Topic 9: Skeletal System Flashcards
When does bone development take place?
~8th week of embryo to 20 years
What are the types of bone ossification?
Intramembranous ossification (flat bones)
develop from fibrous CT membrane
Endochondral ossification (most bones)
Describe endochondral ossification
Hyaline cartilage is used as a “model” for bone construction, which then ossifies to form spongy bone
Periosteum forms and the osteoblasts beneath lay down compact bone
(Articular cartilage and epiphyseal plates are cartilage that has not ossified)
What is the process of intramembranous ossification?
Osteoblasts produce bone along CT fibres
Cells at the periphery form the periosteum
What is appositional growth?
Growth in bone diameter
How does nutrition impact bone growth?
Ca++, PO4: required for matrix production
Vitamin C: required for collagen production
Vitamin D: increases absorption of Ca++ from intestine (lack of vitamin D causes RICKETS: soft bones)
What are the 6 risk factors of osteoporosis?
Increased age (⬇️sex hormones)
Post-menopause (⬇️estrogen)
Inadequate diet (⬇️vitamin D)
Illness, excess parathyroid hormone
Too little/excessive exercise (cortisol)
Drugs (—⬇️osteoblast activity)
What is the process of bone repair?
Begins with formation of a blood clot
Replaced by a callus (consists of fibrous network and fibrocartilage islets)
Callus ossifies (intramembranous and endochondral ossification)
Takes 4-6 weeks (cast required since movement can refracture new matrix)
Endochondral growth at the epiphyseal plates is what causes bone growth in length. Explain the process
Cartilage grows ~> matrix near diaphysis becomes bone
Growth in length stops when epiphyseal plates ossifies into epiphyseal line
What is the process of bone growth in diameter?
Osteoblasts beneath periosteum secrete bone matrix (external bone surface)
Osteoclasts reabsorb bone on the endosteal surface, therefore size of cavity keeps pace with growing bone
Give some examples of how mechanical stress can affect bone growth/remodelling
Moderate exercise: ⬆️osteoblast activity (more bone building than breakdown)
Movement-restricting injury:
⬇️osteoblast activity (⬇️bone mass)
Weights or electric currents: may speed healing by ⬆️osteoblast activity
What hormone stimulates bone growth?
Growth hormone (GH), thyroid
How does estrogen and testosterone affect bone growth?
Increases osteoblast activity
Estrogen (in all people) causes ossification of epiphyseal plate (into line)
How does calcitonin affect bone growth?
Inhibits osteoCLAST activity
Increases Ca++ movement from blood into bone (promoting growth)
How does parathyroid hormone (PTH) affect bone growth?
Breaks down bone
Increases osteoclast activity and decreases osteoblast activity
Releases Ca++ into blood
