How much original filtrate becomes urine

Intuitively, you should realize that minor changes in osmolarity of the blood or changes in capillary blood pressure result in major changes in the amount of filtrate formed at any given point in time. The kidney is able to cope with a wide range of blood pressures. In large part, this is due to the autoregulatory nature of smooth muscle. When you stretch it, it contracts. Thus, when blood pressure goes up, smooth muscle in the afferent capillaries contracts to limit any increase in blood flow and filtration rate.

When blood pressure drops, the same capillaries relax to maintain blood flow and filtration rate. The net result is a relatively steady flow of blood into the glomerulus and a relatively steady filtration rate in spite of significant systemic blood pressure changes. One third of this is 10, and when you add this to the diastolic pressure of 80, you arrive at a calculated mean arterial pressure of 90 mm Hg. Therefore, if you use mean arterial pressure for the GBHP in the formula for calculating NFP, you can determine that as long as mean arterial pressure is above approximately 60 mm Hg, the pressure will be adequate to maintain glomerular filtration.

Blood pressures below this level will impair renal function and cause systemic disorders that are severe enough to threaten survival. This condition is called shock. This is more than just an academic exercise. Since many drugs are excreted in the urine, a decline in renal function can lead to toxic accumulations. Additionally, administration of appropriate drug dosages for those drugs primarily excreted by the kidney requires an accurate assessment of GFR.

GFR can be estimated closely by intravenous administration of inulin. Inulin is a plant polysaccharide that is neither reabsorbed nor secreted by the kidney. Its appearance in the urine is directly proportional to the rate at which it is filtered by the renal corpuscle.

However, since measuring inulin clearance is cumbersome in the clinical setting, most often, the GFR is estimated by measuring naturally occurring creatinine, a protein-derived molecule produced by muscle metabolism that is not reabsorbed and only slightly secreted by the nephron. The entire volume of the blood is filtered through the kidneys about times per day, and 99 percent of the water filtered is recovered.

The GFR is influenced by hydrostatic pressure and colloid osmotic pressure. Under normal circumstances, hydrostatic pressure is significantly greater and filtration occurs. The hydrostatic pressure of the glomerulus depends on systemic blood pressure, autoregulatory mechanisms, sympathetic nervous activity, and paracrine hormones.

The kidney can function normally under a wide range of blood pressures due to the autoregulatory nature of smooth muscle. Answer the question s below to see how well you understand the topics covered in the previous section. 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.

As long as the concentration differs, water will move. There is also an opposing force, the osmotic pressure, which is typically higher in the glomerular capillary.

To understand why this is so, look more closely at the microenvironment on either side of the filtration membrane. Recall that cells and the medium-to-large proteins cannot pass between the podocyte processes or through the fenestrations of the capillary endothelial cells. This means that red and white blood cells, platelets, albumins, and other proteins too large to pass through the filter remain in the capillary, creating an average colloid osmotic pressure of 30 mm Hg within the capillary.

Hydrostatic fluid pressure is sufficient to push water through the membrane despite the osmotic pressure working against it. The sum of all of the influences, both osmotic and hydrostatic, results in a net filtration pressure NFP of about 10 mm Hg. A proper concentration of solutes in the blood is important in maintaining osmotic pressure both in the glomerulus and systemically.

There are disorders in which too much protein passes through the filtration slits into the kidney filtrate. This excess protein in the filtrate leads to a deficiency of circulating plasma proteins. In turn, the presence of protein in the urine increases its osmolarity; this holds more water in the filtrate and results in an increase in urine volume. Because there is less circulating protein, principally albumin, the osmotic pressure of the blood falls.

Less osmotic pressure pulling water into the capillaries tips the balance towards hydrostatic pressure, which tends to push it out of the capillaries. The net effect is that water is lost from the circulation to interstitial tissues and cells.

As you can see, there is a low net pressure across the filtration membrane. Intuitively, you should realize that minor changes in osmolarity of the blood or changes in capillary blood pressure result in major changes in the amount of filtrate formed at any given point in time.

The fluid that remains in the nephron after filtration is called the filtrate. The filtrate enters the proximal tubule. Glucose, amino acids, and water are secreted released into bloodstream. The filtrate begins to darken with less water in it. The filtrate then moves on to the Loop of Henle. On descent, water leaves the filtrate by osmosis and on ascent; sodium and chloride leave the filtrate by active transport.

This is necessary to produce concentrated urine. The loop of henle becomes less permeable as it goes ascends so less sodium and chloride leave the filtrate as the filtrate makes its way up the loop. The filtrate then moves on to the Distal Tubule where pH is regulated and sodium potassium, and calcium levels are controlled. The filtrate becomes more concentrated here. The filtrate then moves into the Collecting Duct. The collecting duct is what connects the nephrons to the ureter.

It participates in electrolyte and fluid balance through reabsorption and excretion. I did this for a Grade 12 Biology lab so this is just a collection of stuff I got off the internet from various good sources! Log in. Urinary System. See Answer. Best Answer. Study guides. Q: What percent of filtrate becomes urine? Write your answer Related questions. Where does filtrate become urine? What is the function of a glomerulus? What is a major difference between filtrate in the nephron and urine leaving the bladder?

Difference between filtrate and urine? The filtrate within the nephron becomes urine only when it passes through the distal convoluted tubules and enters the collecting ducts? WhaT is the difference between filtrate and urine?