Physiology Renal Exam 4 (IP2): Renal Handling of Organic Substances Lecture

where in the nephron are organic nutrients reabsorbed?

proximal tubule

list some organic nutrients that are reabsorbed in the proximal tubule

glucose, amino acids, vitamins, citrate, lactate, glycerol

reabsorption of organic nutrients is (passive/active) (diffusion/facilitated/primary/secondary) and coupled to (K+/Na+/H2O) reabsorption, and (is/is not) carrier mediated

active, secondary, Na+, is

(up/down) hill movement of sodium is used to move glucose and amino acids into the cell

down

(primary/secondary) active transport requires ATP

primary

what were the three considerations listed in lecture for if the reabsorption of a solute is carrier mediated

specificity, competition between substrates, saturation (transport max)

there are (#) sodium/glucose transporters on the (basolateral/apical) membrane of the (proximal/distal) tubule

2, apical, proximal

what are the 2 sodium/glucose transporters located on the apical membrane of the proximal tubule

SGLT1, SGLT2

Sodium Glucose Transporter 1 and 2 (SGLTs)

- (low/high) specificity

- (low/high) competition

- (slightly/highly) efficient

- high : only bind sodium and glucose

- low : don't compete with other substrates

- highly : a large increase in glucose before saturated

SGLT (1/2) are more predominant for the handling of glucose

2

Is the transport maximum for SGLTs under normal glycemic conditions lower or higher than the amount of glucose that gets filtered?

higher

SGLT2 ________ are being used clinically in humans to reduce blood glucose levels in diabetes mellitus

inhibitors

the highest rate at which the kidney’s transport proteins can move a substance out of the filtrate (reabsorb it) or into the filtrate (secrete it) is known as what?

transport maximum

once kidney transporters are fully saturated, what can no longer happen?

reabsorption

how many main amino acid transporters are there on the apical membrane of the proximal tubule?

5

there are 5 main amino acid transporters located on the apical membrane of the proximal tubule, how many of those are coupled to sodium transport?

4

Solute Carriers/Amino Acid Transporters

- (low/high) specificity

- (low/high) competition

- (slightly/highly) efficient

- low

- high : several different amino acids competing for the same binding site

- slightly : transport maximum is still higher than filtered load, but lower than for glucose

T/F: a small amount of protein can be filtered into the tubule

true

reabsorption of protein occurs in the proximal tubule via what mechanism?

endocytosis

what happens to proteins after they are brought into the cell via endocytosis, what are they broken down into in order to be properly reabsorbed?

amino acids

are small linear peptides (such as ADH) able to freely filter into the cells of the proximal tubule?

yes

small linear peptides are broken down into amino acids by peptidases located on the (basolateral/apical) brush border membrane

apical

T/F: waste products, drugs, chemicals are freely filtered, reabsorbed, and secreted into the proximal tubule

false, are not reabsorbed

which numbers are cations (+ charge):

1. saccharine

2. prostaglandins

3. fatty acids

4. procaine

5. dopamine

6. acetylcholine

7. aspirin

8. morphine

9. epinephrine

10. serotonine

11. bile salts

12. diuretics

4, 5, 6, 8, 9, 10

which numbers are anions (- charge):

1. saccharine

2. prostaglandins

3. fatty acids

4. procaine

5. dopamine

6. acetylcholine

7. aspirin

8. morphine

9. epinephrine

10. serotonine

11. bile salts

12. diuretics

1, 2, 3, 7, 11, 12

anions have a (+/-) charge

-

cations have a (+/-) charge

+

waste products, drugs, and chemicals are organic (nutrients/ions)

ions

secretion of organic ions is via carrier-mediated (passive/active) transport on (apical/basolateral) membranes of the tubular epithelium

active, both

Organic Ion Transporters

- (low/high) specificity

- (low/high) competition

- (slightly/highly) efficient

- very low : bind many different substrates

- very high : lots of competing substrates

- inefficient : easily saturated (low TM)

Which numbers are all organic ion transporters found on the apical membrane of the proximal tubule cells:

1. OCT2

2. OCT3

3. NPT1

4. MDR1

5. OAT1/3

6. MRP2

7. MATE2/2k

2, 3, 4, 6, 7

Which numbers are all organic ion transporters found on the basolateral membrane of the proximal tubule cells:

1. OCT2

2. OCT3

3. NPT1

4. MDR1

5. OAT1/3

6. MRP2

7. MATE2/2k

1, 5

urea is a nitrogen waste product generated primarily by ________ metabolism and therefore needs to be (reabsorbed/excreted)

protein, excreted

urea is freely filtered with what excretion percentage range in the urine depending on urine flow and hydration state

20-60%

is urea reabosrbed?

yes

is urea secreted?

yes

urea is transported (actively/passively) down its concentration gradient

passively

urea is "recirculated" (reabsorbed and secreted) in order to help make the (medulla/cortex) more (hyposmotic/isosmotic/hyperosmotic)

medullas, hyperosmotic

urea facilitates H2O reabsorption therefore (concentrating/diluting) urine

concentrating

urea is reabsorbed where in the nephron?

proximal tubule

urea is secreted where in the nephron?

loop of henle

in the medullary collecting duct, urea is (secreted/reabsorbed) and is regulated by what hormone?

reabsorbed, ADH

urea is transported out of the cell via what transporters?

urea tranporters (UT)

reabsorption in the collecting duct is regulated by what two things

ADH, urine flow

ADH activates urea transporters to (increase/decrease) reabsorption which (increases/decreases) its excretion

increase, decreases

urine flow (concentrates/dilutes) the urea in the tubule which (increases/decreases) the concentration gradient for reabsorption therefore (increasing/decreasing) excretion

dilutes, decreases, increasing

when kidney function is disrupted and GFR decreases it leads to a buildup of urea levels in the blood. this is a medical condition called......

azotemia

what are the three kinds of azotemia

pre-renal, renal, post-renal

decreased blood flow to kidneys (dehydration)

- pre-renal azotemia

- renal azotemia

- post-renal azotemia

pre-renal azotemia

urinary tract blockage or rupture (urolithiasis)

- pre-renal azotemia

- renal azotemia

- post-renal azotemia

post-renal azotemia

decreased number of functional nephrons (toxins)

- pre-renal azotemia

- renal azotemia

- post-renal azotemia

renal azotemia

T/F: urea can be a sole measure to test azotemia

false, its levels vary by several factors

if urea cannot be a sole measure to test azotemia because its levels vary by several factors, then what is an important marker (its levels are stable in normal conditions)?

creatinine

azotemia is a (increase/decrease) in (blood/urine) urea nitrogen levels due to kidney dysfunction

increase, blood

urea excretion increase with (decreased/increased) urine flow

increased

urea excretion is (increased/decreased) by ADH

decreased

urea is a metabolic waste product that is reabsorbed and secreted to help do what?

concentrate urine