Hypothalmic pituitary axis physiology Flashcards
What are the hormones secreted by the anterior pituitary gland ?
- TSH, ACTH, FSH, LH
- GH and Prolactin
What are the hormones secreted by the posterior pituitary gland?
ADH and oxytocin
What are some of the pathologies affecting the anterior pituitary gland ?
Hyperfunction:
- Adenoma
- Carcinoma
Hypofunction:
- Surgery/radiation
- Sudden Haemorrhage into gland
- Ischaemic necrosis - Sheehan Syndrome
- Tumours extending into sella
- Inflammatory conditions (Sarcoidosis)
What are some of the pathologies affecting the posterior pituitary gland ?
Diabetes Insipidus:
- Lack of ADH secretion
- Can lead to life threatening dehydration
Syndrome of Inappropriate ADH secretion (SIADH):
- Ectopic secretion of ADH by tumours
- Primary disorder in the pituitary
What is the most common pituitary tumour ?
Pituitary adenomas
How do pituitary adenomas arise ?
Either sporadic or may be due to MEN1 syndrome
How can pituitary adenomas be classified ?
Size (a microadenoma is <1cm and a macroadenoma is >1cm)
Hormonal status (a functional adenoma produces and excess of a particular hormone and a non-functional adenoma does not produce a hormone to excess)
Hormones produced in excess include:
- Prolactin (20-30%)
- ACTH (10-15%)
- FSH/LH (10-15%)
- GH (5%)
- Can produce more than one
- hormone production may be at subclinical levels
What are the typical features of pituitary adenomas ?
- Functional tumours - Excess of a hormone (e.g. Cushing’s disease due to excess ACTH, acromegaly due to excess GH or amenorrhea and galactorrhea due to excess prolactin)
- Non-functioning tumours or those causing compression of normal pituitary gland - present with generalised hypopituitarism
- Headaches
- Compression of optic chiasm - bitemporal heminopia
What investigations are required for someone with a suspected pituitary adenoma ?
- a pituitary blood profile (including: GH, prolactin, ACTH, FH, LSH and TFTs)
- formal visual field testing
- MRI brain with contrast
What is the principle of endocrine dynamic function tests ?
- If there is too much hormone being secreted resulting in a condition - do a test to suppress the hormone
- If there is too little hormone being secreted resulting in a condition - do a test to try and stimulate it
What are the different dynamic pituitary stimulation tests which can be done ?
- Synacthen (synthetic ACTH) test - stimulates cortisol
- Insulin stress test or prolonged glucagon test - stimulates cortisol and GH
- Water depravation test - stimulates ADH, check serum and urine omolarities
What is the water deprivation test used to diagnose ?
Diabetes insipidus
What is the synacthen test used to help diagnose ?
Adrenal insufficiency as measures cortisol response e.g. due to additions disease
What is the insulin stress test (insulin tolerance test) used to asses ?
Assesses GH and ACTH ==> cortisol
It is the gold standard for assessing integrity of hypothalmic-pituitary adrenal axis
What is the relationship between dopamine and prolcatin ?
Dopamine inhibits prolactine secretion
What are some of the non-pathological causes of raised prolcatin ?
- Breast feeding
- Pregnancy
- Stress
- Drugs - dopamine antagonists e.g. metoclopramide, or antipsychotics e.g. phenothiazines
What are some of the pathological causes of raised prolactin ?
- Hypothyroidism
- Stalk lesions - e.g. due to iatrogenic, road accidents
- Prolactinoma
What are some of the clinical signs of raised prolcatin in females ?
- Galactorrhoea - milky discharge from nipples
- Menstrual irregularity
- Ammenorrhoea
- Infertility
- Osteoporosis
What are some of the clinical features of raised prolactin in males?
- Erectile dysfunction (impotence), loss of libido, galactorrhoea
- Decreased body and facial hair
- Uncommonly, enlarged breasts (gynecomastia)
- Visual field abnormal
- Headache
What investigations are done to diagnose a prolactinoma ?
- Serum prolactin
- Pituitary MRI
- Check visual fields - would be a bitemporal heminopia
What is the treatment of a prolactinoma ?
- 1st line dopamine agonist - Cabergoline, bromocriptine
- 2nd line = transphenoidal surgery
What is acromegaly ?
Abnormal growth of the hands feet and face caused by overproduction of GH by the pituitary gland
What is the cause of acromegaly usually ?
- 95% of patients - secondary to a pituitary adenoma
- A minority of cases are caused by ectopic GHRH or GH production by tumours e.g. pancreatic.
What are the characteristic features of acromegaly ?
- Gaint (tall)
- Thickened skin
- Large hands (spade-like) & shoe-size
- Large tongue
- Prognathism = protrusion of lower jaw
- Excessive sweating & oily skin
- Snoring/sleep aponea
- DM
- Features of pituitary tumour: hypopituitarism, headaches, bitemporal hemianopia
How is acromegaly diagnosed?
- 1st line = Measure serum insulin-like growth factor 1 (IGF-1) + serial serum growth hormone (GH)
- 2nd line (done to confirm diagnosis if IGF-1 levels are raised) Oral glucose tolerance test (OGTT) - measure GH during it as when given glucose GH levels should decrease but in acromegaly they remain unchanged
What is the treatment of acromegaly ?
1st line = pituitary surgery (transsphenoidal)
Then retest using OGTT
2nd line = somatostatin analogue (octreotide or lanreiotide) + dopamine agonist (carbergoline)
What are the complications of acromegaly ?
- hypertension
- diabetes (>10%)
- cardiomyopathy
- colorectal cancer
What are the common side effects of somatostatins ?
- Flatulence
- Diarrhoea
- Abdominal pains
- Gastritis
- Gallstones
