Principles of Endocrine Disease and Its Assessment

Question 1

What law are bound and free hormones levels in the blood governed by?

Answer 1

• 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.

Question 2

Describe total hormone assays.

Answer 2

• 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.

Question 3

To overcome problems faced by total hormone assays, we use free hormone assays.
Describe free hormone assays. PART 1

Answer 3

• Measure the amount of free hormone in the bloodstream.
• Representative of the active hormone fraction.
• Not binding protein-dependent.

Question 4

To overcome problems faced by total hormone assays, we use free hormone assays.
Describe free hormone assays. PART 2

Answer 4

• Complex and expensive, and involves a separation step.
• Unreliable, and it can have poor reproducibility.

Question 5

Describe the separation step involved in free hormone assays. PART 1

Answer 5

• 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.

Question 6

Describe the separation step involved in free hormone assays. PART 2

Answer 6

• 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.

Question 7

What problems can arise with assays due to DPP4, and how do we overcome this problem? PART 1

Answer 7

• 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.

Question 8

What problems can arise with assays due to DPP4, and how do we overcome this problem? PART 2

Answer 8

• 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.

Question 9

Describe how you would investigate different conditions of the thyroid gland. PART 1

Answer 9

OVERPRODUCTION:
- thyroid function test
- autoantibodies
- technetium scanning (functional assessment)

UNDERPRODUCTION:
- thyroid function test
- autoantibodies (mainly TPO)

Question 10

Describe how you would investigate different conditions of the thyroid gland. PART 2

Answer 10

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

Question 11

Describe the synacthen test. PART 1

Answer 11

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

Question 12

Describe the synacthen test. PART 2

Answer 12

LONG SYNACTHEN TEST (1 mg):
- used to diagnose secondary adrenal failure (suspected pituitary problem, while adrenal is normal)
- blood taken over 24 hours

Question 13

If a specific hormone is too high/too low, how would testing be completed for it?

Answer 13

TOO HIGH: Suppress it
TOO LOW: Stimulate it

Question 14

What is the oral glucose tolerance test?

Answer 14

→ test for GH excess
→ 75g oral glucose
→ samples for GH taken
→ normal individuals GH fall
→ Acromegaly = rise

Question 15

What is done to test for growth hormone deficiency?

Answer 15

→ Large insulin dose
→ hypoglycaemia
→ cortisol should increase

Question 16

What happens in the long synacthen test if it is pituitary vs Addisons?

Answer 16

→ Cortisol levels rise
→ can cause growth of adrenal gland
→ if addisons the cortisol wouldn’t be raised

Question 17

How do you test for Addisons?

Answer 17

→give synthetic ACTH
→ Cortisol level rises

Question 18

Dexamethasone test in people with ectopic ACTH?

Answer 18

→ low dose = more than 50
→ high dose = less than 50 decrease
→ ACTH very high

Question 19

Dexamethasone test in people with adrenal tumor?

Answer 19

→ low dose = not below 50
→ high dose = less than 50% decrease
→ ACTH is low

Question 20

Dexamethasone test in people with cushings disease?

Answer 20

→ low dose = not below 50
→high dose = more than 50% decrease
→ ACTH are high

Question 21

How should the dexamethasone suppression test be in normal people?

Answer 21

→ Cortisol level should decrease below 50
→ high dose should be 50% of baseline

Question 22

If T4 is low, TSH is low and T3 is normal what is the diagnosis?

Answer 22

→ Sick Euthyroid

Question 23

If TSH is low and T3 and T4 are low what is the diagnosis?

Answer 23

→ Hypothyroidism
→ TSH should increase
→ brain function impaired
→ Secondary

Question 24

If TSH is high and T3 and T4 are low what is the diagnosis?

Answer 24

→ Hypothyroidism
→Less negative feedback
→ TSH should increase
→ Primary because TSH is high - correct brain function

Question 25

If T4 and T3 is high and TSH is low what is the diagnosis?

Answer 25

→Hyperthyroidism because peripheral hormones are high
→ primary because the TSH is low - correct functioning of the brain

Question 26

What is the negative feedback mechanism of thyroxine?

Answer 26

→ TSH sent to thyroid
→ Thyroid produces T3 and T4
→ T4 is end hormone so it inhibits TSH

Question 27

What is the diagnosis if T4 is high and TSH is high?

Answer 27

→ 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

Question 28

Why is thyroiditis sometimes mistaken for overproduction of thyroid hormone?

Answer 28

→ thyroid has a large volume of thyroid hormone stored
→ If it gets infected/inflamed it releases the hormone

Question 29

How does tri iodothyronine get produced?

Answer 29

→ 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

Question 30

How does a radiometric assay work?

Answer 30

→ antibody binds to amide end
→ sticks to test tube
→ wash test tube

Question 31

Why is measuring a peptide hormone difficult?

Answer 31

→ Peptide hormones have a very short half life
→ Enzymes cleave them
→ you have fragments of them in the circulation

Question 32

What does the radiometric assay work on?

Answer 32

→ on peptide hormones

Question 33

Generally, what is the accuracy like in assays with multiple steps?

Answer 33

→ decreases the accuracy
→ transfer errors

Question 34

How do you do a radioimmunoassay in the lab?

Answer 34

→ 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

Question 35

What type of testing do you have to use for hormones and why?

Answer 35

→ dynamic
→ Hormones are pulsatile and vary during the day

Question 36

What type of hormone is thyroid hormones?

Answer 36

Steroid

Question 37

Where do steroid hormones act and why?

Answer 37

→ nuclear receptors because they are aliphatic

Question 38

Where do peptide hormones act and why?

Answer 38

→ surface receptors because they are charged