00:00 / 00:00




Renal system




0 / 14 complete

USMLE® Step 1 questions

0 / 1 complete

High Yield Notes

4 pages



of complete


USMLE® Step 1 style questions USMLE

of complete

A 26-year-old male presents to the emergency department with diffuse muscle aches and fatigue. He was brought via EMS after he suddenly collapsed while running a marathon. The patient has some shortness of breath and is having difficulty urinating. He is otherwise healthy and does not take any medications. Temperature is 37.0°C (98.6°F), pulse is 107/min, respirations are 22/min, blood pressure is 121/64 mmHg, and O2 saturation is 96% on room air. On physical exam, the patient is pale-appearing, has diffuse tenderness to palpation of the upper and lower extremities, and is noted to have increased work of breathing. A catheterized urine specimen appears dark. This patient’s electrocardiogram is most likely to show which of the following?  

External References

First Aid








Acidosis p. 614, 616

hyperkalemia with p. 614

β -blockers p. 247

hyperkalemia p. 614


hyperkalemia and p. 614


hyperkalemia p. 614

Hyperkalemia p. 614

aldosterone in p. 612

aliskiren p. 634

angiotensin II receptor blockers p. 634

cardiac glycosides p. NaN

causes of p. 614

diabetic ketoacidosis p. 357

potassium-sparing diuretics p. 633

primary adrenal insufficiency p. 355

renal failure p. 627

Hyperkalemic tubular acidosis (type 4) p. 617


hyperkalemia with p. 614

Tumor lysis syndrome p. 443

hyperkalemia p. 614


With hyperkalemia, hyper- means over and -kal- refers to potassium, and -emia refers to the blood, so hyperkalemia means higher than normal potassium levels in the blood, generally over 5.5 mEq/L.

Now, total body potassium can essentially be split into two components—intracellular and extracellular potassium, or potassium inside and outside cells, respectively.

The extracellular component includes both the intravascular space, which is the space within the blood and lymphatic vessels and the interstitial space, the space between cells where you typically find fibrous proteins and long chains of carbohydrates which are called glycosaminoglycans.

Now, the vast majority, around 98%, of all of the body’s potassium is intracellular, or inside of the cells.

In fact, the concentration of potassium inside the cells is about 150 mEq/L whereas outside the cells it’s only about 4.5 mEq/L.

Keep in mind that these potassium ions carry a charge, so the difference in concentration also leads to a difference in charge, which establishes an overall electrochemical gradient across the cell membrane. This is called the internal potassium balance.

This balance is maintained by the sodium-potassium pump, which pumps 2 potassium ions in for every 3 sodium ions out, as well as potassium leak channels and inward rectifier channels that are scattered throughout the membrane.

This concentration gradient is extremely important for setting the resting membrane potential of excitable cell membranes, which is needed for normal contraction of smooth, cardiac, and skeletal muscle.

Also, though, in addition to this internal potassium balance, there’s also an external potassium balance, which refers to the potassium you get externally through the diet every day.

On a daily basis the amount of potassium that typically gets taken in usually ranges between 50 mEq/L to 150 mEq/L, which is way higher than the extracellular potassium concentration of 4.5 mEq/L, so your body has to figure out a way to excrete most of what it takes in.

This external balancing act is largely taken care of by the kidneys, where excess potassium is secreted into a renal tubule and excreted in the urine.

Also though, a small amount dietary potassium is also lost via the gastrointestinal tract and sweat.


  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. "Pathophysiology of Disease: An Introduction to Clinical Medicine 8E" McGraw-Hill Education / Medical (2018)
  4. "CURRENT Medical Diagnosis and Treatment 2020" McGraw-Hill Education / Medical (2019)
  5. "Effects of catecholamines on plasma potassium: the role of alpha- and beta-adrenoceptors" Fundamental & Clinical Pharmacology (1993)
  6. "Management of Hyperkalemia: An Update for the Internist" The American Journal of Medicine (2015)
  7. "Management of patients with acute hyperkalemia" Canadian Medical Association Journal (2010)

Copyright © 2023 Elsevier, its licensors, and contributors. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

Cookies are used by this site.

USMLE® is a joint program of the Federation of State Medical Boards (FSMB) and the National Board of Medical Examiners (NBME). COMLEX-USA® is a registered trademark of The National Board of Osteopathic Medical Examiners, Inc. NCLEX-RN® is a registered trademark of the National Council of State Boards of Nursing, Inc. Test names and other trademarks are the property of the respective trademark holders. None of the trademark holders are endorsed by nor affiliated with Osmosis or this website.