The excretory system plays role in maintaining homeostasis by removing waste products and excess substances from the body, ensuring the proper balance of water, salts, and other solutes.
The kidneys are the primary organs of this system, and within each kidney, millions of tiny structures called nephrons act as functional units responsible for filtering blood and producing urine. Nephrons carry out this process through glomerular filtration, selective reabsorption and secretion, facilitated by their distinct structures.
The nephron consists of several key parts, each contributing to the production of urine. The process begins at the glomerulus, a network of capillaries where blood filtration occurs. Blood pressure forces water, ions, glucose, amino acids and waste products through the capillary walls while retaining larger molecules like proteins and blood cells. The filtrate is then collected by the Bowman’s Capsule, a cup-like structure that surrounds the glomerulus, directing the filtrate into the proximal tubule for further processing.
The proximal tubule is the first section of the nephron tubule where selective reabsorption of essential substances such as glucose, amino acids and a significant portion of water and sodium occurs. The filtrate then moves into the Loop of Henle, a U-shaped structure extending into the kidney’s medulla that plays a crucial role in water and salt balance. Here, the descending limb reabsorbs water, while the ascending limb reabsorbs sodium and chloride ions, concentrating the filtrate and conserving water.
The filtrate then passes through the distal tubule, where further selective reabsorption and secretion occur, allowing the fine-tuning of sodium, calcium and water reabsorption, and the secretion of additional wastes like potassium and hydrogen ions. Finally, the collecting duct gathers the filtrate from multiple nephrons, further concentrating urine by reabsorbing water under the influence of antidiuretic hormone (ADH), and transports the final urine to the renal pelvis for excretion.
