Kidneys and Urinalysis

Kidneys and Nephrons

• Kidneys are composed of approximately 1 million nephrons, the major functional unit.
• A nephron consists of a glomerulus and renal tubules.

Glomerulus

• Filters 120 ml/min, or one-fifth (1/5) of renal plasma.
• A coil of capillary vessels.

Renal Tubules

• Proximal tubule:
  • Reabsorbs water, sodium, chloride, bicarbonate, potassium, calcium, amino acids, phosphates, protein, and glucose.
  • Glucose is a threshold substance with a normal range of 160-180 mg/dl.
• Descending Loop of Henle:
  • Reabsorbs water.
• Ascending Loop of Henle:
  • Reabsorbs sodium, chloride, calcium, and magnesium solutes.
• Distal and Collecting tubule:
  • Reabsorbs sodium.
  • Secretes potassium through K ion exchange for Na.

Urine Output Terms

• Normal urine output: average of 1200-1500 ml/day.
• Polyuria:
  • >2500 ml/day.
  • Causes: Diabetes Mellitus, Diabetes Insipidus, Diuretics, Caffeine, and alcohol intake (DDD-CA).
• Oliguria:
  • <400 ml/day.