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USMLE® Step 1 questions

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USMLE® Step 1 style questions USMLE

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A group of researchers is studying the synthesis and secretion of insulin and C-peptide. Which of the following statements is true regarding insulin synthesis?  

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Aspart insulin

β2 -agonists

insulin and p. 333


insulin and p. 333

in insulinomas p. 359

Detemir insulin

Glargine insulin

Glucagon p. 335

insulin and p. 333, 335

Gluconeogenesis p. 76

in insulin deficiency p. 352


insulin and p. 335

Glulisine insulin

Glycogen p. 84

insulin and p. 333


in insulin deficiency p. 352

Insulin p. 335

anabolic effects of p. 333

deficiency in p. 352

diabetic ketoacidosis p. 357

for HHNS p. 357

fructose bisphosphatase-2 and p. 74

GIP effect on p. 380

glucagon and p. 335

glycogen regulation p. 71, 84

hypokalemia from p. 614

in pregnancy p. 333

production of p. 339

secretion of p. 335

signaling pathways for p. 353

somatostatin and p. 380

somatostatinomas and p. 357


insulin and C-peptide in p. 333

Insulin preparations p. 360


insulin deficiency p. 352


insulin and p. 335

in insulin deficiency p. 352

Lispro insulin

Osmotic diuresis

insulin deficiency/insensitivity p. 352

Plasma osmolality

insulin deficiency/insensitivity p. 352

Pregnancy p. 657

insulin in p. 333

Protein synthesis p. 184, 198

insulin and p. 335


in insulin deficiency p. 352

Regular insulin

Sulfonylureas p. 361

insulin and p. 333


insulin and p. 333

Tyrosine kinase

insulin and p. 333


Insulin is a hormone that’s involved in lowering the blood sugar levels or glycemia after a meal. Insulin comes from the latin insula, which means island, because this hormone is produced by some small islands of cells scattered throughout the pancreas that are called pancreatic islets or islets of Langerhans.

The pancreas lies in the upper left part of the abdomen, right behind the stomach. The vast majority of the pancreas is made up by exocrine glands in charge of secreting digestive enzymes into the small intestine to help digestion. But about 1 to 2% of the mass of the pancreas is made up by the islets of Langerhans, which are endocrine glands made up by five different cell types, and each cell type secretes a specific hormone. The most abundant are the beta cells, which produce insulin. But you can also find alpha cells that secrete glucagon, delta cells that secrete somatostatin, gamma cells that secrete pancreatic polypeptide, and finally epsilon cells that secrete ghrelin.

Let’s focus on beta cells. Beta cells are in charge of producing insulin, which is a peptide hormone encoded by the INS gene on chromosome 11. Insulin is first synthesized as a single polypeptide called preproinsulin. A short tail called leader or signal peptide is cleaved from preproinsulin to form proinsulin. Proinsulin consists of three peptide chains in the order B, C for connecting peptide, and A. Proinsulin is then further cleaved at two positions, releasing a fragment called the C-peptide, and leaving the B- and A- chains, and two disulfide bonds which link the B- and A- chains together to form insulin. This mature insulin is stored inside granules within the beta cells where it waits until it’s released into the blood.

The most important trigger for insulin secretion is glucose. Beta cells are sensitive to glucose concentrations in blood, and when blood glucose levels rise, beta cells secrete insulin into the blood to help lower those levels and store glucose. Other stimulatory factors for insulin secretion include hormones like glucagon and cortisol, which stimulate insulin indirectly by increasing blood glucose levels, increased fatty acid or amino acid concentrations in blood, since insulin is also involved in their storage, and acetylcholine from the parasympathetic nervous system, which helps with digestion, and stimulates insulin secretion to decrease the recently absorbed glucose in blood.


Insulin is a hormone that helps the body to metabolize sugar (glucose). It is made by the pancreas, specifically the islets of Langerhans.

Insulin controls how much glucose is in the blood. When you eat, your body breaks down food into glucose and other nutrients. These enter the bloodstream and signal the pancreas to make insulin. The insulin then allows the glucose to enter cells in the body, where it is used for energy or stored for later use.


  1. "Medical Physiology" Elsevier (2016)
  2. "Physiology" Elsevier (2017)
  3. "Human Anatomy & Physiology" Pearson (2018)
  4. "Principles of Anatomy and Physiology" Wiley (2014)
  5. "Insulin: understanding its action in health and disease" British Journal of Anaesthesia (2000)
  6. "Are islet cells the gatekeepers of the pancreas?" Pancreatology (2002)
  7. "A Reappraisal of the Blood Glucose Homeostat which Comprehensively Explains the Type 2 Diabetes Mellitus–Syndrome X Complex" The Journal of Physiology (2003)

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