Growth Hormone

Effects of growth hormone deficits

* Short stature, body continues to develop in appropriate proportion
* Delayed physical maturation – bone maturation and puberty

What are the 2 types of growth?

* Hypertrophy – increase in cell size
* Hyperplasia – increase in cell number

what secretes growth hormone

somatotrophs in anterior pituitary

how is growth hormone secretion regulated?

peptides released from neuroendocrine cells in the hypothalamus (hypothalamic peptides)

Name 3 hypothalamic peptides

* Growth hormone releasing hormone
* Somatostatin
* Ghrelin

How does growth hormone releasing hormone work?

stimulates production of growth hormone from somatotrophs

* GHRH released (caused by a number of factors)
* GHRH moves via hypophyseal system into anterior pituitary to stimulate GH release

How does somatostatin work?

Inhibits production of growth hormone

* Somatostatin released
* Somatostatin moves via hypophyseal system into anterior pituitary to inhibit GH release

What causes somatostatin release?

* increased blood glucose
* increased free fatty acids
* obesity
* aging

how does ghrelin work?

increases growth hormone release from somatotrophs

Name the 2 types of growth hormone secretion

* Diurnal (large increase during sleep)
* Pulsatile (pulses throughout day and night)

How can growth hormone inhibit it’s own release

inhibition of growth hormone releasing hormone

How can growth hormone stimulate its own release

can stimulate somatostatin release

what can be measured to monitor growth hormone release over a longer term

plasma IGF1

What effects can GH have on protein metabolism?

* Increases amino acid uptake and utilization
* Increases protein synthesis
* Decreases protein catabolism

What effects can GH have on lipid metabolism?

* Decreases lipogenesis

What effects can GH have on carbohydrate metabolism?

* Decrease glucose uptake and oxidation
* Increases gluconeogenesis/glycogenolysis
* Increases blood glucose
* GH sometimes referred to as ‘diabetogenic’

How does growth hormone work with serum?

Releases a factor (IGF-1) into serum which mediates actions of growth hormone

What does IGF1 do?

mediates local growth

where is IGF1 produced and what is secretion dependant on?

* produced in liver and locally in tissues
* secretion is GH dependent

IGF1 with age

* very low at birth
* peaks during puberty
* declines with age
* remains above 0 throughout life

benefits of giving GH to elderly?

* Inc in muscle mass
* Inc in bone density
* Dec in body fat

Negative of giving artificial GH?

Up to half receiving GH develop complications

* Diabetes, hypertension, cardiovascular disease, arthritis, tissue oedema, carpal tunnel syndrome
* Question if it could pose increased cancer risk

Direct GH effects

Directly increase blood glucose and affects protein synthesis

Indirect GH effects

Indirectly causes growth by IGF1, and has endocrine effects by IGF1 released by liver by affecting production of hypothalamic hormones which

Effects of excess growth hormone during childhood and adulthood

During childhood (prior to epiphyseal growth plates closing) → Giantism

During adulthood (after epiphyseal growth plates close) → Acromegaly

What are some symptoms of acromegaly

* soft tissue swelling visibly and of internal organs
* skull expansion
* brow protrusion
* lower jaw protrusion
* insulin resistance

type of dwarfism caused by pituitary malformation/tumor

pituitary dwarfism

type of dwarfism caused by GH-R or GHRH-R mutation

Laron dwarfism

Why is growth hormone therapy not as good as natural growth hormone

bolus injections given but GH should be pulsatile