Zones - Growth in length

The clavicle is

+the last bone to stop growing

Zone of hypertrophic cartilage

+this layer consists of large, maturing chondrocytes arranged in columns.

Four zones of epiphyseal plate

+zone of resting cartilage +zone of proliferating cartilage +zone of hypertrophic cartilage +zone of calcified cartilage

The appearance of the epiphyseal line signifiies

+that the bone has stopped growing in length

At about age 18 in females and 21 in males

+the epiphyseal plates close. The epiphyseal cartilage cells stop dviding, and bone replaces all of the cartilage. The epiphyseal plate fades, leaving a bony structure called the epiphyseal line

Zone of proliferating cartilage

+ this layer consists of slightly larger chondrocytes arranged like stacks of coins. +these chondrocytes secrete cartilage extracellular matrix and divide to replace chondrocytes that die at the diaphyseal side of the epiphyseal plate

Mnemonic for zones

+Resting cartilage (Rational) +Proliferating cartilage (People) +Hyertrophic cartilage (Hate/Have) +Calcified cartilage (Cats)

Zone of calcified cartilage

+epiphyseal plate is only a few cells thick and consist mostly of chondrocytes that dead because the extracellular matrix around them has calcified +osteoclasts dissolve the calcified cartilage +osteoblasts and capillaries from the diaphysis invade the area +osteoblast replaces the extracellular matrix with calcified cartilage + as a result the zone of calcified cartilage becomes new diaphysis that is firmly cemented to the rest of the diaphysis of the bone

Zone of resting cartilage

+near to the epiphysis +consist of small, scattered chondrocytes +term "resting" is used because the cells doesn't function in bone growth +anchors the epiphyseal plate to the epiphysis of the bone

As a bone grows

+new chondrocytes are formed on the epiphyseal side of the plate, while old chondrocytes on the diaphyseal side of plate are replaced by bone + therefore the thickness of the epiphyseal plate remains relatively constant, but the bone on the diaphyseal side increases in length

Epiphyseal plate

Layer of hyaline cartilage in the metaphysis of a growing bone that consist of four zones