cartilage

1. Supports tubular organs to keep them open (trachea and bronchus)
2. Forms a semi-flexible union between bones (ribs and sternum)
3. Forms gliding surface between articular surfaces
4. Precursor for bones in development

Cartilage, like CT, contains cells surrounded by an extensive extracellular matrix.

1. Fibers
2. Ground substances (proteoglycans, sulfonated/non sulf. GAGS) and water

Cartilage cells (chondrocytes) are trapped in small holes called lacunae.

Chondrocytes produce and maintain the matrix.

Chondrocytes can divide but there is decreased ability with age

Cartilage is avascular (vascular or avascular)

Cartilage trapped in the matrix receive oxygen and nutrients through diffusion by blood vessels in the surrounding CT or in the case of articular cartilage from the synovial fluid.

The lack of blood vessels of cartilage is responsible for
the low metabolic activity of cartilage and limits its size and ability to be repaired.

Cartilage is classified into 3 types based upon the type of fibers in the matrix

1. Hyaline
2. Elastic
3. Fibrocartilage

Type II collagen fibrils (not visible)

Type II collagen fibrils WITH elastic fibers
(visible with special stains)

Type I collagen (visible acidophillic fibers)

Hylaine cartilage

Hyaline cartilage is a pearly white color on fresh dissection

-Dense connective tissue wrapping
-It has collagen type I fibers, fibroblasts, and blood vessels
-Chondriogenic (appositional growth)

-Trapped in lacunae, fed by diffusion
-Synthesize and maintain matrix
-Round nucleus, glycogen and lipid in cytoplasm

-Hydrated gel with Type II collagen fibrils
-Fibrils are NOT visible in LM
-Avascular

There is a stained basophillic matrix around each cell

Basophilic matrix around isogenous group of cells

Lightly stained areas between cell clusters

2-8 cells formed by mitosis of a single chrondrocyte (interstitial growth)

Division of chondrocytes in lacunae

Fibroblasts to condroblasts to chondrocytes

Chondrogenesis begins in the embryo when chondroblasts differentiate from mesenchyme.

(1) The chondroblasts differentiate from cells in the perichondrium
(2) The chondroblasts secrete matrix against exisiting cartilage and become trapped in matrix (now called a chondrocyte)
(3) Appositional growth adds matrix to outside of cartilage

(1) Chondrocytes in lacunae undergo mitosis
(2) New chondrocutes secrete matrix and separate from each other, becoming trapped in their own lacunae
(3) Interstitial growth added matrix from inside of tissue

-Results in isogenous groups
-Common in development wen the matrix is soft

Calcification and degeneration of cartilage - occurs normally in hyaline cartilage
with aging and is part of the process of endochondral bone development. Chondrocytes
hypertrophy, die, and the matrix calcifies (precipitation of mineral salts).

Repair of cartilage - except for the very young, repair of damaged cartilage is slow and
incomplete, primarily only from the perichondrium. If the damage is too extensive, the
cartilage is replaced by a connective tissue scar. This poor regenerative ability is
primarily due to the avascularity and low metabolism of the tissue.

Articular cartilage is the smooth, friction free layer of hyaline cartilage at the end of
bones in synovial joints.

Articular cartilage does NOT have a perichondrium. It receives oxygen and nutrients
from the synovial fluid of the joint capsule. Because of what it lacks, articular
cartilage has a poor ability to repair itself when damaged.

Osteoarthritis is a common degenerative joint disease, characterized by progressive degeneration and erosion of articular cartilage . Eventually, cartilage is lost and bone is exposed. "Wear and tear" disease

Rheumatoid arthrist is a chronic systematic autoimmune inflmmatory disorder that attacks many tissues and organs. Attacks joints, destroying cartilage and replacing it with a vascular connective tissue

ELASTIC CARTILAGE - present in areas needing more flexibility, as in the external ear,
external auditory canal, Eustachian tubes, epiglottis, and areas of the laryngeal
cartilage.

Elastic cartilage is similar to hyaline cartilage except in addition to Type II collagen fibrils, it has ELASTIC FIBERS

Elastic fibers are only visible with special stains

FIBROCARTILAGE - present where additional strength is necessary, as in the
intervertebral discs, pubic symphysis, joint capsules, ligaments and attachments of
tendons to bone

Fibrocartilage is intermediate in structure between dense CT and
hyaline cartilage. It is always associated with dense regular connective tissue.

Fibrocartilage lacks a perichondrium

1. Matrix made of parallel bundles of Type I collagen firbers aligned in direction of stress (acidophollic and visible in light EM)
2. Chondrocytes are lined in rows between collagen fibers

Hyaline cartilage = chondrocytes in lacunae

Fibrocartilage = condrocytes in lacunae in rows, rounder nuceli and no perichondrium

Dense regular CT = fibroblasts in rows with flat nuclei

The intervertbral disks are made of concentric rings of fibrocartilage called the annulus fribrosis, surround the nucelus pulposus. It can weaken, leading to slipped disk