NR 507 WEEK 6 MASTER Q&A: ALTERATIONS
IN THE ENDOCRINE SYSTEM
MODULE 1: HYPOTHALAMUS & PITUITARY GLAND
.1. A patient is diagnosed with a prolactinoma. Which physiologic mechanism explains
the development of galactorrhea and amenorrhea in this patient?.
A. Prolactin inhibits GnRH release from the hypothalamus, suppressing FSH and LH.
B. Prolactin directly stimulates estrogen production, causing negative feedback on the
ovaries.
C. The pituitary tumor compresses the posterior pituitary, causing ADH excess.
D. Prolactin up-regulates dopamine receptors in the hypothalamus.
.Answer: A.
*Rationale:* Prolactin's primary function is milk production. However, when prolactin is
abnormally high (hyperprolactinemia), it inhibits the pulsatile release of Gonadotropin-
Releasing Hormone (GnRH) from the hypothalamus. Without GnRH, the anterior
pituitary does not secrete adequate FSH and LH, leading to anovulation and
amenorrhea. (Note: Under normal conditions, dopamine *inhibits* prolactin).*
.2. Differentiate between the fluid and electrolyte imbalances seen in Syndrome of
Inappropriate Antidiuretic Hormone (SIADH) versus Diabetes Insipidus (DI)..
* .SIADH:.
, * *Volume Status:* Hypervolemic (mildly)
* *Sodium:* Hyponatremia (dilutional)
* *Serum Osmolality:* Decreased (<280)
* *Urine Osmolality:* Increased (>100, inappropriately concentrated)
* .DI:.
* *Volume Status:* Hypovolemic (severe dehydration)
* *Sodium:* Hypernatremia (due to free water loss)
* *Serum Osmolality:* Increased (>295)
* *Urine Osmolality:* Decreased (<200, inappropriately dilute)
.3. A patient with a known small cell lung carcinoma presents with confusion, muscle
twitching, and a seizure. Lab results show Sodium 118 mEq/L. What is the
pathophysiologic mechanism of this patient's neurologic symptoms?.
A. Rapid sodium depletion causes neurons to hyperpolarize, shutting down brain
function.
B. The low serum sodium creates an osmotic gradient that pulls water into brain cells,
causing cerebral edema.
C. Lung cancer secretes aldosterone, causing massive sodium retention and brain
swelling.
D. Low sodium directly destroys the blood-brain barrier, allowing toxins to enter the
brain.
.Answer: B.
*Rationale:* Small cell lung cancer is famous for ectopic production of ADH (causing
SIADH). The hyponatremia in SIADH is *dilutional* (too much water, normal sodium).
When serum osmolality drops suddenly, it creates an osmotic gradient where
extracellular fluid (with lower solute concentration) moves into the intracellular
compartment (which has a higher relative solute concentration). In the brain, this
influx of water causes cerebral edema, leading to increased ICP, confusion, and
seizures.*
, .4. Why is a random serum Growth Hormone (GH) level useless for diagnosing
Acromegaly, and what marker is used instead?.
A. GH has a 5-minute half-life and is secreted in pulsatile bursts; IGF-1 is used because
it has a steady, 24-hour half-life.
B. Random GH is suppressed by cortisol; ACTH must be measured simultaneously.
C. GH only acts locally in the pituitary; a brain MRI is the only diagnostic test.
D. GH is bound to thyroxine-binding globulin (TBG); free GH must be measured.
.Answer: A.
*Rationale:* GH is secreted in massive, episodic pulses (mostly at night) and has a very
short half-life. A random blood draw could catch a trough or a peak, making it
unreliable. GH stimulates the liver to produce Insulin-like Growth Factor-1 (IGF-1). IGF-
1 has a long half-life (about 24 hours) and reflects the *average* GH production over
days, making it the reliable serum marker for acromegaly.*
.5. A 12-year-old child presents with proportional extreme tallness. Genetic testing
reveals a mutation in the Gs alpha protein. What is the pathophysiologic mechanism of
this child's condition?.
A. Loss of function of the Gs protein, leading to increased somatostatin inhibition.
B. Constitutive activation of the Gs protein, causing continuous cAMP production and
GH hypersecretion independent of GHRH.
C. The mutated Gs protein destroys the pituitary somatotrophs, causing gigantism.
D. The Gs protein binds to insulin receptors, causing massive IGF-1 production from fat
cells.
.Answer: B.
*Rationale:* This describes McCune-Albright syndrome or a somatic activating
mutation of the GNAS gene. The Gs alpha protein is responsible for transducing the
signal from the GHRH receptor inside the cell. If it is mutated to be constitutively
(constantly) active, it continuously produces cAMP, causing the somatotrophs to
secrete GH relentlessly, even without GHRH. This occurs in childhood (before
epiphyseal closure), resulting in Gigantism.*
IN THE ENDOCRINE SYSTEM
MODULE 1: HYPOTHALAMUS & PITUITARY GLAND
.1. A patient is diagnosed with a prolactinoma. Which physiologic mechanism explains
the development of galactorrhea and amenorrhea in this patient?.
A. Prolactin inhibits GnRH release from the hypothalamus, suppressing FSH and LH.
B. Prolactin directly stimulates estrogen production, causing negative feedback on the
ovaries.
C. The pituitary tumor compresses the posterior pituitary, causing ADH excess.
D. Prolactin up-regulates dopamine receptors in the hypothalamus.
.Answer: A.
*Rationale:* Prolactin's primary function is milk production. However, when prolactin is
abnormally high (hyperprolactinemia), it inhibits the pulsatile release of Gonadotropin-
Releasing Hormone (GnRH) from the hypothalamus. Without GnRH, the anterior
pituitary does not secrete adequate FSH and LH, leading to anovulation and
amenorrhea. (Note: Under normal conditions, dopamine *inhibits* prolactin).*
.2. Differentiate between the fluid and electrolyte imbalances seen in Syndrome of
Inappropriate Antidiuretic Hormone (SIADH) versus Diabetes Insipidus (DI)..
* .SIADH:.
, * *Volume Status:* Hypervolemic (mildly)
* *Sodium:* Hyponatremia (dilutional)
* *Serum Osmolality:* Decreased (<280)
* *Urine Osmolality:* Increased (>100, inappropriately concentrated)
* .DI:.
* *Volume Status:* Hypovolemic (severe dehydration)
* *Sodium:* Hypernatremia (due to free water loss)
* *Serum Osmolality:* Increased (>295)
* *Urine Osmolality:* Decreased (<200, inappropriately dilute)
.3. A patient with a known small cell lung carcinoma presents with confusion, muscle
twitching, and a seizure. Lab results show Sodium 118 mEq/L. What is the
pathophysiologic mechanism of this patient's neurologic symptoms?.
A. Rapid sodium depletion causes neurons to hyperpolarize, shutting down brain
function.
B. The low serum sodium creates an osmotic gradient that pulls water into brain cells,
causing cerebral edema.
C. Lung cancer secretes aldosterone, causing massive sodium retention and brain
swelling.
D. Low sodium directly destroys the blood-brain barrier, allowing toxins to enter the
brain.
.Answer: B.
*Rationale:* Small cell lung cancer is famous for ectopic production of ADH (causing
SIADH). The hyponatremia in SIADH is *dilutional* (too much water, normal sodium).
When serum osmolality drops suddenly, it creates an osmotic gradient where
extracellular fluid (with lower solute concentration) moves into the intracellular
compartment (which has a higher relative solute concentration). In the brain, this
influx of water causes cerebral edema, leading to increased ICP, confusion, and
seizures.*
, .4. Why is a random serum Growth Hormone (GH) level useless for diagnosing
Acromegaly, and what marker is used instead?.
A. GH has a 5-minute half-life and is secreted in pulsatile bursts; IGF-1 is used because
it has a steady, 24-hour half-life.
B. Random GH is suppressed by cortisol; ACTH must be measured simultaneously.
C. GH only acts locally in the pituitary; a brain MRI is the only diagnostic test.
D. GH is bound to thyroxine-binding globulin (TBG); free GH must be measured.
.Answer: A.
*Rationale:* GH is secreted in massive, episodic pulses (mostly at night) and has a very
short half-life. A random blood draw could catch a trough or a peak, making it
unreliable. GH stimulates the liver to produce Insulin-like Growth Factor-1 (IGF-1). IGF-
1 has a long half-life (about 24 hours) and reflects the *average* GH production over
days, making it the reliable serum marker for acromegaly.*
.5. A 12-year-old child presents with proportional extreme tallness. Genetic testing
reveals a mutation in the Gs alpha protein. What is the pathophysiologic mechanism of
this child's condition?.
A. Loss of function of the Gs protein, leading to increased somatostatin inhibition.
B. Constitutive activation of the Gs protein, causing continuous cAMP production and
GH hypersecretion independent of GHRH.
C. The mutated Gs protein destroys the pituitary somatotrophs, causing gigantism.
D. The Gs protein binds to insulin receptors, causing massive IGF-1 production from fat
cells.
.Answer: B.
*Rationale:* This describes McCune-Albright syndrome or a somatic activating
mutation of the GNAS gene. The Gs alpha protein is responsible for transducing the
signal from the GHRH receptor inside the cell. If it is mutated to be constitutively
(constantly) active, it continuously produces cAMP, causing the somatotrophs to
secrete GH relentlessly, even without GHRH. This occurs in childhood (before
epiphyseal closure), resulting in Gigantism.*
