Filtration

Filtrate Formation and Modification: Processes

Involve in urine formation: several processes are involved in formation of filtrate and urine

Filtrate Formation:

-Filtration: blood fluid fenestration -> sending things out into nephron
-Reabsorption: taking things back that had been in _____(______)
-Secretion: take things from ___, but into____. Independent of filtration
-Excretion: waste we are talking about/ leaving system

-nephron

-the blood (glucose and ions)

- blood, filtrate

Tubular transport maximum (Tm)

Maximum rate at which a substance can be reabsorbed

Proximal Tubule Reabsorption and Secretion: Area of tubule that is close to glomerulus: take back into ____ what we but out during ______( ______ )
-not always happening with simple diffusion. May need a _____ (saturated)

- circulation, filtration

-(bicarbonate, glucose, nutrients)

-transported

Distal tubule reabsorption and secretion

FINE TUNES

Reabsorbs: Na+, Cl-, Ca2+

Secretion: K+, H+

Collecting duct reabsorption and secretion

BULK RETURN

Reabsorbes: water and urea

Secretion or reabsorption: H+, HCO3 - Na+, K+

Collecting duct reabsorption and secretion: Production of dilute urine

• Late distal tubule and collecting duct not reabsorbing H2O 

• Occurs when extracellular H2O is high (excess fluid)

• Ions still absorbed as needed along way

_______ contributes to concentrating urine

Countercurrent Mechanism

Production of dilute urine

-Start at 300, go down and it gets __________, come back up numbers go down
- Whats happening?: water is ____ as we go down (more conc), back up= no water moving but do see ______ (________)
-If take things out of solution (_____)
-Get to distal tubules, number ___ further because more water _____

-more concentrated

- coming out

-ion movement (active transport process)

-more dilute

-drops, leaves

Countercurrent mechanism contributes to concentrating urine: Where

-Nephron loop

-Uses energy (ATP) to create osmotic gradient 

-Driving water reabsorption

Countercurrent mechanism contributes to concentrating urine: Thick ascending limb

• Na+/k+/2Cl- symporter

• NaCl pumped out of filtrate

• interstitial fluid osmolarity increased

Countercurrent mechanism contributes to concentrating urine: Thin descending limb

• Freely permeable to H2O 

• High interstitial osmolarity (NaCl and Urea) draw H2O out

-Filtrate becomes _______ as it approaches bottom of nephron loop and _______ in the ascending limb

-High NaCl concentration in filtrate ____ symporter activity

-Symporter activity causes filtrate to become ______ as it ascends

-More activity near ____ and less as ascend the limb and NaCl _____ in filtrate

- more concentrated and less concentrated

-increases

-more dilute

-bottom and decreases

Medullary collecting duct and urea recycling contribute to

osmotic gradient

_____ contributes to interstitial osmolarity

Urea

-Urea _____ moves out of collecting duct (30-50% remains in filtrate and is excreted)

-Urea entering interstitium is_____ (maintains osmolarity); _____ highly involved

-passively

- recycled and Vasa recta

_____ is necessary to produce concentrated urine: Water moves according to gradient

Osmotic gradient

_____ and ______ maintain medullary osmotic gradient

Vasa recta and countercurrent exchange

Straight capillary bed surrounding nephron loop and collecting duct

Vasa Recta

Countercurrent exchange…

-H2O and NaCl exchanged between nephron loop, interstitial fluid, and  blood in vasa recta

-Sequence maintains interstitial osmolarity

-Drains into peritubular capillaires

Why are capillaries around the loop and collecting duct advantageous? How? Result?

arrangements maintains interstitial osmolality at the same time that we are taking water away
How? As blood goes to medulla (opposite way of filtrate) it gets concentrated, go around loop (water is going out) pick up water and getting back to NaCl.
End Result: reclaimed water and most of salt back