Diabetes mellitus: Pathology review

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Diabetes mellitus: Pathology review

Endocrine system


Diabetes mellitus: Pathology review

USMLE® Step 1 questions

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USMLE® Step 1 style questions USMLE

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A 13-year-old girl is brought to the emergency department complaining of blurry vision. The patient says that over the past few months she has noticed gradual vision changes in both eyes, which have gotten worse over the past few weeks. The patient recently started the new school year and is finding it difficult to read the homework assignments, and she says she accidentally ran into a tree without seeing it yesterday. The patient has a history of corrected congenital hip dysplasia. The patient’s mother has autoimmune thyroiditis. The patient’s temperature is 37.0°C (98.6°F), pulse is 88/min, respirations are 25/min, and blood pressure is 105/64 mmHg. Physical examination shows a well-appearing adolescent in no acute distress with severe bilateral cataracts and a normal thyroid gland. Laboratory studies show the following:  
Laboratory value  Result
 Sodium  132 mEq/L 
 Potassium  4.2 mEq/L 
 Bicarbonate  16 mEq/L 
 Glucose  532 mg/dL 
Which of the following is the most likely mechanism of this patient’s vision loss?  


In the Emergency Department, two individuals came in. One of them is 12 years old Timmy, who is severely dehydrated, presents with rapid and deep breaths, abdominal pain, nausea and vomiting. On the clinical examination, his breath actually smells fruity and sweet. Timmy’s parents said that he had been eating a lot lately, but he actually lost weight. Also, they said that Timmy is also drinking water all the time and going to the bathroom a lot. The other person is 55 year old Oliver, who also came in with severe dehydration, lethargy and his family said he had a seizure about 2 hours ago, and in the past month, he had lost some weight, although he had been eating. Both individuals underwent several investigations, including glucose levels, ketone bodies BMP and an ABG.

Okay, based on both individuals’ symptoms, we can assume that both suffer from diabetes mellitus. Diabetes mellitus is a condition where glucose can’t be properly moved from the blood into the cells. This leads to high levels of glucose in the blood and not enough of it inside cells. Since cells need glucose as a source of energy, not letting glucose enter means that the cells starve for energy despite having glucose right on their doorstep.

In general, the body controls how much glucose is in the blood with two hormones: insulin and glucagon. Both of these hormones are produced in the islets of Langerhans of the pancreas. Insulin is secreted by the beta cells, while glucagon is secreted by the alpha cells. Insulin reduces blood glucose levels. It does that by binding to insulin receptors embedded in the cell membrane of insulin-responsive tissues, like muscle cells and adipose tissue. When activated, the insulin receptors cause vesicles containing glucose transporter that are inside the cell to fuse with the cell membrane, allowing glucose to be transported into the cell.


  1. "Robbins Basic Pathology" Elsevier (2017)
  2. "Harrison's Principles of Internal Medicine, Twentieth Edition (Vol.1 & Vol.2)" McGraw-Hill Education / Medical (2018)
  3. "Type 1 Diabetes Mellitus in Pediatrics" Pediatrics in Review (2008)
  4. "Hyperglycemic Crises in Adult Patients With Diabetes" Diabetes Care (2009)
  5. "Diabetes mellitus: definition, classification and diagnosis" Wien Klin Wochenschr (2016)

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