A 24-year-old man presents for an annual check-up. He is a bodybuilder and tells you he is on a protein-rich diet that only allows for minimal carbohydrate intake. His friend suggests he try exogenous glucagon to help him lose some excess weight before an upcoming competition. Which of the following effects of glucagon is he attempting to exploit?

Increased lipolysis in adipose tissues

Increased glucose utilization by tissues

Decreased blood cholesterol level

Increased hepatic gluconeogenesis

Increased hepatic glycogenolysis

A 32-year-old woman is found unconscious on the office floor just before lunch by her colleagues. She had previously instructed them on the location of an emergency kit in case this ever happened so they are able to successfully inject her with the substance inside. Her past medical history is significant for type 1 diabetes for which she takes long acting insulin as well as periprandial rapid acting insulin injections. She has previously been found unconscious once before when she forgot to eat breakfast. The substance inside the emergency kit most likely has which of the following properties.

Promotes glycogen breakdown in the liver

Promotes glucose release from skeletal muscles

Promotes glycogen formation in the liver

Promotes glucose uptake in muscles

Inhibits activity of pancreatic alpha and beta cells

A 53-year-old man comes to the physician because of fatigue, recurrent diarrhea, and an 8-kg (17.6-lb) weight loss over the past 6 months. He has a 4-month history of recurrent blistering rashes on different parts of his body that grow and develop into pruritic, crusty lesions before resolving spontaneously. Physical examination shows scaly lesions in different phases of healing with central, bronze-colored induration around the mouth, perineum, and lower extremities. Laboratory studies show: Hemoglobin 10.1 mg/dL Mean corpuscular volume 85 μm3 Mean corpuscular hemoglobin 30.0 pg/cell Serum Glucose 236 mg/dL Abdominal ultrasonography shows a 3-cm, solid mass located in the upper abdomen. This patient's mass is most likely derived from which of the following types of cells?

Gastrointestinal enterochromaffin cells

A 45-year-old man comes to the physician for evaluation of a recurrent rash. He has multiple skin lesions on his legs, buttocks, and around his mouth. The rash first appeared a year ago and tends to resolve spontaneously in one location before reappearing in another location a few days later. It begins with painless, reddish spots that gradually increase in size and then develop into painful and itchy blisters. The patient also reports having repeated bouts of diarrhea and has lost 10 kg (22 lb) over the past year. One year ago, the patient was diagnosed with major depressive syndrome and was started on fluoxetine. Vital signs are within normal limits. Physical examination shows multiple crusty patches with central areas of bronze-colored induration, as well as tender eruptive lesions with irregular borders and on his legs, buttocks, and around his lips. The Nikolsky sign is negative. His hemoglobin concentration is 10.2 g/dL, mean corpuscular volume is 88 μm3, and serum glucose is 210 mg/dL. A skin biopsy of the lesion shows epidermal necrosis. Which of the following additional findings is most likely to be found in this patient?

Increased fasting serum glucagon level

Increased serum vasoactive intestinal polypeptide level

Antibodies against desmoglein 1 and 3

Antibodies against glutamic acid decarboxylase

Antibodies against hemidesmosomes

A 16-year-old girl is brought to the emergency department unresponsive. A witness reports that she became anxious, lightheaded, and began sweating and trembling a few minutes before she lost consciousness. Her vitals are as follows: blood pressure 95/60 mm Hg, heart rate 110/min, respiratory rate 21/min, and temperature 35.5°C (95.5°F). She becomes responsive but is still somnolent. She complains of dizziness and weakness. A more detailed history reveals that she has drastically restricted her diet to lose weight for the past 18 hours, and has not eaten today. Her skin is pale, wet, and cold. The rest of the physical examination is unremarkable. Blood testing shows a plasma glucose level of 2.8 mmol/L (50.5 mg/dL). Which of the following statements is true?

Hypoglycemia in this patient is being compensated with an increased glycogenolysis rate.

Epinephrine-induced gluconeogenesis is the main process that allows for the compensation of a decreased glucose level.

There is an increase in the glycogen synthesis rate in this patient’s hepatocytes.

The patient’s symptoms are most likely the consequence of increased insulin secretion from the pancreatic islets.

The patient’s hypoglycemia inhibits glucagon release from pancreatic alpha cells.

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

A 38-year-old woman presents with hypertension (170/105 mmHg), hypokalemia (2.9 mEq/L), and metabolic alkalosis. Plasma aldosterone is elevated at 35 ng/dL (normal 4-31) and plasma renin activity is suppressed at 0.2 ng/mL/hr (normal 0.5-3.5). CT scan shows a 2.5 cm left adrenal mass. She also reports recent diagnosis of hyperthyroidism and is being evaluated for a neck mass. Synthesize these findings to evaluate for an underlying unifying diagnosis requiring modified treatment approach.

Multiple endocrine neoplasia type 2 requiring RET proto-oncogene testing and comprehensive screening

Ectopic ACTH syndrome from thyroid carcinoma causing bilateral adrenal hyperplasia

Carney complex requiring cardiac myxoma screening before adrenal surgery

Isolated aldosterone-producing adenoma requiring unilateral adrenalectomy only

Coincidental adrenal adenoma and Graves' disease requiring separate standard treatments

A 32-year-old pregnant woman at 28 weeks gestation with type 1 diabetes presents with recurrent severe hypoglycemia despite reducing her insulin dose. Her insulin requirements have decreased by 40% over the past week. She reports decreased fetal movement. Fetal ultrasound shows intrauterine fetal demise. Evaluate the physiological mechanism explaining her changing insulin requirements in the context of pregnancy loss.

Loss of placental lactogen and other diabetogenic hormones that normally increase insulin resistance

Increased maternal growth hormone from pituitary compensation for fetal loss

Maternal thyroid hormone surge causing enhanced glucose utilization

Increased maternal cortisol from stress of fetal loss improving insulin sensitivity

Placental glucose consumption cessation leading to maternal hyperglycemia compensation

Glucagon physiology for USMLE Step 2 CK: High-Yield Physiology Lessons

Glucagon Basics - The Glucose Guardian

Source: α-cells of pancreatic islets of Langerhans.
Action: ↑ blood glucose. The primary counter-regulatory hormone to insulin.
Mechanism: Binds to G-protein coupled receptors (GPCRs) on hepatocytes → activates adenylyl cyclase → ↑ cAMP → PKA activation.
Primary Target: Liver.

⭐ Glucagon, not epinephrine, is the most important glucose counter-regulatory hormone in protecting against hypoglycemia.

Regulation of Secretion - The 'Hangry' Hormone

Primary Stimulus: ↓ Blood glucose (triggers release when < 70 mg/dL).
Other Stimulators:
- ↑ Amino acids (esp. arginine, alanine) → prevents hypoglycemia after a pure protein meal.
- Sympathetic stimulation (β₂-receptors).
- Vagal (cholinergic) stimulation.
- Stress (e.g., cortisol).
Inhibitors:
- ↑ Blood glucose.
- Insulin (paracrine effect).
- Somatostatin (paracrine effect).
- GLP-1.

⭐ After a protein-rich meal, both insulin and glucagon rise. Amino acids stimulate glucagon to offset insulin's hypoglycemic effect, maintaining normal blood sugar.

Mechanism of Action - The Liver's Taskmaster

Receptor: Binds to G-protein coupled receptors (GPCRs) on hepatocytes.
Pathway: Utilizes a Gs-alpha subunit to activate adenylyl cyclase.
Second Messenger: ↑ intracellular cyclic AMP ($cAMP$) from ATP.
Kinase Activation: $cAMP$ activates Protein Kinase A (PKA).

⭐ Exam Favorite: Muscle cells lack glucagon receptors; therefore, glucagon does not cause glycogenolysis in skeletal muscle. Its primary effect is hepatic.

Glucagon signaling and metabolic regulation in liver cell

Metabolic Effects - Flipping the Switch

Glucagon's primary role is to mobilize energy stores, acting as a counter-regulatory hormone to insulin. It primarily targets the liver to raise blood glucose.

Liver (Main Target Organ):
- ↑ Glycogenolysis: Rapid breakdown of stored glycogen.
- ↑ Gluconeogenesis: Synthesis of new glucose from amino acids, lactate, and glycerol.
- ↑ Ketogenesis: Promotes fatty acid oxidation to produce ketone bodies.
Adipose Tissue:
- ↑ Lipolysis: Breaks down triglycerides, releasing Free Fatty Acids (FFAs) and glycerol.

⭐ Glucagon is used to treat severe hypoglycemia in diabetic patients and can also be an antidote for beta-blocker overdose due to its ability to increase cAMP in the myocardium, leading to increased heart rate and contractility.

Glucagon effects on adipose tissue and liver metabolism

Clinical Correlates - When Glucagon Goes Rogue

Glucagonoma: Rare pancreatic α-cell tumor → ↑↑ glucagon.
📌 Mnemonic (The 5 D's):
- Dermatitis (Necrolytic Migratory Erythema)
- Diabetes (new, mild)
- DVT (Deep Vein Thrombosis)
- Declining weight
- Depression
Diagnosis: Markedly ↑ glucagon > 500 pg/mL.

⭐ Necrolytic migratory erythema (NME) is the presenting sign in 70% of glucagonoma cases.

Necrolytic migratory erythema in glucagonoma

High‑Yield Points - ⚡ Biggest Takeaways

Glucagon, from pancreatic α-cells, is the key catabolic hormone of the fasting state.

Its primary goal is to ↑ blood glucose by stimulating hepatic glycogenolysis and gluconeogenesis.

It acts via a Gs-coupled GPCR, leading to an increase in intracellular cAMP.

Secretion is stimulated by hypoglycemia and amino acids (e.g., after a protein-rich meal).

Secretion is inhibited by hyperglycemia, insulin, and somatostatin.

Glucagonoma classically presents with diabetes, necrolytic migratory erythema, and DVT.

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