L12 Loop of Henle and Urine Concentration

At the proximal tubule, how much % of urea is reabsorbed and how?

50% of urea is reabsorbed via passive paracellular diffusion.

What is the role of urea in the medullary osmotic gradient? Where and how does urea become concentrated?

Creates the medullary osmotic gradiet. As water leaves the cortical and outer medullary collecting ducts under the influence of ADH, urea becomes concentrated in the lumen of these segments since urea is impermeable here.

What are three factors that can increase the release of ADH from the posterior pituitary gland?

Decreased Arterial Pressure, Increased Angiotensin II, Increase Plasma osmolality

What does the descending limb of the loop of henle do to certain substances? Na+? Cl-? H2O?

Does not reabsorb/impermeable to Na+ and Cl- Reabsorbs/permeable to H2O water.

From where to where does the Loop of Henle extend from?

From the cortex to the medulla

AntiDiuretic Hormone (ADH) how is it affected with the renin/ angiotenin II release?

Increased in renin/angiontensin II will lead to an increase in ADH and aldosterone with the net effect of increased both Na+ and water reabsorption.

How can the collecting duct system be divided?

Into 3 segments: cortical, outer medullary, inner medullary.

What is the thick ascending loop impermeable to? How does it function then?

It is impermeable to water, sodium, chloride and urea. However a large amount of Na+ and Cl-, K+ due leave via a large quality of NCC ion channels, Na+, K+, 2cl- co transporters. There is increased pumping of Na+ and Cl- from the tubular cell into the interstitium via the sodium-potassium ATPase, cl- channel, K+ also does too via cl-/K+ co transporter found on the basolateral membrane.

What is the role of the Vasa Recta for concentrated urea?

Located near the Loop of Henle. Preserves osmotic gradient. Supplies oxygen and nutrients. Will remove CO2, metabolic wastes(urea) and water from the descending limb.

Species comparison of kidney structure and urine concentrating ability. Does having a high maximum urine concentration correlate to a larger percentage of looped nephrons?

No. eventhough jerboa has high urine concentration, their percentage of loop nephrons are low. So no the number of loop nephrons does not determine the amount of urine concentration made by a species.

AntiDiuretic Hormone (ADH). What type of hormone? What are the steps to get it into circulation? What is its function in relation to reabsorption?

Octapeptide (neuropeptide hormone). It is synthesized by the hypothalmus and released by the posterior pituitary. The function of ADH is to increase water reabsorption (Aquaporins2 on lumen) --recall there is aquaporins 3/4 on basolateral so water is being reabsorbed but with ADH you are increasing the amount of water reabsorbed into the tubule. in the distal tubules and collecting ducts.

AntiDiuretic Hormone (ADH) how is it related to an increase in plasma alcohol?

Plasma Alcohol inhibits the release of ADH. There will be a decrease in ADH release therefore causing a dilute urine. Less water is being reabsorbed and more is excreted

Draw the chart showing relationship of the tubular segment with respect to percent of filtered load reabsorbed(%) of sodium and water respectively

Proximal Tubule: Na+ 65%, H2O 65%. Desending thin limb of loop of henle:sodium-, water 10%. Ascending thin and thick limb if loop of henle: Na+ 25% and water -. Distal Convulated tubule: Na+ 5%, water -. Collecting duct: Na+ 4-5%, water 5%

The distal tubule is permeable to? impermeable to? What hormone controls it?

Similar to thick ascending loop. Impermeable to Na+, Cl, urea or water. It has NCC on lumen to reabsorb Na+ and Cl- into tubule. Na+ reabsorbed into interstitium via Na/K+ ATPase, Cl- leaves by a channel too. Aldosterone will be released by the adrenal gland to control this.

If there is a decrease in plasma volume and arterial pressure. What will the atrial barorecptors do? How is this related to ADH (antidiuretic hormone?

The atrial baroreceptors will let the posterior pituitary to Increase ADH secretion --> and increased tubular permeability to water and increased water reabsorption. Therefore a decrease in water excretion.

The CounterCurrent Multiplier. Why countercurrent? Why multiplication? What are the key factors?

The creation of an osmotic gradient from the cortex to the tip of the papilla (ducts of belleni). Countercurrent because a tubule within a loop is required. Multiplaction because the loop structure allows the maximal osmotic gradient that one cell can generate to be multiplied into a larger gradiet ex. Na+ is actively being pumped out of thick ascending limb of LOH to be reabsorbed. This gradient is used by the collecting ducts under the influcence of ADH to control the amount of water that is excreted or reabsorbed. The key factors are the pumping of sodium chloride out of the thick ascending limb of the loop(which is the main energy source of the mechanism), the permeability of various segments and the loop structure itself.

What happens to urea when it reaches the inner medulla collecting ducts? What is it also influenced by?

The inner medulla collecting duct is permeable to urea so it will move into the interstitium. This permeability is under the influence of ADH. ADH will increase the number of urea transporters on the apical surface/lumen membrane of the inner medullary collecting ducts

What causes the urea to be concentrated in the collecting duct?

The pumping of sodium chloride in the thin acending limb, which ultimately leads to the concentrating of sodium and chloride in the inner medulla.

The thin ascending loop is permeable to? impermeable to?

The thin ascending loop is permeable to Na+,Cl-. Relatively impermeable to water. Virtually the osmolality of the thin ascending tubule is nearly the same as the surrounding interstitial fluid. The tubular fluid becomes more dilute.

AntiDiuretic Hormone (ADH) how is it affected with increased plasma osmolality (Osm/L)? Decreased plasma osmolality?

This will be sensed by the osmoreceptors and send a signal to the thirst center (CNS) and as a result increase intake of water. The osmoreceptors by sensing an increase plasma osmolality will also let the posterior pitutitary gland to release ADH (so increased release of ADH) and therefore increased H2O water reabsorption. With an excess water ingestion, ADH will be decreased and therefore decrease tubular premeability to water and decrease the amount of water being reabsorbed. This increases the water to be excreted.

What happens to the concentrated urea in the interstitium? What does it influence?

Thre urea will will cause water in the inner medulla to leave the descending limb since this segment is permeable to water but not na+ and cl-

At the Thin Descending limb, what is permeable here?

Urea and Water

At the thin and thick ascending limb, what is permeable or impermeable here? what is the percentage of urea entering the thick ascending limb of the amount filtered.

Urea is impermeable in both thin and thick ascending limb. The amount of urea entering the thick ascending limb is 110% of the amount filtered.

In the descending tubule, what substances and permeable? impermeable

Water and urea are permeable in the descending loop of henle. Impermeable: Na+, Cl-. Water will move from the wall of the lumen and into the interstitial because of high solute concentration in the interstitial. Virtually there will be about the same amount of solute in the tubular lumen and interstitial. Therefore, the solutes in the tubular lumen will become concentrated until it reaches the "bend" between descending and ascending tubules.

Urea contributes to the kidney's ability to excrete a _____. Is it freely filtered by glomerulus? What percentage of the filtered urea appears in the urine?

concentrated urine. Urea is freely filtered. 15-50% of filtered urea appears in the urine

Increased urine flow leads to ______

incresed excretion of urea

Cortical segment of the collecting duct in comparison to the outer medullary segment is?

it has a greater capacity to pump sodium and its rate of sodium pumping is more dependent on aldosterone.

What does the Vasa Recta and Countercurrent exchange do?

preserves osmotic gradient. supplies oxygen and nutrients. removes co2 and metabolic wastes. removes water that enters the interstitium from the descending limb.

Cortical and Medullary collecting ducts are relatively impermeable to?

sodium, chloride and urea. However both collecting duct segments are capable of pumping sodium via Na+/K+ ATPase from principal cell. Cl- leave with H+ from intercalated B cell. So we have Na+Cl- Reabsorption.

What effect does aldosterone have on the distal tubule?

the higher the concentration of aldosterone in the plasma, the more active pumping of sodium will be from the lumen of the distal tubule.

Urea permeability of the inner medullary collecting duct is dependent upon?

urea transporters with apical pemeability controlled by ADH