Proximal Tubule (Muster) - W2 Flashcards
What causes the casts we see in urine?
- damage to the cells between the peritubular and lumen space
- the cells may die and show up in the urine.
How much filtrate is reabsorbed in the proximal tubule?
60-70%
Does the proximal tubule make urine hyperosomotic or hypo-osmotic?
What else does it do as a metabolic organ?
- makes it iso-osmotic since sodium and water absorption is equal.
- vitamin D conversion
- Gluconeogensis
How much of glucose, water, sodium and bicarbonate does the proximal tubule reabsorb?
- 100% glucose
- 65% of water
- 65% of sodium
- 80% of bicarbonate
if there is damage to this segment, you’d see everything in the urine.
Movement down a gradient. Primary method across peritubular capillaries and paracellular.
which molecules use it?
Diffusion
- non-polar substances
- H20 paracellularly
- Cl followed by Na, K, Ca
What transporters are found on the lumen side of the proximal tubule?
- Na/H+ antiporter
- Na/glucose (glut 2)
- Na/amino acid
- Na/PO4
Na uses a good gradient and charge difference to move substances UP their electrochemical gradient.
What is the Tm (transport maximum) for glucose?
- 15mM glucose
- once saturated glucose would start accumulating in the urine
How and where is chloride reabsorbed?
- late sections of proximal tubule
- Cl- can go through paracellular transport
- H+ joings with formate, which generates a gradient to bring Cl- into the cell.
- once in the cell, HF dissociates to formate and H+. Formate then flows out and Cl- flows in.
- Cl- and K+ symptorter on basolateral side to allow into capillary.
How is HCO3- reclaimed?
- H+ being pumped out by antiporter combines to form bicarbonate. bicarbonate dissocaites to form cO2 which can enter the cell.
- carbonic anhydrase inside generates more bicarb which is transporter out with sodium.
- 1Na: 3 HCO3- symporter
How is water reabsorbed in the proximal tubule?
- aquaporins on luminal side
- H20 acoss tight junctions (paracellularly)
What are the reabsorbed organic nutrients we must not lose?
- glucose
- amino acids
- acetate
- water soluble vitamins
- lactate acetoacetate
- b-hydroxybutyrate
4 endogenous cations that are SECRETED
- creatinine
- dopamine
- epinephrine
- thiamine
4 cation drugs that are secreted
- cimetidine
- morphine
- quinine
- atropine
4 endogenous anions that are SECRETED
- bile salts
- fatty acids
- oxalate
- prostaglandins
4 anion drugs that are secreted
- furosemide
- pencillin
- acetazolamide
- salicylates
