Connective Tissue.

 Tissue level of organization: Connective Tissue.

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Introduction:

• Groups of cells having similar structure and performing similar functions are called “Tissue.”

• Connective tissue is the most abundant tissue in the body. 

• The connective tissue cells are more widely separated from each other than in epithelial tissues, and the intercellular substance (matrix) is present in considerably larger amounts.

• There are usually fibres present in the matrix, which may be of a semisolid jelly-like consistency or dense and rigid, depending upon the position and function of thentissue.

• The fibres form a supporting network for the cells to attach to. 

• Most types of connective tissues have a good blood supply. 

Basic functions of Connective Tissue.

1. Binding 

2. Structural support

3. Protection

4. Transport

5. Insulation.

Important Cells found in Connective Tissue:

1. Fibroblasts:

• Also called “Fibrocytes”.

• Large cells.

• Produce collagen and elastic fibers.

      B) Fat Cells:

• Also called Adipocytes.

• Occurs as a single cell or in groups.

• Size varies as per amount of fat present inside the cell.

     C) Macrophages:

• These are irregular-shaped cells with granules in the cytoplasm.

• Their basic job is eating and digesting foregin substances.

    D) Leukocytes:

• Normally they are very less in numbers in normal conditions.

• Infections trigger their entry in large numbers in the tissue.

    E) Mast Cells:

• These cells contain large quantities of ‘Histamine” the chemical responsible for many allergies.

Classification of Connective Tissues:

1. Loose Connective Tissue:

1. Areolar Connective Tissue.

2. Adipose Tissue.

1. White Adipose Tissue.

2. Brown Adipose Tissue.

3. Reticular Connective Tissue.

2. Dense Connective Tissue:

1. Fibrous Connective Tissue.

2. Elastic Connective Tissue.

3. Cartilage.

1. Hyaline Cartilage

2. Fibrous Cartilage

3. Elastic Fibrocartilage.

4. Bones:

1. Compact Bones.

2. Spongy Bones.

Areolar Connective Tissue:

• This is the most common type of connective tissue. 

• The matrix is semi solid and contains many cells like fibroblasts, macrophages, adipocytes etc. 

• It is found in almost every part of the body. 

• It connects and supports other tissues,

• It is present under the skin between muscles

• Supporting blood vessels and nerves

• In the alimentary canal

• In glands supporting secretory cells.

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Adipose Tissue:

• Adipose tissue consists of fat cells (adipocytes), containing large fat globules, in a matrix of areolar tissue. 

• There are two types: white and brown.

Reticular Connective Tissue:

• Also called as “Lymphoid Tissue”.

• It contains a semisolid matrix with fine branching reticulin fibres.

• It contains reticular cells and white blood cells (monocytes and lymphocytes). 

• Lymphoid tissue is found in lymph nodes and all organs of the lymphatic system.

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Dense Connective Tissue:

1. Fibrous Connective Tissue:

• This tissue is made up mainly of closely packed bundles of collagen fibres with very little matrix.

• Fibrocytes (old and inactive fibroblasts) are few in number and are found lying in rows between the bundles of fibres. 

• Fibrous tissue is found:

• forming ligaments, which bind bones together

• as an outer protective covering for bone, called periosteum

• as an outer protective covering of some organs, e.g. the kidneys, lymph nodes and the brain

2. Elastic Connective Tissue:

• Elastic tissue is capable of considerable extension and recoil. 

• There are few cells and the matrix consists mainly of masses of elastic fibres secreted by fibroblasts. 

• It is found in organs where stretching or alteration of shape is required, e.g. in large blood vessel walls, the trachea and bronchi and the lungs.

3. Cartilage Tissue: 

• Cartilage is firmer than other connective tissues. 

• The cells are called chondrocytes and are less in numbers. 

• Matrix contains a high amount of collagen and elastic fibres. 

• There are three types: 

• Hyaline cartilage, 

• Fibrocartilage

• Elastic fibrocartilage.

1. Hyaline cartilage:

• It is a smooth bluish-white tissue. 

• The chondrocytes are in small groups within cell nests (Pockets).

• The matrix is solid and smooth. 

• Hyaline cartilage provides flexibility, support and smooth surfaces for movement at joints. 

• It is found:

• on the ends of long bones that form joints

• forming the costal cartilages, which attach the ribs to the sternum

• forming part of the larynx, trachea and bronchi.

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2. Fibrocartilage:

• This consists of dense masses of white collagen fibres in a matrix similar to that of hyaline cartilage

• The cells widely dispersed. 

• It is a tough, slightly flexible, supporting tissue found:as pads between the bodies of the vertebrae: the intervertebral discs.

3. Elastic fibrocartilage:

• This flexible tissue consists of yellow elastic fibres lying in a solid matrix. 

• The chondrocytes lie between the fibres. 

• It provides support and maintains the shape of, e.g. the pinna or lobe of the ear, the epiglottis and part of the tunica media of blood vessel walls.

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D) Bone:

• It is the toughest connective tissue.

• Bone cells (osteocytes) are surrounded by a matrix of collagen fibres strengthened by inorganic salts, especially calcium and phosphate. 

• Two types of bone can be identified by the naked eye:

• compact bone – solid or dense appearance

• spongy or cancellous bone – ‘spongy’ or fine honeycomb appearance.

Commonly Asked Questions.

1. Define Tissue and explain in detail Connective Tissue.

2. Write a short note on “Cartilage Tissue”.