Connective tissue : Connective tissue is a
fundamental animal tissue that has scattered living cells embedded in matrix. The matrix and cells are different in different connective tissues.
Based on the nature of matrix, connective is divided into three types:
I. Connective tissue proper : It is type of connective tissue fibers : white collagen, yellow elastin and reticular fibres. The living cells present may include fibroblasts, mast cells, plasma cells, Macrophages and lymphocytes. I
It is of two types :
(A) Loose connective tissue proper : In this, cells (fibroblasts, macrophages, mast cells etc) and fibres are loosely arranged in a semi-fluid matrix. It has fewer fibres and more of matrix. It is of two types: Areolar tissue and Adipose tissue.
(a) Areolar Tissue : It is the most widely spread connective tissue in the body. The non-living intercellular matrix contains irregular shaped cells and two kinds of fibers. The cells forming the tissue are: Fibroblasts, Macrophages, Mast cells that secrete heparin. Heparin helps in clot¬ting of blood.
Location : Areolar tissues are found inside or-gans, around blood vessels, muscles and nerve.
It also occurs below sub-cutaneous tissue and structures like muscles and skin.
(b) Adipose Tissue : It is a type of connective tis¬
sue that is specialized to store fat called adipose cells. The fats are stored inside cells called adi-pocytes. Adipocytes are large cells with one or more globules of fat and peripheral cytoplasm with nucleus at one end. Like areolar tissue, the adipose tissue has also soft jelly like matrix, living cells like fibroblasts, macrophages, mast j cells etc. and two types of fibers called collagen j and elastin. j
Location : The tissue is found below the skin, I around internal organs and inside yellow bone j marrow. j
(B) Dense connective tissues : In this, fibres and j fibroblasts are compactly packed. It has more of j fibres and less amount of matrix. It is of two types : |
(a) Dense regular connective tissues : They show regular pattern of fibres. Collagen fibres are present in rows between many parallel bundles of fibres. E.g., tendons and ligaments.
(i) Tendon : Tendon is a tough, non-fibrous, dense, white fibrous connective tissue. It has great strength but limited flexibility.
Function : It joins a skeletal muscle to a bone, thereby helping the bone to move on contrac-tion and relaxation of the muscle.
(ii) Ligament: Ligament is a dense yellow fibrous connective tissue. It has considerable strength and high elasticity.
Function: Ligament binds a bone with another bone, thereby allowing bending and rotation movements over a joint.
(b) Dense irregular connective tissues: They have irregular pattern of fibres. It has fibroblasts and many fibres (mostly collagen) that are oriented differently. This tissue is present in skin.
II. Supportive connective tissues : It is a connective tissue in which matrix is rigid and the living cells occur in fluid filled spaces called lacunae
(i) Cartilage:
• Cartilage is a non-porous, firm but flexible sup¬portive tissue. Matrix is solid and pliable (due to chondroitin salts) and resists compression.
• • It has solid matrix which is composed of chon- drin. Chondrin is secreted by the chondro¬cytes. Chondrocytes lie in the matrix singly or in groups of two or four surrounded by fluid filled space called lacunae. Cartilage is usually covered by a tough fibrous membrane called perichondrium.
• Most of the cartilages in vertebrate embryos are replaced by bones in adults.
• Cartilage is present in the tip of nose, outer ear, joints in the vertebral column, limbs and hands in adults.
• It provides support and flexibility to various parts of the body.
(ii) Bones:
• Bone is a strong, rigid and non-flexible tissue. Bone is the hardest tissue of the body. .
• It consists of solid matrix with fluid filled lacu-nae having osteocytes or bone cells.
• Matrix is composed of collagenous protein complex called ossein and mineral matter like salts of calcium, phosphorus, and magnesium.
• The hardness of bone is due to deposition of mineral matter (calcium salts and collagen fi-bres).
• The matrix in mammalian bone like in thigh bone is arranged in concentric rings or lamellae around nutrient filled haversian canals.
• The osteocytes lie on the lamellae and give out branched processes which join with those of the adjoining cells. Some bones have a cen-. tral cavity that contains a tissue that produces blood cells.
• The soft connective tissue present in the bone cavity is known as bone marrow. Sheath of bone is called peristeum. A layer of osteoblasts or bone forming cells lie below it.
Bones are of two types:
(a) Spongy bone, in which bone cells are irregulary arranged. Such bones are found at the ends of the long bones.
(b) Compact bone, in which cells are arranged in circles or lamellae around a central canal, haversian canal.
Location: Bones are found all around the body. It forms the supportive framework of the body.
III. Fluid connective tissue : It consists of cells and matrix without fibers. Plasma is the extra cellular fluid of matrix, the ground substance. Blood and Lymph are two types of fluid connective tissue.