· It links and supports other tissues/organs.
· They are most abundant in complex animals.
· All connective tissues except blood have fibroblast cells. They secrete structural fibrous proteins called collagen & elastin. They give strength, elasticity & flexibility to tissue.
· The cells also secrete modified polysaccharides (matrix), which accumulate between cells and fibres.
· Types of connective tissues: Loose, Dense & Specialised.
1. Loose Connective Tissues
In this, cells (fibroblasts, macrophages, mast cells etc.) and fibres are loosely arranged in a semi-fluid matrix.
It is 2 types: Areolar & Adipose.
o Areolar tissue:
- Present beneath the skin.
- It serves as a support framework for epithelium.
- Seen mainly under skin.
- Its cells (adipocytes) store fats.
- Excess nutrients which are converted into fats are stored in this tissue.
2. Dense Connective Tissues
In this, fibres and fibroblasts are compactly packed. 2 types:
o Dense regular connective tissues:
- Collagen fibres are present in rows between many parallel bundles of fibres.
- E.g. tendons & ligaments.
i. Tendons: Attach muscles to bones.
ii. Ligaments: Attach one bone to another.
Irregular pattern of fibres.
- Fibroblasts & fibres (mostly collagen) are oriented differently.
- This tissue is present in skin.
3. Specialized Connective Tissues
o In this, intercellular material (matrix) is solid and pliable (due to chondroitin salts) and resists compression.
o Cartilage cells (chondrocytes) are enclosed in small cavities within the matrix secreted by them.
o Most of the cartilages in vertebrate embryos are replaced by bones in adults.
o Cartilage is present in the tip of nose, outer ear, joints in the vertebral column, limbs and hands in adults.
o It has hard and non-pliable matrix rich in calcium salts and collagen fibres which give bone its strength.
o Bone cells (osteocytes) are seen in spaces called lacunae.
§ It provides structural frame to the body.
§ Support and protect softer tissues and organs.
§ Limb bones serve weight-bearing functions.
§ Take part in locomotion and movements.
§ Blood cells are produced in bone marrow.
o A fluid connective tissue containing plasma, red blood cells (RBC), white blood cells (WBC) and platelets.
o Helps in the circulation of various substances.