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
T/F. There are more transporters than there are organic solutes.
False. There are fewer transporter mechanisms than organic solutes.
Tranposrters move multiple solutes.
What happens if weak organic acids/bases bypass the proximal tubule?
they will be excreted
how do cations enter the peritubular capillary?
via uniporters driven by the negative membrane potential
How do neutral or negatively charged solutes get reabsorbed into the peritubular capillaries?
- enter with sodium
How do organic anions and cations get excreted?
there are specific tranportes for them on the basolateral membrane.
What happens to polar substances at the proximal tubule?
- they get stuck (can’t cross luminal membrane)
- get excreted into urine
What are some examples of non-polar substances?
How are they reabsorbed?
- steroids, cholesterol, CO2
- diffuse freely across luminal membrane
How does the peritubular capillary reabsorbe substances?
- governed by Starling’s forces
- pressure drops due to resistance
- Pi = 3
- Pgc=20
- Oi = 6
- Ogc = 33
- filtration = 20 +6 = 26
- reabsorption = 3 + 33 = 36
- favors reabsorption
