Pituitary Gland and It's Disorders Flashcards
Two lobes of pituitary
anterior and posterior
what do magnocellular neurones do?
project down from hypothalamus and release hormones directly in the blood: oxytocin and vasopressin
what do parvicellular neurones project into?
they release hormones into median eminence which flows into portal vessels and then into anterioir pituitary to stimulate endocrine tissues to produce hormones
what is a portal vessel?
vessel that goes from a capillary bed to a capillary bed
is there a direct connection between hypothalamus and anterior pituitary?
no
where is the pituitary gland?
below brain in the sella turcica
what forms the pituitary stalk?
notochordal projection connecting the gland to the brain
what is underneath the sella turcica?
sphenoid sinus
what is above the pituitary?
optic chiasm, internal carotid arterides
what are two pituitary cell types?
- acidic (orange G)
- basic (aldehyde fuscin)
Hormones released by anterior pituitary?
- ACTH
- TSH
- GH
- LH/FSH
- Prolactin
hormones released by posterior pituitary?
- ADH
- Oxytocin
what is the endocrine system organised into?
layers
what are the layers of the endocrine system?
- Primary: end organ
- Secondary: pituitary
- Tertiary: hypothalamus
describe the endocrine system
slow and long
what does the hypothalamus do?
takes input of our senses and higher centres and integrates them. releases hormones in response
what is function of pituitary?
amplify signals of the hypothalamus
three considerations when dealing with pituitary lesions?
1) Hormone hypersecretion
2) hormone deficiency status,
3) Space occupying lesion
what is hormone deficiency status?
tumour can squish normal pituitary surrounding it leading to decreased hormone release from those parts
what is space occupying lesion?
as tumour grows more can effect nearby structures = headaches, visual loss
what can tumours of the anterior pituitary cause?
syndromes of hormone excess
what is Acromegaly?
excess GH (gigantism)
what is Cushings disease?
excess ACTH
what is secondary thryotoxicosis?
excess TSH
what is non-functioning pituitary tumour?
excess LH/FSH
what is prolactinoma?
excess PRL
what does GH do?
causes release of IGF-1 from liver which causes linear growth on the bones.
how do we grow?
lipids metabolised and protein synthesised for energy
systemic effects of excess GH?
- acral enlargement
- increased skin thickness
- increased sweating
- skin tags
- changed appearance
- visceral enlargement
metabolic changes of excess GH?
- impaired fasting glucose
- impaired glucose tolerance
- diabetes mellitus
- insulin resistance
- increased TAG
other consequences of excess GH?
- cardiomyopathy
- hypertension
- bowel polyps
- colon cancer
- female looks masculine
what are the actions of cortisol?
- increased plasma glucose levels
- increased lipolysis
- proteins catabolised
how do plasma glucose levels increase?
- increased gluconeogenesis
- decreased glucose utilisation
- increased glycogenesis
- increased glycogen storage
- Na+/H20 rentention
- anti-inflammatory
- increased gastric acid production
why does lipolysis increase?
to give more energy
what does protein catabolises do?
release AA
what does Na+/H20 retention do?
maintains BP
what are the effects of cushings syndrome?
- changes in protein and fat metabolism
- change in sex hormones
- salt and water retention
what is the effect of change in protein and fat metabolism?
- change in body shape
- central obesity
- moon face
- buffalo hump
- diabetes
what is the effect of change in sex hormones?
- excess hair growth
- irregular periods
- problems conceiving
- impotence
what is the effect of salt and water retention?
high BP and fluid retention
how is release of prolactin different to other pituitary hormones?
stimulus for the production is external to the body, relies on mechanical stimulation of the breast
what happens with nipple is mechanical stimulated?
neural signal sent to the brain inhibiting dopamine
what happens when dopamine production is switched off?
instant surge in prolactin production allowing milk to enter breast for baby
how is the milk production terminated?
remove baby from nipple = positive feedback
what drugs interfere with dopamine and PRL secretion?
OCP (oral contraceptive pill), HRT, antemetics, antipsychotics
features of PRL excess?
- infertility
- oligoamenorrhoea
- amenorrhoea
- reduced libido
- impotence
what is oligoamenorrhoea?
reduced periods
what is amenorrhoea?
no periods
treatment of PRL excess?
dopamine agonists (e.g. bromocriptine and cabergoline)
what do non functioning pituitary tumours cause?
headaches and visual defects due to space occupation
treatment for non-functioning pituitary tumours?
surgery or radiotherapy
how does the visual field defect occur?
first visual loss on the sides, due to compression where the fibres cross
how does loss of pituitary function occur with an expanding tumour?
there is a set order in which you lose the pituitary hormones and it is based on their biological importance
what is the order in which the hormones go?
1) FSH/LH as sex/repro is least priority
2) GH as growth unimportant
3) TSH as metabolic rate is important
4) ACTH as stress response needed for survival
what happens to prolactin when hormones are all going?
prolactin levels rise due to compression of pituitary stalk so dopamine cant reach lactotrophs so wont be inhibited
how are pituitary adenomas treated?
- surgery to remove the tumour (unless prolactinoma as this responds to drug therapy)
- if tumour too big = radiotherapy but its slow
- drugs to block hormone production/release
causes of pituitary failure?
- tumour
- trauma
- infection
- inflammation
- latrogenic
what is hypopituitarism?
deficiency of hormones due to hypopituitarism
reduced thyroid?
- bradycardia
- weight gain
- cold intolerance
- hypothermia
- constipation
reduced sex steroids?
- oligomenorrhoea
- reduced libido
- hot flushes
- reduced body hair
reduced cortisol?
- tiredness
- weakness
- anorexia
- postural hypotension
- myalgia
reduced GH?
- tired
- central weight gain
treatment for hypopituitarism
- thyroid = thyroxine
- sex steroids = testosterone and oestrogen
- reduced cortisol = hydrocortisone
- reduced GH = GH
what does ADH do?
stops you peeing and vasoconstricts blood vessels
what stimulates ADH release?
- lack of water in blood causing increase in plasma osmolality
- decreased BP
- reduced PaO2 and increased PaCO2
what senses change in osmolality?
osmoreceptors in hypothalamus
what senses decreased BP?
baroreceptors
what will ADH do?
open aquaporins in the collecting ducts increasing permeability for water. there is increased reabsorption of water into blood and vasoconstriction
syndrome of inappropriate ADH
SIAH
what is SIAH caused by?
injury or infection, or lung cancer and other metabolic causes
Diagnosis of SIAH
- decreased plasma Na+
- decreased plasma osmolality
- increased urine osmolality
- increased urine Na+
what is underproduction of ADH?
diabetes insipidus
what does diabetes mean?
peeing a lot.
sweet = mellitus
watery = insipidus
what could cause underproduction of ADH?
- cranial cause in lack of production
- brain can make it but the kidney is damaged so receptor isnt working
what is polyruia?
peeing a lot
what is polydipsia?
drinking a lot of water
difference between someone dehydrated and someone with diabetes insipidus?
DI cannot reabsorb water and produce conc urine as urine osmolality is similar to plasma
what is the water deprivation test?
testing if someone has diabetes inspidus. keep someone dehydrated, change in weight = water loss
how does water deprivation test happen?
weight patient, work out 3% of body weight and wait until they lose that or wait 8 hours. Check volume and conc of urine and plasma
what is a normal result for water deprivation test?
plasma conc should be normal and urine concentrated
what result suggests DI in water deprivation test?
plasma osmolality increases and urine remains dilute
if it goes away with DDAVP (desmopressin) what does this mean?
cranial cause. If no response = kidney problem
what considerations are made of pituitary tumours?
- tumour hormone production
- effects on normal pituitary function
- effects on surrounding structures
treatment of pituitary tumours
- surgery
- radiotherapy
- medical therapy
how is pituitary failure treated?
hormone replacement
