nephron
Summary
The nephron is the functional unit of the kidney, consisting of a glomerulus, Bowman's capsule, and tubular system. Each kidney contains approximately 1 million nephrons responsible for filtration, reabsorption, and secretion to maintain fluid/electrolyte balance and excrete waste.
Detail
The nephron consists of two main components: the renal corpuscle (glomerulus + Bowman's capsule) and the renal tubule system. The glomerulus performs filtration via a three-layer barrier (fenestrated endothelium, basement membrane, podocyte foot processes), creating an ultrafiltrate. The tubular system includes the proximal convoluted tubule (reabsorbs 65% of filtered sodium, glucose, amino acids, and most filtered water), loop of Henle (creates concentration gradient via countercurrent mechanism), distal convoluted tubule (fine-tunes electrolyte balance), and collecting duct (final concentration under ADH control). Two types exist: cortical nephrons (85%, short loops) and juxtamedullary nephrons (15%, long loops extending deep into medulla, crucial for concentration). The juxtaglomerular apparatus (JGA) at each nephron produces renin and regulates GFR via tubuloglomerular feedback. Nephron loss is irreversible and occurs with aging, diabetes, hypertension, and kidney disease, leading to compensatory hyperfiltration in remaining nephrons.
Sources
- First Aid for the USMLE Step 1
- Robbins Basic Pathology
- Guyton and Hall Textbook of Medical Physiology
- Harrison's Principles of Internal Medicine
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