Process of urine formation
Process of urine formation can be divided in to three sub processes.
1. Pressure Filtration
Arterial blood comes to the glomerulus with pressure exerted by the pumping of blood by the heart. This blood while passing through glomerulus is filtered into Bowman's capsule. Blood is filtered here because walls of the glomerulus are porous, and the fraction of the blood pressure reaching here provides the filtration pressure. This filtrate collected in glomerulus is called as glomerular filtrate. Every thing which is smaller than the pores of the glomerulus is filtered out of the blood. Generally blood cells and plasma proteins are not filtered out whereas water and dissolved salts, sugar, medicines and nitrogenous wastes are filtered out of the glomerulus into the Bowmann's capsule. From here they enter the next part the renal tubule. As many useful substance such as glucose, amino acids, salts etc are still present in Bowmann's filtrate in aqueous solution therefore , absorption of these materials along with a lot of water is done in the urinary tubule.
Internal structure of human kidney
2. Reabsorption
All the useful constituents of the glomerular filtrate are reabsorbed into the blood, in the proximal convoluted tubules and loop of Henle. These include water , nutrients, glucose , amino acids and salts like NACL. When filtrate leaves proximal tubules, it mostly contains nitrogenous wastes.
Process of urine formation
1. Pressure Filtration
Arterial blood comes to the glomerulus with pressure exerted by the pumping of blood by the heart. This blood while passing through glomerulus is filtered into Bowman's capsule. Blood is filtered here because walls of the glomerulus are porous, and the fraction of the blood pressure reaching here provides the filtration pressure. This filtrate collected in glomerulus is called as glomerular filtrate. Every thing which is smaller than the pores of the glomerulus is filtered out of the blood. Generally blood cells and plasma proteins are not filtered out whereas water and dissolved salts, sugar, medicines and nitrogenous wastes are filtered out of the glomerulus into the Bowmann's capsule. From here they enter the next part the renal tubule. As many useful substance such as glucose, amino acids, salts etc are still present in Bowmann's filtrate in aqueous solution therefore , absorption of these materials along with a lot of water is done in the urinary tubule.
Internal structure of human kidney
2. Reabsorption
All the useful constituents of the glomerular filtrate are reabsorbed into the blood, in the proximal convoluted tubules and loop of Henle. These include water , nutrients, glucose , amino acids and salts like NACL. When filtrate leaves proximal tubules, it mostly contains nitrogenous wastes.
Process of urine formation
3. Tubular secretion
The tubular epithelium also secretes substances into its lumen (cavity). This secretion mainly contains hydrogen ions to balance PH value of the filtrate passing through the tubule, ammonium ions and drugs.
Following filtration of blood and further processing through tubular system urine is produced which is collected in the central cavity of the kidney, the pelvis. Urine leaves the kidney through ureter. The ureters of both the kidneys drain into urinary bladder through uretheral orifice. Urine leaves the body, during urination, from the bladder through urethera , which empties near the vagina in females or through the penis in males. A ring of Sphincter muscles near the junction of the urethra and the urinary bladder controls the urine in bladder. When about 300 to 400 ml urine is collected in the bladder , we need to discharge it. In babies this sphincter is not developed properly hence they are not able to control their urination.
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