Physiology Block 3 Week 14 09 Growth Hormone

Question 1

What are the three hormones of the somatomammatropin family?

Answer 1

Prolactin
Growth Hormone
Human placental lactogen (hPL)

Prolactin and growth hormone have sequence homology and don’t usually bind each other’s recepots

hPL may have some growth hormone-like effects in the pregnant woman

Question 2

Direct Effect of Human Growth Hormone (via insulin-like growth factor 1 [IGF1])

Answer 2

Primarily effects on intermediate metabolism

Direct effects on:

• adipose tissue
• liver
• muscle

Question 3

Human Growth Hormone effect on Adipose Tissue

Answer 3

Decreased glucose uptake
Increased lypolysis
Decreased Adiposity

Question 4

Human Growth Hormone effect on Liver

Answer 4

Increased gluconeogenesis

Increased IGF1

Question 5

Human Growth Hormone effect on Muscle

Answer 5

Decreased glucose uptake
Increased AA uptake
Increase in protein synthesis
Increased lean body mass

Question 6

Indirect effect of Human Growth Hormone

Answer 6

Growth promoting effects of GH are mediated by insulin-like Growth factor 1

IGF1 coordinates organ growth and linear growth rates in children

Produced by Liver

Question 7

Human Growth Hormone effect on Bone, Heart, Lung

Answer 7

IGF1 from liver works on these

Increased protein synthesis
increased DNA+RNA expression
Increased cell size/number
Increased organ size
Increased organ function

Question 8

Human Growth Hormone effect on Chondrocytes

Answer 8

IGF1 from liver works on this

Increased AA uptake
Increased protein synthesis
Increased DNA+RNA expression
Increased collagen
Increased cell size and number
Increased linear growth

Question 9

Human Growth Hormone effect on Muscle

Answer 9

IGF1 from liver also works on this (indirect) in addition to Growth Hormone (direct)

Decreased glucose uptake
Increased AA uptake
Increase in protein synthesis
Increased lean body mass

Question 10

Growth hormone effect on children

Answer 10

Infantile growth is NOT controlled by growth hormone–works through IGF1

In fetus, GH does have growth promoting effects

Question 11

Fetal Growth Regulation

Answer 11

GH (direct, not thru IGFs)
IGF-1 (early); IGF-1 (late)
Epidermal and fibroblast growth factor

Maternal thyroid hormone needed in 1st trimester

Question 12

Why is insulin important in fetal growth?

Answer 12

Macrosomy–Birth to large infants when mother has hyperglycemia (with uncontrolled diabetes mellitus)

Mom has high plasma glucose–crosses placenta over to the fetus

Fetus releases insulin
–the release of insulin triggers fetal growth

Question 13

Growth Spurt

Answer 13

Gonadal (sex) steroids from ovaries or testes have two major effects:

• activation of the pubertal growth spurt by stimulating growth hormone release
• terminates pubertal growth spurt by inducing closure of the epiphyseal growth plates in the long bones

Question 14

Stimulation of Growth Hormone

Answer 14

Amino Acids (acute):
-building new tissue

Starvation (chronic):
-counterregulatory support of blood glucose

Hypoglycemia:
-counterregulatory

Exercise:
-promoting new muscle growth

Stage 3/4 sleep:
-children with sleep deprivation often have failure to thrive

Gonadal steroids/Thyroid Hormone

Question 15

Inhibition of Growth Hormone

Answer 15

Glucose, GH, IGF1 inhibit GH release via negative feedback

Cortisol:
-periods of stress limit growth to divert calories for survival

Question 16

What test could you devise to evaluate a 3 year old child for growth hormone deficiency?

Answer 16

Amino Acid stimulation (Arginine Infusion)
Exercise stress test
Sleep Study and pull GH when stage 3/4 sleep

Question 17

Growth Hormone Secretion Control

Answer 17

Secretion of GH is controlled by neural and hormonal input into specific hypothalamic nuclei

Stimulatory: GH-RH
Inhibitory: Somatostatin

GH stimulates target cells (liver to produce IGF-1)

IGF-1:

• directly inhibits GH release from pituitary
• inhibits GL-RH release from hypothalamus
• stimulates somatostatin release (inhibits GH release at pituitary)

GH:

• inhibits GH-RH release at hypothalamus
• GH stimulates somatostatin (inhibits GH release at pituitary)

Question 18

Linear Growth Velocity and Weight Gain Rate from Birth to End of Puberty

Answer 18

Rates greatest at birth

Between 2-onset of Puberty, GH/Thyroid Hormone is necessary for normal growth rate

Female growth spurt earlier in females–estrogen

Growth spurt terminated by effect of gonadal steroids on growth plates of long bones–earlier in females

Linear growth compete by end of puberty

Question 19

Excess Growth Hormone

What is a screening test?
What is a treatment?

Answer 19

Almost always due to pituitary GH-secreting tumor

Gigantism–before puberty
Acromegaly (joints on hands and feet = coarse features)–after puberty

Screening test–IGF-1 (only works when excess GH)

Treatment:

• remove tumor
• somatostatin analog–shrinks the tumor

Question 20

Deficient Growth Hormone

What is a screening test?
What is a treatment?

Answer 20

Short stature–children

Adults–hypopituitary patients have GH deficiency

Screening:

• Arginine test
• exercise study
• sleep study

Treatment: Recombinant human GH injections

Question 21

What would the effect of a somatostatin releasing tumor be?

Answer 21

It would lead to GH deficiency and short stature in children

Question 22

Cushing’s Syndrome effect on growth

Answer 22

Inhibition of GH by cortisol or glucocorticoid

Hypothalamus

• stimulates somatostatin
• inhibits GHRH release

Pituitary
-inhibits pulsatile GH release

Bone

• inhibits growth plate response to IGF-1
• inhibits collagen synthesis

Other
-inhibit GnRH/ LH-FSH/ Androgen release (men)

Ex. Gary Coleman was on prednisone (glucocorticoid analog) after kidney transplant in order to suppress immune response
–resulted in GH deficiency

Question 23

Which of the following will lead to an increase in growth hormone secretion?

A tumor producing IGF-1

An analog of somatostatin.

An antagonist of somatostatin.

An infusion of glucose

Answer 23

An antagonist of somatostatin.