Physiology Unit 5 Unregulated Reabsorption

What kind of filtrate enters the PCT from the renal capsule?

isosmotic

What does the PCT reabsorb?

water and NaCl

What percent of glomerular filtrate is reabsorbed in the PCT?

65%

Is the filtrate volume significantly increased or reduced in the PCT?

significantly reduced

Is it necessary for the descending and ascending limbs of the nephron loops to be in very close proximity to one another?

yes, they must be close for the limbs to interact with one another, allows for the countercurrent multiplier system

Does the nephron loop have to cross into the renal medulla?

yes

What is the mOsm of interstitial fluid entering the the ascending nephron loop?

1200mOsm

Can NaCl enter or exit the descending limb of the nephron loop?

no, it is impermeable

Is the descending limb of the nephron limb permeable to water and if it is how?

yes, simple diffusion

How does the mOsm increase the further down the descending nephron loop you go?

water is leaving through simple diffusion

What is the mOsm entering the descending limb of the nephron loop?

300mOsm

What is the situation at the tip of the U in the nephron loop?

isosmotic

What drives water out of the descending limb of the nephron loop?

high osmotic pressure

The ascending limb of the nephron loop is impermeable to what?

water

What is transported out of the lumen in the ascending limb?

NaCl

How is Na+ transported into the interstitial fluid in the ascending limb of the nephron loop?

Na+/K+ pump

What do the sodium potassium pumps in the ascending limb establish?

Na+ gradient

Because of the Na+ concentration gradient being created by the Na+/K+ pump, what moves down the electrochemical gradient from the filtrate into cells to combat this?

Na+

When Na+ moves down the electrochemical gradient into the cells because of the concentration gradient, what else does it pump into the cell and how?

K+ and 2Cl- into the cell via secondary active transport

In the ascending limb, when K+ and 2Cl- are brought into the cells from the filtrate is this against or with their gradient?

against

What leaves the cells of the ascending limb of the nephron loop and goes into the interstitial space by going down the concentration gradient?

Cl- and K+ through passive transport

What is the change in filtrate from the beginning to the end of the ascending loop of the nephron?

1200mOsm to 100mOsm

Is the 100mOsm fitrate hypotonic or hypertonic to plasma at the end of the ascending limb?

hypotonic, plamsa mOsm is 300

Does the ascending limb make the interstitial fluid more concentrated or more diluted?

more concentrated

Does the NaCl that is transported into the interstitial fluid from the ascending limb then diffuse into capillaries, if not what does it do?

no, it accumulates in the medulla

Why does NaCl not diffuse into capillaries after leaving the ascending limb?

it is necessary for the function of the descending limb and even more important for the function of collecting ducts

Countercurrent multiplication talks about the effects upon what?

the filtrate

The countercurrent exchange is talking about what?

the interstitial fluid and what is happening in the blood

What is the order of the positive feedback loop mechanism formed by the nephron loop?

NaCl extruded by ascending limb, higher interstitial mOsm, more water leaving descending limb, more concentrated filtrate (NaCl) entering ascending limb

The positive feedback loop mechanism in the nephron loop continues until what?

salt in the medulla reaches its maximum concentration

Does NaCl exit the thin segment of the descending limb?

no

Urea is a waste product of the metabolism of what?

amino acids

Where is the highest concentration of urea?

inner medulla

Urea is passively transported out of what and then goes into what by what mechanism?

terminal portion of collecting ducts, goes into the inner medulla by countercurrent exchange

What does urea help to do in the ascending limb?

increases interstitial fluid concentration in region of the thin segment

Where are the descending vessels of the vasa recta?

next to the descending limb

What is the ascending vasa recta next to?

ascending limb of the nephron

All of the vasa recta is permeable to what?

water, salt, and urea

What does the vasa recta prevent the loss of within the medulla through countercurrent exchange?

hypertonicity

What does the vasa recta express?

urea transporters and aquaporins

What does preventing loss of hypertonicity mean?

NaCl and urea are trapped within the system of the descending and ascending limbs and vasa rectas to let water out

Is countercurrent exchange the blood vessels or the lumen?

blood vessels

What is the order of solute concentration in the countercurrent excahnge?

ascending vessels > interstitial fluid > descending vessels

Where does NaCl move in countercurrent exchange?

from the ascending vasa recta to the interstitial fluid to the descending vasa recta

Does osmotic pressure in descending vessels drive water into or out of the vessels?

out of the vessels

Why is water being pulled out of the descending blood vessels in countercurrent exchange?

the blood in the inner medulla is more concentrated

What does the osmotic pressure in the ascending vessels of the vasa recta do to water?

drives water into the vessels

Does NaCl and urea enter or exit the ascending vessels of the vasa recta?

exit

The higher up you go in the ascending vessels does the blood become more dilute or concentrated?

more dilute

What is the osmolality before the beginning of the ascending vasa recta?

1200

What osmolality does the blood in the ascending vasa recta need to be at the end?

300mOsm

When is an isosmotic environment created between the blood vessels, interstitial fluid, and nephron loop?

at the tip of the U

What is the goal of countercurrent exchange?

to reduce the volume of the filtrate to make urine as concentrated as possible

How much of filtrate is reabsorbed in the PCT?

65%

How much filtrate is reabsorbed in the nephron loop?

20%

What percent of Na+ and K+ is reabsorbed in the PCT and nephron loop?

90%

What percent of the total body caloric expenditure is used to make urine?

6%

All of the processes in the PCT and nephron loop are what?

unregulated, can be super hydrated or super dehydrated and nothing changes

1 molal = ?

1 mole of solute dissolved in 1 kg of water

What is the movement of molecules through passive transport?

molecules require selective channel to cross membrane. flow down concentration gradient, no energy cost

What is cotransporter passive transport?

2 molecules moving through 1 channel in the same direction

What is antiporter passive transport?

2 molecules moving through 1 channel in opposite directions

What happens during secondary active transport?

one molecule moves down its concentration gradient which pumps the 2nd molecule against its gradient