Growth Hormones

Question 1

effects of growth hormone

Answer 1

most important hormone for postnatal growth

linear skeletal growth via chondrogenesis
soft tissue growth via increasing cell number and size

increased protein synthesis + amino acid synthesis

increased RNA/DNA synthesis

increase blood glucose

increased lipolysis

increased retention of Na/K/Cl/Mg/phosphate/Ca

Question 2

which cells produce growth hormones?

Answer 2

somatotropes in anterior pituitary

2 mg/gm tissue/24 hours

Question 3

what is different about the first few minutes of HGH administration

Answer 3

the first few minutes it exhibits insulin-like effects

thereafter it is antagonistic of insulin

Question 4

describe the influence of hypoglycemia on HGH

Answer 4

hypo- produces GH-releasing hormone, GHRH, somatotropin releasing factor, somatocrinin that stimulate GH

Question 5

describe the influence of amino acids on HGH

Answer 5

esp arginine, cause GH release

Question 6

describe the effect of sleep on HGH

Answer 6

stages 3 and 4 of deep sleep cause GH release

GH release is inhibited by REM sleep

Question 7

describe the effect of exercise on HGH

Answer 7

exercise causes GH release

Question 8

what hormones from the hypo cause release from anterior pituitary

Answer 8

GHRH, GHRP (grenlin), somatotropin releasing factor, somatocrinin)

Question 9

describe the effect of estrogen on HGH

Answer 9

causes GH secretion

Question 10

describe the effect of somatostatin on HGH

Answer 10

from the hypo, somatostatin inhibits GH release

Question 11

describe the effects of somatomedins on HGH

Answer 11

somatomedins (insulin like growth factor) are locally produced and are stimulated by HGH

they are necessary mediators of HGH

they inhibit GH release

Question 12

describe the effect of hypothyroidism on HGH

Answer 12

excessive TRH will cause inhibition of GH release

Question 13

describe the effect of hyperglycemia on HGH

Answer 13

causes GH inhibition

Question 14

describe the effect of high FFA levels on HGH

Answer 14

causes GH inhibition

Question 15

why is it not useful to assess HGH in a single reading?

Answer 15

HGH levels flucatuate throughout the day, so a series of samples throughout a 24 hour period are necessary

Question 16

how do HGH levels change throughout life?

Answer 16

rise in childhood, peak in adolesence, and decline through adulthood

Question 17

describe HGH excess and its effects

Answer 17

usually caused by pituitary tumor

if it occurs prior to bone plate fusion- pituitary gigantism

after bone plate fusion- acromegaly

Question 18

acromegaly

Answer 18

tumor of anterior pituitary causing excess HGH

causes overgrowth of CT, dermal overgrowth, and extremity enlargement

Question 19

growth hormone deficiency

Answer 19

usually caused by hypothalamic dysfunction, pituitary lesion, ore receptor defects

must be treated prior to full bone maturation or it wont effect linear growth

Question 20

how are insulin levels related to growth?

Answer 20

hyperinsulinism near birth = excess growth

hypoinsulinism near birth = growth deficiency

fulfills “permissive” role

Question 21

how are TH levels related to growth

Answer 21

extremely important for normal growth- necessary for fetus and postnatally

increase protein/RNA/DNA synthesis- somatomedin release

absence causes decreased cell number and cell protein

Question 22

how are sex hormones related to GH?

Answer 22

androgens- muscular growth, linear bone growth, bone maturation and closure of bone plates, promote somatomedin release

estrogens- inhibitory effects on growth, closure of growth plates, inhibit somatomedin release

Question 23

glucocorticoid effects on growth

Answer 23

in general; associated with catabolism

does not interfere w/ somatomedins release, does interfere w/ effect on cartilage

Question 24

somatomedins

Answer 24

IGF-1 (somatomedin C) and IGF-2

released from the liver into blood in response to GH and cause growth

released auto/paracrine from many cells in response to GH

Question 25

somatomedin receptors

Answer 25

a and b subunits, cross reactive w/ insulin (type 1 only).

likewise, IGF-1 and 2 (more type 2) can bind the insulin receptor w/ low affinity

Question 26

plant derived growth factor

Answer 26

promotes growth of fibroblasts and smooth muscle by acting as competence factor- allows them to initiate mitosis

Question 27

fibroblast growth factors

Answer 27

acts as a competence factor

found in pituitary and brain

Question 28

epidermal growth factor

Answer 28

precursor has 2 EGFs and 2 EGF binding subunits, which eventually will cleave the precursor to form active peptide

auto/paracrine stimulator of cell proliferation in cells of mesodermal origin

Question 29

EGF receptor

Answer 29

internal and external components, activates tyrosine kinase

gets completely internalized

Question 30

erythropoietin

Answer 30

stimulates proliferation of hematopoeitic stem cells

regulated by oxygenation status

Question 31

nerve growth factor

Answer 31

has 3 subunits, of which the B subunit is the active form

considered a differentiating factor rather than proliferative

essential for growth and mainenance of ganglia and sympathetic nervous system respectively

Question 32

what stimulates NGF?

Answer 32

androgens and thyroid hormones

Question 33

interleukins

Answer 33

peptide products of lymphocytes

2 and 3 stimulate growth and differentiation of lymphocytes

Question 34

bone growth

Answer 34

GH causes linear bone growth linearly via stimulating chondrogenesis, and increases width by increasing chondrocyte proliferation. these effects are primarily somatomedin but also direct

TH promote cartilage breakdown and bone deposition ie bone maturation

androgens initially promote linear growth, but also increase bone maturation. indirect effects

estrogen inhibits bone growth

cortisol inhibits bone growth- inhibit somatomedins

Question 35

growth hormone receptors are associated w/ what enzymes? IGF-1 receptors?

Answer 35

JAK kinases

tyrosine kinases