15. Specialised connective tissue; adipose tissue, reticular tissue, pigment tissue
Connective tissue is a combination of cells and has lots of intercellular substance. It derives from mesenchyme and has productive, protective and trophic functions.
Consists of a few cells widely separated by a prominent intercellular substance.
Its basic components are ground substance & extracellular matrix which contains cells and numerous fibres.
Connective tissue has a good blood supply.There are two types of connective tissue; embryonic and mature connective tissue.
Mesenchyme and mucous are all types of embryonic connective tissue.
Mature connective tissue is split into two categories; with fibrous intercellular substance and with solid intercellular substance. Fibrous intercellular substance includes loose connective tissue, collagenous connective tissue, elastic connective tissue, reticular tissue, adipose tissue and pigment tissue, whereas solid intercellular substance includes bone, cartilage and dentin.
Adipose tissue is a specialised loose connective tissue that has lots of adipocytes. It functions in insulation and padding and provides a readily source of fuel for metabolic processes.
Adipose tissue normally constitutes 10%-15% of body weight. It is a highly labile tissue, it is specialised for synthesis and storage of lipids.
It has small blood vessels, adipocytes occur singly or in clusters that are arranged in lobules surrounded by fibrous septa, resembles a bunch of grapes.
There are two types; white adipose tissue and brown adipose tissue.
White adipose tissues are unilocular adipocytes and they contain a single large lipid droplet. Brown adipose tissues are multilocular adipocytes containing many lipid droplets and they regulate body temperature.
The lipid droplets coalesce into a large droplet, leaving only a thin rim of cytoplasm, and the nucleus is pushed out to the side.
Staining of adipose tissue can be achieved by Sudan III-H to visualise the lipids and H-E staining is used to visualise the nuclei.
Reticular fibres are made of type III collagen and are finer than the collagen fibres. They are uneven in thickness and form a network.
They are found in lymphoid organs, lymph nodes, bone marrow, and spleen.
The fibres are produced by fibroblast and functions includes hydrophilia, metachromasia and optical homogeneity.
Impregnation with silver nitrate is the staining specific for reticular fibres.
During wound healing in connective tissue, reticular fibres are the first to be synthesised by fibroblasts and are later replaced by type I collagen fibres.
Pigment adipose tissue is also a specialised type of loose connective tissue. It contains pigment cells which contain melanin and can be found on the skin, choroid & iris of the eye, and the meninges of the brain. Melanin is produced by Melanocytes and stored in Melanophores.