3: Bone Physiology

Question 1

what’s included in skeletal system

Answer 1

bones
cartilage
joints
ligaments
other connective tissues
206 bones in body

Question 2

skeletal functions

Answer 2

support
storage of minerals and lipids
blood cell production
protection
leverage

Question 3

classifications of bones

Answer 3

long bones - longer than wide, leverage
short bones - dimensions equal, transfer forces
flat bones - thin and broad, protection
irregular bones - complex shapes
sutural bones - between skull bones
sesamoid bones - small and develop in tendons

Question 4

features of long bones

Answer 4

diaphysis = central shaft, compact dense bone, surrounds marrow cavity
marrow cavity = space that contains bone marrow
epiphyses = ends bone bone, covered by articular cartilage

Question 5

bone (osseous) tissue

Answer 5

ground substance = 2/3 of the bone matrix, made of minerals with other calcium sites and ions
protein = other 1/3 of the bone matrix, provides extra strength, reinforce minerals, stops on being brittle
bone cells = account for 2% of bone mass
mesenchymal stem cells turn to osteoblasts turn to osteocytes

Question 6

types of bone

Answer 6

two types:
compact = dense and solid, forms wall of diaphysis, thin layer covers epiphyses
spongey (trabecular bone) = interlacing network of bony rods separated by spaces, fills the epiphyses and lines marrow cavity

Question 7

periosteum

Answer 7

membrane that covers outer surface of bone
consists of outer fibrous layer (where collagen fibres are continuous with bone, ligaments, tendons and joint capsule) and inner cellular layer
periosteum isolates bone from surrounding tissue
provides route for blood vessels and nerves
takes part in bone growth and repair

Question 8

endosteum

Answer 8

membrane lining bone on inner surface
covers the spongy bone of the marrow cavity
incomplete cellular layer

Question 9

microscopic features of bones

Answer 9

lacunae = small pockets where osteocytes are
lamellae = rows of sheets of calcified matrix
canaliculi = small channels through the matrix

Question 10

compact bone

Answer 10

compact bone has functional and structure units known as osteons - within, osteocytes are arranged in concentric layers around a central canal
perforating canals provide passageways that link the blood vessels of central canal to the ones in periosteum and marrow cavity
osteons parallel to long axis of the shaft to stop bone bending
compact bone usually found where stresses come from limit range of directions

Question 11

spongy bone

Answer 11

no osteons
trabeculae = lamellae that form rods or plates
forms network of spongy bone which supports and protects the cells of red bone marrow
spongy bone found where bones are not heavily stressed or where stresses arrive from many directions
red bone marrow = between trabecular, forms red blood cells, provides nutrients to osteocytes
yellow bone marrow = found in mallow cavity, stores fat

Question 12

cells in bone

Answer 12

osteoblasts = produce new bone through ossification, when osteoblasts become completely surrounded by calcified matrix, it differentiates into osteocytes
osteocytes = mature bone cell, maintain normal bone structure
osteoclasts = secrete acids and enzymes that dissolve bony matrix and release stored minerals

Question 13

intramembranous ossification

Answer 13

bone develops within sheets or membranes of fibrous connective tissue
forms flat bones
1. mesenchymal cells differentiate into osteoblasts
2. ossification forms spicules of bone
3. trabecular bone formed
4. remodelled into compact bone

Question 14

endochondral ossification

Answer 14

bones replace existing cartilage
1. chondrocytes within cartilage enlarge and then die as the matrix calcifies
2. new osteoblasts cover the shaft of the cartilage in a thin layer of bone
3. blood vessels penetrate the cartilage, new osteoblasts form primary ossification centre inside cartilage model, spongy bone forms in centre of shaft
4. bone shaft thickens, cartilage near each epiphysis replaced by shafts of bone
5. blood vessels invade the epiphyses and osteoblasts form secondary centres of ossifcation
articular cartilage = a thin cap of he original cartilage that remains exposed to the joint cavity
epiphyseal line = former location of epiphyseal cartilage when bone fully grown

Question 15

appositional growth

Answer 15

enlargement process by which diameter enlarges as bone lengthens
infant: bone lengthens, diameter enlarges
child: osteoblasts build on other surface, osteoclasts erode on inner surface enlarging marrow cavity
young adult: marrow cavity continues to enlarge
adult: osteoblasts and osteoclasts continue to remodel bone

Question 16

requirements for normal bone growth

Answer 16

minerals - calcium and phosphate
vitamins - D, A, C
hormones - growth hormones, sex + thyroid hormone
loading forces - from physical activity

Question 17

bone remodelling

Answer 17

continuous breakdown and reforming of bone tissue
osteoclasts reabsorb while osteoblasts form bone
osteocytes detect forces in the bone so regular exercise sis important to maintain normal bone structure
99% calcium stored in bone - PTH stimulates bone reabsorption to release calcium, calcitonin stimulates bone formation to store calcium

Question 18

fracture repairs

Answer 18

1. bleeding and formation of clot (fracture haematoma)
2. formation of external callus (cartilage) and internal callus (spongy bone)
3. external callus replaced by bone, internal callus unites broken ends
4. initial swelling eventually remodelled

Question 19

aging

Answer 19

osteopenia = inadequate ossification due to age - bones become thinner and weaker
reduction in bone mass begins between ages of 30 and 40 - osteoblasts activity reduces while osteoclasts continue at same pace