Today we learned in biology a subject on the physiology of the urinary system. The process of urine out of the body can be divided into two stages: at first, brought about by urine accumulates ureters into the bladder, to fill it, then urination occurs, ie the complete emptying of the bladder, with the elimination of urine through of the urethra. The urine is accumulated for a bladder muscle present in the ring junction of the bladder to the urethra, urethral sphincter, remains contracted preventing its exit. On the wall of the urethra are also contracting muscles and prevent the passage of urine.When the bladder becomes full, recepetores nervous on your wall are stimulated and transmit the information to the brain, which causes the urge to urinate.Who one day ever wondered, why is urine yellow? Here is the answer to your question: "The yellow color of urine is due to the presence of a substance called urobilin, obtained mainly from the degradation of hemoglobin from red blood cells. In the spleen and liver, mainly macrophages phagocytize old erythrocytes, with more 120 days of life, and digest their components into the blood by excreting bilirubin, a degradation product of hemoglobin. Bilirubin is extracted from the blood by the liver and excreted in the bile. Bile is released into the duodenum. intestinal bacteria tranformam bilirubin in urobilinogen, most of which about 80%, remains in the intestine, where it is oxidized and causes a substance to brown color estercobilina, responsible for the color feature faeces. About 20% of urobilinogen present in the gut are reabsorbed by the cells intestine and released into the blood. The liver captures most of this urobilinogen and reexcreta it to the bile. But a small portion escapes absorption by the liver and absorbed by the kidneys and released into the urine. So urobilinogen urubilina is oxidized in the urine which is initially colorless, becomes yellow.
By: Jullyane Renata.