Rnwk1- 4-11 Physio Proximal Convoluted Tubule: Bulk Operations

Front 1

Describe the two components the PCT does bulk operations...

Back 1

Take back everything it wants (re-absorption)
Kick out the things that didnt get filtered (secretion)

Front 2

Define the terms...
1. Excretion
2. Reabsorption

Back 2

1. The substance in question is removed from the body in the urine (since we are talking renal).
2. The substance in question is moved from the nephron to the blood after filtration, usually involves a transport protein of some form.

Front 3

Define...
a. Secretion

Back 3

a. The substance in question is moved from the blood to the tubule. It usually (almost invariably) involves a transporter protein

Front 4

What is required for secretion and re-absorption to occur in PCT?

Back 4

secondary capillary bed

Front 5

What are the two routes for a substance to move into or out of the PCT?

Back 5

1. Paracellular route
2. Transcellular route

Front 6

Describe the paracellular route for substances to move into or out of the PCT...

Back 6

Between two cells- complicated by the existence of tight junctions between the cells

Front 7

Describe the transcellular route for substance in the PCT...

Back 7

through the cell- relies on transporter proteins on both the apical and basolateral side of the PCT, although some passive diffusion does occur.

Front 8

What is the tubular maximum and what two issues contribute to the magnitude of the tubular maximum?

Back 8

Due to transports across PCT require protein... the process can saturate, leading to tubular max- most glucose moved per minute
- 1. # transporters
2. How fast operate

Front 9

What is normal urinary concentration of glucose?
How does glucose get in urine?

Back 9

0- it is normally completely reabsorbed

- due to saturation kidney misses it and past PCT it stays

Front 10

What transporter transports glucose into the cell and with what?
What transports it out?
Active or Passive?

Back 10

Co transported with Na into cell using SGLT-2
- GLUT-2 transports on the basolateral membrane to the interstitial fluid/blood
- secondary active transport- Na has to move out via active transport

Front 11

What is renal threshold?

Back 11

180mg/dL
concentration of glucose in blood in which you begin to see glucose in urine

Front 12

What happens to small proteins in the PCT?

Back 12

taken up by receptor mediated endocytosis
- once inside the cell, the vesicle fuses with a lysosome and the protein is hydrolyzed into its individual amino acids

Front 13

Howa re amino acids removed from cells

Back 13

removed from cell at basolateral membrane using facilitated diffusion or passive diffusion

Front 14

Explain the role of the brush border enzymes?

Back 14

The brush border of the tubular epithelial cells has a set of peptidases associated with it. They will break peptide into the individual amino acids

Front 15

What is the OATs and what do they do?

Back 15

organic anion transporters on basolateral side in PCT taking things from blood and secreting them to the lumen

Front 16

List endogenous anions that OATs act on

Back 16

Endogenous anions
Bile salts
fatty acids
hippurates
oxalates
prostaglandins
urate

Front 17

List exogenous anions that OATs work on.

Back 17

Exogenous Anions
acetazolamide
furosemide
penicillin
saccharin
salicylates
sulfonamides

Front 18

What is PAH and its importance?

Back 18

para-aminohippuric acid
- example of an OAT used to access renal function
- 5% protein bound meaning that it will not filter
- eventually thought to be secreted into the lumen using similar OAT

Front 19

Describe the OCTs
What is requirement for OCTs to secrete into the lumen?

Back 19

organic cation transporters

- requires an antiport that moves H+ into cell

Front 20

List endogenous cations the OCTs work on

Back 20

Endogenous cations
acetylcholine
creatinine
dopamine
epinephrine
norepinephrine
serotonin

Front 21

Name the exogenous cations that the OCTs work on

Back 21

Exogenous cations
atropine
isoproterenol
cimetidine
morphine

Front 22

Describe the bulk operations (reabsorption/secretion) of Urea

Back 22

REabsorbed using transporters UT in PCT
- secreted using OCT in thin ascending limb in loop of henle
- reabsorbed in collecting duct

Front 23

Describe the bulk operations involving Sodium... (reabssorbed/secreted)

Back 23

- 99.4% reabsorbed
- PCT takes 60% or work

Front 24

Describe the Na transporters used in the PCT to reabsorb Na...(5)
Which does the most work?
What type of transporters are these?

Back 24

PCT- all secondary active
SGLT-2,
Na/amino acid,
Na/PO4 co-transporter
Na/lactate co-transporter
Na/H antiport (does most work)

Front 25

Describe the PCT bulk operations of Chloride (Cl-)

Back 25

Two PCT processes
- paracellular pathway
- transcellular pathway (Cl- HCO3 anti-port), Chloride channel (related to CLC1)

Front 26

Describe the PCT bulk operations of K
- what kind of pathways does it use

Back 26

-Both secreted and reabsorbed in later parts of nephron, but mostly reabsorbed
- uses paracellular pathways

Front 27

Describe the PCT bulk operations of Calcium

Back 27

40% bound to proteins so not quite freely filtered
- reabsorbed PCT but not as much as DCT
1. Intracellular Ca++ is very low b/c it is a second messenger
2. Toxic at high concentrations (triggers apoptosis)

Front 28

What special mechanisms does the PCT have to make sure not too much Ca builds up in cell...

Back 28

Ca binds to calbindin to keep intracellular Ca low,
- Ca leaves cell either Ca-ATPase or Na/Ca antiport

Front 29

Describe the PCT bulk operations of Phosphate

Back 29

only 10% wont filter
- major re-absorption (in PCT) is via Na-PO4 co-transporter
- nearly always close to saturation
- increase filtered load increases exretion

Front 30

Describe the PCT bulk operations of H+ and HCO3-

Back 30

H- a lot less freely filtered through glomerulus
- PCT tries to get the HCO3 back

Front 31

Describe the steps the PCT does to get HCO3 back...

Back 31

Step1: Cells of PCT use carbonic anhydrase to create H and HCO3
Step 2a: the Na/H antiport is used to kick the newly created H+ into the lumen.
Step 2b: A Na/3 HCO3 symport moves the Na and 3 HCO3 into the blood. The two extra HCO3 are from multiple repetitions of the CA reaction.
Step 3: The filtered HCO3 combines with an H+ in the lumen to recreate the CO2 and H2O
Step 4: The CO2 and H20 will diffuse back into the blood. The water is probably helped along the way

Front 32

Describe bulk operations of H+ secretions

Back 32

PCT cells take glutamine from the liver and run the reaction backwards – combining it with water using glutaminase. The NH4 is moved to the lumen while the glutamate is handled like any amino acid.

Front 33

What % of water does PCT absorbed?
How would you reabsorb water?

Back 33

60%
- through aquaporins (1) located on both apical and basolateral membrance reabsorbs

Front 34

Describe the amino acid transport defect known as hartnup disease?
a. Symptoms
b. Gene
c. type of amino acid transporter
d. system name?

Back 34

a. pellegra like symptoms ("the four D's": diarrhea, dermatitis, dementia and death.)
b. SLC6A19
c. Neutral amino acid transporter
d. B0

Front 35

Describe the amino acid transport defect known as cystinuria?
a. Symptoms
b. Gene
c. type of amino acid transporter
d. system name?

Back 35

a. kidney stones
b. SLC3A1, SLC7A9
c. Basic amino acid transporter
d. B0,+