CSGD Quiz 4 2009

1

Which one of the following statements regarding lactation is correct?


  Prolactin concentrations become elevated prior to puberty.

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

  In the non pregnant state mammary alveoli are usually secretory.

  Oxytocin increases the sensitivity of alveolar cells to prolactin.

  Lactational amenorrhoea is associated with improved fertility.


A is incorrect: Prior to puberty, prolactin production is suppressed due to high levels of PIH. B is correct. C is incorrect: Oestrogen usually inhibits the action of prolactin, preventing mammary alveoli secretion. The exception is the post-partum period when hormonal balance shifts in favour of the action of prolactin and oxytocin. D is incorrect: Oxytocin increases the sensitivity of myoepithelial cells to itself (a self-regulating process). E is incorrect: Lactational amenorrhoea is associated with complete infertility (as long as suckling is regular).

2

The hypothalamic hormone TRH acts on which one of the following?


  The adrenal cortex to stimulate glucocorticoid synthesis and release.

  The ovary to stimulate the release of oestrogen.

  The thyroid follicular cells to stimulate synthesis of transthyretin.

  The anterior pituitary thyrotrophs to evoke TSH secretion.

  The adrenal medulla to evoke adrenaline secretion.

3

Which one of the following hormones is NOT controlled by a hypothalamic hormone released into the portal venous system between the hypothalamus and pituitary?


  Oxytocin.

  Follicle stimulating hormone.

  Luteinizing hormone.

  Thyroid stimulating hormone.

  Growth hormone.


A is correct: Oxytocin is released from the posterior pituitary primarily via a neural suckling reflex.

4

Growth hormone acts on which one of the following?


  A cell surface G protein-coupled receptor to activate adenylate cyclase and increase cAMP levels.

  A cytosolic receptor that migrates into the nucleus following hormone binding.

  A cell surface receptor that has intrinsic guanylate cyclase activity and increases cGMP levels.

  A cell surface receptor that couples to cytosolic tyrosine kinases.

  A nuclear receptor that causes proliferation and enhanced cell growth.


The growth hormone receptor is not a G-protein receptor. A is incorrect: This is a feature of smaller peptide hormones and catecholamines. B is incorrect: This is a feature of steroid and thyroid hormones. C is incorrect. D is correct. E is incorrect: It acts via cell surface receptors.

5

Which one of the following statements is correct about peptide, steroid and thyroid hormone action?


  Thyroid hormones interact with cell surface receptors.

  Steroid hormones interact with nuclear receptors.

  Peptide hormones interact with cytosolic receptors.

  Receptor activation by steroid hormones results in transcription, translation and new protein synthesis.

  Receptor activation by peptide hormones inhibits protein kinase C.


A is incorrect: Although active transport mechanisms exist, thyroid hormones primarily act by binding to cytosolic receptors and affecting transcription. B is incorrect: Steroid hormones bind to cytosolic receptors. C is incorrect: Peptides interact with cell surface receptors. D is correct: This is the primary mechanism of action of steroid hormones. E is incorrect: Peptide hormones generally activate PKC via the diacylglycerol (DAG) second messenger.

6

Which one of the following statements regarding metabolism of circulating hormones is correct?


  Angiotensin II is converted to angiotensin I in plasma.

  Testosterone is converted to dihydrotestosterone in target tissues.

  Oestradiol is converted to testosterone in fat tissues.

  25-hydroxy cholecalciferol is converted to cholecalciferol in the liver.

  Cortisone is converted to cortisol in the kidney.


A is incorrect: The reverse occurs (AT1 is converted to AT2) in the lungs. B is correct: Testosterone is metabolised into dihydrotestosterone (DHT) by 5α reductase in target tissues C is incorrect: Oestradiol is not converted to testosterone. D is incorrect: The reverse is true. E is incorrect: Cortisone is a metabolite of cortisol.

7

Which one of the following statements about thyroxine (T4) and tri-iodothyronine (T3) is correct?


  T4 is available to cells by local conversion from T3.

  T4 has a similar half-life to T3.

  80% of T4 is produced by extrathyroidal conversion.

  Conversion of T4 to T3 leads to increased biologic activity.

  T3 has little, if any, intrinsic biological activity.


A is incorrect: The reverse is true. B is incorrect: T4 has a much longer half-life than T3 (about one week compared to about one day). C is incorrect: T4 is produced only in the thyroid. D is correct: T3 is the more active form. E is incorrect: This is a feature of T4.

8

Which one of the following facts about dihydrotestosterone is correct?


  It is produced from testosterone.

  It is converted into testosterone.

  It acts on the uterus.

  It has no effect on the prostate.

  Its synthesis is regulated by aromatase.


A is correct: It is produced in the testes, prostate, hair follicles and adrenals. B is incorrect: The reverse is true. C is incorrect: DHT's primary role is in male sexual differentiation. D is incorrect: It is implicated in the development of BPH. E is incorrect: Its synthesis is regulated by 5α reductase.

9

Which one of the following is NOT a site of testosterone production?


  The ovary.

  The fetal testis.

  The adrenal medulla.

  The ageing testis.

  The neonate.


The adrenal medulla synthesises catecholamines.

10

Which one of the following facts about cortisone is correct?


  It is the main glucocorticoid.

  It can be converted into cortisol.

  It is synthesized in the adrenal medulla.

  It is synthesized from testosterone.

  It is a potent steroid hormone.


A is incorrect: Cortisol is the main glucocorticoid (cortisone is much less potent). B is correct: This occurs in target tissues. C is incorrect: The adrenal medulla synthesises catecholamines. D is incorrect: It is synthesised from cortisol, ultimately from cholesterol. E is incorrect: Cortisone is a relatively weak steroid compared to (e.g.) cortisol.