Renal Physiology - LoH & Vasa Recta

Loop of Henle - Descending Limb

We are trying to generate a hyperosmolar environement in the intersitial space.
When the filtrate moves into BS and through the proximal convoluted tubule, the rate of absorption for Na and water is proportional.
As a result, when the filtrate comes to the last portion of the proximal tubule, the osmolarity of the filtrate is actually the same as the substances in the filtrate.
- ~300mOsm; the osmolarity of plasma (physiological osmolarity).

Loop of Henle - Ascending Limb

Active transport occurs; Na is reabsorbed going from the lumen into the interstitial space.
Na is followed by Cl- which also moves out.
NaCl is added to the interstitial space. As a result, osmolarity of the interstitial space increases to ~400mOSm.
Mo movement of water. This allows NaCl to build up in the interstitial space.
- Hyperosmotic.

Net Result: gradient difference (Between interstitial space and ascending limb) of 200 mOsm created.

Descending Limb of the Loop of Henle

When the fluid @ 300mOsm moves fown the descending loop, movement of water out of the descending loop occurs.
If water is leaving the descending tubules, this causes a local decrease in the solute conc in the tubule lumen.
As a result, te osmolarity increases to 400mOsm because water is leaving the lumen.
The water will leave the tubule up to the point where diffusional equalibrium is reached.
Diffusional equailibirum will occur when the osmolarity in the tubule lumen & the osmolarity in the space + surroundigns comes to the same #. This # is 400mOsm in the desceding limb & intersistual space.
Net movemtn of water occurs out f the descending limb, and the ascending limb pump out solute or NaCl.
As the fludi is moving down, a hyperosmotic gradient is created in the intersitital space.
The difference in osmolarity from the asednding to descending limb in is ~200mOsm.
The ascending limb is not permeable to water but solute is able to leave, starts off the whole process.
Achievement of a hyperosmolar interstitial environment.

The fluid is flowing in two opposite directions int eh two limbs of the LoH.
In the descending limb, the osmolarity starts off at 300mOsm. When water moves out of the descednign limb, the osmolarity changes to 400mOsm.
As the fluid flows down, mpore water flows out in the descending limb.
The highest osmolarity is reached at the hairpin loop.
What is also being created is the multiplication of that gradient in the interssitial space.

Multiplication:

As fluid moves down the loop, the graidnet is multiplied.
At the bottom, it is very hyperosmolar.
A hyperosmolar gradient is created, such that when fluid reaches the collecting duct, the duct, whvih is under the influence of ADH, can reabsrob as much water in the intersistial space as possible.
ADH acts to conserve water.
Multiplicaton of gradient down the length of the loop of Henle. This mechanism is called counter-current multiplier.

COunter-Current Multiplier:

Flow Along the Loop and Beyond

Fluid becomes concentrated fluid in the descending limb
Dilutes fluid again as it climbs up the ascending limb and enters the distal tubule.
- Distal convoluted tubule has very dilute fluid 100 mOsm/L → the fluid is hypoosmotic compared to our normal plasma osmolarity. In the distal convoluted tubule there are no aquaporins and Na+ + Cl- are still being pumped out → very hyperosmolar.
- ADH works on the collecting duct and fluid inside the tubule becomes isoosmotic with the interstitial space (300 mOsm/L)
- More water is reabsorbed from the cortical collecting duct due to ADH effect
The high osmolarity gradient that is established in the interstitial space helps the water to permeate out of the medullary collecting tubule.
Osmolar gradient created in the intersistial space.
THe juxtamedullary nephrons the hyperosmolar gradient and have the vasa recta around them.
Capillaries take up the water and remove it through the renal vein.
Urine concentration depends on the temp of surroundings, humidity, and hydration.

Water Conservation:

Beaver → does not have to conserve much water in its body for survival. They are surrounded by water.
Human → conserve water as much as possible before it escapes via the collecting duct.
Camel rat → live in dry, hot conditions. Pelleted urine; conserves most of the water in their body. Also has a countercurrent hairpin loop system.

Vasa Recta

PURPLE

The hyperosmotic gradient allows water to be drawn.
- The juxtamedullary type creates the gradient.
Whatever gradient is established by the inflow and outflow assult into the nephron tubules.
The vasa recta creates loop-like circles at each gradient level. By doing so, it maintains the self-gradient that the nephrons have created.

NAVY BLUE:

As a result of diffusion of Na + Cl into the BVs and the diffusion of water out of the vessel, the osmolarity of the lood will increase.
- Occurs at the expense of the intersitital gradent, washing it away.
The hyperosmolarity would eb washed out into the blood.

LIGHT PINK:

The blood in the vasa recta flows in the opposte direction of the fluid in the nephron.
It runs parallel.

DARK PINK - definition of the vasa recta:

Is permeable to solutes and water.
When filtrate is mvoing from the proximal tubule into the descending limb of the LoH @ an osmolarity of 300mOSm, water moves out (descending loop).
Water goes into the interstitial space into the ascending limb of the vasa recta.

LAVENDER:

On the other hand, NaCl moves out of he ascending limb of the LoH.
- Active transport against the gradient.
Some of the sat will enter the vasa recta as the blood is flowing into it.
The osmolarity of blood is around ~300mOsm when it is entering the vasa recta.
Salt creates a low → hgih gradient.
At the bottom, the osmolarity is the highest (~1200mOsm).

LIGHT BLUE:

In the descending limb of the vasa recta, salt enters but water exits.
At each level, there are small little mini circuits where water comes in and salt goes out fo the vasa recta.
Maintains the gradient that was created.