Principles of Endocrine Disease and Its Assessment Flashcards
what are the three level the endocrine system split into?
primary - end organ
secondary - pituitary
tertiary - hypothalamus
what are the types of endocrine disease?
hyper-functioning
hypo-functioning
eu-functioning
what is the role of the hypothalamus?
integration of signals and conversion of them to a chemical messenger
what amplifies signals from the hypothalamus?
pituitary gland containing hormones that get diluted and travel around the body
where do the hormones act?
end organs
what do end organs do?
switch off production of the central hormones = negative feedback
why is the area around the pituitary important?
the hypothalamus is above then there is the optic chiasm and pituitary stalk. These structures get compressed if there is a tumour
what is the cavernous sinus?
its just below hypothalamus containing cranial nerves supplying extra-ocular muslces.
what happens if the extra-ocular muscles are squished?
double vision and loss of sight from compression of optic chiasm
how can you see the hypothalamus?
from a saggital section with the pituitary fossa sitting on top of the sphenoid sinus
what do hormones act as?
receptors: surface or nuclear
what is different about peptide hormones?
they are charged and act as surface receptors
what are steroid hormones like?
they are aliphatic (fat soluble) so act on nuclear receptors
what is most hormone release like?
pulsatile and varies during the day
what is a dynamic test?
shows meaning of the two extremes shown in a one off blood test
apart from causing secretion from target hormone what else do hormones do?
cause growth of the target organs. therefore the target organ shrinks if hormone taken away
what is principle of endocrine testing based on?
law of mass action
how is endocrine testing carried out?
coloured dyes. Radioactive Immunoassay (RIA)
how is RIA carried out?
we have a binding site, usually an antibody and then the hormone. Forms an equilibirum in a test tube, so there will be some bound horomone-antibody and some free.
there is a radioactive tracer bound to the hormone
how do you measure the RIA results?
- make sure every binding site is full of the marker
what is the first stage of measurment?
- construct a curve of known amounts of un-labelled hormone which will displace labeled hormone and drop the radioactivity
how do we assess the radioactivity?
via centrifuge. the bound stuff falls to the bottom and you measure the radioactivity in there. unknown samples are then compared
what are the two types of assays used?
- total hormone assay
- free hormone assay
total hormone assay
cheap, easy but have physiological problems as in plasma most hormone is bound to a binding protein (designed to protect hormone from enzymatic breakdown until reaches target site)
which hormones are biologically active?
the free ones, they can activate receptors on cells
what is a free hormone assay
representative of the active hormone fraction, not binding protein dependent
what is the drawback of free hormone assays?
complex and expensive, have to get rid of all the binding protein and the hormone bound to it (could lose some hormone via this)
when are free hormone assays used?
thyroid hormone testing
what causes TSH release?
TRH
what does TSH cause?
release of T3 and T4
which is more active, T3 or T4?
T3
why does T4 provide negative feedback?
T4 is an intravascular store of thyroid hormone, so when cell wants it, it expresses deiodinase which converts it to T3
how do we investigate thyroid over production?
- thyroid function test
- autoantibodies
- technesium scanning (tells type)
how do we investigate thyroid under production?
- thyroid function
- autoantibodies
how do we investigate thyroiditis (irritation of thyroid gland)?
- thyroid function
- ESR (erythroyte sedimentation rate)
- technesium scanning
why is a technesium scan used?
technesium is taken up into the thyroid gland like iodine is, so by doing it you can see if thyroid gland is taking up iodine to show over activity
how is the thyroid gland in proper thyrotoxicosis?
biologically overactive
how is the thyroid gland in thyroiditis?
destructive, something makes the gland leaky so it leaks stores into the circulation but biological function is fine.
how would technesium scan be in thyroiditis?
negative as it will not take up technesium as its being destroyed.
Thyroid nodule
ultrasound scan and FNA
what is the cortisol rhythm?
diurnal
investigation of cushings: screening
test urinary free cortisol and diurnal rhythm
confirmation of cushings diagnosis
low dose dexamethasone suppression testing
differentiation of cause of cushings
- high dose dexamethasone suppression test
- plasma ACTH
- localisation via radiology
when is cortisol highest?
morning
why is dexamethasone testing used?
to see the effect on ACTH and what source of ACTH might be if body is producing too much cortisol
what should dexamethasone do in a normal person?
inhibit ACTH production via negative feedback
what is psuedocushings syndrome?
display signs of cushings
- depression
- alcholism
- anorexia nervosa
- obesity
