A scientist is trying to design a drug to modulate cellular metabolism in the treatment of obesity. Specifically, he is interested in understanding how fats are processed in adipocytes in response to different energy states. His target is a protein within these cells that catalyzes catabolism of an energy source. The products of this reaction are subsequently used in gluconeogenesis or β-oxidation. Which of the following is true of the most likely protein that is being studied by this scientist?

It is stimulated by epinephrine

It is inhibited by acetylcholine

A 65-year-old obese man presents to his primary care clinic feeling weak. He was in the military and stationed in Vietnam in his youth. His current weakness gradually worsened to the point that he had to call his son to help him stand to get on the ambulance. He smokes a pack of cigarettes every day and drinks a bottle of vodka a week. He has been admitted for alcohol withdrawal multiple times and has been occasionally taking thiamine, folic acid, and naltrexone. He denies taking steroids. His temperature is 98°F (36.7°C), blood pressure is 170/90 mmHg, pulse is 75/min, and respirations are 20/min. He is obese with a significant pannus. Hepatomegaly is not appreciable. Abdominal striae are present. His workup is notable for the following: Serum: Na+: 142 mEq/L Cl-: 102 mEq/L K+: 3.9 mEq/L HCO3-: 25 mEq/L BUN: 24 mg/dL Glucose: 292 mg/dL Creatinine: 1.5 mg/dL Ca2+: 10.1 mg/dL AST: 7 U/L ALT: 14 U/L 24-hour urinary cortisol: 400 µg (reference range 5 pg/mL). What is the best next step in management?

Low-dose dexamethasone therapy for 3 months

High-dose dexamethasone therapy for 3 months

An investigator studying hormone synthesis and transport uses immunocytochemical techniques to localize a carrier protein in the central nervous system of an experimental animal. The investigator finds that this protein is synthesized together with a specific hormone from a composite precursor. The protein is involved in the transport of the hormone from the supraoptic and paraventricular nuclei to its destination. The hormone transported by these carrier proteins is most likely responsible for which of the following functions?

Upregulation of renal aquaporin-2 channels

Stimulation of thyroglobulin cleavage

Hyperplasia of the adrenal zona fasciculata

Increased insulin-like growth factor 1 production

Maturation of primordial germ cells

A newborn female is found to have ambiguous genitalia and hypotension. Laboratory workup reveals hyperkalemia, hyperreninemia, and elevated levels of 17-hydroxyprogesterone in the patient's urine. Which of the following enzymes would you expect to be deficient in this patient?

3β-hydroxysteroid dehydrogenase

11β-hydroxysteroid dehydrogenase

A 45-year-old woman presents to her physician with a four-month history of headache. Her headache is nonfocal but persistent throughout the day without any obvious trigger. She was told that it was a migraine but has never responded to sumatriptan, oxygen, or antiemetics. She takes amlodipine for hypertension. She does not smoke. She denies any recent weight loss or constitutional symptoms. Her temperature is 98°F (36.7°C), blood pressure is 180/100 mmHg, pulse is 70/min, and respirations are 15/min. She is obese with posterior cervical fat pads and central abdominal girth. Her neurological exam is unremarkable. In her initial laboratory workup, her fasting blood glucose level is 200 mg/dL. The following additional lab work is obtained and is as follows: Serum: Na+: 142 mEq/L Cl-: 102 mEq/L K+: 4.1 mEq/L HCO3-: 24 mEq/L BUN: 20 mg/dL Glucose: 135 mg/dL Creatinine: 1.3 mg/dL Ca2+: 10.0 mg/dL AST: 8 U/L ALT: 8 U/L 24-hour urinary cortisol: 500 µg (reference range < 300 µg) Serum cortisol: 25 µg/mL (reference range 5-23 µg/dL) 24-hour low dose dexamethasone suppression test: Not responsive High dose dexamethasone suppression test: Responsive Adrenocorticotropin-releasing hormone (ACTH): 20 pg/mL (5-15 pg/mL) Imaging reveals a 0.5 cm calcified pulmonary nodule in the right middle lobe that has been present for 5 years but an otherwise unremarkable pituitary gland, mediastinum, and adrenal glands. What is the best next step in management?

Inferior petrosal sinus sampling

CT-guided biopsy of the pulmonary nodule

Repeat high dose dexamethasone suppression test

You have been asked to deliver a lecture to medical students about the effects of various body hormones and neurotransmitters on the metabolism of glucose. Which of the following statements best describes the effects of sympathetic stimulation on glucose metabolism?

Epinephrine increases liver glycogenolysis.

Norepinephrine causes increased glucose absorption within the intestines.

Without epinephrine, insulin cannot act on the liver.

Peripheral tissues require epinephrine to take up glucose.

Sympathetic stimulation to alpha receptors of the pancreas increases insulin release.

A 60-year-old man with type 2 diabetes on metformin and insulin presents with 3 days of nausea, vomiting, and diffuse abdominal pain. He appears ill and confused. Vital signs: BP 95/60 mmHg, HR 115/min, RR 28/min, T 37.2°C. Labs show glucose 380 mg/dL, pH 7.28, HCO3 18 mEq/L, anion gap 24, serum osmolality 310 mOsm/kg, negative urine ketones, creatinine 2.8 mg/dL (baseline 1.1), lactate 8.2 mmol/L. Apply physiological principles to determine the primary acid-base and metabolic disturbance.

Hyperosmolar hyperglycemic state complicated by lactic acidosis from metformin

Sepsis-induced lactic acidosis with stress hyperglycemia

Alcoholic ketoacidosis with concurrent diabetic emergency

Diabetic ketoacidosis with renal failure from volume depletion

Mixed metabolic acidosis from uremia and starvation ketosis

Glucocorticoid synthesis and regulation for USMLE Step 2 CK: High-Yield Physiology Lessons

Glucocorticoid Synthesis - Cholesterol's Makeover

Source: Cholesterol, primarily from circulating LDL.
Location: Zona Fasciculata of the adrenal cortex.
- 📌 Mnemonic: "The deeper you go, the sweeter it gets." (Salt → Sugar → Sex)
Rate-Limiting Step: Conversion of Cholesterol to Pregnenolone by Cholesterol Desmolase (CYP11A1), stimulated by ACTH.

Adrenal Gland Histology and Hormone Production

⭐ Exam Favorite: Deficiencies in enzymes like 21-hydroxylase are common causes of Congenital Adrenal Hyperplasia (CAH). Precursors are shunted towards the androgen pathway, leading to virilization.

HPA Axis Regulation - The Stress Command Chain

Central Control: The hypothalamus releases Corticotropin-Releasing Hormone (CRH) in response to stress (e.g., illness, hypoglycemia) and follows a diurnal rhythm (peak in AM).
Pituitary Response: CRH stimulates the anterior pituitary to secrete Adrenocorticotropic Hormone (ACTH).
Adrenal Action: ACTH acts on the adrenal cortex (zona fasciculata) to synthesize and release cortisol.

HPA Axis: Hypothalamus, Pituitary, Adrenal Feedback

Negative Feedback: Cortisol inhibits the secretion of both CRH and ACTH, maintaining homeostasis. This is a critical regulatory step.

⭐ Dexamethasone Suppression Test: This test exploits the negative feedback loop. Dexamethasone (a potent synthetic glucocorticoid) should suppress ACTH and cortisol production in healthy individuals. Failure to suppress suggests Cushing's syndrome pathology.

Physiological Actions - Cortisol's Body Tour

Metabolic Effects (Catabolic): Overall ↑ blood glucose.
- Gluconeogenesis & Glycogenolysis: ↑ in liver.
- Proteolysis: ↑ muscle protein breakdown → provides amino acids for gluconeogenesis.
- Lipolysis: ↑ fat breakdown → releases free fatty acids & glycerol.
- Insulin Antagonism: ↓ peripheral glucose uptake.
Anti-inflammatory & Immunosuppressive:
- Inhibits phospholipase A2 (PLA2) via ↑ Lipocortin synthesis.
- ↓ production of prostaglandins & leukotrienes.
- ↓ release of histamine & serotonin from mast cells.
- Demargination of WBCs → neutrophilia (but eosinopenia, lymphopenia).
Cardiovascular:
- ↑ vascular responsiveness to catecholamines (permissive action).

⭐ Cortisol upregulates α1-adrenergic receptors on arterioles, increasing their sensitivity to norepinephrine and epinephrine, which is crucial for maintaining blood pressure.

Other Key Actions:
- Bone: ↓ bone formation by inhibiting osteoblast activity.
- CNS: Affects mood, sleep, and memory.
- Stomach: ↑ gastric acid secretion.

📌 Mnemonic (BBIIG):

Blood pressure ↑
Bone formation ↓
Inflammation ↓
Immune response ↓
Gluconeogenesis ↑

High‑Yield Points - ⚡ Biggest Takeaways

Cortisol is produced in the zona fasciculata from cholesterol, driven by the HPA axis (CRH → ACTH).

ACTH stimulates the rate-limiting enzyme, cholesterol desmolase.

17α-hydroxylase is the essential enzyme for cortisol synthesis.

Cortisol exerts negative feedback on both CRH and ACTH release.

21-hydroxylase deficiency is the most common cause of Congenital Adrenal Hyperplasia (CAH), shunting precursors to androgens.

Exogenous steroid use suppresses the entire HPA axis.

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