Pituitary gland and regulation of endocrine system Flashcards
where does the pituitary gland sits in relation to the optic chiasm and sphenoid sinus
- Sits superior and posterior to sphenoid sinus
- Sits inferior to optic chiasm
where does the pituitary gland sit
sits in the Sella turcica – saddle shaped depression in the sphenoid bone
Pituitary gland is composed of what 2 lobes and how is it connected to the hypothalamus
Anterior and posterior lobes
Connected to hypothalamus by an infundibulum
what cells does the anterior pituitary gland consist of
secretory adenohypophysis cells
how does hypothalamus send signals to the anterior pituitary gland
Hypothalamus secretes neuroendocrine messengers which travel to the anterior pituitary in the hypophyseal portal system
what is the anterior pituitary gland supplied by
superior hypophyseal artery
Posterior pituitary gland is an extension of Hypothalamic neurons axons from:
Paraventricular nuclei
Supraoptic nuclei
what are the most common anterior pituitary cell type
Somatotrophs (50%)
Give examples of 5 anterior pituitary cell types, the hormone they release and their target organ
1) Somatotrophs (50%) - Growth hormone - multiple organs
2) Gonadotrophs (10%) - FSH and LH - Ovaries/testes
3) Corticotrophs (10-15%) - Adrenocorticotrophic hormone (ACTH) - adrenal cortex
4) Thyrotrophs (5%) - Thyroid stimulating hormone (TSH) - Thyroid
5) Lactotrophes (20%) - Prolactin - Breast/Uterus
what does hypothalamus secrete which stimulates GH release from anterior pituitary
GHRH- Growth hormone releasing hormone
This acts on the pituitary to release GH
GH secretion is ______, occurs mainly ________
Pulsatile
Overnight
How does growth hormone affect its target organs
Either direct effects or via production of insulin-like growth factor-1 (IGF-1) from liver
what does hypothalamus secrete which stimulates prolactin release from anterior pituitary
Dopamine- Under negative hypothalamic control (inhibits prolactin levels)
Oestrogen- opposite effect, increases prolactin levels
when does dopamine level increase
under stress
oxytocin is produced by anterior or posterior pituitary?
Posterior pituitary
what are disorders of the anterior pituitary gland
Hormone excess:
- Prolactin
- GH
- ACTH
- TSH
Hypopituitarism
what are disorders of the posterior pituitary gland
- Diabetes insipidus
- Syndrome of inappropriate ADH -leading cause of euvolemic hyponatremia
what is AVPR2 (vasopressin receptor 2) action
- Found in the Basolateral membrane of kidney collecting ducts
- Inserts aquaporin channels to increase renal water reabsorption
what is diabetes insipidus
Rare condition in which large volumes of dilute urine are produced ( >3L/day) due to lack of ADH
what are clinical features of diabetes insipidus
Polyuria, polydipsia, nocturia
what are the cranial causes of diabetes insipidus
Cranial: Deficiency of ADH
Causes:
- Idiopathic
- Genetic – mutations of ADH genes
- Trauma (Iatrogenic – post surgical)
- Tumours
- Infections
- Inflammatory conditions of posterior pituitary e.g. sarcoid
what are the nephrogenic causes of diabetes insipidus
Nephrogenic- Resistance to ADH
Causes: - Genetic – AVPR2 mutations Secondary due to: - Drugs – lithium - Metabolic upset - Renal disease
what is the diagnosis of diabetes insipidus
Water deprivation test:
- Deprive patients of water for 8h
- Measure plasma and urine osmolality at start and finish and every 2-4hs in between
- After 8h give synthetic ADH and reassess urine osmolality
Normal response- concentrated urine
Diabetes insipidus response- continue to pee large volume of pee, even if water intake is denied
what is the cranial treatment of Diabetes Insipidus
Synthetic ADH- Desmopressin
Can be given orally/nasal spray/injection
Monitor plasma sodium and osmolality
what is the nephrogenic treatment of Diabetes Insipidus
Treat cause e.g. address renal disease, drugs, metabolic upset
High doses of ddAVP – synthetic ADH
Management is very difficult
what are non-functioning pituitary adenoma
Found in 10% of population (mostly elderly)
Often asymptomatic – incidentalomas
if non functioning pituitary adenoma are discovered, then what is carried out
Need to exclude hormone dysfunction:
- Check for hormone excess (in 65%)
- Check for hypopituitarism (if > 1cm)
why is vital to ensure that there is no effect on visual field when a non-functioning pituitary adenoma is discovered
- Pituitary located just below optic chiasm
- Tumour can expand upwards and push on chiasm causing loss of peripheral vision (‘bitemporal hemianopia’)
what is the management of non functioning pituitary adenoma
Surgical removal if visual field impaired – transphenoidal or transcranial
Give examples of secretory pituitary adenomas
Prolactin- ‘Prolactinomas’ (Commonest; 30%)
ACTH- ‘Cushing’s Disease’ (20%)
Growth hormone - ‘Acromegaly’ (15%)
TSH – ‘TSHomas’ (Very rare, < 1%)
what are the clinical features of prolactinomas
- Galactorrhoea- breast lactates in non pregnancy state. can happen in both men and women
- Menstrual disturbance and subfertility in women
- Reduced libido/erectile dysfunction in men
what is the management of prolactinomas
Dopamine agonists (cabergoline) Surgery if large tumour with visual field effects
what is acromegaly
Excessive production of GH (and its effect on IGF-1) in adults.
Usually due to a pituitary adenoma which is often large
Called gigantism in children
what are the clinical features of acromegaly
Symptoms
Sweats, headache, tiredness, increase in ring or shoe size (IN ADULTS), joint pains
Signs Coarse facial appearance Enlarged tongue Enlarged hands and feet Visual field loss increased frontal bossing
Complications
Hypertension, diabetes or impaired glucose tolerance, increased risk of bowel cancer, heart failure
how to diagnose acromegaly
Glucose tolerance test
- Glucose load fails to suppress GH
- May reveal underlying DM or IGT (impaired glucose tolerance)
IGF-1 level
- long half life, protein bound
- So more useful than plasma GH
Pituitary MRI
- Tumour usually large (macroadenoma, > 1 cm) and often extends into surrounding structures
how to manage acromegaly
Surgery
- By transsphenoidal route
- Often not curative
Medical therapy Before and after surgery - Somatostatin (normally produced by hypothalamus to inhibit GnRH production) analogues used to inhibit GH secretion - GH receptor antagonist - Dopamine agonists
Pituitary radiotherapy
- To treat residual tumour
- Risk of hypopituitarism and long term problems
What is hypopituitarism
Failure of (anterior) pituitary function Can affect single hormonal axis (may just affect gonadotrophins e.g. FSH/LH most commonly) or all hormones (panhypopituitarism)
what can hypopituitarism lead to
Leads to secondary gonadal/thyroid/adrenal failure
what are the causes of hypopituitarism
Tumours Radiotherapy Infarction (apoplexy) - if post partum then called Sheehan’s syndrome Infiltrations (eg sarcoid) - Can affect posterior pituitary too Trauma Congenital
what is the treatment of hypopituitarism
Need multiple hormone replacement but always give cortisol first – can lead to secondary adrenal insufficiency, hypogonadotropic hypogonadism
