5.2 Ossification Flashcards
Prefix “os-“
Bone
Ossification means
The production of bone
Two types of ossification
Intramembranous & Endochondral
Intramembranous ossification
- from Mesenchyme to bone tissue
- starts early fetal to age 2 yo
- Most bones in the skull (flat bones),
& clavicles
Fontanels
Soft spot after birth in skull (pliable)
Endochondral ossification
- from Mesenchyme to cartilage (hyaline) then bone
- completes end of puperty
Steps of Endochondral ossification
- plug of hyaline cartilage (mostly water with protein)
- becomes infiltrated from outside layer (periosteum) with osteocytes
- forms primary ossification center
- bone takes over, cartilage persists
- secondary ossification centers form
Epiphyseal plate
- aka “growth plate” where we grow.
- the line where cartilage expands/persists as ossification expands with it.
Endochondral ossification regulated by
Several hormones (endocrine system)
- growth hormone (GH) (expansion of cartilage and epiphyseal plates) from pituitary
- parathyroid hormone (PTH) removes extra bone tissue so they don’t get too thick (maintains proportions)
- sex horomones (last expansion) forming epiphyseal lines
Short bones arise from
Single ossification center
Irregular bones arise from
Distinct various ossification centers
Long bones arise from
Primary and 1+ secondary ossification centers
Osteoclasts
- stimulated by PTH cause osteoclasts to release HCl (which dissolves calcium/ bone tissue) aka resorption
Resorption is
Process of removing bone tissue
Blood calcium levels
- regulated by negative feedback loop
- if low, PTH released, tells kidneys to maintain Ca2+
- also triggers osteoclasts to produce HCl and release Calcium from bones
