Connective tissue l General Histology & Biology MCQ for dental students

 

Connective tissue l General Histology & Biology MCQ for dental students

 

Connective tissue

Introduction

• Connective tissue is one of the four types of tissue in traditional classifications (the others being epithelial, muscle, and nervous tissue.) 
• Connective tissue consists of cells separated by varying amounts of extra cellular substance. In connective tissues cells typically account for only a small fraction of the tissue volume. The extra cellular substance consists of fibers which are embedded in ground substance containing tissue fluid.
• Fibers in connective tissue can be divided into three types: Collagen fibers, reticular fibers and elastic fibers.

Types of Connective Tissue:

According to matrix there are 4 types of Connective tissue:

1. Blood: with fluid matrix.
2. CT proper: with soft matrix (loose CT, mucous CT, adipose CT, dense CT, reticular CT and elastic CT).
3. Cartilage: with rubbery matrix.
4. Bone: with solid matrix

According to characters there are 3 types of Connective tissue :

1. CT proper: loose CT and dense CT.
2. CT with special properties: mucous CT, adipose CT, elastic CT and hematopoietic CT.
3. Supportive CT: cartilage and bone.

Connective tissue proper

• CT proper is formed of CT cells in a soft matrix (formed of CT fibers and ground substance).

Ground substance: 

• The ground substance is formed of tissue fluid containing the following amorphous materials:

1. Glycos-amino-glycans (GAGs): 

• a basophilic un-branched polysaccharide chain of repeating disaccharides (amino sugar and uronic acid).
• It is hydrophilic ® exchange of ion and nutrients between CT and blood.

2. Proteo-glycans: 

• a core of protein to which molecules of GAGs (as chondroitin sulfate, keratan sulfate and hyaluronic acid) are bound ® bottle brush appearance.
• Carbohydrate (90-95%) is greater than protein.

3. Glyco-protains: 

• a globular protein molecule to which branched chains of mono-saccharides are attached.
• Protein is greater than carbohydrate.
• It binds CT cells and CT fibers together.

Connective    tissue   fibres

Collagenous fiber

Characters:

• Color: white.
• Strong and resist stretch.
• It forms wavy bundles. The bundles branch but the single fiber does notbranch.
• Can be:

1. Converted into gelatin by boiling.
2. Destroyed by acids and alkalies.
3. Digested by pepsin and collagenase enzyme (of bacterial origin).

Light microscope : 

• Hx & e.: acidophilic.
• Mallory trichrome stain: blue.

Yellow elastic fibres

Characters:

1. Colour: yellow.
2. Elastic in nature.
3. Fibers are thin, long , branching and highly refractile.
4. The fibers branch and may form elastic membranes.
5. Can be digested by elastase enzyme

Light microscope : 

1. Hx & e.: acidophilic
2. Van gieson's stain: yellow
3. Ver-hoff's stain: black.

Sites

1. In the walls of arteries.
2. In the trachea, bronchi and bronchioles.
3. Ligamentum flavum between vertebrae.

Reticular fibres

Characters:

• They are very thin fibres that branch and anastomose to form a network.

Light microscope : 

•         Hx & e: not stained.
•        Silver: black.
•       Pas:  magenta coloured.

Sites

• Stroma of parenchymatous organs e.g.liver, spleen, ln Reticular lamina of the basement membrane .

 connective tissue matrix (ground substance)

Definition:

•  jelly-like material in which the connective tissue fibres and matrix lie.

Composed of three components:

•  amorphous component (glycosaminoglycans and glycoproteins).
• Fibrous component: collagenous, elastic and reticular fibers.
• Tissue fluid: derived from capillaries.

 connective tissue cells

A-fixed connective tissue Cells:

1. Undifferentiated mesenchymal cells.
2. Fibroblasts and fibrocytes.
3. Adipose cells.        
4. Reticular cells.
5. Macrophages

B- free connective tissue cells:

• mast cells.
• free macrophages.
• plasma cells.              
• pigment cells.
• blood leucocytes.

Connective tissue cells

• Connective tissue cells are usually divided into two groups based on their ability to move within the connective tissue. Fibrocytes (or fibroblasts) and fat cells are fixed cells
• Macrophages, monocytes, lymphocytes, plasma cells, eosinophils and mast cells are wandering cells

 essential cells:

• Such as fibroblast, which are the most common cells of adult connective tissue. They are essential component of connective tissue Tissue. When they are mature they become larger and narrower. They proliferate in the process of repair of injury. When they multiple excessively they produce much of dens connective tissue .

Lipoblast (fat cells or adipoblast):

• Are recognized only in the embryonic connective tissue; fat cells are large, oval or rounded with  a thinner amount cytoplasm. When these cells accumulate in large number, they constitute adipose tissue. In such tissue the fat cells supplied by reticular fibers.

• Fat cells are of two types:

Uni-locular fat cells (of white adipose CT) :

•  Light microscope :

1. large and oval in shape (50-150 μm)
2. contain single large fat globule
3. peripheral flat nucleus and thin rim of cytoplasm
4. with Hx and E stain they show signet ring appearance

• Electron microscope :

few mitochondria ® few cytochrome pigments.

• Sites : Present in white adipose CT at the following sites:

1. around kidney and blood vessels.
2. ♀ subcutaneous areas ® ♀ shape contour
3. omentum and abdominal wall NB: the white color of this type of adipose CT is due to:

• ¯ blood capillaries
• ¯ cytochrome pigments in its mitochondria

Function

1. Heat insulator (storage house of fat)
2. Support some organs as kidney…
3. Energy reservoir (¯ by regimen)

Multi locular fat cells (of brown adipose CT) :

• Light microscope :

1. small and rounded in shape
2. contain multiple small fat droplets
3. central rounded nucleus
4. with Hx and E stain they show multiple vacuoles

• Electron microscope :

1. many mitochondria ® many cytochrome pigments

• Sites :- Present in brown adipose CT at the following sites:

1. in newborn: form 2-5% of body weight and present in back, neck and shoulders
2. in adults: around aorta and in mediastinum

• NB: the brown color of this type of adipose CT is due to:

1. blood capillaries
2. cytochrome pigments in its mitochondria

• Function

1. Heat generator

Macrophage (histiocytes):

• They are one component of loose connective tissue. They are the component of the reticular- endothelial system and areolar connective tissue . These macrophage are oval or irregular in shape with bluntly amount of cytoplasm and oval nucleus, which contains a cross of chromatin, these cells are easily distinguished when they have ingested a particular material by process called phagocytosis.

Mast cells:

• They are large and found especially in the blood vessels, and areolas connective tissue they have numerous cytoplasm granules (large achromatic granules , this substance suggested by some scientist that they may have anticoagulant material (heparin) and also liberate the histamine. The primary action of histamine released from mast cells, is response to any allergy or antigen-antibody reaction.

Other cells are extra cells:

•  which are mainly found in the loose connective tissue, such as the plasma cells. They are rounded or oval cells with basophilic cytoplasm . When stain with lishmain stain has a good di-cytoplasm in their cytoplasm of these cells which have a secretory function such as synthesis of immunoglobulin.

• Immunoglobulin: cellular (plasma, lymphocyte, neutrophil) humeral (IgA, IgM, IgG, IgE, IgD). The plasma cells are mainly present in the lymphoid tissue but are seeing in varying number in loose connective and dense mucous membrane of stomach.

Cartilage cells(chondroblast):

• They are oval cells with relatively large nuclei and abundant cytoplasm containing glycogen or lipids. The adult (mature) cells are called chondrocyte.

Bone cells (osteoblast):

• Are oval with a single round nucleus near the cell surface they have high alkaline phosphate activity. These cells may surround by the bone matrix.