principles of growth Flashcards
1st trimester growth
rapid growth + differentiation of organs with formation of embryonic disk containing
ectoderm (skin, hair, brain, nerves)
mesoderm (cardiac, skeletal, renal, bloods)
endoderm (lung, gut, thyroid, pancreas)
2nd trimester growth
cellular hypertrophy –> peak foetal length velocity of 2.5cm/week
3rd trimester growth
maturation of organs occurs + max weight gain, subcutaneous fat is added to embryo
where does IGF1 act
growth plates of bones
Periosteum
outer membranous cover of long bones
Subperiosteal apposition
widening of bones, adding layers onto existing layers
Endosteal resorption
bone removed in central portion of bone so spongey bone is removed
PTH effect on plasma calcium
increases resorption of bone therefore increases plasma levels of calcium
Calcitonin effect on plasma calcium
decreases resorption of bone so reduces plasma calcium
what do thyroid C cells of thyroid release
calcitonin
Epiphyseal plate:
area of growth, layer of hyaline cartilage where ossification occurs
Reserve zone:
region closest to epiphyseal plate, contains small chondrocytes within matrix which don’t participate in bone growth but secure the epiphyseal plate to the osseous tissue of the epiphysis
Proliferative zone
next layer toward diaphysis, contains stacks of slightly larger chondrocytes making new chondrocytes (via mitosis) to replace those that die at diaphyseal plate
Zone of maturation + hypertrophy:
older, larger chondrocytes in next layer closer to diaphyseal plate
why longitudinal bone growth
cellular division in proliferative zone, maturation of cells in zone of maturation, hypertrophy
Zone of calcified matrix:
has most chondrocytes, closest to diaphysis, dead because matrix around them has calcified, capillaries + osteoblasts from diaphysis penetrate
