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Discover the incredible role of kidneys in our body's functioning, the secrets of their intricate filtration system, and how to maintain optimal kidney health for a vibrant and energetic life.

USMLE Guide: Kidneys


The kidneys are vital organs responsible for maintaining fluid balance, filtering waste products, and regulating electrolyte levels in the human body. Understanding the structure, function, and common disorders of the kidneys is essential for medical professionals preparing for the United States Medical Licensing Examination (USMLE). This guide will provide comprehensive information about the kidneys, helping you master this topic for your exam.

Anatomy of the Kidneys

The kidneys are bean-shaped organs located on either side of the vertebral column, behind the peritoneum. Each kidney is approximately 11 cm long and consists of three main regions:

  1. Renal Cortex: The outermost layer that contains the glomeruli, proximal and distal convoluted tubules, and the cortical collecting ducts.
  2. Renal Medulla: The middle region composed of renal pyramids, which contain the loop of Henle and collecting ducts.
  3. Renal Pelvis: The innermost region that collects urine from the collecting ducts and transports it to the ureters.

Functions of the Kidneys

The kidneys perform several crucial functions:

  1. Filtration: The glomeruli filter blood to remove waste products, toxins, excess ions, and water, resulting in the formation of filtrate.
  2. Reabsorption: Essential substances like glucose, amino acids, and electrolytes are reabsorbed from the filtrate back into the bloodstream.
  3. Secretion: Certain substances, such as drugs and waste products, are actively secreted into the filtrate from the bloodstream.
  4. Maintenance of Fluid and Electrolyte Balance: The kidneys regulate the concentration of sodium, potassium, calcium, and other electrolytes in the bloodstream.
  5. Acid-Base Balance: By controlling the excretion or reabsorption of hydrogen ions and bicarbonate ions, the kidneys help maintain the body's acid-base balance.

Common Kidney Disorders

Several kidney disorders frequently tested on the USMLE include:

  1. acute kidney injury (AKI): Sudden loss of kidney function due to conditions like decreased blood flow, kidney infections, or drug toxicity.
  2. Chronic Kidney Disease (CKD): Progressive and irreversible damage to the kidneys, often caused by conditions like diabetes, hypertension, or glomerulonephritis.
  3. Renal Calculi: Formation of kidney stones due to the crystallization of minerals and salts within the urinary tract.
  4. urinary tract Infections (UTIs): Bacterial infections affecting the kidneys, bladder, or urethra, commonly caused by escherichia coli or Enterococcus species.
  5. Renal Cell Carcinoma: The most common type of kidney cancer, typically presenting with hematuria, flank pain, and a palpable mass.

Diagnostic Tools and Treatment

To diagnose kidney disorders, various tools and tests are utilized:

  1. Urinalysis: Examination of urine for the presence of blood, protein, glucose, or abnormal cells.
  2. Blood Tests: Measurement of creatinine, blood urea nitrogen (BUN), and electrolyte levels to assess kidney function.
  3. Imaging Studies: Renal ultrasound, CT scan, or MRI to visualize kidney structure and detect abnormalities.
  4. Biopsy: Removal of a small tissue sample from the kidney for microscopic examination in suspected cases of renal pathology.

Treatment options for kidney disorders depend on the specific condition but may involve lifestyle modifications, medications, dialysis, or kidney transplantation.


A comprehensive understanding of the kidneys is crucial for success on the USMLE. Familiarize yourself with the anatomy, functions, and common disorders of the kidneys. Remember to integrate clinical knowledge and diagnostic tools to effectively manage kidney-related conditions. Good luck on your exam!

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