Principles of Endocrine Disease and Its Assessment Flashcards
What law are bound and free hormones levels in the blood governed by?
- Bound and free hormones are in equilibrium.
- Governed by the Law of Mass Action
- Rate of a chemical reaction is directly proportional to concentration of the reactants.
Describe total hormone assays.
- Measure all the hormones in the bloodstream.
- Dependant on binding protein levels.
- Not always reflective of the free hormones levels, as it measures everything.
- Cheap.
To overcome problems faced by total hormone assays, we use free hormone assays.
Describe free hormone assays. PART 1
- Measure the amount of free hormone in the bloodstream.
- Representative of the active hormone fraction.
- Not binding protein-dependent.
To overcome problems faced by total hormone assays, we use free hormone assays.
Describe free hormone assays. PART 2
- Complex and expensive, and involves a separation step.
- Unreliable, and it can have poor reproducibility.
Describe the separation step involved in free hormone assays. PART 1
- Use a dialysis membrane to ‘sieve’ out the free hormones.
- Membrane only allows free hormones to cross - can measure active hormone fraction.
- As free hormones move, equilibrium altered.
- More free hormone may pop up to balance out the change - can be unreliable.
Describe the separation step involved in free hormone assays. PART 2
- To overcome this, use an ultracentrifuge, where you allow it to centrifuge
- Also add various precipitating agents to bind the proteins, which are precipitated out
- Can measure the amount of free hormones.
What problems can arise with assays due to DPP4, and how do we overcome this problem? PART 1
- When the enzymes are done working, DPP4 will cut them at specific motifs, switching them off.
- Protein fragments stay in the circulation until they are filtered out by the kidney.
- Measured as units of biological activity in assays when they are not.
What problems can arise with assays due to DPP4, and how do we overcome this problem? PART 2
- To overcome this, raise antibodies for ends of full biologically active protein.
- Put that on the side of the test tube, let it sit to bind, then wash out all the unbound protein fragments.
Describe how you would investigate different conditions of the thyroid gland. PART 1
OVERPRODUCTION:
- thyroid function test
- autoantibodies
- technetium scanning (functional assessment)
UNDERPRODUCTION:
- thyroid function test
- autoantibodies (mainly TPO)
Describe how you would investigate different conditions of the thyroid gland. PART 2
THYROIDITIS (inflammation of the gland):
- thyroid function test
- ESR (erythrocyte sedimentation rate)
- technetium scanning
THYROID NODULE (small swelling):
- ultrasound scan
- FNA (fine needle aspiration) biopsy
Describe the synacthen test. PART 1
Synacthen is synthetic ACTH. Used to test adrenal function.
SHORT SYNACTHEN TEST (250 mcg):
- used to diagnose primary adrenal failure
- blood taken over an hour
Describe the synacthen test. PART 2
LONG SYNACTHEN TEST (1 mg):
- used to diagnose secondary adrenal failure (suspected pituitary problem, while adrenal is normal)
- blood taken over 24 hours
If a specific hormone is too high/too low, how would testing be completed for it?
TOO HIGH: Suppress it
TOO LOW: Stimulate it
What is the oral glucose tolerance test?
→ test for GH excess
→ 75g oral glucose
→ samples for GH taken
→ normal individuals GH fall
→ Acromegaly = rise
What is done to test for growth hormone deficiency?
→ Large insulin dose
→ hypoglycaemia
→ cortisol should increase
What happens in the long synacthen test if it is pituitary vs Addisons?
→ Cortisol levels rise
→ can cause growth of adrenal gland
→ if addisons the cortisol wouldn’t be raised
How do you test for Addisons?
→give synthetic ACTH
→ Cortisol level rises
Dexamethasone test in people with ectopic ACTH?
→ low dose = more than 50
→ high dose = less than 50 decrease
→ ACTH very high
Dexamethasone test in people with adrenal tumor?
→ low dose = not below 50
→ high dose = less than 50% decrease
→ ACTH is low
Dexamethasone test in people with cushings disease?
→ low dose = not below 50
→high dose = more than 50% decrease
→ ACTH are high
How should the dexamethasone suppression test be in normal people?
→ Cortisol level should decrease below 50
→ high dose should be 50% of baseline
If T4 is low, TSH is low and T3 is normal what is the diagnosis?
→ Sick Euthyroid
If TSH is low and T3 and T4 are low what is the diagnosis?
→ Hypothyroidism
→ TSH should increase
→ brain function impaired
→ Secondary
If TSH is high and T3 and T4 are low what is the diagnosis?
→ Hypothyroidism
→Less negative feedback
→ TSH should increase
→ Primary because TSH is high - correct brain function
If T4 and T3 is high and TSH is low what is the diagnosis?
→Hyperthyroidism because peripheral hormones are high
→ primary because the TSH is low - correct functioning of the brain
What is the negative feedback mechanism of thyroxine?
→ TSH sent to thyroid
→ Thyroid produces T3 and T4
→ T4 is end hormone so it inhibits TSH
What is the diagnosis if T4 is high and TSH is high?
→ Check peripheral hormone
→ high - hyperthyroidism
→ decide whether primary or secondary
→ if T4 is high then TSH should be low (inhibits)
→ Has not happened so the problem is secondary
Why is thyroiditis sometimes mistaken for overproduction of thyroid hormone?
→ thyroid has a large volume of thyroid hormone stored
→ If it gets infected/inflamed it releases the hormone
How does tri iodothyronine get produced?
→ TRH is released from the hypothalamus
→ goes to the pituitary and causes the release of TSH
→ TSH acts on the thyroid
→ tri-iodothyronine is the biologically active hormone
How does a radiometric assay work?
→ antibody binds to amide end
→ sticks to test tube
→ wash test tube
Why is measuring a peptide hormone difficult?
→ Peptide hormones have a very short half life
→ Enzymes cleave them
→ you have fragments of them in the circulation
What does the radiometric assay work on?
→ on peptide hormones
Generally, what is the accuracy like in assays with multiple steps?
→ decreases the accuracy
→ transfer errors
How do you do a radioimmunoassay in the lab?
→ a labelled hormone that is a marker (radioactive)
→ antibody
→ Limited number of binding sites
→ centrifuge and measure how much radioactivity is in the bound fraction
→ do a standard curve
What type of testing do you have to use for hormones and why?
→ dynamic
→ Hormones are pulsatile and vary during the day
What type of hormone is thyroid hormones?
Steroid
Where do steroid hormones act and why?
→ nuclear receptors because they are aliphatic
Where do peptide hormones act and why?
→ surface receptors because they are charged
