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  #1  
Old 10-29-2012
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Arrow Billy Step 1 Questions # 56

A 56-year-old man with a 60 pack-year smoking history and normal fl uid intake presents to his physician with 2 months of fatigue and weakness
accompanied by cough and mild dyspnea. The patientís vital signs are normal, but a lower left lobe mass is noted on x-ray of the chest. Biopsy leads to the diagnosis of small cell carcinoma.

Laboratory tests show:
Plasma Na+: 125 mEq/L
Plasma K+: 3.9 mEq/L
Plasma CO2: 24 mEq/L
Plasma osmolality: 253 mOsm/L
Urine Na+: 48 mEq/L
Urine osmolality: 280 mOsm/L


The hormone most likely responsible for this patientís abnormal laboratory values has whichof the following direct effects?


(A) Activation of G-protein coupled receptors in the adrenal cortex elevates cAMP levels and leads to increased production and secretion of corticosteroids
(B) Activation of G-protein coupled receptors in the hypothalamus results in elevated cAMP levels and inhibition of hypothalamic- induced thirst mechanism
(C) Cleavage of angiotensinogen to angiotensin I leads to an increase in both aldosterone levels and total peripheral resistance
(D) Activation of V2 receptors leads to an increase in total peripheral resistance; activation of V1 receptors results in the concentration of urine
(E) Activation of V2 receptors results in the insertion of aquaporins into the collecting duct; activation of V1 receptors leads to a decrease in total peripheral resistance
(F) Activation of V2 receptors results in the insertion of aquaporins into the renal collecting duct; activation of V1 receptors leads to an increase in total peripheral resistance
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  #2  
Old 10-29-2012
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Default FF

SIADH.
Answer is F.
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Old 10-29-2012
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Default

SCC>>>SIADH>>>>thru aquaporin V2 receptor>>>increased water retension
v1 receptor activation>>>>IP3/DAG>>>>increase Ca2+>>>>smooth muscle contraction
my ans is F
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Old 10-29-2012
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Correct Answer F is correct

In healthy people, osmoreceptors in the wall of the third ventricle sense increased body fl uid osmolarity and trigger the release of ADH from the posterior pituitary. ADH exerts its main effects on the V2 receptors located in the principal cells of the late distal tubule and collecting duct, where a Gs protein-coupled mechanism directs the insertion of aquaporin water channels into the luminal wall. These channels are permeable
only to water and result in a reabsorption of water, concentration of urine, and dilution of body fluids. Activation of the V1 receptor
found in the vascular smooth muscles results in activation of Gq protein second-messenger cascade and contraction of vascular smooth
muscle, leading to an increase in total peripheral resistance. In patients with the syndrome of inappropriate ADH secretion (SIADH), which can be caused by central nervous system disturbances (e.g., stroke, hemorrhage, infection), small cell lung carcinoma, intracranial neoplasms, and occasionally by pancreatic tumors, the unregulated release of ADH leads to the persistent excretion of concentrated urine high in sodium. This causes hyponatremia and
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  #5  
Old 10-30-2012
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Default my answer :)

(F) Activation of V2 receptors results in the insertion of aquaporins into the renal collecting duct; activation of V1 receptors leads to an increase in total peripheral resistance
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