What is the difference between urine and filtrate

Further bulk reabsorption of sodium occurs in the loop of Henle. Regulated reabsorption, in which hormones control the rate of transport of sodium and water depending on systemic conditions, takes place in the distal tubule and collecting duct. Even after filtration has occured, the tubules continue to secrete additional substances into the tubular fluid. This enhances the kidney's ability to eliminate certain wastes and toxins.

Renin-angiotensin mechanism — triggered by the juxtaglomerular apparatus; when filtration rate decreases, the enzyme renin is released. Renin converts a plasma protein called angiotensinogen into angiotensin I.

Angiotensin I is quickly converted into angiotensin II by another enzyme. Angiotensin II causes 3 changes:. Secretion — waste products such as urea and uric acid, drugs and hydrogen and bicarbonate ions are move out of the peritubular capillaries into the filtrate; this removes unwanted wastes and helps regulate pH.

The volume of filtrate formed by both kidneys per minute is termed the glomerular filtration rate GFR. The heart pumps about 5 L blood per min under resting conditions. Approximately 20 percent or one liter enters the kidneys to be filtered. Ninety-nine percent of this filtrate is returned to the circulation by reabsorption so that only about 1—2 liters of urine are produced per day.

If a person has a hematocrit of 45, then the renal plasma flow is 55 percent. It is the renal plasma flow times the fraction that enters the renal capsule 19 percent. It is the GFR times the fraction of the filtrate that is not reabsorbed 0. Recall that filtration occurs as pressure forces fluid and solutes through a semipermeable barrier with the solute movement constrained by particle size. Hydrostatic pressure is the pressure produced by a fluid against a surface.

If you have a fluid on both sides of a barrier, both fluids exert a pressure in opposing directions. Net fluid movement will be in the direction of the lower pressure.

Osmosis is the movement of solvent water across a membrane that is impermeable to a solute in the solution. This creates a pressure, osmotic pressure, which will exist until the solute concentration is the same on both sides of a semipermeable membrane. Urinary System Structures. Give It Up for the Kidneys. Urine Storage and Elimination. Common Diseases and Disorders. When you select "Subscribe" you will start receiving our email newsletter. Use the links at the bottom of any email to manage the type of emails you receive or to unsubscribe.

See our privacy policy for additional details. Learn Site. The Glomerulus Filters Water and Other Substances from the Bloodstream Each kidney contains over 1 million tiny structures called nephrons. Get our awesome anatomy emails! Besides, it contains electrolytes including sodium, potassium, chloride, and bicarbonate.

Urine is the yellowish color fluid formed as a result of the kidney function. The three steps in the formation of urine in the kidney include filtration, reabsorption, and secretion. Filtration step, which forms the glomerular filtrate, is described in the above section. Reabsorption is the second step involved in the re-uptake of water, small molecules, and ions into the circulatory system. It occurs at the proximal and distal convoluted tubules , the loop of Henle, and the collecting duct.

Moreover, the osmolarity of the filtrate changes as a result of reabsorption. The final step of the urine formation is the secretion; this involves secretion of some molecules including creatinine, drugs, and hydrogen ions into the filtrate at the proximal and distal convoluted tubules. Also, it contains urea 9.