Endocrine I

Question 1

What is ‘basal’ hormone testing?

Answer 1

Generally used for screening, rarely diagnostic
can be more appropriate for disorders where the enzyme is lacking rather than disorders where there is too much

Question 2

What is ‘Dynamic’ Testing?

Answer 2

Testing the hormone at different levels
You measure the basal level
Then adminsiter a substance that will go on to influence the hormone
then measure the hormone at one or more specified time points to evaluate the change in levels

Question 3

What is a stimulation dynamic test

Answer 3

The administration of a synthetic hormone or substance in a known quantity that will maximally stimulate the pathway required for production of the hormone of interest

• Healthy/ unaffected individuals will only respond to a limited level
• Affected individuals will produce increased hormone levels in response, above a cut off value

Question 4

What is a supression stimulation test?

Answer 4

administration of a substance that is known to have negative feedback on a pathway
* Healthy individuals will supress
* Affected will not supress at all

Question 5

Explain how the thyroid releases T3 and T4

Answer 5

1. TRH is released via the hypothalamus
2. TRH stimulates the production and release of TSH
3. TSH binds to TSH receptors in the thyroid causing release of T3 and T4
4. T4 is produced by the thyroid
5. T3 is produced partly by the thyroid and predominantly via the conversion of T4 and T3

Question 6

What is the majority of T4 bound to in circulation?

Answer 6

Proteins

Question 7

How would you go about measuring the thyroid?

Answer 7

Serum is the preffered sample, without gel (as hormones absorb onto the gel)
Measure T4 and free TSH

Question 8

When will measured T4 levels be low?

Answer 8

Hypothyroidism but also whenever the patient is unwell

T4 levels will remain low unless the underlying disease is solved
TSH levels will remain within normal limits

Question 9

What may cause a decreased production in T4?

Answer 9

• Primary hypothyroidism
• Secondary hypothyroidism
• Defective thyroxine production

Question 10

What are some unknown mechanisms that can cause a decrease in T4?

Answer 10

• Hyperadrenocortcism, inflammatory diseases
• glucocorticoids
• any diet high in energy, protein, copper, zinc…

Question 11

How may primary hypothyroidism present in dogs?

Answer 11

• Alopecia (non-pruritic)
• Heat-seeking
• Lethargy and Weight gain
• Tragic face due to muscle atrophy
• Mild increase in liver enzymes

Question 12

How may you assess primary hypothyroidism?

Answer 12

Increased auto-antibodies towards thyroglobulin

Question 13

What does hyperthyroidism look like?

Answer 13

Increased production via thyroid neoplasia
Can be caused by a functional thyroid adenoma
Thyroid adenocarcinoma

Question 14

What can cause hyperthyroidism?

Answer 14

Administration of T4
Administration of compounds containing iodine
Ingestion of food stuffs containing T4

Question 15

How may you assess feline hyperthyroidism?

Answer 15

tT4 levels are usually increased
and within the upper half of the reference interval

Question 16

How does t4AA effect tT4 measurements?

Answer 16

binds to the receptors in the tube
prevents tt4 from binding
therefore the resilt may be lower than expected

Question 17

What is Euthyroid Sick syndrome?

Answer 17

Patient is unwell and the T4 level is depressed
T4 level remains low until the underlying disease is resolved and then it acn return to normal limits