Excretory system.

The human excretory system is essential for maintaining internal homeostasis by removing metabolic wastes. The primary organs are the kidneys, which contain millions of functional units called nephrons.Urine formation occurs through three critical phases:

Glomerular Filtration: Blood is filtered in the glomerulus under pressure.

Selective Reabsorption: Essential components like glucose, amino acids, and ions are returned to the blood in the tubules.

Tubular Secretion: Metabolic waste (H⁺, K⁺, ammonia) is directly added to the filtrate.This process is strictly regulated by hormones like ADH, ANF, and the Renin-Angiotensin system to balance water and electrolyte levels. Beyond the kidneys, the lungs, liver, and skin also play auxiliary roles in eliminating substances like CO_2, bile pigments, and sweat. When renal function fails, clinical procedures like hemodialysis become necessary to support survival.