CSGD Quiz 4 2006

1

Which ONE of the following statements about growth hormone is NOT CORRECT?


  Its release is pulsatile.

  Its release is stimulated by hypothalamic GHRH secretion.

  Its release is inhibited by hypothalamic somatostatin secretion.

  Insulin induced hypoglycaemia suppresses its release.

  It acts via insulin-like growth factor-1 (IGF-1) produced in the liver.


GH usually rises with insulin levels.

2

The MOST COMMON type of functioning pituitary adenoma is:


  An ACTH secreting tumour.

  A GH secreting tumour.

  A prolactin secreting tumour.

  An ADH secreting tumour.

  An FSH secreting tumour.

3

Which ONE of the following facts about hypothalamic control of pituitary function is NOT CORRECT?


  GnRH results in the release of FSH and LH from the pituitary.

  GHRH results in the release of growth hormone from the pituitary.

  CRH results in the release of ACTH from the pituitary.

  TRH results in the release of TSH from the pituitary.

  Dopamine results in the release of prolactin from the pituitary.


Dopamine suppresses prolactin release.

4

Which ONE of the following statements about lactation is NOT CORRECT?


  During pregnancy, progesterone and oestrogen block the action of prolactin on the breast.

  Lactation is stimulated by a neuro-endocrine reflex.

  Milk ejection is largely stimulated by prolactin.

  Oxytocin induces contraction of the myo-epithelial cells during lactation.

  Initiation of lactation requires a decrease in oestrogen and progesterone levels in the woman concerned.


Milk ejection is stimulated by oxytocin (via the mechanism in D).

5

Which ONE of the following statements regarding thyroglobulin is CORRECT?


  It oxidizes iodide in the presence of H202.

  It is responsible for transport of iodide from the circulation into the thyroid cell.

  It is of particular relevance in the follow-up of patients with thyroid cancer.

  It is routinely measured as a clinical index of thyroid function.

  It has 13 membrane spanning domains with carboxy terminus in the cytoplasm and amino terminus located outside the cell.


A is incorrect: This is the function of TPO (Thyroid Peroxidase). B is incorrect: This is performed by the NIS (Sodium Iodide Symporter). C is correct: The complete removal of the thyroid following a thyroid cancer should result in zero TG. It is therefore used as a tumour marker, because its presence indicates cancer recurrence. D is incorrect: It is a sensitive but non-specific marker of thyroid activity. E is incorrect: This describes the NIS.

6

Thyroid hormones are critical determinants of brain and somatic development and affect many pathways and different organs. Which ONE of the following statements concerning such hormones is CORRECT?


  The active thyroid hormone is reverse T3.

  The major hormone produced by the thyroid is T4.

  50% of circulating thyroid hormone is free; the remainder is bound reversibly to thyroid binding globulin.

  Thyroid hormone is activated by glucuronidation.

  The majority of T4 is bound to prealbumin.


A is incorrect: The active thyroid hormone is T3. B is correct. C is incorrect: The vast majority of thyroid hormone is bound to circulating proteins. D is incorrect: Thyroid hormone is activated (conversion of T4 to T3) by deiodination. E is incorrect: The majority of T4 is bound to thyroid binding globulin (TBG).

7

The MOST COMMON cause of hypothyroidism in Australia is:


  Iodine deficiency related to recent decreases in use of iodine in baking and milk processing.

  Hashimoto’s thyroiditis.

  Reduced secretion of TSH from the pituitary gland.

  Tissue resistance to thyroid hormone.

  Inherited deficiency of thyroid binding globulin.

8

All of the following are common features of Cushing’s disease (pituitary dependent hypercortisolaemia) EXCEPT:


  Diabetes mellitus.

  Failure of low dose dexamethasone to suppress the plasma cortisol levels.

  Proximal myopathy.

  A bitemporal visual field defect.

  Hypertension.


Low dose dexamethasone tends not to suppress cortisol levels in Cushing's disease while high dose dexamethasone does (neither will suppress serum cortisol in primary adrenal hypercortisolism). Bitemporal visual field defects may occur with pituitary adenomas. The other options are all features of Cushing's syndrome in general.

9

A 32 year-old woman, who is complaining of excessive facial and body hair, has the following endocrine profile:

17-hydroxy progesterone - Normal
Testosterone - Upper limit of normal
DHEAS - Slightly elevated
LH/FSH ratio - Slightly elevated

The MOST LIKELY diagnosis is:


  Congenital adrenal hyperplasia.

  5-alpha reductase deficiency.

  A masculinizing ovarian tumour.

  Polycystic ovarian syndrome.

  The “empty sella” syndrome.


A is incorrect: CAH usually presents at a much younger age. B is incorrect: This enzyme catalyses the conversion of testosterone to DHT. C is incorrect: Possible(?), but less likely than D. D is correct: PCOS often presents with mild masculinisation and is a relatively common syndrome. E is incorrect: Empty sella syndrome is rare, and usually presents with obesity and hypertension.

10

Sestamibi is used to help in the diagnosis of:


  A pituitary tumour.

  An adrenal tumour.

  An ovarian tumour.

  A thyroid tumour.

  A parathyroid tumour.


Sestamibi (a protein labelled with 99m Technetium) is used in nuclear medicine for parathyroid imaging. Mitochondria in the abnormal parathyroid gland will retain more sestamibi than normal glands.