Piuitary Gland Flashcards
What is hypothalamus pituitary system
Hypothalamus secretes hormones which stimulate the PG
Hormones secreted by anterior pituitary
ACTH
LH FSH
prolactin
TSH
GH
Hormones secreted from posterior pituitary
Oxytocin
Vasopressin (ADH)
Where is pituitary situated
Base of brain
Sella turcica
How is hypothalamus secretion regulated
Via hormone mediated signals (negative feedback)
Via neural inputs (ACh)
Which nuclei regulate endocrine functions
Paraventricular
Supraoptic
Ventromedial
Hypothalamus’ non endocrine functions
Regulation of body temp
Thirst
Food intake
Blood pressure
How is pituitary gland connected to hypothalamus
Infundibulum stalk
Which hypothalamus hormones relate to anterior pituitary gland hormones
GHRH - GH
GnRH - LH/FSH
CRH - ACTH
TRH - TSH
TRH + GnRH - prolactin
What is GH stimulated by
Hypoglycaemia
Exercise
Sleep
Supported by hyperglycaemia
How are the effects of GH mediated
IGF-1
What is the pattern of GH secretion
Released through out life
Pulsatile
Peaks when asleep
Function of GH
Linear growth in children
Acquisition of bone mass
Stimulate:
- Protein synthesis
- Lipolysis
- Glucose metabolism
Regulation of body composition
Psychological well-being
What happens to secretion of gonadotropins during puberty
Sensitising of hypothalamus and PG to negative feedback of gonadotropins decrease
So increase production of testosterone and oestrogen
Allows development of secondary sex characteristics
What does testosterone release cause
Spermatogenesis
Male secondary sec characteristics
What does oestrogen release cause
Folliculogenesis
Female sex secondary characteristics
Function of prolactin
Essential for lactation
Level increase pregnancy and breast feeding
Inhibits gonadal activity by suppressing GnRH
Can cause disease in excess
Function of ACTH
Promotes secretion of cortisol
Secretion pattern of ACTH
Pulsatile
High in morning
Drops throughout day
When sleeping cortisol undetectable
Where is ADH synthesised
In supraoptic and paraventricular nuclei of hypothalamus
What kind of hormone is ADH
Peptide hormone
How is ADH transmitted to posterior pituitary gland
Migrate via axons of the supraopticohypophyseal tract into posterior lobe
Function of ADH
Primary physiological determinant of the rate of free water excretion
Augments the water permeability of luminal membranes of cortical and medullary collecting tubules
Via V2 receptor (kidney)
Retains water and decreases water excretion
What are the major stimuli for increased secretion of ADH
Hyperosmolality - thick blood
Effective circulating volume depletion
Function of oxytocin
Stimulates contraction of smooth muscle of breast and uterus
Under positive feedback
More contraction = more oxytocin
Roles in: milk ejection reflex and birth
What is synthetic oxytocin used for your
Inducing labour
Main effects of parasellar (located around sella turcica) lesions
Neurological
Visual
Hypopituitarism
Most common pituitary lesion
Pituitary adenoma
How visual defects are caused
Pressure on optic nerve/ optic chiasm
Neurological/ visual effects due to pituitary lesion
Headaches
Brain damage
Cranial nerve damage - III, IV, V, VI (in cavernous sinuses)
CFS leak
How can peripheral visual fields be compromised due to pituitary lesion
Impinges on medial nerves
Medial nerves cross over at optic chiasm
So pressure on optic chiasm causes temporary loss of peripheral vision
Major causes of hypopituitarism
Pituitary tumours
Radiotherapy
Pituitary infatction (apoplexy) - death of area of PG
Infiltration of PG
Trauma
Isolated hypothalamic releasing hormone deficiency
Manifestations of GH deficiency
Children: poor growth
Adults: increases abdominal fat, decreases lean body mass
Impaired lipid profile
Decreases muscle strength and exercise capacity
Impaired cardiac function
Decreases bone mineral density
Impaired psychological well being
How to diagnose GH deficiency
Tests:
ITT - insulin tolerance test. Make patient hypoglycaemic. Stimulates GH. Record GH levels.
Glucagon
GHRH + Arginine
Measure IGF-1
What is IGF-1
Mediates the secretion of GH
Treatment for GH deficiency
Hormone replacement:
Recombinant human GH
Injection at night- mimics physiology. GH high at night.
Manifestations of FSH/ LH deficiency in men
Men: decrease libido, infertility, loss secondary sex features, decrease muscle mass, decrease mood and wellbeing, osteoporosis and anaemia
Manifestations of FSH/ LH deficiency in children
Children: delayed puberty
Manifestations of FSH/ LH deficiency in women
Decrease libido, menstrual disorders, infertility, dyspareunia (painful intercourse), osteoporosis, premature atherosclerosis (narrowing arteries)
How FSH/ LH deficiency is diagnosed
Females: FSH LH oestradiol (menstrual history)
Males: FSH LH and morning (afternoon not representative) testosterone
Treatment for FSH LH deficiency
Hormone replacement
Oestrogen and progesterone
Testosterone
Manifestations of ACTH deficiency
Fatigue
Weakness
Nausea/ vomiting
Anorexia
Weight loss
Hypoglycaemia - corticosteroids are insulin antagonist
Hypotension
Anaemia
Diagnosis of ACTH deficiency
9.00am serum cortisol and ACTH levels
Dynamic tests:
Short synathen test - synthetic ACTH test see if cortisol is secreted
Insulin tolerance test - cause hypoglycaemia. Stress induces cortisol.
Glucagon test
ACTH deficiency treatment
Replace what is missing (steroids)
No need for aldosterone replacement - not regulated via ACTH/ HPA
Manifestations of TSH deficiency
Fatigue
Weakness
Cold intolerance
Bradycardia
Weight gain
Puffiness
Pale + dry skin
Constipation
Diagnosis of TSH deficiency
Serum TSH
Serum T3
Serum T4 levels
Treatment for TSH deficiency
Hormone replacement (levothyoxine)
What is central diabetes insipidus
Deficient secretion of ADH
Causes of ADH deficiency
- Idiopathic (autoimmune destruction)
- Familial
Mutations - Tumours
- Neurosurgery or trauma
- Infiltrative disorders
- Infections
- Hypoxia encephalopathy or severe ischaemia
Manifestations of ADH deficiency
Water not retained in kidneys so more urine passed
Polyuria (output >3L/ day and 2L/day for children)
Polydipsia
Nocturia
Major causes of Polyuria in common clinical practice
Osmotic diuresis:
Diabetes mellitus
Renal failure
Primary polydipsia
Diabetes insipidus
Diagnosis of ADH deficiency
Measure Urine output
Osmolalities (plasma, urine)
Blood electrolytes
Glucose
Urea
Creatinine
Kidney function
Water deprivation test - derive patient of fluid
In normal patient urine would be low
Treatment of ADH deficiency
ADH analogues
Two types of pituitary adenomas
- Pressurises optic pathway
- Benign that hypersecretes hormones
What does hypersecretion of GH cause
Acromegaly
How to diagnose acromegaly
Oral glucose test- hyperglycaemia suppresses GH
IGF-1 - marker of GH secretion
Pituitary imaging - identify where GH secreting tumour is
Treatment of acromegaly
Pituitary surgery
Medical treatment
- dopamine agonists
- somatostatin analogues
- GH receptor antagonists
Radiotherapy - radiate tumour
What is a prolactinoma
Benign tumour secreted excess prolactin
Manifestations of prolactinoma
Hypogonadism - prolactin inhibits GnRH
Galactorrhoea - breast discharge
Mass effects
Diagnosis of prolactinoma
Exclude other causes of prolactin
Pituitary imagining
Treatment of prolactinoma
- Medical treatment
Dopamine agonists - Surgery
- Radiotherapy
Diagnosis of Cushing’s syndrome
ACTH dependant
- cushings disease: pituitary adenomas
- ectopic tumours
ACTH Independent
- adrenal disease
Latrogenic: Exogenous steroids
Diagnosis of Cushing’s syndrome
24hr Urinary free cortisol
Midnight serum/ salivary cortisol - levels should be undetectable
Low dose dexamethasone suppression test
Diagnosis of cushings disease
9.00am ACTH - if ACTH dependant then ACTH will be elevated
High dose dexamethasone suppression test
CRH test
Imaging (pituitary, ectopic so may be lungs)
Management of cushings
Pituitary surgery
Radiotherapy
Drugs
Bilateral adrenalectomy
What hormones does the placenta produce
Oestrogen
Progesterone
