Principles of Tubular Transport

Question 1

What are the 3 processes in urine formation?

Answer 1

Ultrafiltration
Reabsorption
Secretion

Question 2

What is usually never found in urine?

Answer 2

Proteins

Question 3

How does water move throughout the nephron?

Answer 3

Passive transport. There are no active transport processes for water.

Question 4

What processes use facilitated diffusion?

Answer 4

Glucose transport into RBCs

Question 5

What processes use active transport?

Answer 5

Active Na resorption and endocytosis for protein transport and requires the use of ATP.

Question 6

What processes use secondary active transport?

Answer 6

Requires an indirect energy source in an ion gradient and it can be saturated as it is limited by carriers (Tm)

Examples are Na+-H+ exchangers

Question 7

What is the transcellular pathway?

Answer 7

Uses a specific pump such as an Na/K-ATPase pump

Question 8

What is the paracellular pathway?

Answer 8

Movement of ions via solvent drag and it occurs with ions like Ca2+, Mg2+ and K+

Question 9

What is CaO2 - CvO2?

Answer 9

It is the O2 extraction from the blood

Question 10

How does the (CaO2 - CvO2) change as O2 demand and O2 supply both increase in the heart?

Answer 10

No change in CaO2 - CvO2

Question 11

How does the (CaO2 - CvO2) change as O2 supply decreases and O2 demand remains constant in the skeletal muscle?

Answer 11

The CaO2 - CvO2 will increase, indicating increased extraction of O2 from the blood

Question 12

How does decreased O2 supply affect the kidney?

Answer 12

In the kidney, it will decrease the O2 demand with no change in CaO2 - CvO2. This means as blood flow decreases to the kidney, it requires less O2.

Question 13

What is the normal handling of glucose in the kidney?

Answer 13

Normally 100% of the glucose is reabsorbed

Question 14

What is the reabsorption of glucose equal to in an equation?

Answer 14

R = F - E

S = 0

Question 15

When can the tubular transport maximum (Tm) be calculated?

Answer 15

Only when the Tm is exceeded

Question 16

What is the Tm for glucose equal to?

Answer 16

Tm (glucose) = (Pa GFR) - (UV)

Question 17

What is the renal plasma threshold (RPT) of glucose?

Answer 17

The RPT is the point where glucose first appears in urine.

Question 18

Describe the normal handling of PAH.

Answer 18

Normally over 90% of PAH is secreted

Question 19

What is the equation for the secretion of PAH?

Answer 19

S = E - F

R = 0

Question 20

What is the Tm for PAH equal to?

Answer 20

Tm (PAH) = (UV) - (PaGFR)

Question 21

What is the RPT of PAH defined as?

Answer 21

The RPT of PAH is the point where the secretion slope of PAH first decreases

Question 22

What is diuresis?

Answer 22

It is a urine flow greater than 1 mL per minute

Question 23

What is the function of mannitol?

Answer 23

It acts as an osmotic diuretic

Question 24

What is the fate of mannitol in the nephron?

Answer 24

It is filtered but not reabsorbed

Question 25

How does mannitol function as an osmotic diuretic?

Answer 25

It holds excess water in the tubule by osmotic forces which leads to increased urine flow.

Question 26

How can glucose function as an osmotic diuretic?

Answer 26

Normally glucose is 100% reabsorbed but if some is left in the tubule, it will hold excess water by osmotic forces and leads to increased urine flow. It will also cause dehydration and thirst.