Pituitary anatomy and intro - booklet Flashcards
Anatomy of pituitary gland
- Size pea
- Sits in pituitary fossa at base of brain
Anterior vs posterior origin
- Anterior - derived from upgrowth of gut
- Posterior - downgrowth of primative brain tissue
Relationships of pituitary gland
- Optic chiasm above
- Cavernous sinus laterally - containing CN III, IV, Va Vb and VI and internal carotid artery
How does hypothalamus act on pituitary?
Secretes inhibiting and releasing factors transported down hypophyseal portal tract to anterior pituitary
Axis of pituitary
- Growth axis
- Adrenal axis
- Gonadal axis
- Thyroid axis
- Prolactin axis
Growth axis - what happens?
- GH secreted in pulsatile manner
- Peak pulses during REM sleep
- GH acts on liver to produce IGF-1 (marker of GH activity)
- Plays role in MSK growth in children
- Under control of GHRH and somatostatin
Adrenal axis - what happens?
- ACTH has circadian rhythm
- Peaks pulses in early morning and lowest activity at midnight
- ACTH stimulates cortisol release
- Positive control of CRH and cortisol has -ve feedback on ACTH
Gonadal axis - what happens?
- FSH leads to ovarian follicle development in women, sperm production in men
- LH causes mid cycle ovulation and drives testosterone synthesis in male testes (Leydig cells)
- Stimulated by pulsatile GnRH
- Testosterone, prolactin and oestrogen inhibit FSH and LH
Thyroid axis - what happens?
- TSH drives thyroxine release via stimulation of TSH receptors on thyroid gland
- TRH stimulates TSH secretion and also stimulates prolactin (weak)
- Thyroxine has -ve feedback
Prolactin axis - what happens?
- Prolactin causes lactation and directly inhibits LH and FSH
- Controlled by dopamine
- Stimulated weakly by TRH
- Anything that blocks dopamine = elevated prolactin
How can pituitary tumours present?
- Mass effect - compression of surrounding structures
- Hormone excess
Functional pituitary tumours can present as…
- Acromegaly (GH)
- Cushings disease (ACTH)
- Prolactinoma
- TSHoma
Non functioning pituitary tumours may present with…
- Compression of local structures
- Hypopituitarism
What happens to hormones in hypopituitarism?
Usually all hormones go down except prolactin
This goes up due to disinhibition hyperprolactinaemia - reduced dopamine or compression of stalk dopamine is not released
Visual defect of pituitary tumours
Bi temporal hemianopia
When is surgery indicated for non-functioning tumours?
Usually if visual defect is present = surgery
Basal tests for pituitary tumour
- Prolactin and TSH - anytime
- Women LH and FSH - within 1st 5 days of menstrual cycle
- Men - LH, FSH and testosterone at 9am when deficiency is expected
- IGF-1 is a marker for GH
Dynamic tests for pituitary tumour
- Synacthen test
- Insulin tolerance test - gold standard for ACTH and GH reserve
- ACTH and GH should rise with ITT
Who should insulin tolerance test not be done on?
- Ischaemic heart disease pts
- Epilepsy
- Risk of triggering coronary ischaemia and seizures
Imaging for pituitary tumour
- MRI + contrast
- CT may be adequate if unable to do MRI
- PET and functional MRI increasing popularity to see functionality of tumours
Macro vs micro adenoma
- Macro if more than 1cm
- Less than 1cm - microadenoma
