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Urination is the release of urine from the bladder to the outside of the body. Urine is released through the urethra and exits the penis or vulva through the urinary meatus in placental mammals, [1] [2]: 38, 364 but is released through the cloaca in other vertebrates.
Following filtration of blood and further processing, wastes (in the form of urine) exit the kidney via the ureters, tubes made of smooth muscle fibres that propel urine towards the urinary bladder, where it is stored and subsequently expelled through the urethra during urination. The female and male urinary system are very similar, differing ...
Sample of human urine. Urine is a liquid by-product of metabolism in humans and in many other animals. In placental mammals, urine flows from the kidneys through the ureters to the urinary bladder and exits the urethra through the penis or vulva during urination.
During urination, parasympathetic pelvic splanchnic nerves act primarily on postganglionic M 3 receptors to cause contraction of the detrusor muscle. [ 1 ] [ 2 ] [ 3 ] At other times, the muscle is kept relaxed via sympathetic branches from the inferior hypogastric plexus to allow the bladder to fill.
The internal urethral sphincter is a urethral sphincter muscle which constricts the internal urethral orifice.It is located at the junction of the urethra with the urinary bladder and is continuous with the detrusor muscle, [1] [2] but anatomically and functionally fully independent from it. [3]
Reabsorption is a two-step process beginning with the active or passive extraction of substances from the tubule fluid into the renal interstitium (the connective tissue that surrounds the nephrons), and then the transport of these substances from the interstitium into the bloodstream.
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Excretion is elimination of metabolic waste, which is an essential process in all organisms. In vertebrates, this is primarily carried out by the lungs, kidneys, and skin. [1] This is in contrast with secretion, where the substance may have specific tasks after leaving the cell.