Renal Phys--> Proximal tubule

Question 1

How much filtrate is resorb in the proximal tubule?

Answer 1

60-70%

• Iso-osmotic
• Total water resorbed is same as solutes

Question 2

What else metabolically happens in the proximal tubules?

Answer 2

Gluconeogenesis

Vitamin D conversion

Question 3

What gets handled in the proximal tubule?

Answer 3

1. Na
2. Cl
3. Bicarbonate/acid secretion
4. Glucose
5. AA
6. phosphate resorb
7. weak organic acids resorption and polar substances

Question 4

What are some things that increase the Na/H antiporter?

Answer 4

1. increased CO2
2. AGII
3. Sympathetics
4. Decrease pH

Question 5

What is the saturation point for SGLT2?

Answer 5

15mM Glucose

- synporter at proximal tubules

Question 6

Where are the formate antiporters located? What is their purpose?

Answer 6

For Chloride resorption

• Late in the proximal tubule
• Enough Cl- has accumulated to have favorable conc. gradient

Question 7

What would the lumen become after removing tons of Cl-?

Answer 7

Slightly positive

- thus + charge molecules like Na+ are pushed out of the lumen (filtrate) through the paracellular space

Question 8

What is carbonic anhydrase used for?

Answer 8

To combine H20 and Co2 to make H2Co3 and later H+ and Hco3-.

• found intracellularly
• found on brush border

Question 9

how does bicarbonate get out of the cell?

Answer 9

Na/Hco3- synporter
1:3 ratio
Basallateral side

Question 10

Can water move paracellularly? If so how much?

Answer 10

Yes

about 1/3

Question 11

How much Weak organic acid and bases does the proximal tubule handle?

Answer 11

about 6mM

• large filter load
• need to save most of the WOA

Question 12

What are some examples of organic nutrients that you must not lose?

Answer 12

Glucose
AA
Acetate
Water soluble vitamins
Lactate acetoacetate
B-hydroxybuterate

Question 13

What are some endogenous cations that are secreted?

Answer 13

Creatinine
Dopamine
Epinephrine
Thiamine

Question 14

What are some endogenous anions that are secreted?

Answer 14

Bile salts
Fatty acids
Oxalate
Prostaglandins

Question 15

If WOAs and WOBs aren’t absorbed in proximal tubule are they resorbed distally?

Answer 15

nope

mostly secreted distally

Question 16

How do neutral, negative and positively charged get into the cell?

Answer 16

Neutral and negative via synporter with Na+

• Positive via negative membrane gradient
• All share same transporters

Question 17

Do we usually absorb polar substances?

Answer 17

no

• these are usually excreted
• liver usually metabolizes drugs to make polar which is both water soluble and is secreted!

Question 18

what synporter do neutral and negative organic substances use?

Answer 18

MCA
Mono carboxylic acid
- into with Na and out of cell via diffusion

Question 19

What are OCT’s and OAT’s?

Answer 19

How our body gets ride of drugs that are too big to be filtered. They are on the basolateral side and leave pericapillary. Then enter cell via this and leave cell into filtrate lumen via facilitated diffusion

Question 20

B- hydroxybutyrate is found in the urine .What do you suspect?

Answer 20

DKA
- we are making tons of ketones and since our MCA’s transporter has a Tmax (saturated), we can only absorb so much. Rest is excreted

Question 21

Why would a drug need to use OCT and OAT to get out of body? Complications?

Answer 21

bond to albumin, thus too big to be filtered

• If to many drugs on board that use these transporters they will be longer acting if effects are in blood.
• They would be less efficient if effect is in tubules like Lasix… Thus you would need to increase dosage

Question 22

What are some non-polar substances that are freely absorbed?

Answer 22

Steroids
Cholesterol
CO2

Question 23

What causes resorption, in regards to hydrostatic and oncotic pressures?

Answer 23

Negative net pressure

- due to decrease in pressure due to increase resistance in peri-tubular capillaries