Download Connective tissue cells

8th lesson
Medical students
Medical Biology
Connective Tissue
Connective tissue is a form of fibrous tissue. Collagen is the main protein of connective
tissue in animals and the most abundant protein in mammals, making up about 25% of the
total protein content. Connective tissue are found in all organs of the body except the
central nervous system, you see it underlying epithelia, between layers of smooth muscles,
separating glandular tissue into lobules and lobes and every providing a framework for
blood vessels.
Connective Tissue is characterized by:
Binding and supporting the organs.
It is vascular except the cartilage.
It is derived from mesoderm layer.
It consists of cell immersed in large amount of intercellular substance, which is formed by
cells.
The major constituent of connective tissue is:
Extracellular matrix: composed of fibers and ground substance.
Connective tissue cells.
Functions of connective tissue:
• Support, surround, connect other tissues
• Structural framework for body
• Protect organs
• Transport fluids and dissolved materials
• Store energy and minerals
• Immunity
Extracellular matrix:
The extracellular matrix composed of:
Ground substance: is a hydrated colorless and transparent, amorphous material, It is
binding cells to the fibers of connective tissue. Ground substance is found in all cavities
and clefts between the fibers and cells of connective tissues, but its main structural
constituent is proteoglycans which consists of proteins (~5%) and polysaccharide chains
(~95%). The polysaccharide chains belong to one of the five types of glycosaminoglycans,
which form the bulk of the polysaccharides in the ground substance.
Fibers: there are three types of connective tissue fibers as shown:
Collagenous fibers (white fiber): they are the most numerous and strongest fibers in the
body derived from connective tissue cells called "fibroblasts". These fibers are straight or
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wavy, unbranched consist of protein called "collagen". They always run parallel to each
other forming bundles. Collagen is the most abundant protein in mammals, making up
about 25% to 35% of the whole-body protein content. Collagen found in fibrous tissues
such as tendon, ligament and skin, cartilage, bone and blood vessels. So far, 28 types of
collagen have been identified and described.
The five most common types are:
Collagen I: skin, tendon, dentin, cementum and bone.
Collagen II: cartilage (main component of cartilage).
Collagen III: reticulate (main component of reticular fibers), commonly found along side
type I.
Collagen IV: forms bases of cell basement membrane.
Collagen V: cells surfaces, hair and placenta.
Elastic yellow fibers: they differ from collagen that they are thinner than fibers (the white
fibers), they branched and unite with one another forming irregular network. They formed
from protein called "elastin", which resist boiling, dilute acids, alkaline and gastric juice.
They are generally formed by fibroblasts. They are found ligaments and vocal cords
Reticular fibers: they are very fine fibers, branched forming a network, they are found
around spleen, lymph nodes, red bone marrow, liver, endocrine glands and kidney. They
are associated with special cells called reticular cells. Reticular fibers consist of collagen although the main type of tropocollagen found in reticular fibers. Reticular fibers give
support to cells, for example, in muscle and adipose tissue.
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Connective tissue cells:
There are many types of cells found in connective tissue:
A-Fibroblast: it is the most common cell found in the connective tissue, the young
fibroblast is star in shape with many processes, the nucleus is large oval & pale in color
while the mature cell is called "fibrocyte", which is smaller than fibroblast, it is spindle
in shape have few processes, the nucleus is smaller, darker & elongated. The function of
fibroblast is the formation of fiber & matrix.
B-Undifferentiated mesenchymal cells (cells of regeneration):
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These cells have ability to give rise any kind of cells, it form the muscle cells, they are
smaller than fibroblast but have the same appearance, they have an elongated nucleus.
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C-Macrophages: they are either fixed or wandering, the fixed macrophage
known as histiocytes, while the wandering macrophage is called amoeboid. The fixed
macrophages are spindle or star in shape have an ovoid nucleus while the wandering is
irregular in shape and the nucleus is round. The functions of macrophage is engulf of the
foreign bodies and accumulate it in their cytoplasm in the form of granules by their thick
pseudopodia.
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D-Pigment cell: they are elongated cells with short irregular outgrowth, the cytoplasm
contains small granules of melanin (brown or black pigment granules). it is seen in the
skin and eyes.
E-Reticular cells: they are star in shape with processes extending in several directions
and often in contact with the processes of neighboring cells, they have a large pale nucleus
and centric, they lie between the reticular fibers, they engulf the foreign bodies, they
found in lymphatic nodes, spleen and liver.
F-Plasma cell: it is ovoid in shape with eccentric nucleus , the chromatin granules in the
nucleus are coarse and deeply stained, they arranged at the periphery of the nucleus
forming a cart- wheel or o'clock face appearance .Above the nucleus there is a pale
colorless area which represent the Golgi region called Golgi image, the function of plasma
cell is the formation of antibodies against antigen which enter the body.
G-Mast cells: they are large ovoid in shape with small ovoid nuclei and coarse
cytoplasmic granules .The function of mast cell is the production of heparin
(anticoagulation) and also produce histamine (vasodilator) which cause dilation of
capillaries, it produce third substance serotonin in some animals.
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H-Fat cells: these cells found singly or in groups contain fat globules, are derived from
undifferentiated mesenchymal cells. The function is the synthesis and storage of
triglycerides. There are two types of fat cells:
i. Unilocular fat cells: cells with a single, large lipid droplet form white a dispose tissue.
ii. Multilocular fat cells: cells with multiple, small lipid droplets, form brown adipose
tissue.
I-Some blood cells: some types of blood cells might be seen in the connective tissue, in
special conditions such as neutrophils in the site of infection, eosinophil in the site of
sensitivity and lymphocytes in the chronic infection.
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