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 33-year-old woman, gravida 1, para 0, at 26 weeks' gestation comes to the physician for a routine prenatal examination. Her pregnancy has been uneventful. Physical examination shows a uterus consistent in size with a 26-week gestation. She is given an oral 50-g glucose load; 1 hour later, her serum glucose concentration is 116 mg/dL. Which of the following most likely occurred immediately after the entrance of glucose into the patient's pancreatic beta-cells?

Generation of adenosine triphosphate

Closure of membranous potassium channels

Increased expression of hexokinase I mRNA

Depolarization of beta-cell membrane

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.

Certain glucose transporters that are expressed predominantly on skeletal muscle cells and adipocytes are unique compared to those transporters found on other cell types within the body. Without directly affecting glucose transport in other cell types, which of the following would be most likely to selectively increase glucose uptake in skeletal muscle cells and adipocytes?

Increased levels of circulating insulin

Increased plasma glucose concentration

It is physiologically impossible to selectively increase glucose uptake in specific cells

Decreased plasma glucose concentration

Decreased levels of circulating insulin

A 33-year-old woman presents to the physician because of abdominal discomfort, weakness, and fever. She has had a significant weight loss of 15 kg (33.1 lb) over the past 2 months. She has no history of medical illness and is not on any medications. Her pulse is 96/min, the blood pressure is 167/92 mm Hg, the respiratory rate is 20/min, and the temperature is 37.7°C (99.8°F). Her weight is 67 kg (147.71 lb), height is 160 cm (5 ft 3 in), and BMI is 26.17 kg/m2. Abdominal examination shows purple striae and a vaguely palpable mass in the left upper quadrant of the abdomen, which does not move with respirations. She has coarse facial hair and a buffalo hump along with central obesity. Her extremities have poor muscle bulk, and muscle weakness is noted on examination. An ultrasound of the abdomen demonstrates an adrenal mass with para-aortic lymphadenopathy. Which of the following is the most likely laboratory profile in this patient?

Impaired glucose tolerance, elevated serum cortisol, elevated 24-h urinary free cortisol, and low plasma ACTH

Impaired glucose tolerance, elevated serum cortisol, elevated 24-h urinary free cortisol, and high plasma ACTH

Normal glucose tolerance, elevated serum cortisol, normal 24-h urinary free cortisol, and normal plasma adrenocorticotropic hormone (ACTH)

Impaired glucose tolerance, reduced serum cortisol, normal 24-h urinary free cortisol, and low plasma ACTH

Impaired glucose tolerance, elevated serum cortisol, normal 24-h urinary free cortisol, and normal plasma ACTH

A neurophysiology expert is teaching his students the physiology of the neuromuscular junction. While describing the sequence of events that takes place at the neuromuscular junction, he mentions that as the action potential travels down the motor neuron, it causes depolarization of the presynaptic membrane. This results in the opening of voltage-gated calcium channels, which leads to an influx of calcium into the synapse of the motor neuron. Consequently, the cytosolic concentration of Ca2+ ions increases. Which of the following occurs at the neuromuscular junction as a result of this increase in cytosolic Ca2+?

Exocytosis of acetylcholine from the synaptic vesicles

Generation of an end plate potential

Increased Na+ and K+ conductance of the motor end plate

Binding of Ca2+ ions to NM receptors

Release of Ca2+ ions into the synaptic cleft

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

Glucose homeostasis mechanisms for USMLE Step 1: High-Yield Physiology Lessons

Glucose Homeostasis - The Sweet Balance

Glucose Homeostasis: Pancreas, Liver, Insulin, Glucagon

Insulin (Pancreatic β-cells): The "storage" hormone. Released with ↑ blood glucose. It drives glucose into muscle and fat cells (via GLUT4), promotes glycogen synthesis in the liver, and stimulates fat storage. Its net effect is to lower blood glucose.
Glucagon (Pancreatic α-cells): The "release" hormone. Secreted during fasting or with ↓ blood glucose. It primarily targets the liver, stimulating glycogenolysis and gluconeogenesis to raise blood glucose.

⭐ In Type 1 Diabetes, the absence of insulin leads to unopposed glucagon action, a key driver of diabetic ketoacidosis (DKA).

Fed State - Insulin's In Charge

Following a meal, elevated blood glucose stimulates pancreatic β-cells to release insulin, the primary anabolic hormone.

β-Cell Insulin Secretion Mechanism:
- Glucose enters β-cells via insulin-independent GLUT2 transporters.
- Metabolism ↑ ATP, increasing the cellular ATP/ADP ratio.
- This closes ATP-sensitive K⁺ (KATP) channels, preventing K⁺ efflux.
- The membrane depolarizes, opening voltage-gated Ca²⁺ channels.
- Ca²⁺ influx triggers exocytosis of insulin storage vesicles.

Key Anabolic Actions:
- Muscle/Adipose: Stimulates GLUT4 translocation to the membrane, ↑ glucose uptake.
- Liver/Muscle: ↑ Glycogen synthesis.
- Adipose Tissue: ↑ Lipogenesis and triglyceride storage.

⭐ C-peptide is secreted in equimolar amounts with endogenous insulin; its level can differentiate type 1 diabetes from type 2 and factitious hypoglycemia.

Insulin secretion mechanism from pancreatic beta cells

Fasting State - Glucagon's Gambit

Trigger: Hypoglycemia (↓ blood glucose < 70 mg/dL) stimulates pancreatic α-cells to release glucagon.
Primary Action (Liver): Glucagon acts on hepatocytes to ↑ blood glucose via:
- Glycogenolysis (Rapid): The immediate breakdown of stored glycogen.
- Gluconeogenesis (Sustained): Synthesis of new glucose from amino acids (e.g., alanine), lactate, and glycerol. This process is vital in prolonged fasting.
Other Counter-Regulatory Hormones: Epinephrine, cortisol, and growth hormone provide synergistic or backup effects to maintain glucose levels during stress or extended fasting.

⭐ High-Yield: Glucagon inhibits glycolysis by decreasing fructose-2,6-bisphosphate, which simultaneously stimulates gluconeogenesis.

Glucagon and insulin signaling in glucose homeostasis

Glucose Gatekeepers - The GLUT Family

Transporter	Key Locations	Insulin-Dependence	Key Fact / $K_m$
GLUT1	Erythrocytes (RBCs), brain (BBB), cornea, placenta.	No	Low $K_m$ (~1 mM). Constant, basal glucose uptake for tissues with high, continuous need.
GLUT2	Liver, pancreatic β-cells, renal tubules, small intestine.	No	High $K_m$ (~15 mM). Bidirectional transporter; acts as a glucose sensor in pancreas.
GLUT3	Neurons, placenta, testes.	No	Very low $K_m$ (<1 mM). Highest affinity; ensures glucose supply to critical areas during hypoglycemia.
GLUT4	Skeletal/cardiac muscle, adipose tissue.	Yes	Medium $K_m$ (~5 mM). Insulin stimulates translocation from intracellular vesicles to the cell surface. 📌 GLUT 4 is in 4-letter tissues.

High‑Yield Points - ⚡ Biggest Takeaways

Insulin is the primary anabolic hormone; it drives glucose into muscle and adipose tissue via GLUT4.

Glucagon is the main catabolic hormone; it stimulates hepatic glycogenolysis and gluconeogenesis.

Pancreatic β-cells release insulin when ↑ glucose leads to ↑ ATP, closing K+ATP channels.

GLUT2 is insulin-independent and facilitates glucose transport in the liver and pancreas.

Fasting state is dominated by glucagon; the fed state is dominated by insulin.

Cortisol and epinephrine are key counter-regulatory hormones that also raise blood glucose.

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