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:
i. *Volume Status: * Hypervolemic (mildly)
ii. *Sodium: * Hyponatremia (dilutional)
iii. *Serum Osmolality: * Decreased (<280)
iv. *Urine Osmolality: * Increased (>100, inappropriately concentrated)
DI:
i. Volume Status: * Hypovolemic (severe dehydration)
ii. Sodium: * Hypernatremia (due to free water loss)
iii. Serum Osmolality: * Increased (>295)
iv. 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).
IGF1 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.
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:
i. *Volume Status: * Hypervolemic (mildly)
ii. *Sodium: * Hyponatremia (dilutional)
iii. *Serum Osmolality: * Decreased (<280)
iv. *Urine Osmolality: * Increased (>100, inappropriately concentrated)
DI:
i. Volume Status: * Hypovolemic (severe dehydration)
ii. Sodium: * Hypernatremia (due to free water loss)
iii. Serum Osmolality: * Increased (>295)
iv. 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).
IGF1 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.
