proximal convoluting tubule physiology

Question 1

what is osmolality?

Answer 1

number of particles per Kg of solute (moles/Kg)

Question 2

what is the osmolality in the proximal convoluted tubule?

Answer 2

300 mosm/L

Question 3

what is tubular secretion?

Answer 3

substances moving from the blood into the kidney tubule (this is an active process)

Question 4

what is tubular reabsorption?

Answer 4

-moving substances from the kidney tubule to the blood (Can be passive or active)

Question 5

role of sodium potassium ATPase?

Answer 5

• pumps 2 K+ into the cell

- pumps 3Na+ out of the cell

Question 6

role of sodium glucose transporters?

Answer 6

• Sodium is low in the cell (due to sodium potassium ATPase pumping out 3 sodium) so sodium can enter the cell with passive diffusion through the sodium glucose transporter
• there are high levels of glucose in the cell so it cannot diffuse into the cell
• however due to secondary active transport with the sodium glucose transporter, glucose can enter the cell through the sodium glucose transporter

Question 7

what substances move into the cell with sodium through secondary active transport?

Answer 7

• glucose (SGLT)
• amino acids
• lactate
• H+ (sodium hydrogen antiporter, it moves out when sodium moves in)
• H2O (water follows salt)
• chloride

Question 8

how does glucose enter the blood stream from the proximal convoluted tubule?

Answer 8

• sodium potassium ATPase causes 3 Na+ ions to leave the cell, decreasing concentration of Na+ in the cell
• Sodium then enters the cell through diffusion through the sodium glucose transporters, allowing glucose to also enter
• glucose then passes through glucose transporters at the cell basolateral membrane and into the blood stream (capillaries)
• lactate can also enter with glucose

Question 9

how do amino acids enter the blood from the proximal convoluting tubule?

Answer 9

• sodium-potassium ATPase pumps out 3Na+ from the cells causing a decrease of sodium concentration in the cell
• sodium then moves from the proximal convoluted tubule and into the cell, allowing amino acids to also enter the cell, agaisnt their concentration gradient through secondary active transport
• amino acids then leave the cell and enter the blood stream through their transporter

Question 10

in normal physiological conditions how much glucose, lactate and amino acids are reabsorbed from the kidney tubules and into the blood?

Answer 10

100% of it

Question 11

what allows H+ to enter the proximal convoluting tubule from the cell?

Answer 11

-the sodium hydrogen antiporter

Question 12

how do Calcium, magnesium and potassium leave the proximal convoluting tubule and enter the blood stream?

Answer 12

-through paracellular transport (moving between the cells) and into the blood stream

Question 13

what type of substance is urea?

Answer 13

lipid

Question 14

how do lipids pass out of the proximal convoluting tubule?

Answer 14

• lipid soluble substances can pass through the phospholipid bilayer
• urea (lipid) can just pass straight from the proximal convoluting tubule, through the cell and into the blood stream

Question 15

how much glucose is reabsorbed in the proximal convoluting tubule?

Answer 15

100%

Question 16

how much salt and water is reabsorbed in the proximal convoluting tubule?

Answer 16

67%

Question 17

how does glucose pass out of the proximal convoluted tubule?

Answer 17

through facilitated diffusion

Question 18

how does O2 and CO2 get reabsorbed in the proximal convoluted tubule?

Answer 18

through diffusion through the lipid bilayer

Question 19

what affect does PTH have on the proximal convoluting tubule?

Answer 19

-it causes phosphate excretion from inside the cells into the proximal convoluting tubule

Question 20

what is plasma clearance?

Answer 20

• the volume of plasma completely cleared of a particular substance per minute
• each substance has its own specific plasma clearance value

Question 21

what can be used to clinically determine GFR and why?

Answer 21

• inulin
• as it is freely filtered and not absorbed, secreted or metabolised

therefore GFR= PC of inulin

Question 22

what is the plasma clearance of glucose and why?

Answer 22

plasma clearance of glucose= 0

-as glucose is filtered and then fully absorbed and not secreted

Question 23

what is the plasma clearance of urea and why?

Answer 23

-urea is filtered and partially reabsorbed, and not secreted

PC < GFR

Question 24

what is the plasma clearance of H+ and why?

Answer 24

H+ is filtered, secreted but not reabsorbed

the PC> GFR