Exam 3 - Lecture 37 (Tubular Reabsorption)

Question 1

What is reabsorption?

Answer 1

Pulling things from the nephron into the bloodstream

Question 2

How does blood get from the nephron back to the bloodstream?

Answer 2

Through peritubular capillaries

Question 3

What is the opposite of reabsorption?

Answer 3

Secretion

Question 4

What is passive transport?

Answer 4

Movement across membrane by random motion down electrochemical gradient without energy (diffusion and facilitated diffusion)

Question 5

What is active transport?

Answer 5

Movement across membrane via carrier protein against electrochemical gradient using energy (primary active and secondary active)

Question 6

What is the luminal membrane?

Answer 6

Side of cell that separates tubular cell from tubular fluid

Question 7

What is the basolateral membrane?

Answer 7

Side of cell that separates cell from peritubular interstitium (blood)

Question 8

What is transepithelial potential difference?

Answer 8

Potential difference between tubular lumen and peritubular interstitium (blood).
- Changes bt tubular sections and contributes to electrochemical gradient

Question 9

What is the transcellular route?

Answer 9

Reabs. thru cytoplasm of tubular cells.

Question 10

What route does passive transport take?

Answer 10

Transcellular and paracellular

Question 11

What route does active transport take?

Answer 11

Transcellular only

Question 12

What % of reabsorption happens thru the transcellular route?

Answer 12

80-90%

Question 13

What is the paracellular route?

Answer 13

Reabs. between tubular cells across tight junctions

Question 14

What is Na+K+ATPase critical for?

Answer 14

Tubular reabsorption

Question 15

Where is Na+K+ATPase located?

Answer 15

Basolateral membrane of all tubular epithelia

Question 16

What is the role of Na+K+ATPase?

Answer 16

Moves 3 Na+ out of the cell and 2 K+ in (to decrease [Na+] inside cell)

Question 17

What type of transporter is Na+K+ATPase?

Answer 17

basolateral antiporter

Question 18

What type of transport does Na+K+ATPase do?

Answer 18

active

Question 19

Why does Na+K+ATPase maintain low IC Na+?

Answer 19

To establish the electrochemical gradient upon which all reabsorption depends.

Question 20

Which molecule’s [ ] is not the same in filtrate as in EC space?

Answer 20

glucose

Question 21

Which of the following statements about Na+K+ATPase is correct?

A) It transports Na+ and K+ at the luminal membrane of nephron epithelia
B) It moves 3 Na+ into the cells in exchange for 2 K+ out of the cell
C) Na+ movement is by facilitated diffusion
D) It requires energy in the form of ATP
E) It moves K+ paracellularly

Answer 21

D) It requires energy in the form of ATP

Question 22

PT reabsorbs ___% of filtered water, Na+, and solutes.

Answer 22

67%

Question 23

PT reabsorbs ___% of filtered glucose, AAs, and ___% bicarb.

Answer 23

99%; 90%

Question 24

What are the 4 steps to tubular reabs. in the 1st half of the PT?

Answer 24

1. Na+K+ATPase generates Na+ gradient (decreases IC [Na+])
2. Na+ enters down electrochemical gradient via Na+H+ antiporter AND Na+ glucose symporter
3. Glucose moves down its [ ] gradient into the blood
4. Water follows Na+ down osmotic gradient

Question 25

What does Na+ enter the cell with during tubular reabs. in the 2nd half of the PT?

Answer 25

Cl-

Question 26

What does Na+ enter the cell with during tubular reabs. in the 1st half of the PT?

Answer 26

Glucose

Question 27

What are the 6 steps to tubular reabsorption in the 2nd half of the PT?

Answer 27

1. Na+K+ATPase generates Na+ gradient 2. Na+ enters down electrochemical gradient via Na+H+ antiporter 3. Cl- enters down electrochemical gradient via Cl- anion antiporter AND via paracellular route 4. K+ leaves cell with Cl- symporter 5. Lumen positive PD drives Na+ down paracellular route 6. Water follows by osmosis thru aquaporins

Question 28

What happens to proteins that end up being filtered by the glomerulus (3 steps)?

Answer 28

1. Pts partially degraded by enzymes in luminal membrane and reabsorbed by endocytosis 2. Pts further degraded by enzymes in lysozyme --> AAs and leave via basolateral membrane. 3. Process can be easily saturated so pts can appear in urine/

Question 29

What is proteinuria?

Answer 29

Proteins present in urine

Question 30

The LoH reabsorbs ___% of filtered NaCl and ___% of filtered water.

Answer 30

25%; 15%

Question 31

Which limb of the LoH reabsorbs water?

Answer 31

descending only

Question 32

Which limb of the LoH reabsorbs NaCl?

Answer 32

ascending only (passive transport)

Question 33

Up to this point, which statement about tubular reabsorption is correct? A) Most water is reabsorbed in the descending Loop of Henle B) Na+ is reabsorbed actively at the luminal membrane in the proximal tubule C) Glucose is reabsorbed via facilitated diffusion D) Cl- reabsorption is both transcellular and paracellular

Answer 33

D) Cl- reabsorption is both transcellular and paracellular

Question 34

DT and CT reabsorb ___% of filtered NaCl and ___% of filtered water.

Answer 34

7%; 8-15%

Question 35

DT and CT are _____ to water.

Answer 35

impermeable

Question 36

What are the 4 steps to tubular reabsorption in the early distal tubule?

Answer 36

1. Na+K+ATPase generates Na+ gradient 2. Na+ enters cell via NKCC1 symporter and Na+H+ antiporter. 3. Positive transmembrane PD means cations move down electrochemical gradient via paracellular route. 4. Water does NOT follow

Question 37

Loop diuretics (e.g. furosemide) inhibit _____.

Answer 37

NKCC1

Question 38

What is an example of a loop diuretic?

Answer 38

Furosemide

Question 39

Why is reabsorption of water in the DT variable?

Answer 39

Depends on presence of anti-diuretic hormone

Question 40

What are the 2 steps to tubular reabsorption in the late DT?

Answer 40

1. Na+K+ATPase generates Na+ gradient | 2. Na+ enters cell via Na+Cl- symporter.

Question 41

What inhibits NaCl- symporter?

Answer 41

Thiazide diuretics

Question 42

When is the only time water is reabsorbed in the DT?

Answer 42

In the presence of ADH

Question 43

What two cell types make up the CT epithelium?

Answer 43

principal and intercalated cells

Question 44

What are the 5 steps to tubular reabsorption in the CT through principal cells?

Answer 44

1. Na+K+ATPase generates Na+ gradient 2. Na+ enters cell via amiloride sensitive Na+ channels 3. Water follows via aquaporins but ONLY with ADH 4. K+ leaves thru K+ channels down its gradient 5. Na+ reabs. generates negative PD so Cl- is abs. paracellularly

Question 45

Which of these molecules transports Na+ at the luminal membrane of the late DT? A) Na-Cl symporter B) NKCC1 C) Na-glucose symporter D) Na-H antiporter

Answer 45

A) Na-Cl symporter

Question 46

What do intercalated cells secrete during tubular reabsorption?

Answer 46

H+ or HCO3- | Maybe important for maintaining acid-base balance

Question 47

Prioritize these tubular sections in terms of Na+ reabsorption: most Na+ reabsorption first, least Na+ reabsorption last: A) Proximal tubule, Distal tubule, Loop of Henle B) Loop of Henle, Proximal henle, Distal tubule C) Distal tubule, Proximal tubule, Loop of Henle D) Distal tubule, Loop of Henle, Proximal tubule E) Proximal tubule, Loop of Henle, Distal tubule

Answer 47

E) Proximal tubule, Loop of Henle, Distal tubule