PBL 7 - Hormone Problems Flashcards
1) What is the common mode of action of thyroid hormones, cortisol and growth
hormone on glucose metabolism of the liver? [
All 3 hormones activate gluconeogenesis in the liver.
Why does the endocrinologist perform an insulin tolerance/stress test? (ii)
What is the test based on and what is the procedure? [
Growth hormone levels are pulsatile and almost undetectable for most of the
day and so growth hormone levels are measured by their response to stimulation
[1 mark]
(ii) Gold standard is insulin-induced hypoglycaemia [1 mark]
Blood is taken for growth hormone, cortisol and glucose and then fast-acting
insulin is injected intravenously. Blood is taken again for growth hormone, cortisol
and glucose after 30, 45, 60, 90 and 120 minutes. [1mark]
i) Why is the doctor surprised to see normal levels of TSH? (ii) How could this
be explained? [1 mar
With a low T4, you would expect an elevated TSH (as seen in previous
scenario) [1/2].
(ii) The fact that it is normal indicates that there is pituitary damage (the gland
is not able to produce high levels of T4) [1/2].
What is NSILA and which hormone accounts for it? [2
NSILA: nonsuppressible insulin-like activity. [1 mark]
The insulin-like biological effects of IGFs accounts for NSILA [1 mark
) Of all the hormonal deficiencies Sarah is suffering from, which one is the most
dangerous and life threatening?
Cortisol deficiency
Define bitemporal hemianopia and explain why Sarah had the disorder.
Absence of the outer half of field of vision in both eyes [1]. The enlarged pituitary
gland presses on the optic chiasma – the site at which the two optic nerves cross
over
which hormones are released from the AP
LH, FSH TSH Prolactin GH ACTH
Adrenocorticotrophic Hormone (ACTH)
o Coded by POMC + Secreted in response to biological stress
o Stimulates cortisol and androgen release from adrenal gland
o Circadian rhythm – starts to rise at 3am and peaks before waking, lowest in evening
Growth hormone
o Stimulates growth, carbohydrate metabolism and cell proliferation
o GH- insulin antagonist – removes excess lipids, lipolysis, gluconeogenesis
o Growth effects due to IGFs produced in liver
o Pulsatile secretion – higher in night and increases in hypoglycaemia
Prolactin
o Pulsatile secretion – causes milk production, role in metabolism and immune system
o Dopamine on D2 receptors inhibits release, stress, exercise and pregnancy rise
o High levels inhibit HPG axis as inhibits kisspeptin
Thyroid stimulating hormone
o Glycoprotein stimulates thyroid gland to produce thyroxine and triiodothyronine
o TH – increase BMR, protein synthesis
LH and FSH
o Produced by gonadotrophs in AP
o Pulsatile secretion and cycle in female–> stimulate gonadal function and produce oestrogen and testosterone
Why does she have low cortisol
Low ACTH
Effects of low cortisol
Most dangerous so replaced first
o Fatigue, weight loss, vomiting, abdominal pain, low blood sugar, hyperpigmentation
o When acute/rapid – hypovolemic shock – confusion, psychosis
Why elevated prolactin
Stalk damage (patient) so dopamine not being delivered from hypothalamus to pituitary which inhibits the prolactin
(STALK EFFECT)
Prolactin inhibits kisspeptin so no GnRH activation
Why is TSH normal
o T4 low, expect a high TSH but her TSH is low/normal, hence pituitary damage that does not allow for TSH production
o Low glucose as TH increase gluconeogenesis and glycogenolysis, stimulate gluconeogenesis
Low GH symptoms
(Causes low igf-1)
o Maintains normal muscle function, deficiency results in inadequate energy –> fatigue reduced strength and stamina
o Low as only high at night
o Causes High LDL- GH normally removes lipids
Loss of LH and FSH symptoms
loss of menstrual periods and Loss of oestrogen – loss of libido
How to measure growth hormone
Suppression test
GH function
o Promotes lipolysis in adipocytes and removes excess lipids
o Stimulates protein production (counteracts insulin in the blood) to retain electrolytes + needed for brain function
o Lowers glucose uptake by skeletal muscle + increases hepatic gluconeogenesis
• Growth hormone deficiency
o Caused by pituitary adenoma
o High LDL, increase CV mortality risk, fatigue
GH axis
If stress, circaidian rhythm, hypoglycasemia ==> GHRH from hypothalamus stimulates SS and GH
which inhibits GH release - Negative feedback via SS and IGF-1
GH causes IGF-1 release from liver –> growth
ACTH axis
Circaidian, stress, hypoglycaemia –> CRH from ht –> ACTH causes release of cortisol from adrenals
Cortisol function
o Stimulate gluconeogenesis
o Mobilise amino acids
o Suppress immune system
o Inhibit uptake by muscles and adipocytes
o Stimulate lipolysis to produce glycerol for glucose production.
o Plays a role in regulation of electrolyte balance in particular sodium and potassium so a deficiency in cortisol –> low sodium and high potassium
