endocrine control of growth Flashcards
endocrine glands are …
duct less
where do endocrine glands secret
into circulation
so hormones travel round the body
long bone
growth plate where endochonral growth is taking place
mostly a transient structure in long bones
causes a cartilage prescursor to grow during childhood
growth hormone
regulates the amount of growth in long bones
what releases GH
anterior pituitary gland
what is anterior pituitary glands under
stimulation of growth releasing growth hormone and somatostatic
- forms negative feedback loop
what is released from posterior pituitary gland
growth releasing growth hormone and somatostatic
what is the posterior pituitary gland under
influence of nerves from hypothalamus
signalling occurs in pulses allows growth hormone to be constant throughout day
gigantism
before growth plate closure
- growth hormone excessive before closing
- due do anterior pituitary adenoma which is often egentic
where is the pituitary gland found
slightly anterior is the optic chaism (optic nerves cross)
pituitary tumour causes
tends to compress optic nerves loss of peripheral vision tends to be slow patients dont notice at first - can lose visual acuity and colour
agremegaly
after growth plates have clsoed
- can have earlier onset
- bone is laid down in an appositional fashion
- gives lumps/bumps around face and bone
- pituiriyt tumour has occurred in mid life
- or the tumour can also be in other tissues, and release the growth hormone (tends to be I. the lung or pancreas)
- patients can notice the tongue enlarging, and rings becoming small
carney complex
melanin patches seen intraorally
due to tumours of melanin producing cells
can have in heart, thyroid gland
condition due to new genetic mutation no family history
what can growth hormone directly infleuce
the growth plate and cause proliferation of the progenitor cells
- acts on liver to increase release of insulin like GF
what does IL GF do
hypertrophy of cells inside growth plae
- acts on hypothalamus and pituitary gland to reduce secretion of growth hormone
(negative feedback)
what is used as an indicator of GH levels ad why
ILGF
more stable than GF istelt
what does oestrogen do
influences bone growth and interact with GH
maintenance of bone density
can increase GH secretion, therefore indirect effect on bone growth
direct action on growth plate itself
what eventually stops bone growth and what does this effect
ongoing levels of oestrogen- may cause programmed senescence of the growth plate (biomodal influence)
- delayed pubertal growth spurt may lead to a taller stature, due to the growth plate not being restricted and stop growth early by oestrogen
what is the typical androgen
testosterone
what can androgens do
modified by enzymes to act on oestrogen receptors
androgens can act on androgen receptors
androgens can be modified by enzymes to act on oestrogen receptors…
- therefore bimodal influence of the growth plate to initially cause lengthening of the bone then following cessation
what can androgens do when binding with androgen receptor
can cause increase in radial growth of bone
what is mandibular sexual dimorphism
shape of mandible different between 2 genders
prominnant angle is typically
may be due to interaction of testosterone and oestrogen
what is found in the mandible
secondary cartilages
what occurs at secondary cartialges
endochrondral ossification
what happens at the condyle
ECO
growth around he condyle is where mandibular sexual dimorphism occur
- tester one increases growth
this increases the height and ascending raus
increases sharpness md angle
muscle loading may contribute
what does growth hormone also influence and how does it
muscle growth
- GH acts via IGF1 receptors to increase myofibril proliferation
- muscle growth is usually proportional to body size
- little evidence that GH promotes hypertrophy beyond the proportional body size
- paracrine IGF1 has a role in load induced hypertrophy
growth hormone performance enhancement
- may have little effect on hypertrophy
- positive effect on connetive Tissue strength
- reduce recover time – anticatabolic
- increase VO2 max (allows more intense anaerobic exercise)
what do glucocorticoids do
modulate GH
- increases GH secretion
- Affect SST (somatostatin) and GHRH, indirect reduction in growth hormone
- Chronic exposure reduces GH release
treatment of children with corticosteroids
those with chronic juvenile arthritits
- likely to reduce growth
due to reduction in GH effect at growth plates
what do GCC act as
- regulate expression of growth hormone receptors
- outcome related to dose and exposure time to give difference in outcome due to short and long exposures
what happens when GCC is present for a long time in adults
- increase risk of osteoporosis, protein loss and raised serum lipids
- Chronic glucocorticoid mitigated by recombinant GH
- this can lead to glucose intolerance i.e. diabetic
what does GH promote (to do with sugars)
release of glucose from fatty acids stores (glycogenesis, glycogenolysis, liposis)
- in responce insulin is release to compensate to restore blood glucose levesl
(lead to insulin resistance?)
what happens in a healthy individual
- GH levels fluctuate
- after carb meal, high level of insulin will then reduce the level of GH
- will steady out
what happens to an inidividual if insulin levels are persistently high
- if insulin levels are persistently high
- can lead to increase in height
- insulinopenia reduces childrens growth
- the growth plate is excessively active, insulin acts as a IGF1 homologue
what does thyroid hormone do and how
increases linear growth of bones
Directly by
- affecting chondrocytes and osteoblasts in the growth plate
- also stimulates release of GH, which acts on long bone itselt
also drive IGF1 synthesis prepubertal, encouraging growth
hypothyroidism
reduced levels
reduced adult height
pre/post puberty hormone levels
1) Before puberty thyroid hormone drives synthetic of insulin like growth factor which then acts on the bones
2) thyroid hormones levels drops, GH levels increase partly due to oestrogen
3) causes increase in insulin like GF levels, which then causes an increase in bone length
Therefore overall Insulin like growth factor may be the overall factor on height
what are the headline hormones
GH
IGF1
