Reabsorption/Secretion in the Proximal Tubule

Question 1

How many times is the entire plasma filtered through the glomerulus every day?

Answer 1

60 times, equivalent to 5 times for whole body fluid

Question 2

What percentage of reabsorption of glomerular filtrate is absorbed through the proximal tubule?

Answer 2

2/3rd

Question 3

What is the primary role of the proximal tubule?

Answer 3

reabsorbtion of most of the filtered water and solutes

Question 4

What is the gold standard for mesasuring GFR?

Answer 4

Inulin

Question 5

Why is inulin the gold standard for measuring GFR?

Answer 5

It is neither reabsorbed or secreted in the tubules.

Question 6

Is reabsorption in the proximal tubule is iso-osmotic?

Answer 6

yes

Question 7

what are the major solutes that contribute to the isotonic reabsorption in the proximal tubule?

Answer 7

sodium, choride, bicarbonate

Question 8

Does the concetration of inulin decrease or increase compared to the distance from the glomerulus?

Answer 8

increase

Question 9

What absorption requires the most amount of energy?

Answer 9

sodium, using active transport, accounting for the majority of oxygen consumption in the kidney

Question 10

where does sodium reabsorption occur?

Answer 10

throughout the entire nephron,

Question 11

Is the concentration of sodium high or low in the tubular lumen, tubular epithelial cells and the renal interstitium?

Answer 11

high in tubular lumen
low in the tubular epithelial cells
high in the renal interstitium

Question 12

In the tubular epithelial cell, where is the only place the na/k atpase pump located?

Answer 12

on the basolateral membrane, near the renal interstitium

Question 13

what are the two results and overall purpose of the nka pump?

Answer 13

1. decrease the intracellular sodium conc.
2. decreased membrane potential

allows for the driving force for na absorption

Question 14

why does sodium flow through the apical membrane without energy?

Answer 14

it’s flowing down it’s electrochemical gradient

Question 15

the passive diffusion of sodium down it’s electrochemical gradient allows for what?

Answer 15

a passive, coupled transport of other solutes from the renal epithelial cell into the lumen for reabsorption. either through antiport or cotransport

Question 16

what is the only quantitatively important substance whose transport is directly coupled to metabolic energy in proximal tubule?

Answer 16

sodium, all others are secondarily related.

Question 17

what solutes are related to metabolic energy through secondary means?

Answer 17

bicarbonate, glucose, amino acids, organic acids

Question 18

Na reabsorption is coupled with an equivalent movement of what to allow ofor electroneutrality?

Answer 18

anions

Question 19

What drives the movement of chlorine out of the tubule?

Answer 19

the rapid na reabsorption leaves the lumen with a -5mv charge. This charge this pushes the chlorine into the renal interstitium.

Question 20

Explain the general idea behind a leaky epithelium of the proximal tubule.

Answer 20

it favors anion transport via paracellular space. leaky in the context of allowing more anions to move on purpose…

Question 21

In the straight proximal tubule, how does the absorption of chlorine change?

Answer 21

chlorine absorption is reduced.

Question 22

what is absorbed more rapidly within the straight proximal tubule than chlorine?

Answer 22

hco3-, outcompetes the chlorine

Question 23

What drives water reabsorption?

Answer 23

the osmotic gradient, facilitated by the lekay epithelium with high hydraulic conductivity (high kf value).

Question 24

What does massive solute reabsorption lead to in terms of osmolarity?

Answer 24

slight decrease in osmo of tubular luminal fluid and increase in interstitial fluids

Question 25

what is the name of the type of corce that is involved in capillary uptake of fluid from the interstitium?

Answer 25

starling forces

Question 26

what are starling forces?

Answer 26

acoss the peritubular capillary endothelium that drives rapid uptake of fluid from the interstitial compartment

Question 27

what three pressures allow for uptake of fluid into the capillaries from the interstitial spaces? aka peritubular factors

Answer 27

positive interstitial fluid pressure low hydrostatic pressure in peritubular capillaries high oncotic pressure in peritubular capillaries

Question 28

In the proximal tubule, absorption of mculs is iso-osmotic but it is selective?

Answer 28

yes, not all mculs are absorbed to the same extent

Question 29

Is bicarbonate preferred in over chlorine for absorption in proximal tubule?

Answer 29

yes

Question 30

where is H+ actively secreted into?

Answer 30

pt, dt, cd

Question 31

how is proton secretion regulate in pt?

Answer 31

at the apical membrane, na-h exchanger (driven by na gradient) on the basolateral membrane, hco3 is secreted into interstitial space, through the hco3-na cotransporter

Question 32

how is glucose reabsorbed?

Answer 32

it is through a cotransporter na-glucose

Question 33

what are the names of the two na glucose co transporters?

Answer 33

sglt1 sglt2

Question 34

what is the threshold level for glucose?

Answer 34

200-220 mg/dl

Question 35

what is the transport maximum?

Answer 35

where secretion rate d.n change. compared to threshold, which is when you're going to start seeing gluocse in the urine.

Question 36

what does glucosuria cause?

Answer 36

thirst and nocturia (due to osmotic diuresis)

Question 37

what are the causes of glucosuria?

Answer 37

pregnancy diabetes mellitus renal glucosuria (mut in sglt1 and sglt2)

Question 38

what is amino acid reabsorption coupled to

Answer 38

soidum

Question 39

where is the sodium-amino acid transport located on the epithelial cells?

Answer 39

apical membrane

Question 40

what three conditions have high protein excretion?

Answer 40

multiple sclerosis hemoglobinemia myoglobinemia

Question 41

in what condition will you have excessive excretion of organic acids?

Answer 41

diabetic ketoacidosis

Question 42

is phosphate never excreted or continuously excreted in the urine? why?

Answer 42

continuously, because the threshold for phosphate is very low

Question 43

what are the two reasons chlorine is passivley absorbed?

Answer 43

concentration gradient created by water reabsorptino electrochemical potential gradient created by sodium reabsorption

Question 44

what are the absorption characteristics of diuretics?

Answer 44

they are freely filtered and not reabsorbed, can increase osmolarity and cause diuresis

Question 45

what is mannitol

Answer 45

a diuretic, not produced or metabolized in the body, no transporters for mannitol