It Is the Group of Tissue Predominantly Composed of Intercellular Matrix

CONNECTIVE TISSUE

CONNECTIVE TISSUE

• It is the group of tissue predominantly composed of intercellular matrix.

•It supports and connects the other tissues in the body.

•It differs from epithelium in having few cells and large amount of intercellular substance.

•Main components of connective tissue are cells, fibers and ground substance.

Cells

Fibroblasts

Histiocytes

Plasma cells

Mast cells

Fat cells

Pigment cells

Migratory cells

Fibers

Collagen

Reticular fibers

Elastic

Ground substance

It contains proteoglycan and glycoprotein.

Proteoglycan are:

 Hyaluronic acid

 Chondriotin sulphate

 Keratin sulphate

 Heparin sulphate.

Connective Tissue Cells:

1-Fibroblasts

They are large cells with branching processes.

Nucleus is large with prominent nucleolus.

Cytoplasm is basophilic in active cells.

Organelles are clearly visible.

Their function is the production of fibers and ground substance.

2- Histiocytes

They are as numerous as fibroblasts.

They are irregularly shaped cells, with short and blunt processes.

Nucleus is small and round.

Cytoplasm is filled with granules and vacuoles of ingested material.

Inactive cell is difficult to differentiate from fibroblasts.

Active cell is large with more prominent nucleus

Ingested material is in the form of phagosome.

If the ingested material is large, many macrophages surround it to form foreign body giant cell.

Their function is phagocytosis

3- Plasma Cells

They are ovoid or irregularly shaped cells.

Nucleus is small and eccentric.

Chromatin forms clumps along the nuclear membrane, so the nucleus shows typical cartwheel appearance.

Plasma cell in blood smear

Cytoplasm is basophilic due to large amount of rough endoplasmic reticulum.

Function of plasma cells is the production of antibodies.

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4- Mast Cells

They are large cells with pale nucleus.

Cytoplasm is filled with basophilic granules, which are not visible in routine sections as the granules are dissolved in water during tissue processing.

These granules contain histamine and a vasoactive substances heparin.

When stained by toluidine blue (dye) they are stained red, this property is known as ‘Metachromasia’.

They are found in skin, wall of GIT, and around blood vessels.

Their function is to produce heparin, which is an anticoagulant and histamine, which causes hypersensitivity reaction.

5- Fat Cells

They are also known as ‘adipocytes’.

They are usually found in groups.

Fat cells are large, and filled with fat droplet.

The nucleus and cytoplasm is pushed to one side of cell.

In routine histological sections cells appear empty because the fat is dissolved out.

6- Pigment Cells

They are satellite cells with long processes.

They contain numerous dark black pigment granules in their cytoplasm.

The pigment is synthesized by melanocytes.

These cells are found in the dermis of skin, especially in dark races, in iris and choroids of eye.

Their function is absorption of light.


7- Migratory Cells

Migratory cells from blood and lymph are also seen in connective tissues.

They include lymphocytes, neutrophil and eosinophils.

Fibers of connective tissue

•Collagen fibers

•Elastic fibers

•Reticular fibers

Collagen Fibers


1- Collagen

 Collagen fibers are made up of a protein collagen.

Molecules of collagen are aligned side by side in a staggered fashion with three quarter of length of each molecule.

Length of each molecule is 300nm.

Collagens are of 14 types.

Type-I is found in dermis, fascia, bone, tendon, ligament, blood vessels.

Type-II is found in cartilage and viterous body.

Type-III is found in dermis of skin.

Type-IV is found in basal lamina.

Collagen I, II, III, V, and XI form fibrils, others are in dissolved form.

Type-III collagen when glycosylated, forms ‘reticular fiber’.

Reticular fibers

Type-III collagen when glycosylated, is known as ‘reticular fiber’.

They are very thin, 0.5-2 µm in diameter usually not visible in H&E stained sections.

They are found in loose connective tissue all over the body.

Reticular fibers form the framework of certain organs, like liver, bone marrow.

Elastic Fibers

They are made up of a protein elastin.

Elastic fibers are yellow in color.

The fibers branch and rejoin freely.

They are thinner than the collagen.

No banding pattern.

The fibers are stained by special stain.

They are stretched easily and then recoil perfectly.

Elastic fibers are present in lungs, skin and large blood vessels

Elastic fibers

Connective Tissue Classification

Connective tissue is classified into two types

1-Embryonic

2-Adult type.

1- Embryonic connective tissue

It is further divided into:

Mesenchyme

Mucous

The mesenchyme is the most primitive connective tissue. Here the fibroblasts are embedded in a jelly like matrix.

Mucoid tissue is found primarily where the connective tissue is developing from mesenchyme. It consists of mucoid substance, fine meshwork of type II collagen fibers and few fibroblasts which are highly branched.

Adult connective tissue

It varies from place to place in their appearance and composition according to their functional requirements and can be subdivided into:

Connective tissue proper
Bone
Cartilage
Blood

I- Connective tissue proper

•They are called "proper" because they are the types usually meant when using the phrase "connective tissue".

Connective tissue proper includes the following five types:

1- Loose (areolar) connective tissue

2- Dense connective tissue

3- Elastic tissue

4- Reticular tissue

5- Adipose tissue

Few connective tissue types

1-Loose connective tissue.

Loose connective tissue is characterized as being composed of meshwork of collagen bundles, intermingled with elastic fibers.

Gel like ground substance and variety of cell types are present.

This type of connective tissue forms superficial and deep fascia, and part of framework of most of the organs.

Loose Connective Tissue

2-Dense connective tissue

It is either irregularly arranged or it may be regular.

Dense irregularly arranged connective tissue is composed mainly of collagen fibers, fibroblasts and macrophages.

Fibers interlace and form coarse network.

Examples are dermis of the skin, periosteum and capsule of the testis

 Dense Irregularly Arranged Connective Tissue

Dense regularly arranged connective tissue occurs as bands or cords.

The fibers are densely packed and lie parallel to each other, they are mainly collagen fibers.

They form a structure of great tensile strength.

This type of tissue comprises the tendons ligaments and aponeuroses

Dense Regular Connective Tissue

3- Reticular connective tissue

It is special tissue, forming the supporting framework of bone marrow and most lymphoid tissue.

In contrast to other sites, reticular tissue of thymus is derived from endoderm.

4-Adipose tissue

It is composed of adipocytes contained in loose areolar tissue.

All the other cell types are also present.

Adipose tissue is divided into loculi by fibrous septa, which contain blood vessels.

Adipocytes are round or polygonal in shape with signet ring appearance.

 Adipose Tissue

 Brown adipose tissue

Functions of adipose tissue

Adipose tissue is the energy storehouse of nutrition.

It serves as insulation against cold external environment.

It serves as shock absorber.

Adipose tissue fills empty spaces in the body.

In time of nutritional deficits, it releases stored fat.

In some races it has cosmetic function.

In newborn infants there are areas of specialized adipose tissue called brown fat, which is related to the temperature regulation.

Brown fat is also present in adults at few sites in the body.

In pigmented connective tissue the cytoplasm is filled by a brown or black pigment, usually melanin.

This type of connective tissue is found in choroids and iris of eye.