THE CONNECTIVE TISSUE

 The connective tissue supports and connects various tissues and organs.
 Types: 1- Connective tissue proper
2- Cartilage.
3- Bone.
THE CONNECTIVE TISSUE PROPER
- Formed of: cells, fibers and matrix.
TYPES OF CONNECTIVE TISSUE FIBRES
1- WHITE COLLAGENEOUS FIBRES
Characters:
1. Color: the bundles are white in color in the fresh state.
2. Tuff and resist stretch.
3. It forms wavy bundles. The bundles branch but the single fiber does not branch.
E.M.
1- Each collageneous fiber is composed of fibrils. Each fibril is formed of type-I
tropocollagen molecules that are synthesized by fibroblasts.
2- YELLOW ELASTIC FIBRES
Characters:
1- Color: yellow in the fresh state.
2- Elastic in nature (can be stretched but recoil after release of the stretch).
3- The fibers branch and may form elastic membranes.
E.M :
- Each fiber is formed of;
 Amorphous protein in the center called elastin.
 Microfibrills in the periphery called oxytalan fibres.
Sites :
- In the walls of arteries.
- In the trachea, bronchi and bronchioles.
- Ligamentum flavum between vertebrae.
3- RETICULAR FIBRES
Characters:
- They are very thin fibers that branch and anastomose to form a network.
E.M:
Composed of type- III collagen coated by glycoprotein.
Sites:
- Stroma of parenchymatous organs e.g. Liver, spleen and lymph nodes.
CONNECTIVE TISSUE MATRIX (GROUND SUBSTANCE)
Composed of two components:
1- Amorphous component.
2- Tissue fluid; derived from capillaries.
CONNECTIVE TISSUE CELLS
UNDIFFERENTIATED MESENCHYMAL CELL (UMC)
- The mother of all types of C.T. cells.
- Shape: branched cell with large, oval Nucleus and basophilic Cytoplasm.
--------------------------------FIBROBLAST-----------------------------------Origin: develop from U.M.Cs. It is the most common type of C.T. cells
L.M.
- Site: Very numerous in the loose C.T.
- Shape: branched, spindle-shaped cells.
- Nucleus: oval, vesicular.
- Cytoplasm: basophilic.
E.M.
- The cytoplasm is rich in rER with prominent Golgi and mitochondria.
Functions:
1- Synthesis of the components of C.T. matrix and fibers.
2- Responsible for growth of C.T. and healing of wounds.
N.B.
Fibrocytes: are old fibroblasts characterized by:
- The cell is spindle-shaped and has few processes.
- Nucleus is darker and cytoplasm is less basophilic.
----------------------------------------MACROPHAGES--------------------------------- Origin: develop from blood monocytes that originate from UMCs in bone marrow.
L.M.
- Shape: large branched cells with processes or pseudopodia.
- Nucleus: Small, eccentric in position and kidney-Shaped.
- Cytoplasm: pale basophilic.
E.M.
- The cytoplasm contains rER, Golgi and lysosomes.
- Some phagocytosed particles.
- Few mitochondria.
Functions:
1- Phagocytic function: can phagocytose foreign bodies e.g. bacteria.
2- Play a role in immunity as they present antigens to T-helper lymphocytes.
3- The cells may fuse together and form multinucleated foreign body giant cell to
surround a large foreign body.
4- Secretory function: the cells secrete cytokines.
----------------ADIPOCYTE=ADIPOSE CELL=FAT CELL------------------- Oval or rounded C.T. cells that have the ability to store fat.
- Origin: develop from U.M.C.
L.M.
- Site: in the adipose and loose C.T.
- Shape: an oval cell containing a large fat globule which pushes the nucleus to one
side giving a signet-ring appearance.
- Nucleus: flattened and peripheral in position.
E.M.
- Little cell organelles around the nucleus.
- A large lipid globule.
Function: storage of extra energy and heat insulation.
-------------------------------------------MAST CELL----------------------------------L.M.
1- Site: - in groups around blood vessels.
- In the mucosa of the GIT and the respiratory tract.
2- Shape: Oval or rounded with few and short processes.
3- Nucleus: Rounded and central.
4- Cytoplasm: contains large basophilic granules containing heparin and histamine.
E.M.
The cytoplasm contains much of membranous electron dense granules, ribosomes, rER
and mitochondria.
Functions:
1- Secretion of heparin (natural anti-coagulant).
2- Secretion of histamine in cases of inflammation and allergy.
---------------------------------PLASMA CELL--------------------------------------
Origin: activation of B-lymphocytes by specific antigen leads to formation of
plasmablasts which is converted into plasma cells.
L.M.
1. Site: more in Lymphatic organs.
2. Shape: Oval or rounded.
3. Nucleus: Rounded and eccentric. Cart-wheel in shape (clock-face appearance)
due to special arrangement of its chromatin.
4. Cytoplasm: deep basophilic.
E.M.
- The cytoplasm is rich in rER and prominent Golgi.
Functions:
-Secretion of antibodies (responsible for humoral immunity).
--------------------------EXTRAVASATED LEUCOCYTES-----------------Blood leucocytes leave the blood stream and appear in the C.T. in certain conditions,
e.g.:
- Eosinophils: in allergy.
- Neutrophils: in acute infections.
- Monocytes & lymphocytes: in chronic infections.
TYPES OF CONNECTIVE TISSUE PROPER
1- Loose connective tissue.
2- White fibrous C.T.
3- Yellow elastic C.T
4- Adipose C.T.
5- Mucoid C.T.
6- Reticular C.T.
LOOSE CONNECTIVE TISSUE
Functions: 1- It binds tissues and organs together.
2- It carries blood vessels, lymphatics and nerves to supply other tissues.
Sites: It is found around blood vessels, in the submucosa of the digestive system and in
the serous membranes e.g. peritoneum.
Structure:
- Fibres: collageneous and elastic fibers.
- Cells: mainly fibroblasts, much macrophages and some fat cells.
- The matrix is rich in hyaluronic acid.
WHITE FIBROUS CONNECTIVE TISSUE
It is formed principally of collageneous fibers, with few cells and matrix
1-Regular type:
- Site: - tendons and cornea of the eye.
- Structure: - Parallel collageneous bundles with Fibroblasts or fibrocytes between the
bundles.
2-Irregular type:
- Site: - sclera of the eye, capsule of organs and outer fibrous layer of the
periosteum & perichondrium.
- Structure: - Irregular collageneous bundles with Fibroblasts or fibrocytes between the
bundles.
YELLOW ELASTIC CONNECTIVE TISSUE
- Sites:
- Arteries
- Bronchial tree.
- Ligamentum flavum between vertebrae.
- Suspensory ligament of the penis.
- Structure: - Regular elastic fibers with Fibroblasts or fibrocytes between the fibers.
ADIPOSE CONNECTIVE TISSUE
White adipose C.T.
Brown adipose C.T.
Color
White.
Brown.
Sites
The majority of adipose
C.T. in adults e.g.
subcutaneous tissue and
perinephric fat.
In newborn infants.
In adults:
- Mediastinum.
- Between the 2 scapulae.
Structure
EM
Functions
 Lobules of large white
adipocytes separated by
loose C.T.
 Cytoplasm contains a large
fat globule (single)
 The large fat globule
pushes the nucleus to one
side → signet ring
appearance.
 Less blood capillaries
 Lobules of small brown
adipocytes separated by
loose C.T.
 Cytoplasm contains numerous
fat droplets.
 The nucleus is central and
rounded.
- Few mitochondria and
sER around the nucleus.
- Numerous mitochondria
surrounding the fat droplets.
 More blood capillaries.
1-Storage of fat (energy depot). Rapid heat production on
2- Heat insulation.
exposure to cold.
3-body contour.
4-support organs (kidney).
MUCOID CONNECTIVE TISSUE
- Site: - Wharton's jelly of the umbilical cord.
- Vitreous body of the eye.
- Pulp of the teeth.
- Structure: - The matrix is soft as it is rich in mucin and hyaluronic acid.
- Young fibroblasts which intercommunicate with long processes.
RETICULAR CONNECTIVE TISSUE
Sites:
- Stroma of parenchymatous organs e.g. liver, spleen, lymph nodes and bone marrow.
Structure:
- Formed of reticular cells and reticular fibers that form a network.