Connective Tissue

• Connective tissues are most abundant and widespread in the body of complex animals and are named as connective tissues due to their special function of linking and supporting other tissues/organs of the body. They range from soft connective tissues to specialised types, which include cartilage, bone, adipose, and blood.

• In all connective tissues except blood, the cells secrete fibres of structural proteins called collagen or elastin. The fibres provide strength, elasticity and flexibility to the tissue. These cells also secrete modified polysaccharides, which accumulate between cells and fibres and act as matrix (ground substance). 

Connective tissues are of three types:

·        Loose connective tissue

·        Dense connective tissue

·        Specialised connective tissue

Loose connective tissue:

• Loose connective tissue has cells and fibres casually arranged in a semi-fluid ground substance, example, areolar tissue present underneath the skin. Often it assists as a support framework for epithelium. It comprises fibroblasts (cells that produce and secrete fibres), macrophages and mast cells.

Loose connective tissue : Areolar tissue

• Adipose tissue is another type of loose connective tissue located mostly beneath the skin. The cells of this tissue are specialised to store fats and the excess of unused nutrients are changed into fats and are stored in this tissue.

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Loose connective tissue : Adipose tissue

Dense connective tissue:

• Fibres and fibroblasts are compactly packed in the dense connective tissues. Orientation of fibres show a regular or irregular pattern and are called dense regular and dense irregular tissues.

Dense regular connective tissue:

• In the dense regular connective tissues, the collagen fibres are present in rows between many parallel bundles of fibres. Tendons, which attach skeletal muscles to bones and ligaments which attach one bone to another are examples of this tissue.

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Dense connective tissue : Dense regular

Dense irregular connective tissue:

• Dense irregular connective tissue has fibroblasts and many fibres (mostly collagen) that are oriented differently. This tissue is present in the skin. 

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Dense connective tissue : Dense irregular

Specialised connective tissue:

• Cartilage, bones and blood are various types of specialised connective tissues. 

Cartilage:

• The intercellular material of cartilage is solid and pliable and struggles density. Cells of this tissue (chondrocytes) are walled in small cavities within the matrix secreted by them. Most of the cartilages in vertebrate embryos are replaced by bones in adults.

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Specialised connective tissues : Cartilage

• Cartilage is present in the tip of nose, outer ear joints, between adjacent bones of the vertebral column, limbs and hands in adults.

Bones:

• Bones have a hard and non-pliable ground substance rich in calcium salts and collagen fibres which provide bone its strength. It is the main tissue for structural frame to the body, bones support and protect softer tissues and organs. 

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Specialised connective tissues : Bones

• The bone cells (osteocytes) are present in the spaces called lacunae. Limb bones, such as the long bones of the legs, perform the weight -bearing functions and they also interact with skeletal muscles attached to them to bring about movements. The bone marrow in some bones is the site of production of blood cells. 

Blood:

• Blood is a fluid connective tissue containing plasma, red blood cells (RBC), white blood cells (WBC) and platelets. It is the main circulating fluid that supports in the carriage of many substances.

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Specialised connective tissues : Blood