Hypothalamic–Pituitary Relationships II Step 1 Practice Exam

B. Normal physiology: hyperglycemia strongly inhibits GH via central feedback (↑somatostatin, ↓GHRH). After 75g oral glucose, GH should fall below 1 ng/mL in healthy subjects. Failure to suppress is the hallmark of autonomous GH secretion from a pituitary adenoma. Combine with elevated IGF-1 and MRI → diagnose acromegaly. Directly tests LO 4 and the clinical application of GH regulation.

A. GH is highly pulsatile. Between pulses, GH is often near-undetectable — a random daytime value is uninformative. The largest physiologic pulse occurs during stage 4 slow-wave sleep, around midnight. Integrated measures (IGF-1) or overnight serial sampling are far more meaningful. Random GH is only useful if very HIGH (suggests acromegaly). Tests LO 3 pulsatility principle directly.

C. Somatopause (age-related decline in GH/IGF-1) is a normal physiologic phenomenon and is NOT equivalent to documented hypopituitary GH deficiency. Randomized trials of GH in older adults show modest gains in lean mass and loss of fat mass, but significant rates of insulin resistance, edema, arthralgias, carpal tunnel, cardiomegaly, and theoretical cancer risk. GH is NOT FDA-approved for anti-aging. Pragmatic LO 3 application.

B. Long-loop feedback in the GH axis has two arms: IGF-1 directly INHIBITS GHRH (at hypothalamic GHRH neurons) AND stimulates SOMATOSTATIN neurons (periventricular nucleus), and also acts directly at the pituitary to reduce GH release. The net effect is suppression at every level — producing the observed pattern. Short loop (GH itself → ↓GHRH) and ultra-short loop (GHRH auto-inhibition) contribute to pulsatility but don't drive sustained chronic suppression. Direct LO 4 / 5 conceptual test.

B. Growth failure is a classic pediatric feature of Cushing syndrome — a counterintuitive finding given her weight gain. Mechanisms:
• Chronic high cortisol SUPPRESSES GH release (↑ somatostatin, ↓ GHRH)
• Cortisol directly INHIBITS chondrocyte activity at growth plates
• Cortisol antagonizes the anabolic effects of IGF-1 on bone and muscle
Obesity in pediatric Cushing comes with DELAYED growth — the opposite of typical simple obesity (where growth often accelerates). Treatment of the underlying Cushing → catch-up growth is possible if growth plates are still open. Reinforces LO 4 inhibitors.

C — MEN 1. Classic "3 P's": Parathyroid hyperplasia (hypercalcemia, inappropriately high PTH), Pituitary adenoma (here GH-secreting → gigantism given pre-epiphyseal closure), Pancreatic endocrine tumors (would manifest as ZES ulcers, insulinoma, etc). Autosomal dominant MEN1 gene (tumor suppressor). Family history strengthens this. MEN 2 (D) involves medullary thyroid + pheo, NOT acromegaly. McCune-Albright (B) is mosaic, not inherited, and has café-au-lait + fibrous dysplasia.

B. Standard algorithm: transsphenoidal surgery first (done). With residual disease and elevated IGF-1, somatostatin analog (octreotide LAR or lanreotide) is first-line medical therapy — can both control IGF-1 AND shrink tumor (~30–50% shrinkage). Cavernous-sinus invasion often precludes complete surgery. Pegvisomant (C) is next option if SST analogs fail or are not tolerated — it blocks peripheral GH action but doesn't shrink tumor. Radiation (D) is reserved for refractory cases; slow action (years) + high rate of hypopituitarism. GH (E) would worsen disease.

B — Mecasermin. This is Laron syndrome: HIGH GH + LOW IGF-1 + failure of IGF-1 to rise with exogenous GH. The defect is in the GH RECEPTOR (GHR) → liver cannot make IGF-1 regardless of how much GH is given. Treatment is the missing downstream mediator: recombinant IGF-1 (mecasermin). Interesting aside: observational studies of Laron patients (classically in Ecuador and Israel) show striking protection from cancer and T2DM — linking IGF-1 signaling to both. Directly tests LO 5 treatment logic.

B. Turner syndrome (45,X): short stature + webbed neck + cardiac defects (bicuspid AV, coarctation) + gonadal failure. GH axis is intact but SHOX gene haploinsufficiency + absent estrogen-driven pubertal growth spurt explain short stature. Recombinant GH therapy starting in early childhood adds 5–8 cm to final height. Estrogen replacement is needed at pubertal age for secondary sexual development and bone health. Mecasermin (C) is for Laron. Vosoritide (E) is for achondroplasia. Tests LO 5 with the broader short-stature DDx.

B — Colonoscopy. Acromegaly is associated with a 2–3× increased risk of COLORECTAL POLYPS and colon cancer. Guidelines recommend colonoscopy at diagnosis and every 3–5 years thereafter. IGF-1 is a classic mitogen for colonic epithelium. Other monitoring in acromegaly: echocardiogram (cardiomyopathy is the #1 cause of death), OSA screening, diabetes screening (HbA1c), thyroid and adrenal axis checks (for compression effects), and periodic MRI to monitor residual adenoma. Integrates LO 5 with clinical practice.

E — All of the above. This is the one-stem composite of LOs 1/3/4. GH is released from anterior pituitary somatotrophs in pulses mainly during deep (stage N3) sleep plus a basal level — this is the "dynamic circadian" property in LO 3. It is stimulated by hypothalamic GHRH and inhibited by somatostatin (SST) — the two antagonistic tonic inputs in LO 4. Peripherally, GH drives IGF-1 synthesis primarily in liver but also in bone, muscle, kidney — completing the "hypothalamus → pituitary → liver → target tissues" circuit in LO 1.

D — Growth hormone. GH released from pituitary somatotrophs binds the GH receptor (JAK2-STAT5 cytokine-family) on hepatocytes and other tissues → induces IGF-1 (somatomedin C) synthesis. IGF-1 is the primary mediator of GH's anabolic growth effects on cartilage (long bones), muscle, and many visceral organs. Direct GH effects (anti-insulin / metabolic) are distinct from the IGF-1-mediated growth effects — a key LO 2 distinction. None of the other pituitary hormones in this list drive IGF-1.

C — Growth hormone. LO 2 fully mapped out: GH is anabolic for protein synthesis (positive N₂ balance, muscle growth via IGF-1) but simultaneously diabetogenic — it decreases peripheral glucose uptake and stimulates hepatic gluconeogenesis/glycogenolysis to maintain serum glucose during fasting/stress. It stimulates lipolysis in adipose (shifts fuel source to fatty acids) and supports Ca²⁺ retention and bone mineralization (important for longitudinal bone growth). Cortisol (A) also increases lipolysis and decreases glucose uptake but DECREASES protein synthesis (catabolic). PTH (E) handles Ca²⁺ homeostasis but not the metabolic effects listed.

C. LO 1 end-organ step: GH acts on hepatocytes → IGF-1 synthesis. In liver failure, hepatocellular dysfunction means GH cannot drive normal IGF-1 production (and cannot deiodinate T4 to rT3 — explaining the concurrent low rT3). GH itself stays normal because its feedback is largely driven by IGF-1, which is lost. The same cirrhotic liver also fails to 25-hydroxylate vitamin D → hypocalcemia (positive Trousseau, paresthesias) and weak bones (vertebral fracture). This elegantly illustrates that a normal pituitary signal can still produce clinical GH deficiency IF the liver target tissue is broken — a frequent Step 1 pitfall.

D — Hyperprolactinemia, not acromegaly. This is the "stalk effect" — KEY LO 4 teaching for GH. GHRH TONICALLY STIMULATES somatotrophs; losing GHRH means GH secretion FALLS, so acromegaly is impossible after portal disruption. Only prolactin goes UP because PRL is the sole anterior pituitary hormone under tonic inhibition (by hypothalamic dopamine). Contrast with Ext Q7 below: tumors of the hypothalamus that OVERPRODUCE GHRH DO cause acromegaly. Choice A is the tempting wrong answer — it confuses disrupting a stimulatory pathway (↓ GH) with oversupplying it (↑ GH).

B — Acromegaly. Adult excess GH causes acral enlargement without added height because epiphyses are already closed (the same GH excess BEFORE closure = gigantism). The jaw, hands, feet, and soft tissues thicken. Diabetes mellitus frequently coexists because GH stimulates gluconeogenesis and opposes insulin at the tissue level — LO 2 physiology driving the LO 5 clinical picture. Other diagnostic features not listed: carpal tunnel syndrome, deep voice, macroglossia, obstructive sleep apnea, and ~2× cardiovascular mortality.

A — Hypothalamus. The patient shows classic acromegaly features (acral/soft-tissue overgrowth, mandibular prognathism with interdental spacing = "spaces between all her teeth"). LO 1 pathway: a hypothalamic tumor producing excess GHRH drives the pituitary to hypersecrete GH → liver IGF-1 ↑ → acral growth. Although most clinical acromegaly is a pituitary somatotroph adenoma, the Step 1 teaching is that hypothalamic GHRH-omas and ectopic GHRH (e.g., pancreatic neuroendocrine tumors, small-cell lung) are also important causes. Pearl: serum GHRH ↑ in ectopic causes but would be ↓ in a pituitary somatotroph adenoma (where feedback from IGF-1 suppresses hypothalamic GHRH).

B — Failed GH suppression. This is THE gold-standard screening test for acromegaly — tests LOs 3 & 5 together. Normally, a glucose load causes hyperglycemia → ↑ somatostatin → GH suppression below 1 ng/mL within 2 hours (part of LO 3 regulation). A somatotroph adenoma secretes GH autonomously — it fails to suppress. Elevated IGF-1 is the best confirmatory test, but in the OGTT the DIAGNOSTIC finding is that GH does NOT fall (C is the wrong direction — IGF-1 should already be HIGH at baseline, not rise in response to glucose). Ghrelin (A) and somatostatin (E) decline physiologically after glucose and cannot be used diagnostically.