Reabsorption/Secretion in the Proximal Tubule - Rao Flashcards
How many times is entire plasma filtered through glomerulus every day?
60 times = 5 times whole body fluid
What is the equation for rate of flow into the loop of Henle?
Vl = GFR * P in / TF in
What is the tonicity of reabsorption in the proximal tubule?
Iso-osmotic
What is reabsorbed in the proximal tubule?
Water Urea Sodium Chloride Bicarbonate Potassium Phosphate Glucose Amino acids Organic acids
What is secreted in the proximal tubule?
Organic acids and bases
Creatinine
PAH
Drugs
How is sodium reabsorbed in the PT?
Active Transport
- Basolateral Na K ATPase
- Luminal Na channel (secondary active)
What is reabsorbed via Na cotransporters in the PT?
Glucose
Amino acids
Organic acids
What is reabsorbed via Na antiporters in the PT?
Hydrogen Ion
How is water reabsorbed in the PT?
Osmotic gradient through leaky epithelium
Aquaporins
How is bicarbonate reabsorbed in the PT?
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)
How is glucose reabsorbed in the PT?
Na / Glucose cotransport (apical)
What is the threshold level of glucose reabsorption?
200-220 mg/dL
What is the transport maximum of glucose reabsorption?
370-390 mg/dL
What does glucosuria cause?
Thirst
Nocturia
What causes glucosuria?
Pregnancy (lactose and galactose excretion)
Diabetes mellitus
Mutation in SGLT1/2 (glucose cotransporters)
How are amino acids reabsorbed in the PT?
Na / amino acid cotransport (apical)
How much glucose is typically reabsorbed?
100%
What percentage of amino acids are typically excreted?
.5-2%
How are organic acids (Krebs cycle intermediates) reabsorbed in the PT?
Na / organic acid cotransport
What could condition could overwhelm reabsorption capacity of organic acids?
Diabetic ketoacidosis
What conditions have high protein excretion?
Multiple sclerosis
Hemoglobinemia
Myoglobinemia
How is phosphate reabsorbed in the PT?
Coupled to Na electrochemical gradient
What is the threshold of phosphate reabsorption?
Normal plasma [phosphate] (2.5-4.5 mg/dL)
What is the transport maximum of phosphate regulated by?
PTH - decrease Tm
How is chloride reabsorbed in the PT?
Passive transport (water and Na gradients)
Is chloride or bicarbonate preferentially reabsorbed in the PT?
Bicarbonate
How is potassium reabsorbed in the PT?
Passive transport along concentration gradient through permeant epithelium
How is urea reabsorbed in the PT?
Passive transport (slow - 50% reabsorbed)
What is the clinical significance of substances that are freely filtered but not reabsorbed? (Poorly permeant solutes)
Reduction of intracranial and intraocular pressure
Promote excretion of toxins
Edema
Diuresis
What is an example of a poorly permeant solute?
Mannitol
