Summary principals of endocrine disease and its assessment

Principals of Endocrine Disease and its Assessment

Topics include:

 Hormone Assays
 Thyroid function
 Testing for Cushing's syndrome
 Acromegaly testing
 SYNACTHEN tests

Physiology

The endocrine system is split into three levels;
Primary – End organ
Secondary – Pituitary
Tertiary – Hypothalamus

In endocrine diseases, a person is either hyper-functioning, hypo-functioning or
eu-functioning.

The role of the hypothalamus is integration of signals and conversion of them to a
chemical messenger. This is so that the chemical messenger can go through our body.
To amplify the signal we have our pituitary gland, which contain a large amount of
hormone, enough to be diluted and travel around the body.
These hormones then act on the end organs.

The end organs switch off the production of the central hormones, which is the
principle of negative feedback.

, The area around the pituitary gland is important, there is the hypothalamus above,
optic chiasm and pituitary stalk. These structures may get compressed if there is a
tumour.
There is also the cavernous sinus just below, which contains various cranial nerves
supplying the extra-ocular muscles. Therefore any squashing of these could lead to
double vision, as well as loss of actual sight from compressing the optic chiasm.

You can only see the hypothalamus in a saggital section. The pituitary fossa sits on
top of the sphenoid sinus.

Remember to learn the names of hormones, as its function is usually in the name, e.g.
progesterone = pro-gestational hormone, getting someone ready for pregnancy.

Hormones act at receptors, these receptors can be surface or nuclear.
Peptide hormones are charged, (on average negatively due to their side chains)
will act at surface receptors.
Steroid hormones are aliphatic (fat soluble) and so will act on nuclear receptors.
-> Anything that comes from the brain, pituitary or gut is a peptide that will act on
surface receptors
-> Anything that comes from the gonads or adrenals are steroids and will be fat
soluble so will act at the nuclear receptor [TH also has a nuclear receptor)

Most hormone release is pulsatile and vary during the day. This is because, apart
from the thyroid (which has a long half life), doing a one-off blood test doesn’t tell us
very much. We need to do a dynamic test.
- The principle of a dynamic test is that although we can’t tell what the one-off
blood test means, we can tell what the extremes of physiology are. E.g. if looking
for deficiency, can see when it should be highest. Or if looking for excess can see
when it should be lowest. So defining normality by looking at the extremes.

Nomenclature of Pituitary Hormones

trophe’ means food

LH and FSH = Gonadotrophin -- Hypothalamic hormone = Gonadotrophin Releasing
Hormone
Growth and Hormone = Somatotrophin – Growth Hormone Releasing Hormone
TSH = Thyrotrophin – Thyrotrophin Releasing hormone
ACTH = Corticotrophin – Corticotrophin Releasing Hormone

Remember that these hormones as well as causing secreting from the target organ
they also cause growth of the target organs.
So if you take away these hormones, the target organ will shrink.

Tests

The principle of endocrine testing is based on the law of mass action. In old days
they used radioactive tracers, but nowadays using coloured dyes. This is radioactive
immunoassay (RIA).