function and structure of bone

Question 1

what type of tissue does bone fall under?

Answer 1

connective tissue - a large component of bone is its ECM.

Question 2

what are a few functions of bone?

Answer 2

protection of organs (e.g. rib cage), support, movement, storage of minerals and blood cell formation.

Question 3

what is the main mineral composition of bone?

Answer 3

calcium hydroxyapatite

Question 4

periosteum

Answer 4

fibrous layer that covers internal (endosteum) and external surfaces of bone not covered by articular cartilage. contains osteogenic progenitor cells which divide to produce osteoblasts and chondroblasts. also contains fibroblasts which synthesise collagen and osteoclasts.

Question 5

epiphysis

Answer 5

‘head’ of a long bone. secondary centre of ossification. has an articular surface covered by hyaline cartilage.

Question 6

diaphysis

Answer 6

‘shaft’ of a long bone. composed of compact bone and a central medullary cavity which contains bone marrow. also contains the nutrient foramen which is where the blood vessels enter the bone to provide nutrients.

Question 7

osteoclasts

Answer 7

bone cells derived from macrophages. secrete powerful digestive lysosomal enzymes and acids that digest the protein and mineral matrix of bone. found concentrated in the endosteum (inner membrane between compact bone and medullary cavity)

Question 8

osteoblasts

Answer 8

bone cells derived from osteoprogenitor cells on the periosteum. deposit the collagen matrix of bone and cause mineralisation. some become entombed in the bone matrix to become osteocytes.

Question 9

osteons/haversian systems

Answer 9

microscopic cylinders within compact bone. In the centre there is a haversian canal which contains blood vessels, lymphatic vessels and nerves

Question 10

lamellae

Answer 10

rings of calcified bone matrix surrounding the haversian canals that form from collagen fibres running in different directions.

Question 11

lacunae

Answer 11

embedded osteocytes within the bone matrix in the haversian systems.

Question 12

canaliculi

Answer 12

small, finger-like projections radiating away from the lacunae which connect different osteocytes and allow them to communicate between each other and also with the central canal. these allow oxygen and nutrients to diffuse through the bone.

Question 13

cancellous bone

Answer 13

also known as spongy bone or trabecular bone, found in the epiphysis of long bones. helps to reduce weight while providing strength. trabecular are laid down along lines of stress.

Question 14

trabecule

Answer 14

irregular lattice of bone matrix in the spongy (cancellous/trabecular) bone.

Question 15

what does a deficiency of vitamin D cause?

Answer 15

rickets

Question 16

what does a deficiency of vitamin C cause?

Answer 16

scurvy, inadequate quantity of collagen is produced.

Question 17

osteocytes

Answer 17

mature bone cells formed from osteoblasts. some can become embedded in the bone matrix forming lacunae. Important in maintaining bone matrix through communicating via caniliculi.

Question 18

van buchem’s disease

Answer 18

caused by an absence of osteocytes. Abnormal deposition of calcium by osteoblasts. Increased mass of bones.

Question 19

bone hypertrophy

Answer 19

when the rate of bone formation outweighs the rate of bone resorption. Increased activity of osteoblasts.

Question 20

bone atrophy

Answer 20

when the rate of bone resorption outweighs the rate of of bone formation. Increased activity of osteoclasts.

Question 21

calcitonin

Answer 21

hormone that deceases the activity of osteoclast, decease in blood calcium ion levels

Question 22

parathyroid hormone (PTH)

Answer 22

increase in the activity of osteoclasts, increase in the level of blood calcium ions

Question 23

bone remodelling cycle

Answer 23

quiescence (nothing needs changing, homeostasis achieved); resorption (osteoclast activity); reversal (osteoblasts accumulate on the eroded surface); formation (osteoblasts lay down the new bone matrix)

Question 24

what does Wolff’s law represent?

Answer 24

bone adapts to the load which it is placed under (e.g. orthodontic braces)

Question 25

what is the sequence of events for bone fracture?

Answer 25

osteoblasts quickly form woven bone to bridge the gap. this woven bone is weak as the collagen fibres are irregular. this woven bone is remodelled by the osteoclasts in the local periosteum after 2-4 weeks. lamellar bone is laid down with organised collagen fibres in regular sheets to give resilience and strength.

Question 26

what cells is the cartilage model in a foetus made up of?

Answer 26

chondrocytes and chondroblasts

Question 27

what is the process of replacing the cartilage model caused in long bones?

Answer 27

endochondrial (this process begins before birth)

Question 28

what is the process of replacement of the cartilage model in flat bones called?

Answer 28

intremembranous

Question 29

what is the epiphyseal plate?

Answer 29

the cartilage junction between the diaphysis and the epiphysis where ossification takes place and where new bone cells are made, increasing the length of the long bone.

Question 30

what is the order of zones in the epiphyseal plate? (from top to bottom; from the diaphysis to the epiphysis)

Answer 30

ossification/osteogenic zone; calcification zone; hypertrophic zone; growth/proliferating zone; resting zone

Question 31

what is happening in the resting zone?

Answer 31

the cartilage cells created by the chondroblasts are resting

Question 32

proliferation/growth zone

Answer 32

the chondroblast cells divide and proliferate

Question 33

hypertrophic zone

Answer 33

chondroblast cells start to swell,become chondrocytes and spontaneous mineralization takes place

Question 34

ossification zone

Answer 34

osteoblasts and osteoclasts work together to replace the cartilage cells with osteoblasts and mineralization takes place