Urine is formed through a series of processes that occur in the kidneys.
1. Filtration: Blood flows into the kidneys through the renal arteries, which carry waste materials and excess substances. Inside the kidneys, the blood enters the nephrons, the functional units of the kidneys. Within these units, there are small blood vessels called glomerulus and tiny tubes known as tubules. As the blood passes through the glomerulus, water, waste products, and small molecules like salts, glucose, and amino acids are filtered out of the blood into the tubules. This process is called filtration.
2. Reabsorption: After filtration, the filtrate, which contains the waste products and useful substances, moves through the tubules. Along the tubules, the body's vital substances such as water, glucose, amino acids, and electrolytes are reabsorbed back into the bloodstream. Reabsorption takes place through the walls of the tubules, which selectively reabsorb the required substances.
3. Secretion: In addition to filtration and reabsorption, the tubules also play a role in secreting waste products that were not filtered out initially. Substances like drugs, toxins, and excess ions are secreted into the tubules from the blood vessels surrounding them. This secretion process helps in removing additional waste products from the body.
4. Concentration: As the filtrate passes through the tubules, the amount of water and certain substances are adjusted based on the body's needs. The walls of the tubules are permeable to water and certain ions, allowing them to move freely. The movement of water out of the filtrate and back into the bloodstream helps in concentrating the urine.
5. Collection: Once the filtrate has passed through the tubules, it is now referred to as urine. The urine is collected in the renal pelvis, a funnel-shaped structure in the kidney base, where it gathers before passing down the ureters into the bladder. From the bladder, urine is eventually eliminated from the body through the urethra during urination.
It is important to note that the process of urine formation is complex and involves various mechanisms in order to maintain the body's fluid balance, pH balance, and excrete waste materials efficiently.
Describe how urine is formed
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