CONNECTIVE TISSUE PROPER -

1.      AREOLAR TISSUE ( = Loose connective tissue) -

• Widely distributed connective tissue in the animal body.
• It consists of ground substance, the matrix, white, yellow and reticular fibres and cells like fibroblasts, mast cells, macrophages (histocytes or clasmato-cytes), lymphocytes, plasma cells, mesenchyme cells, chromatophores.
• It is present under the skin as subcutaneous tissue in between the around muscles, nerves and blood vessels in submucosa of gastor-intestinal tract and respiratory tract, in the bone morrow, between the lobes and lobules of compound glands.
• To bind parts together is the primary function of areolar tissue.

2.      ADIPOSE TISSUE -

• It is a fat strong connective tissue.
• It consists of adipose cells (= adipocytes or fat cells).
• Each adipose cell contains fat globules.
• These cells are often called signet ring cells.
• There are two types of adipose tissue - White (or yellow) fat and Brown fat.
• White fat contains large adipose cells, each having a single large fat globule and hence called monolocular.
• The cytoplasm in these cells is pushed to a peripheral layer containing nucleus.
• The adipose cells of brown fat are multilocular, each cell with several small fat globules.
• Brown colour is due to iron containing cytochrome pigment in fat.
• Brown fat found in those mammals which have an oxidation power 20 times more than that of yellow fat because brown fat cells are loaded with a large number of mitochondria.
• The adipose tissues are found in the subcutaneous tissue, around the heart, kidneys, eyeballs, where fat is stored.
• Adipose tissue is also found in the blubber of whales and elephants, hump of camal, fat bodies of frog and yellow bone marrow.

3.      DENSE CONNECTIVE TISSUE -

• It is of two types : white fibrous connective tissue and yellow elastic connective tissue.

(i) White fibrous connective tissue -

• It consists of mainly white (collagen) fibres which are arranged in bundles.
• It forms cords called tendons which connect the skeletal muscles with the bones.
• It occurs in the dermis of the skin, connective tissue sheaths of muscles and nerves and tunica adventitia (= outer coat) of large blood vessel, periosteum of the bone, perichondrium of the cartilage, pericardium of the heart, duramater of the brain and spinal cord, renal capsule of the kidney, sclera and cornea of the eye ball and fibrous capsules of penis and tests and between skull bones.

(ii) Yellow elastic connective tissue -

• This tissue is mainly made up of much thicker branched loose network of yellow fibres.
• The fibroblasts are regularly scattered.
• It also contains mast cells macrophages and often some adipose cells.
• The yellow elastic connective tissue form cords called ligaments which join bones to bones.
• The sheets formed by this tissue occur in the walls of blood vessels, lungs, bronchioles, true vocal cord, cartilage of larynx, trachea, capsules of spleen and ligamenta flava which connect adjacent vertebrae.

4.      RETICULAR CONNECTIVE TISSUE-

• This tissue consists of star-shaped reticular cells whose protoplasmic processes join to form a cellular network.
• The reticular fibres are present on the reticular cells. They are composed of a protein called reticulin.
• Matrix and some other cells such as macrophages, lymphocytes and adipose cells are also present.
• Reticular connective tissue is present in the liver, spleen, lymph nodes, thymus, tonsils, bone marrow and lamina propria of the gut wall.

5.      PIGMENTED CONNECTIVE TISSUE-

• The cells are irregular in shape and are called pigment cells which contain yellowish brown, black or blue melanin pigment granules.
• Melanin is in fact, produced by other cells called melanocytes.
• Chromatophores simply phagocytise the melanin from melanocytes like macrophages.
• Pigmented connective tissue is present in the choroid, ciliary body and iris of the eye and dermis of the human skin.
• Mucoid tissue - It occurs as a foetal or embryonic connective tissue. It is present in the umbilical cord. The most conspicuous component of the mucoid tissue is a jelly like substance, called Whartsons jelly.Mucoid tissue (Mucous connective tissue) also occurs in vitreous humour of the eye and in comb of cock.

MEMORY QUANTA -

• Connective tissue forms 30% of body weight.
• Hertwig (1883) : Called the connective tissue as mesenchyme.
• Areolar connective tissue is simplest connective tissue. It is also called loose fibrous or spongy connective tissue. It is also most abundant type of connective tissue.
• Fibroblasts are most abundant cell type of areolar connective tissue. When old, these are called fibrocytes.
• Histiocytes are also called clasmatocytes and are modified monocytes of blood act as scavengers. These form 'mopping up' operations. These are chief phagocyte of the body. These are involved in phagocytosis (first reported by Metchnikoff-1882).
• Dust cells: Histiocytes of lung septa.
• Mast cells are modified basophils of blood.
• Plasma cells of areolar connective tissue secrete antibodies.
• Collagen protein of white fibre' mainly contains glycine and proline amino acids.
• In tanning, collagen fibres become tough and insoluble to form leather.
• On boiling, collagen of white fibres changes to gelatin protein, while elastin is resistant to boiling.
• White fibrous connective tissue is also called dense connective tissue.
• Tendons join the muscles to bones while ligaments join bone to bone.
• Sprain: Excessive pulling of ligaments.
• White adipose connective tissue found in blubber of whale, hump of camel and tail of merzno sheep is mainly formed of monocular adipocytes, while brown adipose connective tissue is mainly formed of polylocular adipocytes.
• Mucoid tissue: An embryonic tissue found in umblical cord. Also called Wharton's jelly. It is most primitive type of tissue. Found in viterous humour of eye and cock's comb.
• Brown fats: Also called hibernating gland as found in hibernating mammals e.g. bats and squirrels, Kangaroo rats and newly born human babies. Each brown fat cell is polylocular and contains iron-contailling cytochrome pigments. These produce more energy than white fats.
• Mummies: Preservation of elastic fibres of body by chemical treatment.
• Aponeurosis: Bands of white fibrous connective tisslle in which fibres are thinller and interwoven.
• Kupffer cells: Modified reticulocytes of liver and act as phagocytes.
• Pigmented connective tissue: Found in iris and choroid of eye and has large number of chromatophores or pigment cells.
• Hassal cells: Phagocytes found in thymus.
• Matrix of areolar C. T. is mainly formed of chondroitin sulphate (heteropolysaccharide).
• Sharpey's fibres: White fibres strands which fix the fish scales in the skin.
• Omenta: Mesentries with adipose tissue.
• Collagen : Most abundant protein of body and forms 40% of total body proteins. In old age, rigidity of collagen decerases which causes wrinkles on skin.
• Astrocytes : Histocytes of brain.