Connective Tissue

Connective Tissue

This is a type of supporting tissue which connect • tissues to tissue • tissues to structures • tissues to skeleton Tissue which provides • structural and metabolic support Tissue which functions as • medium of exchange of nutrients and metabolites

Functions: 1.Acts as biological packing material between cells and other tissues eg. loose supporting tissue seen in superficial fascia, stroma of organs and around nerves and blood vessels. 2. Forms dense supporting tissue as in the dermis of the skin, in the capsule that surrounds organs, and in tendons and ligaments.

3. Act as specialized types of supporting tissue forming a rigid supporting framework. eg. Cartilage and bone 4. Has a metabolic function * in the storage of fat in white adipose tissue * regulation of the body temperature of the new born by brown adipose tissue. 5. Plays a major role in defence mechanisms against pathogens. 6. It functions in tissue repair.

Main components –

cells Extracellular matrix Cells - responsible for the • synthesis and maintenance of the EC matrix • storage and metabolism of fats • defence and immune functions.

• EC matrix determines the physical properties of supporting tissue • made up of organic material that forms the ground substance variety of fibres embedded in it. • contains structural glycoproteins that allows the interaction of the cells with other constituents • The nature of the EC matrix determines the differences in the various types of supporting tissue.

• Most types of supporting tissue are derived from primitive mesenchyme. • Mesenchymal cells are * irregular cells *spindle shaped cells *with slender processes. • Mucoid tissue- The EC matrix has no mature fibres in its ground substance and this permits free diffusion of metabolites. • This type seen is in the foetus

CELLS OF SUPPORTING TISSUE Three types in relation to their basic functions. 1.Fibroblasts are responsible for the synthesis of EC matrix. 2.Tissue macrophages, mast cells and leucocytes - for defence and immune functions. 3.Adipocytes- for the storage and metabolism of fats.

Fibroblasts• most numerous cells. • main function- produce the fibres and the ground substance of the EC matrix. • large flattened cells with ovoid nuclei • long cytoplasmic processes • When functionally active - the nucleolus is prominent and fine chromatin granules are seen. • Well developed ribosomes, rER and Golgi complex indicate its activity in protein synthesis.

Fibroblasts-

Rough endoplasmic reticulum

• Fibroblsts among collagen fibres

Defence cells of supporting tissue: Two types1.Fixed (intrinsic) type which include tissue macrophages and mast cells 2.Wandering (extrinsic) which include cells of the white blood series. • Ovoid cells with an oval nucleus indented towards one end. • The nucleus is irregular and contains heterochromatin.

• In an active state lysosomes are abundant but these are reduced in actively phagocytic cells. • Active cells have pseudopodia and exhibit,an amoeboid movement and are used in phagocytosis • Macrophages are derived from blood monocytes which migrate to the peripheral tissue and assume the role of macrophages. • Macrophages play an important role in the immune mechanism.

• Macrophages

• MAST CELLS- are found in all types of supporting tissue • particularly beneath the skin deep to the lining of the GI and respiratory tracts and around blood vessels. • are very similar to basophils. • The extensive cytoplasm of these cells is packed with large granules* (toluidene blue stains the granules red.) • The granules are membrane bound (EM) and contain a dense amorphous material

• Mast cells with granules

• Mast cells – deep purple metachromatic granules

Leucocytes- Their appearance differs from that of similar cells seen in blood smears. • Plasma cells- extensive basophilic cytoplasm (RER and ribosomes) • pale stained perinuclear area (well developed, active Golgi) • an eccentric nucleus with chromatin in a radiating arrangement (cart wheel), • are immunologically active lymphocytes that produce antibodies. • They are larger than lymphocytes.

• Plasma cell- in loose areolar tissue

• Plasma cell in the centre, fibroblast on right

• Neutrophils are rare except in acute or chronic inflammation • Eosiniphils are present in large numbers. • Lymphocytes are recognized by their dense nucleus and thin rim of cytoplasm.

Eosiniphil

• Eosinophils and neutrophils

Adipocytes - *are adopted for the storage of fat *found in clusters in loose supporting tissue. *main cell type in adipose tissue. • Two main types- White adipose tissue Brown adipose tissue White adipose tissue - found throughout the body in the deep layers of the skin. • forms an energy store and an insulator • functions as a cushion against mechanical shock.

• The fat stored collects as lipid droplets which accumulate to form large droplets in the cytoplasm • cytoplasm is reduced to a small rim • nucleus is compressed. • With EM the main droplet has an irregular outline and smaller droplets are seen at the periphery. • Mitochondria are seen in the peripheral cytoplasm.

Adipocytes

cytoplasm

nucleus

Brown adipose tissue - highly specialized • is found in the new born • plays a part in temperature regulation. • small amounts are found in adults • arranged in lobules separated by fibrous septa. • lipid is stored as minute droplets (multilocular) in the cell. • The cytoplasm is copious and stains intensely due to the mitochondria. • These have numerous closely packed cristae rich in cytochromes involved in energy production.

• Nuclei are eccentrically located and are rounded.

Fibres - Fibres are mainly of two types collagen (white) fibres elastic (yellow) fibres. Collagen - found in all types of supporting tissue • most abundant protein in the human body • flexible it provides a high tensile strength. • Collagen is secreted by the fibroblasts into the EC matrix in the form of tropocllagen molecules

Areolar connective tissue. • All pink fibers - collagenous fibers. • Dark, thin, more tortuous fibers - elastic ) fibers. • Most of the nuclei belong to fibroblasts.

• Reticulin fibres - form the frame work in cellular organs(liver, lymphoid tissue) • The fine network of branching fibres is anchored to the collagenous capsule and septae • These fibres are not clearly seen with H&E stain. They stain black with silver stains. • Reticulin fibres are the earliest collagen fibres to be produced. • Elastic fibres - thinner than collagen, exihibit no banding. They are short branching fibres that form an irregular network

A - Elastic Fibres

• Ground substance - an amorphous transparent material in the form of a semifluid gel in which the cell and fibres are arranged. • composed of glycosaminoglycans* (mucopolysaccharides) mainly in the form of hyaluronic acid linked to a protein molecule to form proteoglycans (mucoproteins). • Tissue fluids loosely associated with the ground substance serve as a medium by which nutrients, gases and metabolites can be exchanged between cells and capillaries.

• The ground substance forms a mechanical barrier to bacteria • plays an important role in preventing the spread of microorganisms. • Hyaluronidase present in some bacteria may help in their spread. • The ground substance may also act as selective barrier to inorganic ions and charged molecules. • **Structural glycoproteins are made up of protein chains bound to branched polysaccharides.

TYPES OF SUPPORTING TISSUE

1.Loose irregular ordinary supporting tissue (areolar tissue) • widely distributed in the body • consist of a meshwork of thin collagen and elastic fibres forming a network. • all supporting tissue cells are found among the fibres in the ground substance. 2. Dense irregular supporting tissue • found in the dermis, capsules of organs, periosteum. • made up of a network coarse collagen fibres with a few elastic or reticular fibres. Fibroblasts are few.

3.Dense regular supporting tissue- consist of collagen fibres that are densely packed in a regular arrangement -reflect the mechanical needs of the tissue. • Tendons • Aponeuroses • Ligaments • In tendons, the collagen fibres are packed in parallel bundles. The only types of cells are the fibroblasts that lie in rows between the bundles.

B- collagen fibres A - fibroblasts

Aponeuroses• the collagen fibres are arranged in a broad sheets • may be in a number of layers with the fibres of one layer running at an angle to the adjacent layer. In ligaments• the arrangement of fibres is not so regular. •

In certain sites as in the ligamentum nuchae and ligamentum flava they are mainly made up of elastic fibres.

4.Adipose tissue (see section on adipocytes) 5.Mucoid tissue is found in the umbilical cord (Wharton’s jelly). • The ground substance is mucoid with a scanty meshwork of collagen fibres and a few cells. • The vitreous body is a persistent form of mucoid tissue. 6.Basement membrane- condensed layer of the EC matrix of supporting tissue. • provides mechanical and nutritional support. It is found in relation to epithelia, nerve and muscle where they form the external lamina.