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55 Cards in this Set

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What is the structure of Growth Hormone like?
Big with lots of disulfide bridges
What does the GH gene share homology with?
It has similar AA sequence to:
-Human chorionic gontpn (HCG)
-Human Placental Lactogen (Prl)
What does Growth Hormone counteract in general?
Insulin
What are GH's 2 main stages of effects?
-Direct
-Indirect
3 Tissues that GH acts on directly:
-Fat
-Liver
-Muscle
3 effects of GH on fat:
-Increased lipolysis
-Decreased glucose uptake
-DECREASED ADIPOSITY
2 effects of GH on liver:
-Increased gluconeogenesis
-Increased IGF-1
4 effects of GH on muscle:
-Decreased glucose uptake
-Increased amino acid uptake
-Increased protein synthesis
-INCREASED LEAN BODY MASS
What does GH do when starving?
Acts with cortisol to keep glucose in the blood, not taken up by adipocytes; decreases adipocyte glucose uptake.
What is IGF1?
Insulin like growth factor; released by the liver.
What tissues does IGF1 act on?
-Bone/heart/lung
-Chondrocytes
What does IGF1 do to bone/heart and lung?
-Increases protein synthesis
-Increases RNA/DNA expression
-Increases cell size/number
So the main effects of IGF1 on bone/heart/liver are:
-Increased organ function
-Increased organ size
What does IGF1 do to chondrocytes?
Increases linear growth
What regulates growth in infants up to 1 yr old?
We don't really know
What regulates growth in 1-yr olds up to adolescence?
Growth hormone and T3
What regulates growth after adolescence?
Sex hormones
What regulates growth all throughout life?
Probably insulin
How do we know insulin can regulate growth in prenatal babies?
Because moms with diabetes have so much sugar it crosses the placenta and stimulates baby's insulin which makes it grow really big.
What are 6 stimulants of GH secretion?
-Amino acids (acute)
-Starving (chronic)
-Hypoglycemia
-Exercise
-Stage 3/4 sleep
-Gonadal steroids/Thyroid hormone
What are 4 inhibitors of GH secretion?
-Glucose (neg fb)
-GH (shortloop fb)
-IGF1 (neg fb)
-Cortisol
Why is it important to remember that CORTISOL INHIBITS GH RELEASE?
Because if you were to inject cortisol in an asthmatic kid, you could stunt their growth.
How is it helpful to know that amino acids stimulate GH secretion?
It allows you to test for hypopituitarism - diagnosed if there is a lack of GH in spite of Arginine injection.
When does GH naturally peak?
At midnight - during the first few hours of deep sleep.
What else can make GH peak even more than midnight?
Strenuous exercise
2 things that can impair growth in children:
-Shaken baby syndrome
-Lack of sleep
What are the 2 hypothalamic controllers of GH secretion, and how do they act?
GHRH - stimulates secretion
SST - inhibits secretion
What causes longloop feedback to turn off GH secretion?
IGF1
What causes shortloop feedback to turn off GH secretion? How?
GH - it inhibits GHRH release from the hypothalamus
How does IGF-1 turn off GH secretion?
By turning on SST secretion from the hypothalamus
How does a fetus grow?
First in length, then in weight
When is the velocity of growth highest in a developing child?
During gestation; it peaks halfway through.
What happens to growth after birth?
Velocity decreases but growth still occurs and peaks after about 2 years.
When does the velocity of growth increase again?
At puberty
What is the avg puberty onset in
-Females
-Males
Females = 10-12 yrs old
Males = 14-16 yrs old
What causes growth to stop after puberty?
The gonadotropins cause the epiphyseal growth plates to close.
What is the main difference in how males vs females grow in height?
They are similar until puberty, where boys on average grow taller.
When does brain mostly develop?
In fetal life and infancy
When does the skeleton mostly develop?
In fetal life, infancy, and adolescence (less in childhood)
When does muscle development occur?
All throughout fetal life, infancy, childhood (less) and adolescence.
When does all growth sort've dip?
During childhood
What is Gigantism?
Too much GH before puberty
What is Acromegaly?
Too much GH after puberty
What is the best screening test for GH excess?
IGF-1
Why is IGF1 measurement a good screening test for GH excess?
Because it provides an average measurement of GH levels which peak and decline at various times throughout the day; it's like measuring Hgb A1C
Characteristic feature of Acromegaly:
Coarse features
What is the screening test for GH deficiency?
Arg-stimulation or GHRH injection to see if the pituitary responds.
What type of study can be used to see if GH levels peak in children?
Sleep studies - looking for the peak during Stage 4 NREM sleep
What will GH deficient kids look like?
Scrawny and thin
What would you suspect in a short fat kid?
Cushings
Why does Cushings make a kid fat?
Because cortisol has a direct effect to increase SST which inhibits GH release
Why was Gary Coleman short?
Because he had a kidney transplant and had to be on steroids to prevent Gvhd which stunted his GH secretion/growth.
What do you need to remember when giving kids steroids?
That if you give too much they won't grow.
What if a kid has adrenal insufficiency and doesn't have enough glucocorticoids?
Be careful not to give too much cortisol that it suppresses GH release.
4 ways that Cortisol inhibits GH's actions:
1. Stimulates SST
2. Inhibits growth plate from responding to IGF1 from liver
3. Inhibits CT/collagen synthesis
4. Inhibits the adrenal glands