Endocrinology Flashcards
Where is thyrotropin-releasing hormone released from?
Hypothalamus
What releases thyroid-stimulating hormone?
Pituitary gland
What would TFTs show in primary hyperthyroidism?
High T4 and T3
Low TSH
What would TFTs show in secondary hyperthyroidism?
High T4 and T3
High TSH
What would TFTs show in primary hypothyroidism?
Low T4 and T3
High TSH
What would TFTs show in secondary hypothyroidism?
Low T4 and T3
Low TSH
What can be the cause of abnormal TFTs in a patient with an acute illness?
Sick euthyroid syndrome
What would TFTs show in sick euthyroid syndrome?
Low T4 and T3
Low/normal TSH
What releases corticotropin-releasing hormone and what does it stimulate release of?
Hypothalamus
Stimulates release of ACTH from pituitary
What does ACTH do?
Acts on adrenal cortex to release glucocorticoids
What causes Cushing syndrome?
Excess glucocorticoids
What are some endogenous causes of Cushing syndrome?
Primary adrenal disease - adrenal tumour
ACTH excess - Cushing disease, ACTH-producing tumour
What will the ACTH level be in Cushing syndrome caused by primary adrenal disease?
Low ACTH
What will the ACTH level be in secondary hyperadrenalism?
Normal/High ACTH
What are the four methods used to diagnose Cushing syndrome?
Measure free cortisol in 24-hour urine collection
Measure cortisol in late-night salivary sample
Perform 1mg overnight dexamethasone suppression test
Perform 2mg 48-hour dexamethasone suppression test
What will cortisol and ACTH levels show in primary hypoadrenalism (e.g. Addison’s disease)?
Low cortisol
High ACTH
What will cortisol and ACTH level show in secondary hypoadrenalism?
Low cortisol
Low ACTH
What test can used to assess hypoadrenalism?
Short Synacthen Test
What will the result of the Synacthen test be in primary hypoadrenalism?
Poor rise in cortisol levels (less than 600nmol/l 30 mins after Synacthen administered)
What will the result of the Synacthen test be in secondary hypoadrenalism?
Result will be normal
What are the two forms of diabetes insipidus?
Cranial
Nephrogenic
What would ADH levels be in cranial diabetes insipidus and why?
Low ADH - problem with release of ADH from hypothalamus
What would ADH levels be in nephrogenic diabetes insipidus and why?
Normal/High ADH - failure to exert effect on kidney
What are the common causes of SIADH?
Intrathoracic causes - infection, tumour
Intracranial causes - infection, tumour, head injury
Medications - carbamazepine, antipsychotics
