What does the majority of body growth occur?
up to 40% occurs within the first 2 yrs of life. Thus, adequate diet is vital in these years. After this time, the rate decreases until puberty where it increases again (11 yo in girls, and 12-13 in boys)
T or F. Most neural growth is complete by the 2nd year of life
T. Thus there is a significant need for thyroid hormone in these years
What hormone promotes GH release?
GHRH from the hypothalamus stimulates GH release from the anterior pitutiary
(and somatostatin inhibits GH release)
What are the effects of GH (aka somatotropin) action?
protein synthesis and linear growth (growth is more of a long-term effect)
And produces IGF-1 at the liver to mediate other effects of GH
Where is IGF-1 made and what are its roles?
IGF-1 is generated in the liver (and some locally in tissues) and promotes more of the same as GH such as protein synthesis and AA uptake (and also neg. feedbacks on GH and GHRH release)
NOTE: The role of IGF-II is not as clear as that of IGF-1
What are the effects of GH on adipose tissue in the short term?
increased lipolysis and reduces re-esterification of FFA back into TAGs (so FFA levels will be elevated)
reduced glucose uptake into adipose
leading to an overall effect of reduced body fat mass
What are the effects of GH on skeletal muscle in the short term?
reduces glucose uptake into muscle (inhibits GLUT-4) and
increases LPL activity and B-oxidation
How does GH affect the liver in the short term?
increases VLDL secretion, HL activity, and
reduces PPARa expression (NOTE: PPAR-alpha is activated under conditions of energy deprivation and is necessary for the process of ketogenesis, a key adaptive response to prolonged fasting)
leading to increased production and uptake of IDL, LDL, and HDL
T or F. Hyperplasia and hypertrophy of soft tissues are short term effects of GH
T. GH limits apoptosis and promotes cell differentiation and protein synthesis
These are the effects of GH acting on bone. So GH mainly acts in the growth (proliferation) zone to induce cartilage cell mitosis and in the calcification zone
What is the half-life of free IGF in blood?
How is IGF transported in blood and how does that affect its half-life?
It first binds to IGFBP which increases its half-life to 20-30 min, and then that complex is engulfed by ALS from the liver to increase half-life to 16-24 hrs
What factors stimulate GH secretion?
hypoglycemia and decreased fatty acid conc.
arginine (high protein diet)
fasting or starvation
puberty hormones (estrogen and testosterone)
exercise and stress
Stage III/IV sleep
What factors inhibit GH secretion?
senescence (being old AF)
somatostatin and somatomedins
It has been hypothesized that the effects of GH depend on their oscillation from the mean (because GH levels in older people are somewhat normal, but as seen below, are not released in the same fashion)
What hormnes work synergistically with GH?
thyroid hormone (especially within the first two years of life)
androgens and testosterone during development/puberty