Integrated endocrine physiology Flashcards
what is lipolysis
- What is it inhibited by
- What is it stimulated by
Fat turned into FFA + glycerol
- INhibted by insulin
- Stimulated by glucagon, cortisol, GH and catecholamines
What is synergistic activity
Produce much greater enhanced response than sum of either of hormones alone
What is permissive activity
Presence of one hormone allows a second hormone to act
Where are growth hormones synthesised
Somatotrophs in anterior pituitary
What are the roles of the growth hormone
Where do they act
Growth and metabolism
Act via GH receptor on target cells
Action of growth hormone on metabolism (direct)
Liver- increased gluconeogenesis
Muscle- increased amino acid uptake, increased protein synthesis, decreased glucose uptake
Adipose tissue- increased lipolysis, decreased glucose uptake
overall effect- increased blood glucose
What is growth hormone synergistic with
Cortisol
What is the indirect effect of growth hormone
Promotes growth by stimulating release of growth factors such as IGF-1 (insulin-like growth factor) and IGF2 (somatomedins) from liver and other cell types
How does growth occur
Via the action of IGF1 on cells
-Stimulate protein synthesis, increase cell size (hypertrophy)
- Stimulate cell division, increase cell number (hyperplasia)
- Promote skeletal growth
What does the action of growth hormone on growth require
Presence of thyroid hormones (has a permissive role)
What role does thyroid hormone have
Permissive role on GH activity in promoting growth
Key role in CNS development
Other hormones important for growth and their roles
INsulin- important growth promoter. Also important intra-uterine growth factor
Sex hormones- dramatic rise during puberty. Linear growth, muscle building and stop bone elongation. by promoting epiphyseal plate closure
How do these affect bone growth and bone maturation:
- Growth hormone
- Thyroid hormone
- Androgens
- Oestrogens
- Glucocorticoids
GH- bigger increase in liner growth than the increase in bone maturation
Thyroid- Increase in linear growth and maturation
Androgens and oestrogens- Increase in linear growth but bigger effect on bone maturation
Glucocorticoids- Decrease in linear growth and increase in bone maturation
What trophic effect do these anterior pituitary hormones have:
- Prolactin
- LH, FSH (gonadotropins)
- TSH (thyrotropin)
- ACTH (corticotropin)
Prolactin- breast
LH, FSH- testes, ovaries
TSH- Thyroid
-ACTH- adrenal cortex
Low levels of these cause atrophy
How does growth hormone have an effect on growth
Acts on liver and other tissues and via somatomedins has an indirect effect on growth
How is the release of GH controlled
Hypothalamus releases growth hormone releasing hormone which increases action of anterior pituitary which increases growth hormone release
Hypothalamus releases somatostatin which decreases action of anterior pituitary
How does a decrease in blood glucose, decrease in FFA and increase in AA conc affect GH release
They increase the action of hypothalamus which releases more GHRH which acts on anterior pituitary and so more GH released.
This means there is increased gluconeogeneiss, increased lipolysis and increased amino acid uptake and protein synthesis which helps to increase blood glucose
What effect do stress, sleep and exercise have on growth hormone secretion
Increase growth hormone secretion.
What is the release of GH like during the day
Intermittent peaks throughout the day but 70% of the release is during sleep
What does cortisol (glucocorticoid) have a synergistic effect with and what do they do
GH
Mobilise reserves and increase availability of glucose (esp. prolonged hypoglycaemia)
What effect do chronic high glucocorticoid concentrations have and when might this be the case
Inhibit GH release (such as Cushing’s syndrome, long term use of high doses of steroids)
What can stunted growth be because of
Pituitary dwarfism (GH deficiency)
Hypothyroidism
Cushing’s syndrome
CAH (congenital adrenal hyperplasia)
Sexual precocity
What is used to treat growth hormone deficiency
Recombinant HGH (human growth hormone)
Growth hormone deficiency symptoms
- Psychological changes
- MAlaise, excessive tiredness, anxiety and depression
- Ostoporosis
- Poor muscular tone, decrease in lean body mass
- Impaired hair growth
- Increase in adipose tissue especially around the waist
How does Cushing’s lead to stunted growth
Excess cortisol inhibits GH release
Inhibits linear bone growth
What is sexual precocity
Entering puberty before
f-age 8
m-age 9
How do CAH and sexual precocity cause stunted growth
Increased androgens result in early/rapid bone maturation
What can cause accelerated growth (tall stature)
Gigantism
Hyperthyroidism
Sexual precocity
Eunuchoidism
How does gigantism cause accelerated growth
Tumour with GH excess
How does hyperthyroidism cause accelerated growth
Excess thyroid hormones promote GH
Difference between acromegaly and gigantism
Gigantism - excess GH in childhood
Acromegaly- excess GH in adulthood
Symptoms of acromegaly
Coarsening of facial features Enlarged hands and feet Headaches, vision disturbance Sleep apnoea, general tiredness Hypertension, cardiomegaly Glucose intolerance (diabetes) Irregular or loss of periods (females); impotence in males
How does sexual precocity cause accelerated growth
Initial accelerated bone growth (early growth spurt)
How does eunuchoidism cause accelerated growth
Low sex hormone levels result in extension of long bone growth (delayed bone maturation)
