Gene models + nephron function (1)

Question 1

What is the 1st step in urine production?

Answer 1

Glomerular filtration

Question 2

During filtration, what is permitted to move and what is restricted?

Answer 2

-permitted = H2O + small molecules
-restricted = blood cells + proteins

Question 3

What does the ultrafiltrate in the Bowman’s capsule consist of?

Answer 3

(almost) protein free plasma

Question 4

What is the second step in urine production?

Answer 4

Filtrate modification

Question 5

Describe how the filtrate is modified

Answer 5

-tubular reabsorption - lots of things are taken out (h2o, Na+, sugars, amino acids) as filtrate passes through nephron
-tubular secretion - some things are secreted from peritubular capillaries into distal tubule to be lost in urine

Question 6

What are the types of tubular transport?

Answer 6

-transcellular reabsorption
-transcellular secretion
-paracellular secretion or absorption

Question 7

What is transcellular reabsorption?

Answer 7

Movement from the lumen across the cell into the interstitial fluid, then into the peritubular capillary

Question 8

What is transcellular secretion?

Answer 8

Movement from the peritubular capillary across the cell and into the lumen

Question 9

What is paracellular secretion/absorpiton?

Answer 9

Transport that occurs between the cells

Question 10

What are the membranes of the tubular epithelium?

Answer 10

-apical membrane on the side of the tubule lumen
-basolateral membrane on the side of the peritubular capillary

Question 11

Which organelle do tubule cells have many of?

Answer 11

Many mitochondria - ATP for transport

Question 12

Describe how ATPase works on the basolateral membrane

Answer 12

-hydrolysis provides energy to transport sodium out and potassium in
-3 sodium out + 2 potassium in

Question 13

Describe how glucose enters the cell

Answer 13

-sodium moves out and potassium moves in using ATPase on basolateral membrane
-K+ recycled out of cell using K+ channel
-ATPase creates low Na+ conc. in cell, creating large electrochemical driving force for Na+ uptake
-on apical membrane, Na+-glucose cotransport protein binds Na+ + glucose, moving both into cell driven by Na+ uptake driving force

Question 14

How is glucose absorbed from the cell into the capillary?

Answer 14

-moves out across basolateral membrane using protein
-from high to low conc.

Question 15

What else can be transported into cells by the same mechanism as glucose?

Answer 15

-amino acids
-have a sodium-amino acid cotransport membrane on apical membrane

Question 16

What other transporter is on the apical membrane?

Answer 16

-sodium-phosphate cotransporter (NaPilla)
-phosphate leaves by phosphate transport protein on basolateral membrane

Question 17

How is water reabsorbed?

Answer 17

-mainly paracellular
-small amount is transcellular via aquaporins