Bone growth

Question 1

what are the functions of bone

Answer 1

supports body (muscles hang off)
protection for organs
movement
mineral homeostasis
triglyceride storage (in yellow marrow of adipose tissue)
hoaemopoesis (red bone marrow)

Question 2

how is bone classified and what are the categpries

Answer 2

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

Question 3

name the parts of a long bone

Answer 3

proximal and distal epiphysis
metaphysis
diaphysis
medullary cavity
endosteum
periosteum

Question 4

what are
proximal and distal epiphysis
metaphysis

Answer 4

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

Question 5

what are
the medullary cavity
endosteum
periosteum

Answer 5

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

Question 6

bone tissue types?

Answer 6

spongy bone- inner

compact/ cortical bone- outer

Question 7

spongy bone

Answer 7

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

Question 8

compact/ cortical bone

Answer 8

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.

Question 9

what is bone

Answer 9

highly vascular, mineralised connective tissue

Question 10

composition of bone

Answer 10

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

Question 11

red vs yellow bone marrow

Answer 11

red bone marrow: haemopoeitic stem cells

yellow bone marrow: adipose tissue

Question 12

what is an osteoprogenitor cell

Answer 12

squamous stem cells of bone
mainly differentiate into osteoblasts

can become fibroblasts, chondrocytes, adipocytes

Question 13

what is an osteoblast

Answer 13

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

Question 14

what is an osteocyte

Answer 14

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

Question 15

what is an osteoclast

Answer 15

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

Question 16

what is cartilage

Answer 16

an avascular, specialised form of connective tissue

cells: chondrocytes
matrix: water, collagens, proteoglycans

hyaline cartilage most relevant in bone growth

Question 17

what is endochondrial ossification

Answer 17

bone formation from a hyaline cartilage model

Question 18

endochondrial ossification in depth

Answer 18

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

Question 19

endochondrial ossification outline

Answer 19

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

Question 20

what are the osteoblasts and clasts continuously doing

Answer 20

bone continuously deposited by osteoblasts and resorbed by osteoclasts, usually at equal rate. Bone has high turnover rate.

=remodelling

Question 21

what are the benefits of remodelling

Answer 21

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

Question 22

calcium homeostasis bones

Answer 22

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

Question 23

how do these things affect bone cell/ bone activity

Growth Hormone
Thyroxine
Sex hormones
Vitamin D

Answer 23

GH= increase cell growth
Thyroxine= increase osteoblast activity
Sex hormones= increase osteoblast activity

vit D= calcium resorption from GIT, promoting bone calcification

Question 24

order of growth plate zones

Answer 24

reserve
proliferative
maturation
hypertrophic
invasion 

(zone)

Question 25

IGF-1 and Growth hormone stimulate growth in epiphyseal plates. How does growth happen here?

Answer 25

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

Question 26

what hormone is responsible for closing the growth plate and how

Answer 26

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

Question 27

what are thyroid hormones important for in bone growth

Answer 27

important in hypertrophic zone of growth plate, stimulate chondrocyte hypertrophy