Histology of Cartilage

Study Notes

Cartilage is a type of connective tissue with a firm consistency of the extracellular matrix.
There are three types of cartilage: hyaline cartilage, yellow elastic fibrocartilage, and white fibrocartilage.

Appearance: translucent pale blue in fresh state
Consistency: firm or rigid with some degree of flexibility
Structure:
- Formed of perichondrium, cartilage cells (chondrocytes), and cartilage matrix
Sites:
- Constitutes the majority of the foetal skeleton
- Articular surface of bones
- Costal cartilage in the thoracic cage
- Nose, trachea, and bronchi

A vascular connective tissue membrane that surrounds the cartilage except at the articular surfaces of the joints
Formed of two layers: outer fibrous layer and inner chondrogenic layer
Function:
- Acts as a source of O2 and nutrients to the cartilage cells
- The inner chondrogenic layer is responsible for new cartilage formation

There are two types of chondrocytes: young chondrocytes and mature "old" chondrocytes
Young chondrocytes:
- Arise from the inner chondrogenic layer
- Flat cells with open-face nuclei and pale basophilic cytoplasm
- Present singly in their lacunae at the periphery of the cartilage and parallel to the perichondrium
Mature "old" chondrocytes:
- Site: deep in the cartilage in the form of rows perpendicular to the perichondrium
- Shape: oval or rounded when single, and triangular or semicircular when in groups
- Have rounded and open-face nuclei and granular, basophilic cytoplasm rich in glycogen, fat, and phosphatase enzyme
Function:
- Synthesize and secrete the components of the cartilage matrix
- Can divide, responsible for the growth of the cartilage

General characters:
- Rubbery in consistency
- Non-vascular
Staining reaction:
- Appears homogenous basophilic by Hx and E due to the presence of sulphated glycosaminoglycans
- Shows strong PAS positivity
Components:
- Collagen fibers (Type II)
- Proteoglycans (chondritin 4 sulphate and 6 sulphate)
- Glycoprotein (chondronectin)
- Protein (chondrocalcin)

Appearance: yellow in color due to the presence of elastic fibers
Consistency: elastic and flexible due to the presence of elastic fibers
Structure:
- The matrix contains an abundant network of elastic fibers
- Can be stained by standard elastic stains (e.g. Verhoeff's stains)
Sites:
- Auricle of the ear
- External auditory meatus
- Eustachian tube
- Epiglottis

Appearance: white in fresh state
Consistency: tense and resists stretch due to the presence of collagen fibers
Structure:
- Differs from hyaline cartilage in:
  - Not covered by perichondrium but surrounded by dense C.T. rich in blood vessels
  - Chondrocytes are arranged in rows or columns
  - Matrix contains bundles of coarse type I collagen fibers in between rows of chondrocytes
Sites:
- Intervertebral discs
- Semilunar cartilage of knee joints
- Symphysis pubis
- Lips of glenoid cavity
- Terminal parts of tendons