Pituitary Physiology Flashcards
Which hormones can be produced by the anterior pituitary?
- ACTH
- TSH
- FSH
- LH
- PRL
Which hormones can be produced by the posterior pituitary?
- ADH
- Oxytocin
Describe how thyroxine can be produced with hypothalmic stimulation
- Stress stimulus on hypothalamus
- Thyrotropin releasing hormone released
- Anterior pituitary releases thyrotropin
- Thyroid releases thyroxine
What releases corticotropin releasing hormone?
Hypothalamus
What effects does corticotropin releasing hormone have?
Acts on the pituitary to cause ACTH release
Where does ACTH act and what is the result of this?
Adrenal gland
Cortisol release
Why is prolactin different to other hormones in terms of its release?
Its release is under constant suppression by dopamine
If the pituitary hormone is GH, what is the peripherally acting hormone?
IGF-1
(insulin-like growth factor)
If hormone levels appear high, which type of test will be used?
Suppression test
Why is it a worry if a hormone suppression test fails?
It may suggest a tumour causing autonomous hormone release
If there is too little hormone, which test would be used?
Stimulation test
Which hormones are tested in an insulin stress test?
- Cortisol
- GH
Describe an insulin stress test
Hypoglycaemia induced
Hormone (cortisol and GH) measured at 30 minute intervals for 2-3 hours
How can pituitary release of cortisol be tested?
Synacthen (synthetic ACTH) administered
Cortisol levels measured at 0, 30 and 60 minutes
Describe a water deprivation test
- Serum and urine osmolalities tested for 8 hours
- IM DDAVP (desmopressin - an anti-diuretic) is administered
- Serum and urine osmolalities tested for 4 hours
- If urine/serum osmolar ratio > 2 then this is normal, any less confirms Diabetes inspidus
How are pituitary tumours classified based on size?
= 1cm microadenoma
> 1cm macroadenoma
Which cranial nerves are potentially most impacted in a pituitary tumour?
CN 3, 4 and 6
What is bitemporal hemianopia?
Loss of peripheral vision
What causes bitemporal hemianopia?
- Nasal retinal fibres detect peripheral light
- These fibres cross over at the optic chiasm which can be compressed by a pituitary tumour
- Hence, peripheral vision is lost
What are the two main causes for prolactin increases?
- Physiological
- Drugs
What are the main physiological causes for prolactin increase?
- Breastfeeding
- Pregnancy
- Stress
- Sleep
Which types of drugs can cause increases in prolactin?
- Dopamine antagonists (metoclopramide)
- Antipsychotics
- Antidepressants
- Oestrogen, cocaine etc
What are the key pathological reasons as to why prolactin may increase?
- Hypothyroidism
- Stalk lesions (iatrogenic or RTA)
- Prolactinoma
How does the timing of presentation of a prolactinoma differ in males and females?
Males - Late presentation
Females - Early presentation
What are the symptoms of a prolactinoma in females?
- Menstrual irregularities/ammenorrhoea
- Galactorrhoea
- Infertility
What are the symptoms of a prolactinoma in males?
- Impotence
- Visual field problems
- Headache
- Antertior pituitary malfunction
What are the relevant investigations for a prolactinoma?
- Prolactin concentration
- MRI (size of tumour, pituitary stalk/optic chiasm damage)
- Visual field check
- Pituitary function tests
Dopamine agonists are treatment for prolactinoma, what is the most commonly used drug?
Cabergoline
What are the benefits of cabergoline in prolactinoma treatment?
- Least side effects compared with other drugs
- Normalises prolactin in 96%
- Can induce tumour shrinkage
- Pregnancy rates increase
Acromegaly is due to an excess in which hormone?
GH
When does giantism occur?
Excess GH release before growth plate fusion
What is the typical appearance of someone with acromegaly?
- Thickened skin
- Large jaw
- Sweaty, large hands
What other abnormalities occur with acromegaly besides appearance?
- Hypertension and CF
- Headaches
- Snoring and sleep apnoea
- DM
- Visula field abnormalities
- Hypopituitarism
- Colonic polyps and colon cancer
What causes the headache in acromegaly?
Vascular effects and rapid bloodflow
How can acromegaly be diagnosed?
- IGF-1 elevated
- Failure of GH to suppress <0.4ug/L (usually exceeding 1ug/L) after GTT
- Visual field problems
- CT/MRI
- Pituitary function tests
How can acromegaly be treated?
- Surgery
- Radiotherapy (much less effective than surgery)
- Somatostatin analogues
If after surgery, a patient with acromegaly still has GH levels >1ug/L after GTT which drugs may be used for treatment?
- Dopamine agonist
- Octreotide
- Pegvisomant
What are the beneficial effects of somatostain analogues e.g. octreotide?
- Reduces tumour size
- Releives headaches in 1 hour
- Reduces GH in most
What are the side effects of somatostain analogues?
- Local stinging
- Flatulence
- Diarrhoea
- Abdominal pain
- Gastritis
- Gallstones (inhiition of GB contraction)
What is pegvisomant?
GH receptor antagonist
What are the beneficial effects of pegvisomant?
IGF-1 decreases
What tests/investigations should eb undertaken for an acromegaly follow up?
- BP/lipids/glucose (for CV risk)
- GH < 0.4ug/L (post GTT) and < 2ug/L (random)
- Normal IGF-1 levels
- Other pituitary hormones
- Cancer surveillance e.g. colon/tubulovillous adenoma
- Sleep apnoea tests
