Overview of the Human Excretory System
The human excretory system plays a crucial role in maintaining homeostasis by eliminating waste and regulating various bodily functions. It primarily comprises the kidneys, ureters, bladder, and urethra.

Components of the Excretory System
- Kidneys: The primary organs responsible for filtering blood, removing waste, and producing urine. Each kidney contains around one million nephrons, which are the functional units that carry out filtration and reabsorption.
- Ureters: Tubes that transport urine from the kidneys to the bladder. Each kidney has one ureter.
- Bladder: A muscular sac that stores urine until it is excreted from the body. It can expand and contract to hold varying amounts of urine.
- Urethra: The final duct through which urine exits the body. In males, it also serves as a passage for semen.

Functions of the Excretory System
- Filtration: Blood enters the kidneys, where waste products, excess salts, and water are filtered out.
- Reabsorption: Essential substances like glucose, certain ions, and water are reabsorbed back into the bloodstream.
- Secretion: Additional waste products are secreted into the urine from the blood.
- Excretion: The final urine is stored in the bladder and expelled through the urethra.

Importance of the Excretory System
- Homeostasis: Helps maintain the balance of fluids and electrolytes in the body.
- Detoxification: Eliminates harmful substances and toxins from the bloodstream.
- Acid-Base Balance: Regulates blood pH by excreting hydrogen ions and reabsorbing bicarbonate.
Understanding the human excretory system is fundamental for comprehending how the body functions and maintains health.