Pituitary Disorders Flashcards
Hypothalamo-pituitary (HP) axis
- communication between the hypothalamus and the pituitary
- the link between the endocrine and the nervous system
- is the endocrinal response to the external environment
Pituitary tumours
Upwards growth causes tunnel vision Sideways growth (cranial nerve palsy) causes double vision
Posterior pituitary
primitive brain tissue
Neurological stimuli
Hypothalamic nuclei
- secretes ADH and oxytocin
ADH deficiency or resistance = diabetes insipidus (water not reabsorbed by the kidney, polyuria and polydipsia, high serum osmolality - concentrated blood, low urine osmolality - disease of the hypothalamus or pituitary stalk
Anterior pituitary
primitive gut tissue
Exocrine stimuli
- secretes GH, ACTH, LH/FSH, TSH and prolactin
Growth Hormone
GH
GH (growth hormone) - increases blood sugar by mobilising glycogen reserves (high IGF-1 = too much GH) mostly secreted during sleep
GHRH stimulates GH, somatostatin inhibits GH
GH acts on all tissues
GH is needed for skeletal growth, metabolism, muscle strength, bone density, cardiac function and quality of life
Deficiency can be mistaken for depression and leads to short stature in children - not so noticeable in adults (causes acromegaly)
Sometimes GH is abused by athletes
ACTH
Lack of ACTH is potentially fatal - most important axis to preserve life
- stress causes ACTH release (increased in the morning, reduced in the evening)
Development of pituitary
Anterior is primitive gut tissue
Posterior is primitive brain tissue
LH/FSH
Luteinising hormone - LH
Follicle stimulating hormone - FSH
- differential functions in men and women
IN MEN
LH drives testosterone secretion (highest in the morning)
FSH drives sperm production
IN WOMEN
- in follicular phase of cycle LH pulses cause oestrogen release
- in mid-late phase of cycle LH causes progesterone release
- there is positive feedback during mid-cycle LH/FSH surge
Pituitary-thyroid axis
TRH stimulates secretion of TSH from thyroid into the circulation
- TSH activates follicular cells in the thyroid to produce T3 and T4
- negative feedback
Primary gland failure
- end organ hormone low
- pituitary hormone high
Secondary gland failure
- pituitary and end organ hormone low
Excess hormone production by primary gland
- end organ hormone high
- pituitary hormone low
Excess hormone production by pituitary gland
- end organ hormone and pituitary hormone high
Prolactin
- initiates and maintains lactation
- acts on peripheral tissues with no target gland
- high levels can cause lactation and menstrual disturbances in women
- under negative control (inhibitory control by dopamine, minor positive control by TRH, oestrogen increases prolactin) - slightly higher at night
- high levels caused by pregnancy, stress, dugs (dopamine antagonists), tumours - stalk effect, polycystic ovaries
Presentation of pituitary disease
Abnormal pituitary function - hypopituitarism (low GH p, LH/FSH, TSH, ACTH and high prolactin levels) - poor growth in children, loss of body hair, lethargic, pallor Compression of local structures (optic chiasmata compression - upwards growth of tumour - tunnel vision - cavernous sinus invasion - sideways growth - double vision Cranial nerve (3rd nerve) palsy - dilated pupil and one drooped eyelid
Prolactinoma
(non cancerous tumour, adenoma, of the pituitary gland causing an overproduction of prolactin
- prolactin-secreting tumours
- menstrual disturbances
- galactorrhoea
- infertility
- microprolactinoma (small tumour)
- macroprolactinoma - can shrink with dopamine agonists without surgery
Non functioning adenoma
- high prolactin due to loss of inhibition not because of active secretion
- will need surgery if symptoms are compressive
Acromegaly
GH secreting pituitary tumour
- growth of hands and feet
- coarse features
- sweating
- headaches
- hypertension
- diabetes
- tissue swelling can cause carpel tunnel and sleep apnea
Untreated acromegaly can cause premature cardiac death
Medical treatment involves monthly injections of octreotide and lanreoride or GH receptor blocker - expensive
Gigantism
Prepubescent pituitary tumour
Cushing’s
Cushing’s disease - ACTH secreting PITUITARY tumour
- 50% mortality within 5 years if untreated
- rounded face, central obesity with striae, easy bruising, thin arms, hypertension, diabetes
- increases ACTH secretion can lead to increased cortisol secretion (ACTH dependent Cushing’s) - could be due to pituitary or ectopic (tumour) ACTH secretion
(ACTH independent Cushing’s) - cortisol secreting adrenal tumour
Cushing’s syndrome
- ACTH suppression test
- dexamethasone suppression test - failure to suppress cortisol
Alcohol can give psuedo-Cushing’s
Dynamic tests
- hormone deficiency - try and stimulate gland into action
- hormone excess - try to suppress the gland
Insulin tolerance test
Best test of GH reserve
- patient gets iv insulin injection
- hypoglycaemia can be prolonged (need medical supervision)
Can’t do with epileptic patients or those with cardiac disease
Glucose tolerance test
- GH suppression test
- give 75g of glucose orally
- glucose and GH measured
Failure to suppress GH suggests acromegaly
Treatments for pituitary disease
control or removal of tumour (surgery, radiotherapy or medical therapy)
- transsphenoidal surgery - through nose and sinuses
- radiotherapy - external beam or gamma knife - prevention of tumour growth and protection of vision, but possible damage to normal pituitary gland and an increased risk of stroke
- medical treatments - dopamine agonists(reduce prolactin), GH receptor antagonists
reduction of excess hormone secretion
replacement of hormone deficiencies
