Chapter 6: Cartilage & Bone
mature cartilage is ___________
avascular (non penetrated by blood vessels) so nutrients must diffuse through the matrix
chondroblasts
cells that produce the matrix of cartilage
Steps of appositional growth
1. Undifferentiated stem cells at the internal edge of the perichondrium begin to divide (perichondrium contains mesenchymal & stem cells) 2. New undifferentiated stem cells & committed cells that differentiate into chondroblasts are formed & are located at the periphery of the old cartilage where they begin to produce & secrete new cartilage matrix 3. chondroblasts push apart as a result of matrix formation & become chondrocytes; each occupying its own lacuna 4. Cartilage continues to grow at the periphery as chondrocytes continue to produce more matrix
Steps of interstitial growth
1. chondrocytes in lacunae are stimulated to undergo mitosis 2. 2 cells occupy a single lacuna after cell division; now called chondroblasts 3. As chondrocytes begin to secrete & synthesize new cartilage matrix, they are pushed apart. These cells now reside in their own lacuna and are called chondrocytes 4. Cartilage continues to grow in the internal region as chondrocytes continue to produce more matrix
osteoblasts
Formed from osteoprogenitor stem cells Cuboidal structure Secrete osteoid - initial semisolid, organic form of bone matrix Later calcified & hardens Once osteoblasts become entrapped in the matrix they produce & secrete & differentiate into osteocytes
appositional growth
Growth along the cartilage outside edge
Interstitial growth
Growth from within the cartilage itself
3 types of cartilage
Headline Elastic fibrocartilage
Interstitial lamellae
Leftover parts of osteons that have been partially reabsorbed; no central canal; incomplete
osteoclasts
Multi-nuclear pahagocytic cells Derived from fused bone marrow cells
Spongy bone is composed of ___________
Parallel lamellae
hemopoiesis
Process of red blood cell production - produces in red bone marrow in spongy bone
Growth hormone
Produced by the anterior pituitary gland Stimulates the formation of somatomedin which is produced in the liver and directly stimulates the growth of cartilage in the epiphyseal plate
osteolysis
Release of stored calcium and phosphate from the bone matrix
Osteoclasts ______ while osteoblasts _________ to the matrix
Remove; add
Concentric lamellae
Rings of bone connective tissue that surround the central canal Each contains collagen fibers oriented in perpendicular directions
circumferential lamellae
Rings of bone immediately internal to the periosteum of the bone; runs around the edge of the bone
Perforating canals
Run perpendicular to the central canals; connecting them under w/ blood vessels and nerves
Thyroid hormone
Secreted by thyroid gland Influences the basal metabolic rate of bone cells
osteoprogenitor cells
Stem cells Derived from mesenchyme Located both in the periosteum & endosteum When they divide, they produce another stem cell & a "command cell" that matures to become an osteoblast
Perforating fibers
Strong collagen fibers
Functions of bone
Support & protection Movement hemopoiesis Storage of mineral and energy reserves
3 major functions of cartilage
Supporting soft tissues Providing a gliding surface at articulations where 2 bones meet Providing a model for the formation of most of the bones in the body
canaliculi
Tiny, interconnecting channels within the bone tissue that extend from each lacuna, travel through the lamellae & connect to other lacunae & the central canal
Central canal
Where blood vessels & nerves that supply the bone travel
Osteocytes
lacunae - small spaces within the matrix in which osteocytes reside Maintain the bone matrix & detect mechanical stress on a bone
Spongy bone contains no ____________
osteons
Cells of bone
osteoprogenitor osteoblasts osteocytes osteoclasts
chondrocytes
when chondroblasts become encased within the matrix they have produced & secreted & occupy small spaces called lacunae