Core High-Yield Fact Ledger
- Homeostasis maintains internal environment within a narrow range around a set point using negative feedback loops.
- Feedback loop sequence: Receptor (detects stimulus) > Control Center (integrator) > Effector (muscle or gland).
- Kidneys lie retroperitoneally between T12 and L3 vertebrae; right kidney is lower due to liver.
- Functional unit is the nephron (~1.0 to 1.2 million per kidney).
- Cortical nephrons comprise 70 to 80% with short loops; juxtamedullary nephrons comprise 20 to 30% with long loops and vasa recta.
- Glomerulus sits between two arterioles; wider afferent arteriole generates elevated capillary hydrostatic pressure (~55 to 60 mmHg).
- Glomerular filtration rate is 125 ml/min, generating 180 Liters of filtrate per 24 hours.
- Over 99.5% of filtrate is reabsorbed; normal daily urine excretion is 1.0 to 1.5 Liters.
- Proximal Convoluted Tubule (PCT) reabsorbs 100% of filtered glucose and amino acids via secondary active transport.
- Counter-Current Multiplier: Descending limb is permeable to water and impermeable to solutes; ascending limb actively pumps $NaCl$ and is impermeable to water.
- Medullary interstitial gradient rises from 300 mOsm/L in cortex to 1200 mOsm/L at hairpin turn in inner medulla.
- Antidiuretic Hormone (ADH) from posterior pituitary stimulates aquaporin insertion in collecting ducts, concentrating urine.
- Aldosterone from adrenal cortex stimulates active $Na^+$ reabsorption and $K^+$ excretion in distal convoluted tubules.
- Calcium oxalate constitutes 70% of kidney stones; struvite 15 to 20%; uric acid 5 to 10%; cystine 1 to 3%.
- Non-invasive stone fragmentation uses Extracorporeal Shock Wave Lithotripsy (ESWL).
- End-Stage Renal Disease (ESRD) requires dialysis or kidney transplantation when functional level drops below 10% (loss of ~90% function).