Pituitary gland and regulation of endocrine system Flashcards by Zainab Munir

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

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where does the pituitary gland sit

sits in the Sella turcica – saddle shaped depression in the sphenoid bone

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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

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what cells does the anterior pituitary gland consist of

secretory adenohypophysis cells

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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

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what is the anterior pituitary gland supplied by

superior hypophyseal artery

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Posterior pituitary gland is an extension of Hypothalamic neurons axons from:

Paraventricular nuclei

Supraoptic nuclei

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what are the most common anterior pituitary cell type

Somatotrophs (50%)

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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

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what does hypothalamus secrete which stimulates GH release from anterior pituitary

GHRH- Growth hormone releasing hormone

This acts on the pituitary to release GH

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GH secretion is ______, occurs mainly ________

Pulsatile

Overnight

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How does growth hormone affect its target organs

Either direct effects or via production of insulin-like growth factor-1 (IGF-1) from liver

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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

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when does dopamine level increase

under stress

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oxytocin is produced by anterior or posterior pituitary?

Posterior pituitary

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what are disorders of the anterior pituitary gland

Hormone excess:

Prolactin
GH
ACTH
TSH

Hypopituitarism

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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