Bone growth Flashcards
what are the functions of bone
supports body (muscles hang off) protection for organs movement mineral homeostasis triglyceride storage (in yellow marrow of adipose tissue) hoaemopoesis (red bone marrow)
how is bone classified and what are the categpries
according to shape
irregular- eg face sesamoid- embedded in tendons flat- thin, sometimes curved, usually protective, eg skull long- longer than wide short- similar length and width
name the parts of a long bone
proximal and distal epiphysis metaphysis diaphysis medullary cavity endosteum periosteum
what are
proximal and distal epiphysis
metaphysis
proximal and distal epiphysis are the very ends of bone, the protrusion
metaphysis is between epiphysis and body of bone, where curves into flat
epiphyseal plate is located in metaphysis
what are
the medullary cavity
endosteum
periosteum
medullary cavity is hollow, within diaphysis, where bone marrow is stored, lined by endosteum
endosteum lines inner cavity (medullary cavity)
periosteum lines outer bone, except at joints
bone tissue types?
spongy bone- inner
compact/ cortical bone- outer
spongy bone
also called trabecular bone, cancellous bone
forms inner layer of all bones, lines medullary cavity
loose structure of branching rods (trabeculae), adjacent to irregular cavities that contain marrow
trabeculae arranged such that one side of bone bears tension whilst other side withstands compression
compact/ cortical bone
forms the hard external layer, very dense, composed of osteons
Osteons (also called Haversian systems) are cylindrical, pipe-like structures.
Central canal- the Haversian canal, contains blood vessels and nerves.
Lamellae (the rings) radiate out from haversian canal andf contain the matrix
Between lamellae are lacuna, which are small spaces in which osteocytes are located
Cannaliculi are small channels between lacunae and haversian canal.
what is bone
highly vascular, mineralised connective tissue
composition of bone
bone is a specialised type of connective tissue.
Connective tissue composed of cells and matrix. In bone:
matrix: 95% collagen, ground substance with fluid like composition
cells: osteoprogenitor, osteoblasts, osteocytes, osteoclasts
minerals: hydroxyapatite, calcium phosphate
red vs yellow bone marrow
red bone marrow: haemopoeitic stem cells
yellow bone marrow: adipose tissue
what is an osteoprogenitor cell
squamous stem cells of bone
mainly differentiate into osteoblasts
can become fibroblasts, chondrocytes, adipocytes
what is an osteoblast
osteoBlast= Bone Builder
bone building cells, responsible for bone formation,
secrete collagen and the organic matrix of bone (osteoid) which becomes calcified soon after it is deposited
will eventually become trapped in their secretions of matrix and become an osteocyte
what is an osteocyte
the trapped osteoblast differentiates into the less active osteocyte.
responsible for maintenance and homeostasis of bone
sit within lacuna, ram through bone to form gap junctions with other osteocytes
what is an osteoclast
osteoClasts= bone Chewers
formed by 50+ monocytes, so have 50+ nuclei
responsible for breakdown and removal of bone by releasing lysosymal enzymes and acids that dissolve matrix
this releases minerals into the blood so regulates mineral levels, may also be reabsorbed for remodelling
what is cartilage
an avascular, specialised form of connective tissue
cells: chondrocytes
matrix: water, collagens, proteoglycans
hyaline cartilage most relevant in bone growth
what is endochondrial ossification
bone formation from a hyaline cartilage model
endochondrial ossification in depth
cells in mesenchyme at site of future bone (mesenchymal cells= stem cells) differentiate into chondrocytes (chondro= cartilage) that produce a hyaline cartilage model. as matrix develops, central chondrocytes enlarge
matrix calcifies, stopping diffusion of nutrients, chondrocytes die, disintegration of surrounding cartilage. Matrix breaks down, forms a cavity
Blood vessels invade and supply nutrients and mesenchymal cells that mostly differentiate into osteoblasts
osteoblasts lay down compact bone in bony collar around centre of diaphysis of cartilage model
osteoblasts begin to lay down bone, replacing cartilage. = primary ossification centre
primary ossification centre grows towards ends of long bone as osteoblasts continue laying down. osteoclasts resorb bone in cavity, form medullary cavity
by birth, cartilage remains only on articulate joint surfaces and at epiphyseal plates, which will be the secondary/tertiary ossification centres where growth happens in length of bones after birth
endochondrial ossification outline
mesenchyme to chondryocytes to cartilage model
central chondrocytes enlarge as matrix develops
matrix calcifies, chondrocytes die, matrix breaks down in middle, cavity formed
blood vessels invade, bringing mesenchymal cells that become osteoblasts
lay down bony collar, then primary ossification centre, grows middle to ends, replacing cartilage with bone
osteoclasts resorb bone in cavity forming medulllary cavity
at birth only epiphyseal plates and joints still cartilage
what are the osteoblasts and clasts continuously doing
bone continuously deposited by osteoblasts and resorbed by osteoclasts, usually at equal rate. Bone has high turnover rate.
=remodelling
what are the benefits of remodelling
bone thickens in response to heavy loads (eg athletes bones thicker, bones in plastercast thinner)
shape adjusts to stresses on bone (reheal breaks over time sometimes)
renews matrix, which maintains toughness of bone
calcium homeostasis bones
bones= body’s biggest source of calcium
low calcium= parathyroid hormone= increases osteoclast activity= calcium released
high calcium= calcitonin hormone, decreases osteoclast activity= calcium into bone
how do these things affect bone cell/ bone activity
Growth Hormone
Thyroxine
Sex hormones
Vitamin D
GH= increase cell growth
Thyroxine= increase osteoblast activity
Sex hormones= increase osteoblast activity
vit D= calcium resorption from GIT, promoting bone calcification
order of growth plate zones
reserve proliferative maturation hypertrophic invasion
(zone)
IGF-1 and Growth hormone stimulate growth in epiphyseal plates. How does growth happen here?
Reserve zone- contains clusters of osteprogenitor cells, move into
Proliferative zone- osteoprogenitor cells differentiate into chondroblasts, undergo expansion and proliferation to form organised cell columns
Maturation zone-chrondroblats become chondrocytes, secrete matrix and enlarge as mature
Hypertrophic zone- the largest will differentiate into hypertrophic chondrocytes, secrete type 10 collagen. Cells undergo apoptosis, forming holes (the lacunae), seperated by artilaginous septae
Invasion zone: this acts as scaffold for new bone, is laid down by osteoblasts which invade from the bone marrow
what hormone is responsible for closing the growth plate and how
oestrogen closes growth plate so long bone growth can no longer occur
causes apoptosis of progenitor cells in reserve zone so can no longer supply chondroblasts
what are thyroid hormones important for in bone growth
important in hypertrophic zone of growth plate, stimulate chondrocyte hypertrophy
