Introduction
- Derived from Mesorderm |
- Acts as supportive tissues:
+ Structural framework
+ Organ procection
+ Stores energy
+ Nutrient transportation
+ Protection against pathogens |
- Consists of CELLS and MATRIX
Matrix: fibers + ground substance (from fibroblast) --> surrounds cells and make up majority of volume |
Categories
- Connective tissue proper:
+ Cells: mainly fibroblast
+ Matrix: Semi fluid
- Supportive connective tissue:
+ Cartilage: chondrocytes, gel-like fluid
+ Bones: osteocytes, calcified matrix
- Fluid connective tissue:
+ Blood: blood cells, fluid matrix |
Connective Tissue Proper
Constituents:
- Scattered cells that are either fixed or migratory
- Fibres
- Viscous ground substance |
Fixed cells:
- Fibroblasts
- Adipocytes
- Mesenchymal cells
- Macrophages |
Migratory cells:
- Lymphocytes
- Mast cells
- Plasma cells
- Macrophages |
Fibroblast
- Most abundant |
- Always present |
- Secretes components of ground substance |
- Secretes protein sub-units --> form fibres |
- Involved in wound healing |
- Elongated along fibres, elliptical nucleus, moderately dense |
Mesenchymal cells
- Smaller, less differentiated than fibroblasts |
-Differentiated into other connective tissue cells when injured/infected |
-Star (stellar)/spindle (fusiform) shape |
- Oval nucleus, can be seen clearly |
- Lie along capillaries |
-Present in many types of connective tissues |
Adipocytes
-Lipid synthesis and storage |
-Contain 1 or more lipid droplets |
-Displaced nucleus; narrow cytoplasm's rim |
- Main cell of adipose tissue |
-Also present in loose connective tissue (clumps or single |
- Non - dividing |
Macrophages (ALSO Histiocytes)
-Derived from Monocytes |
-Phagocytosis of: dead tissue; foreign materials |
- If stimulated --> Release chemicals triggering immune system |
- Store antigenic materials to present to antibody-producing cells |
- Stallate/Fusiform shape, lie along fibres |
- Large, irregular nucleus |
-Difficult to distinguish these and fibroblasts |
|
|
Migratory cells
Besides Mast cells, all migratory cells immigrated from blood |
Amoeboid:
- Neutrophils
- Eosinophils
- Monocytes
- Lymphocytes --> Plasma cells (differentiated) |
Mast cells
-From immune system |
- Large cells, shape varied amongst species |
-Small, maybe binucleus |
- Basophilic granules, contains heparin and histamine --> Released in response to injury/infection |
- Similar to basophils |
Plasma cells
-Ovoid, basophilic cytoplasm |
- Eccentric "cart wheel" nucleus |
- A lot in lymph nodes and connective tissues of G.I Tract |
- Produce antibodies |
Classification of CT Proper
Based on physical and histological characteristics |
- Loose (areolar) connective tissue |
- Dense CTissue (Regular, Irregular) |
- Elastic CT |
- Reticular CT |
-Adipose tissue (White, Brown) |
Ground substance
- Surrounds cells and fibres |
- Clear and viscous
--> Slow pathogens --> Facilitates phagocytosis |
- Contains proteoglycans and glycoproteins |
Elastic Fibres
-Composed of protein elastin |
-branches and wavy |
-Stretch and recoil to relaxed state |
-Yellowish when fresh |
-Difficult to see with H&E, use specialised stain |
-Forms Elastic fibres ligmants (in continuous vertebrae) or discontinuous sheets (skin, lung, blood vessels) |
Reticular Fibres
-Composed of same protein as collagen |
-thinner than collagen |
-tough, flexible, branching, interweave network |
-stabilise position of cells, blood vessels, nerves |
-difficult to see histologically(need silver chain) |
-Found in: parenchyma of spleen, liver, lymph nodes, glands and bone marrows. |
Collagen fibres
-Long, straight |
-Flexible, strong |
-Polypeptide chains twisted into a rope |
-white/clear when fresh |
-Stained pink with eosin |
- Most common in CT proper |
- Form almost entirely Tendons and Ligaments |
|
|
Loose CT (areolar)
- Volume mostly made of ground substance
--> inhibits passage of microorganisms |
-Loosely arranged fibres |
- Fixed/migratory cells are common |
- Cells resist infection and assist wound healing |
- Very vascular |
- Packing around organs, support epithelial tissue |
Dense CT
- Collagen fibres dominate --> fewer cells
--> Sometimes called Collagenous tissue |
- Less physiologically active (less nerves and blood vessels) |
- High strength, low to moderate elasticity |
-Collagen fibres either PARALLEL:
--> Regular Dense CT (ligaments, tendons, joint capsules)
- Or RANDOMLY ARRANGED:
--> Irregular dense CT (dermis, organ capsules) |
Elastic CT
- Elastic fibres dominate (irregular or regular dense) |
- Moderate mechanical strength and high elasticity |
- Found in: Airways of Respiratory tree, arteries, ligaments of abdominal cavity and vertebral column. |
Reticular CT
- Forms framework of softer tissues: spleen, liver, lymph nodes and bone marrows. |
Adipose tissue
Mostly fat cells
Reserve energy and water |
White adipocytes
- Bulk of body fat
|
Brown adipocytes:
- Smaller, multilocular cells |
- Large, unilocular
|
- Round, central nuclei |
- Signet ring: peripheral nucleus, lipid removed during processing --> leaving a vacuole |
- Involved in heat production |
| |
- Many blood vessels and nerves |
| |
- Many in young animals and hibernators |
|
