Reabsorption/Secretion in the Proximal Tubule - Rao

Question 1

How many times is entire plasma filtered through glomerulus every day?

Answer 1

60 times = 5 times whole body fluid

Question 2

What is the equation for rate of flow into the loop of Henle?

Answer 2

Vl = GFR * P in / TF in

Question 3

What is the tonicity of reabsorption in the proximal tubule?

Answer 3

Iso-osmotic

Question 4

What is reabsorbed in the proximal tubule?

Answer 4

Water
Urea
Sodium
Chloride
Bicarbonate
Potassium
Phosphate
Glucose
Amino acids
Organic acids

Question 5

What is secreted in the proximal tubule?

Answer 5

Organic acids and bases
Creatinine
PAH
Drugs

Question 6

How is sodium reabsorbed in the PT?

Answer 6

Active Transport

• Basolateral Na K ATPase
• Luminal Na channel (secondary active)

Question 7

What is reabsorbed via Na cotransporters in the PT?

Answer 7

Glucose
Amino acids
Organic acids

Question 8

What is reabsorbed via Na antiporters in the PT?

Answer 8

Hydrogen Ion

Question 9

How is water reabsorbed in the PT?

Answer 9

Osmotic gradient through leaky epithelium

Aquaporins

Question 10

How is bicarbonate reabsorbed in the PT?

Answer 10

Lumen
*HCO3 + H -> H2CO3 via CA -> H2O + CO2
*CO2 -> ISF
Cell
*H2O + CO2 via CA -> H2CO3 -> H + HCO3
*HCO3 -> ISF via Na / HCO3 cotransport (basolateral)
*H -> lumen via Na / H antiport (luminal)

Question 11

How is glucose reabsorbed in the PT?

Answer 11

Na / Glucose cotransport (apical)

Question 12

What is the threshold level of glucose reabsorption?

Answer 12

200-220 mg/dL

Question 13

What is the transport maximum of glucose reabsorption?

Answer 13

370-390 mg/dL

Question 14

What does glucosuria cause?

Answer 14

Thirst

Nocturia

Question 15

What causes glucosuria?

Answer 15

Pregnancy (lactose and galactose excretion)
Diabetes mellitus
Mutation in SGLT1/2 (glucose cotransporters)

Question 16

How are amino acids reabsorbed in the PT?

Answer 16

Na / amino acid cotransport (apical)

Question 17

How much glucose is typically reabsorbed?

Answer 17

100%

Question 18

What percentage of amino acids are typically excreted?

Answer 18

.5-2%

Question 19

How are organic acids (Krebs cycle intermediates) reabsorbed in the PT?

Answer 19

Na / organic acid cotransport

Question 20

What could condition could overwhelm reabsorption capacity of organic acids?

Answer 20

Diabetic ketoacidosis

Question 21

What conditions have high protein excretion?

Answer 21

Multiple sclerosis
Hemoglobinemia
Myoglobinemia

Question 22

How is phosphate reabsorbed in the PT?

Answer 22

Coupled to Na electrochemical gradient

Question 23

What is the threshold of phosphate reabsorption?

Answer 23

Normal plasma [phosphate] (2.5-4.5 mg/dL)

Question 24

What is the transport maximum of phosphate regulated by?

Answer 24

PTH - decrease Tm

Question 25

How is chloride reabsorbed in the PT?

Answer 25

Passive transport (water and Na gradients)

Question 26

Is chloride or bicarbonate preferentially reabsorbed in the PT?

Answer 26

Bicarbonate

Question 27

How is potassium reabsorbed in the PT?

Answer 27

Passive transport along concentration gradient through permeant epithelium

Question 28

How is urea reabsorbed in the PT?

Answer 28

Passive transport (slow - 50% reabsorbed)

Question 29

What is the clinical significance of substances that are freely filtered but not reabsorbed? (Poorly permeant solutes)

Answer 29

Reduction of intracranial and intraocular pressure Promote excretion of toxins Edema Diuresis

Question 30

What is an example of a poorly permeant solute?

Answer 30

Mannitol