Urine is produced and excreted by the kidneys in several steps. Here are the main processes of urine production:
Filtration (glomerular filtration): The production of urine first occurs in the glomerular part. Blood passes through the glomeruli's filtering unit, which includes the filtration membrane on the blood vessel wall and the glomerular lumen. Here, water, waste products, salts, and some ions like sodium, potassium, and chloride in the blood are filtered into a space called glomerular filtrate.
Reabsorption: Tubules are long, thin tubes that connect to the glomeruli and extend deep into the kidneys. In the renal tubules, the filtered fluid is transported through multiple segments, in which a large amount of reabsorption of the substance takes place. For example, nutrients, water, and other substances useful to the body in the blood are reabsorbed back into the bloodstream for the body to use.
Secretion: In addition to filtration and reabsorption, the renal tubules also function as secreting substances. Some waste products, drugs, and other substances, such as acidic metabolites and certain drugs, can be actively secreted into the urine by tubular cells to remove excess or harmful substances from the body.
Concentration and dilution: In the renal tubules of the descending segment, urine can be further concentrated or diluted depending on the body's needs. Depending on the amount of water you drink and the balance of fluids in your body, the concentration of your urine can be adjusted to maintain a balance of water in your body.
Delivery: The renal tubules eventually transport the treated urine into the collecting ducts, which then transport it through the ureters to the bladder. Once the bladder is full, urine is excreted through the urethra.
Each step in this process is accomplished through complex physiological mechanisms and the regulation of kidney structure. Through the process of urine formation in the kidneys, the body can eliminate metabolic wastes, regulate fluid balance, and maintain the normal operation of various physiological activities.
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