L12: Growth and development Flashcards
4 phases of growth
intrauterine
infancy
childhood
pubertal
3 ways cell grow
hypertrophy
hyperplasia
volume of intracellular material
when does apoptosis happen in fetal development
webs of fingers
formation of hollow organs
when is foetal growth greatest
16-20 weeks
when does fat deposition primarily occur in gestation
last weeks
when is peak velocity of foetal weight gain greatest
34 weeks
what happens to growth after 34 weeks
rate of growth gradually declines
senescence=
ageing
when is ossification of cartilage completed by
3rd decade
what growth is responsible for increasse in height during childhood and adolescence
long bone growth
how do long bones grow
proliferation and hypertrophy of chondroblasts lying beneath growth plates
what cells then extend into the diaphysis of bone
chondrocytes
what happens after puberty to growth plates
the growth plate thins and is replaced by bone
epiphysis and diaphysis fuse
where is GH produced
anterior pituitary gland
what are the indirect actions of GH mediated by
insulin-like growth factors (IGFs) or somatomedins
2 principal IGFs
IGF-1
IGF-2
where are IGFs made
liver kidneys muscle cartilage bone
before birth how is IGF-1 secreted
independant of GH
after birth how is IGF-1 secreted
stimulated by GH
how is IGF-2 secreted
largely independant of GH
what happens with overexpression of IGF-2 in foetuses
disproportionate growth of tongue, muscles, kidney, heart and liver
highest conc of IGF-1 in
puberty
name 5 other growth factors
T3, T4 prolactin placental lactogen PTH oestrogen/ testosterone
when does T3 and T4 secretion begin
15-20 weeks gestation
what can inadequate levels of thyroid hormone during late foetal development and early prenatal periods lead to
severe mental retardation (cretinism)
excess cortisol leads to
inhibitory growth actions
do GH or IGF-1 levels drop in corticosteriods use
no
would GH correct retardation in corticosteriod treated children
no
what can corticosteriod treatment lead to
osteoporosis
what is your growth spurt due to
interactions between sex steriods GH and IGF-1
in girls GH secretions causes
oestradiol-17 beta from ovaries
in boys GH secretion causes
testosterone from leydig cells
what limits bone growth at end of puberty
epiphyseal fusion
what triggers GH release
GHRH
what inhibits GH release
somatostatin
pattern of GH secretion
in pulsatile bursts in slow wave (deep sleep)
how does IGF-1 effect GH release
inhibits GH release by suppressing somatotrophs
achondroplasia=
a common form of dwarfism in humans
mutation in achondroplasia
chromosome 4 that codes for fibroblast growth factor receptor 3
mutation in achondroplasia leads to
decreased endochondral ossification
chondrocyte proliferation inhibition
decreased cellular hypertrophy
what develops normally in achondroplasia
other organs -normal intelligence
acromegaly =
hyper-secretion of GH
what most commonly causes acromegaly
adenoma of pituitary somatotroph cells
What does GH deficiency in childhood suggest
pituitary dwarfism
what can GH deficiency be accompanied by
under secretion of other pituitary hormones
hypopituitary dwarfism can be caused by
pituitary or hypothalamic tumours infection infarction vascular malformations head trauma
normal proportions in which dwarfism
hypopituitary dwarfism
what dwarfism mimics GH deficiency but has high GH levels
laron dwarfism
what causes laron dwarfism
IGF-1 lack of response
classic features of hypothyroidism
sluggish dry-haired thick-skinned deep voiced wt gain cold intolerance bradycardia
children with hypothyroidism=
puffy face
low hair line
jaundice
choke frequently
treatment of hypothyroidism
T4
if T4 commenced at birth outcome=
good prognosis for normal growth and development
