Lecture 9: Principles of the Skeletal System

Question 1

what is the axial system

Answer 1

skull, vertebrae, sternum, hyoid bone

Question 2

what is the appendicular system

Answer 2

bones of the pectoral and pelvic girdle, and limbs

Question 3

functions of the skeletal system

Answer 3

• protection of organs
• supporting the body
• movement
• production of new red blood cells (bone marrow)
• metabolic reservoir of calcium and phosphate

Question 4

when does bone development begin and end

Answer 4

starts at 8 weeks finishes at 20 years

Question 5

where is bone derived from

Answer 5

paraxial and lateral plate mesoderm

Question 6

what are the 2 ways of ossification

Answer 6

intramembraneous and endochondreal

Question 7

describe intramembraneous ossification

Answer 7

• mesenchyme (embryonic connective tissue) is mineralised into bone, starting from primary ossification centre
• cells divide and condense around capillary network
• grows radially, finally fusing together and replacing the connective tissue
• undifferentiated mesenchyme leads to bone marrow

Question 8

examples of bone formed by intramembraneous ossification

Answer 8

skull, mandible and clavicle

Question 9

describe endochondreal ossification

Answer 9

• cartilage template made from mesenchyme
• osteogenesis: template replaced with bone
• primary ossification centre in diaphysis develops from bone collar and secondary in epiphysis with epiphyseal plate growing between them

Question 10

what is the diaphysis

Answer 10

shaft of bone

Question 11

what is the epiphysis

Answer 11

ends of bone

Question 12

what is the epiphyseal plate

Answer 12

growth plate

Question 13

what is the name of cartilage cells

Answer 13

chondrocyte

Question 14

what is the name of cartilage

Answer 14

hyaline

Question 15

how does bone grow

Answer 15

• partial reabsorption of previously laid down bone and laying down of new bone
• developing bone is penetrated by blood vessels at week 9
• with maturity the epiphyseal plate is abolished

Question 16

things required for bone development and maintenance

Answer 16

• vitamin A for bone remodelling
• vitamin C for connective tissue
• vitamin D for calcium absorption
• dietary intake of calcium and phosphorus
• parathyroid hormone and growth hormone

Question 17

what does excess growth hormone lead to

Answer 17

acromegaly, with a large jaw and enlarged features

Question 18

what does deficiency of growth hormone lead to

Answer 18

proportional dwarfism

Question 19

what does vitamin C deficiency lead to

Answer 19

scurvy with bleeding gums as connective tissue breaks down

Question 20

what does vitamin D deficiency lead to

Answer 20

• rickets, characterised by impeded growth and deformity of the long bones
• earliest sign is craniotabes: abnormal softening or thinning of the skull

Question 21

describe cartilage

Answer 21

• connective tissue
• forms in parts where flexibility is required
• avascular

Question 22

describe bone

Answer 22

• hard form of cartilage
• provides rigid framework
• vascular
• two types, compact and spongey

Question 23

what is the connective tissue surrounding bone

Answer 23

periosteum

Question 24

what is the connective tissue surrounding cartilage

Answer 24

perichondrium

Question 25

4 cell types of bone

Answer 25

• osteoprogenitor cells: stem cells that differentiate to osteocytes and osteoblasts
• osteoblasts: form new bone in bone marrow
• osteocytes: derive from osteoblasts and are “fixed”
• osteoclasts: reabsorb and recycle bone (eat the bone)

Question 26

osteoclasts

Answer 26

• has 5-50 nuclei
• sits in enzymatically etched depressions on the lamellae
• have an irregular ruffled border
• controlled by cytokines

Question 27

what is a lamella

Answer 27

concentric layers of inorganic matrix

Question 28

compact bone

Answer 28

• lamellae are laid down by osteoblasts
• lamellae form the haversian canal in the middle, which contains the vascular and nerve supply
• osteoblasts become trapped and become osteocytes
• each osteocyte occupies its own lacuna
• radiating from each lacunae are minute canals called canaliculi
• nutrients travel in the canaliculis to the osteocyte

Question 29

spongey bone

Answer 29

• also known as cancellous bone
• irregular lamellae
• surrounded by red bone marrow
• highly vascular

Question 30

types of bones

Answer 30

• long bones: mainly responsible for movement, eg femur humerus and ribs
• flat bones: tend to be more protective, eg skull and sternum
• short bones: give flexibility of movement eg carpals
• irregular bones: adapted over time, eg sacrum
• sesamoid bones: found within tendons, eg patella
• accessory bone: sometimes can get them, eg extra cervical rib

Question 31

what is a facet

Answer 31

shallow articulating surface

Question 32

what is a groove

Answer 32

depression where tendons run

Question 33

what is a foramen

Answer 33

round opening

Question 34

what is a crest

Answer 34

a ridge-like formation

Question 35

what is a condyle

Answer 35

rounded projection

Question 36

what is an epicondyle

Answer 36

projection above the condyle

Question 37

what is a spine

Answer 37

a slender process, eg spine of the scapula

Question 38

what is a protuberance

Answer 38

non-articulate prominences

Question 39

what is a tuberosity

Answer 39

rough process

Question 40

what is a trochanter

Answer 40

massive process

Question 41

what is a trochlea

Answer 41

pulley

Question 42

what is a process

Answer 42

marked prominence

Question 43

what are the types of joints (articulation)

Answer 43

• synovial: has a joint capsule and synovial cavity and permits movement
• fibrous: connected by collagen and don’t permit movement, eg sutures of the skull
• cartilogenous: connected by cartilage to allow some movement, eg growth plates and intervertebral disc

Question 44

types of synovial joints

Answer 44

• plane, eg intercarpal
• hinge, eg knee
• saddle, eg carpometacarpal
• condyloid, eg metacarpophalangeal
• ball and socket, eg hip
• pivot, eg radioulnar