Topic 9 - SKeletal System

What are the functions of the skeletal system? (5)

• structural support

• protection of vital organs

• attaches muscles + allows movement

• red marrow produces all blood cells

• stores calcium

What is bone ossification?

• bone formation beginning around the 8th week → 20 years

What is the skeleton of an embryo made of before week 8?

• fibrous membranes + hyaline cartilage

What are the types of bone ossification? (2)

• intramembranous ossification

• endochondral ossification

What is intramembranous ossification?

• ossification of flat bones - some skull bones, mandible, clavicle

What does intramembranous ossification develop from?

• fibrous connective tissue membrane

What is the process of intramembranous ossification? (2.1)

• osteoblasts produce spongy bone along CT fibres

• cells at the periphery form periosteum

  • osteoblasts under it lays down compact bone

What are fontanels?

• unossified membranes in the skull that remain at birth (intramembranous ossification)

What is endochondral ossification?

• the ossification of most bones

What is the process of endochondral ossification? (1.1 + 1.1)

• hyaline cartilage is used as a model for bone construction

  • gets ossified to form spongy bone

• periosteum forms

  • osteoblasts beneath lays down compact bone

What is articular cartilage + epiphyseal plates?

• cartilage not ossified (endochondral ossification)

What is endochondral growth?

• growth in length - at epiphyseal plates

What is the process of endochondral growth?

• cartilage grows + matrix near diaphysis (shaft) becomes bone

When does endochondral growth end?

• when epiphyseal plate ossifies into epiphyseal line (closure)

What is appositional growth?

• growth in diameter

What is the process of appositional growth? (2)

• osteoblasts beneath periosteum secrete bone matrix (external bone surface)

• osteoclasts resorb bone on the endosteal surface = size of cavity keeps pace with growing bone

What are the osteoblast + osteoclast functions in bone formation?

• osteoblasts - deposit bone on outer surface

• osteoclasts - widen the medullary cavity from within

What factors affect bone growth/remodeling? (3)

• mechanical stress

• nutrition

• hormones

How does mechanical stress affect bone growth/remodeling? (1.3)

• due to muscle action -

  • moderate exercise

  • injury that restricts movement

  • weights or electric current

How does moderate exercise affect bone growth/remodeling?

• increases osteoblast activity in areas of stress

  • more building than breaking down = stronger bones

How does an injury that restricts movement affect bone growth/remodeling? (2)

• decreases osteoblast activity

• no change in osteoclast activity = decrease in bone mass

How do weights or electric currents affect bone growth/remodeling?

• may speed up healing ; increases osteoblast activity

What nutrients affect bone growth/remodeling?

• calcium (Ca²) + phosphate (PO₄)

• vitamin C

• vitamin D

How does calcium + phosphate affect bone growth/remodeling?

• required for bone matrix production

How does vitamin C affect bone growth/remodeling?

• required for collagen production

How does vitamin D affect bone growth/remodeling?

• increases absorption of calcium from intestine

What are rickets?

• soft bones due to vitamin D deficiency

What hormones stimulate bone growth? (5)

• growth hormone (GH)

• thyroid hormone

• estrogen

• testosterone

• calcitonin

How does estrogen + testosterone affect bone growth/remodeling? (2)

• increases osteoblast activity

• estrogen - also helps ossification of epiphyseal plate → epiphyseal line

How does calcitonin affect bone growth/remodeling? (2)

• inhibits osteoclast activity

• increases calcium movement from blood → bone = promotes bone growth

How does parathyroid hormone (PTH) affect bone growth/remodeling?

• increase osteoclast activity

• decrease osteoblast activity = increases blood calcium

What is osteoporosis?

• disease characterised by a reduction in bone density + mass = more brittle bones prone to fracturing

What are risk factors for osteoporosis? (7)

• increasing age

• post-menopause

• inadequate diet

• illness

• excess PTH

• too little/excessive exercise

• drugs

How is increasing age a risk factor for osteoporosis?

• decrease in sex hormones

How is post-menopause a risk factor for osteoporosis?

• decrease in estrogen

How is an inadequate diet a risk factor for osteoporosis?

• low vitamin D, calcium

How is too little/excessive exercise a risk factor for osteoporosis?

• stress = cortisol

How are drugs (alcohol, cortisone) a risk factor for osteoporosis?

• reduces osteoblast activity

How is smoking a risk factor for osteoperosis?

• decreases estrogen production

What is the process of bone repair? (3)

• begins with formation of a blood clot

• clot replaced by a callus

• callus ossifies → intramembranous + endochondral ossification

What is a callus?

• a fibrous network + fibrocartilage islets

How long does bone repair take?

• 4-6 weeks ; cat requires since movement can refracture new matrix