 -Connective tissue

Connective tissue : 

• It is most widely spread tissue in the body. 
• It binds, supports and provides strength to other body tissues and organs. 
• It consists of a variety of cells and fibres. 
• These are embedded in the abundant intercellular substance called matrix.
• Connective tissue protects the vital organs of the body. 
• It is highly vascular except cartilage.
• It acts as packing material and also helps in healing process.

Connective tissue is classified on the basis of matrix present, as-

1. connective tissue proper
2. supporting connective tissue and 
3. fluid connective tissue. 

Connective tissue proper is further classified as -

1. loose connective tissue (ex. areolar connective tissue and adipose tissue) and 
2. dense connective tissue (ex. ligament and tendon). 

Supporting connective tissue also called skeletal tissue includes -

1.  cartilage and
2. bone. 

Fluid connective tissue includes -

1. blood and 
2. lymph

A. Connective Tissue Proper :
a. Loose connective tissue : 

• Matrix of loose connective tissue is semisolid, jelly like, viscous matter made up of gelatin.

1. Areolar tissue (Areola : air pockets):

• Matrix of this tissue contains two types of fibres namely -

1.  white fibres and 
2. yellow fibres.

White fibres -

• are made up of collagen. 
• They give tensile strength to the tissue. 

Yellow fibres

• are made up of elastin and are elastic in nature.
• The tissue also contains four different types of cells -

1. Fibroblast 
2. Mast cells
3. Macrophages 
4. Fat cells

• Fibroblast the large flat cells having branching processes. They produce fibres as well as polysaccharides that form the ground substance or matrix of the tissue. 
• Mast cells are oval cells that secrete heparin and histamine.
• Macrophages are amoeboid, phagocytic cells.
• Fat cells, also called adipocytes have eccentric nucleus. These cells store fat. 

• This tissue acts as packing material, helps in healing process and connects different organs or layers of tissues. 
• It is found under the skin, between muscles, bones, around organs, blood vessels and peritoneum.

2. Adipose tissue (adipo : fat) : 

• In this tissue large number of adipocytes are present.
• Cells are rounded or polygonal. 
• Nucleus is shifted to periphery because fats are stored in the cell in the form of droplets. 
• Matrix is less and fibres and blood vessels are few in number.
• There are two types of adipose tissue - 

1. white adipose tissue 
2. Brown adipose tissue

1. white adipose tissue

• appears opaque due to presence of large number of adipocytes.
• It is commonly seen in adults. 

2. Brown adipose tissue

• is reddish brown in colour due to presence of large number of blood vessels.

Function :

• Adipose tissue is a good insulator, acts as a shock absorber and a good source of energy because it stores fat. 
• The tissue is found in sole and palm region as well as around organs like kidney.

Achilles Tendon :

• Achilles Tendon connects the calf muscles to heel bone. 
• Pain at the back of ankle or lower calf may signal a problem with an Achilles Tendon. 
• Athletes who participate in track and field may face Achilles tendon injury. 
• Most tendon injuries occur near joints such as the shoulder, elbow, knee and ankle.

b. Dense Connective Tissue :

• In this tissue, fibres and fibroblasts are compactly arranged. 
• There are two types, namely -

1. dense regular tissue
2. dense irregular tissue.

Dense regular connective tissue :

• collagen fibres are arranged in parallel manner. 
• Two major examples of this tissue are -

1. tendons and 
2. ligaments. 

Tendons

•  connect skeletal muscles to bones. 
• To give tensile strength to the tissue, tendons contain bundles of white fibres.
• E.g. Achielles tendon, Hamstring tendon.

Ligaments

• Are made up of elastic or yellow fibres arranged in regular pattern. 
• These fibres make ligaments elastic. 
• They are present at joints. They prevent dislocation of bones.

 Dense irregular connective tissue :

•  fibres and fibroblast are not arranged in orderly manner. 
• This tissue is found in dermis of skin.

B. Supporting Connective Tissue

• It is characterized by presence of hard matrix. 
• It is classified into two types -

1. cartilage and 
2. bone.

Cartilage : 

• This is a pliable yet tough tissue.
• It forms endoskeleton of cartilagenous fishes like shark. 
• It is widely distributed in vertebrate animals. 
• In cartilage, abundant matrix is delimited by a sheath of collagenous fibres called perichondrium. 
• Matrix is called chondrin. 
• Just below the perichondrium, immature cartilage forming cells called chondroblast are present.
• Chondroblasts mature and get converted into chondrocytes. 
• Chondrocytes are seen scattered in the matrix. They are enclosed in lacunae.
• Each lacuna contains 2-8 chondrocytes.

Types of cartilage :  [Based upon the type of matrix]

1. Hyaline cartilage
2. Elastic cartilage 
3. Fibrocartilage
4. Calcified cartilage

1. Hyaline cartilage (Hyline : Glass like) : 

• In this type of cartilage, perichondrium is present.
• Matrix is bluish white and gel like. 
• Very fine collagen fibres and chondrocytes are present. 
• Hyaline cartilage is elastic and compressible in nature. 
• It acts as a good shock absorber as well as provide flexibility. It reduces friction. 
• It is found at the ends of long bones, epiglottis, trachea, ribs, larynx and hyoid.

2. Elastic cartilage : 

• In elastic cartilage perichondrium is present. 
• Matrix contain elastic fibres. 
• Chondrocytes are few in number.
• It gives support and maintains shape of the body part. 
• It is found in ear lobe, tip of nose, etc.

3. Fibrocartilage : 

• Perichondrium is absent in fibrocartilage. 
• Matrix contains bundles of collagen fibres and few chondrocytes, scattered in fibres. Fibrocartilage is most rigid cartilage.
• It maintains position of vertebrae. 
• Intervertebral discs are made up of fibrocartilage. 
• It is also found at pubic symphysis.

4. Calcified cartilage : 

• This type of cartilage becomes rigid due to deposition of salts in the matrix. This reduces flexibility of joints in old age 
• e.g. Head of long bones.

Bone : 

• Bone is characterised by hard matrix called Ossein. 
• Ossein is made up of mineral salt hydroxy-apatite (Ca10(PO4)6(OH)2). 
• Outer tough membrane called periosteum encloses the matrix. 
• Blood vessels and nerves pierce through periosteum. 
• Matrix is arranged in the form of concentric layers called lamellae.
• Each lamella contains fluid filled cavities called lacunae. 
• Fine canals that radiate from each lacuna are called canaliculi.
• Canaliculi of adjecent lamellae connect with each other as they traverse through the matrix.
• In the lacunae osteoblasts, active bone cells and osteocytes, the inactive bone cells and osteoclasts are present. 
• Mammalian bone shows peculiar haversian system. 
• Haversian canal encloses an artery, vein and nerves.

Types of bones : [According to presence of matrix]-

1. spongy bones
2. compact bones

1.Spongy bones  :

• haversian system is absent.
• Reticular matrix is arranged in the form of trabeculae. 
• It contains red bone marrow. 

2. Compact bones :

• matrix shows haversian system without any space between lamellae.

C. Fluid Connective tissue (Vascular)

• Blood and lymph are fluid connective tissue present in the body of an animal.