Physiology: Endocrine #8: Growth Hormone

Front 1

GH - what's another name and what cells make it?

Back 1

somatotropin - made by somatotrophins.

NOTE - they make up 50% of the hormone secreting cells of the anterior pituitary.

Front 2

what are the main functions of GH?

Back 2

post-natal growth is biggest effect.

in adulthood, it continues to regulate things like body composition and metabolism.

Front 3

what are the two hormones from the hypothalmus that control GH release?

Back 3

GHRH (growth factor releaseing hormone) and

SOMATOSTATIN.

somatostatin is also called somatotropin release-inhibiting factor, or SRIF.

So, SRIF = SOMATOSTATIN = opposes GHRH.

Both come from the hypothalmus

Front 4

through what second messenger does GHRH work?

Back 4

cAMP/adenylate cyclase. Increases intracellular Ca++ as well.
probably a little IP3/PKC as well.

Front 5

what does GH release that can feedback to shut itself down?

Back 5

feedback comes from IGF (insulin-like growth factor, AKA somatomedin), released from the liver, which feeds back on both the hypothalmus to stop GHRH secretion and stop GH release from the pituitary.

Front 6

try again - after release of GH, what feeds back to stop it?

Back 6

both GH and IGF-1 (somatomedin) feed back on the hypothalmus, and increase the secretion of SOMATOSTATIN from the hypothalmus - this stops release of GH from the pituitary.

IGF feeds back on the pituitary itself to stop GH release as well.

Front 7

insulin and GH : eating what causes both to be increased? what causes differential regulation?

Back 7

eating protein causes both to go up. this leads to a conflicting net effect of caloric storage/mobilization, with no real change.

eating carbs causes GH to go down and insulin to increase (this leads to storage of calories).

fasting leads to up of GH and down of insulin, leading to caloric mobilization.

Front 8

does GH work by itself to increase linear growth and organ size and lean body mass?

Back 8

a lot of its affects are through IGF-1, mostly released by the liver in response to GH.

Front 9

what tissues CAN GH work on by itself?

Back 9

works on the liver, on adipose tissue, and on muscle.

the rest of the body seems to be affected mostly by IGF-1

Front 10

when is GH concentration highest? what about secretion?

Back 10

20th week of gestation.

secretion is highest during adolescence and GOES DOWN as you get older. So, levels are higher in kids than in adults.

Front 11

metabolic regulation of GH: what happens when the blood concentration of FFA's, and glucose?

What does obesity do? are males or females more sensitive to GH?

Back 11

Think of GH as being kinda opposite to insulin - so when FFA's or glucose level drops, GH gets secreted.

When they go up, GH concentration drops. For example, short fasting = GH up.

obesity decreases sensitivity of GH response to metabolic stimulation

females are generally more responsive to GH (imagine obese dudes being immune)

Front 12

what happens during sleep that affects GH levels?

what about stressors/traumas?

Back 12

light sleep (REM) causes GH to drop.

deep sleep causes GH to spike (think that you need to sleep deeply to grow)

stress/trauma causes GH to go way up.

Front 13

what happens to kids who don't make GH or are insensitive to it?

Back 13

they end up being delayed sexually and developmentally, end up short and obese.

Front 14

what does growth hormone receptor look like? what pathway does it work through?

what's a somatomedin?

Back 14

it's a single pass, works through JAK/STAT (kinda like insulin). the receptor dimerizes upon binding of GH.

somatomedins are things like IGF-1 ... a lot of GH's effects are mediated through these.

Front 15

IGF - are they hormones, autorcine, paracrine, etc?

do they circulate bound to proteins?

Back 15

yes, they circulate bound to proteins.

they're generally like hormones and can circulate, but also exhibit paracrine and autorcine functions.

Front 16

what kinds of tissues do IGF's work in?

Back 16

cartilege, bones, TUMORS, muscles, adipose tissues, fibroblasts.

note that GH can work directly on muscles and adipose.

Front 17

fetuses - how do they get IGF's floating around?

Back 17

they make their own GH. Also, the placenta really early on makes its own GH which can up the IGF's floating around in the fetus.

Front 18

how does fasting affect IGF's?

Back 18

this is where it's weird. we know short fasting ups GH, which you'd think should increase IGF secretion. This doesn't happen - so something else is also regulating IGF.

NOTE - Gh and IGF are big promoters of LONGITUDINAL growth.

Front 19

how do cortisol, estrogen affect IGF?

Back 19

they both suppress it.

Front 20

how do bones get longer with GH?

Back 20

GH makes pre-chondrocytes become chondrocytes.

these chondrocytes make lots of IGF-1, which causes the chondrocytes to undergo clonal expansion and really go to making bones.

Front 21

giving IGF's to people - does this increase/decrease anabolism?

how does GH affect aging?

Back 21

they encourage anabolism - so the plasma concentration of amino acids begins to steadily drop upon administration of IGF's.

GH is involved in lots of stuff - DNA/RNA synthesis, collagen, everything - so dropping GH levels may play a role in aging.

Front 22

insulin and GH's effects - how do they compare?

Back 22

GH opposes the action of insulin, generally. So, glucose uptake by cells drops with lots of GH, so pasma concentration of these go up. Gh also causes lipolysis, so FFA's in the blood goes up (as do KETOACIDS), while simultaneously bringing down the amount of adipose tissue.


this is why GH is DIABETOGENIC.

Front 23

so GH is opposite to insulin, kinda...but IGF's are considered anabolic?

Back 23

yes. weird.

remember, IGF's decrease plasma AA concentration, while GH increases FFA in the blood.

it's thought GH might help oppose hypoglycemia?

Front 24

what's a symptom of too mugh GH secretion, like from a GH tumor?

Back 24

acromegaly - get thick/oily face skin and weird scalp folds.

long limbs?

Front 25

how does GH look in comparison to prolactin, its neighbor?

Back 25

similar, except prolactin has an extra disulfide bond loop.

Front 26

what inhibits prolactin secretion?

Back 26

dopamine secretion from the hypothalmus helps stop it. Called PIF (prolactin-inhibiting factors).

so does somatostatin and a weird form of GnRH.

Front 27

what turns it on?

Back 27

big one is TRH,

Front 28

if you disconnect the hypothalmus from the pituitary, what generally happens to hormone secretion?

what does prolactin do?

Back 28

most things stop secreting, but not prolactin - it turns on big time.

note that prolactin's big job is breast development and milk production in women.

also may be important for sexual develoment in both men and women.

also, probably instills protective instinct in men and women towards babies.

Front 29

what can excess prolactin do?

Back 29

it can inhibit GnRH to cause infertility.

Front 30

REVIEW:

Back 30

GHRH feeds back on itself in the pituitary. Prolactin is the same way.

IGF's (somatomedins) feed back on both the anterior pituitary and hypothalmus to make somatostatin.

gh released by sleep, stress, puberty, hypoglycemia, starvation, exercise.

GHRH works through both pathway: cAMP and IP3, and Ca++


estrogen, testoesterone, thyroid, cortisol all TURN UP GH