L5 Proximal Tubular Reabsorption and Secretion Flashcards
What does the proximal tubule absorb? Percentage of each?
Na+ (_____________________)
Cl- (_____________________)
Glucose (_____________________)
Protein/amino-acids (_____________________)
HCO3 (_____________________)
Water (_____________________)
Na+ (⅔ filtered is reabsorbed)
Cl- (⅔ filtered is reabsorbed)
Glucose (virtually all)
Protein/amino-acids (virtually all)
HCO3 (80% filtered is reabsorbed)
Water (absorbed osmotically along with solutes)
________ of all human genes code for transport proteins.
5%-10% of all human genes code for transport proteins.
In first half of PCT, Na+ reabsorbed primarily with ____________ and ______________
In second half of PCT, Na+ reabsorbed with ____________ and ________________
In first half, Na+ reabsorbed primarily with Bicarbonate (HCO3-) and Glucose
In second half, Na+ reabsorbed with Cl- and Glucose
In the early proximal tubule, there is a _______________________ across the cells created by Na+ cotransporters (bringing net positive charge into the cell and leaving negative charge in the lumen)
In the early proximal tubule, there is a lumen-negative potential difference across the cells created by Na+ cotransporters (bringing net positive charge into the cell and leaving negative charge in the lumen)
First Half of PCT
______________ are on the apical membrane and bring in Glucose along Na+ concentration gradient (#?)
_________________ on the basolateral surface allow glucose into the interstitial space
_____________ brings Na+ into the cell and H+ ions from cellular metabolism are secreted in the first half of the PCT
____________ transports bicarbonate from cells of the first half of the PCT into interstitial space
SGLT2 Glucose Symporters are on the apical membrane and bring Glucose along Na+ concentration gradient (1 Na+ w/ 1 Glucose)
Glucose Uniporters (GLUT2) on the basolateral surface allow glucose into the interstitial space
Na+/H+ Antiporter (NHE3) brings Na+ into the cell and H+ ions from cellular metabolism are secreted in the first half of the PCT
Na+/HCO3 Symporter (NBC1) transport bicarbonate from cells of the first half of the PCT into interstitial space
Why does the concentration of tubular Cl- along the length of PCT rise?
The concentration of tubular Cl- along the length of PCT RISES due to:
- more water being reabsorbed than Cl
- preferential reabsorption of Na+ with HCO3-in first half of PCT (NO Cl- Transporters)
Second half of the PCT
Tubular fluid has little ______ and high ______
____________ on the apical membrane bring Glucose along the Na+ concentration gradient into cells (#?)
_________on the basolateral surface allow glucose into the interstitial space
The second half of PCT Tubular fluid has little Glucose and high Cl-
SGLT1 Glucose Symporters on the apical membrane bring Glucose along Na+ concentration gradient into cells (2 Na+ w/ 1 Glucose)
Glucose Uniporters (GLUT1) on the basolateral surface allow glucose into the interstitial space
________________________: Antiporter on apical surface of the proximal tubule that secretes organic ANIONs into the tubule lumen
_______________________: ATPase transporter on the apical surface of the proximal tubule that secretes organic ANIONs into the tubule lumen
Example Anion?
Organic Anion Transporter (OAT4): Antiporter on apical surface of the proximal tubule that secretes organic ANIONa into the tubule lumen
Multidrug resistance-associated protein (MRP2): ATPase transporter on the apical surface of the proximal tubule that secretes organic ANIONs into the tubule lumen
__Example:_: PAH, Urate
Antiporters on apical surface of the proximal tubule that secrete organic CATIONs into the tubule lumen?
Multidrug resistance-associated protein (MRP1)- Large cations
Organic cation transporter (OCTN/OCT)- Small cations
Organic Cation secretion (PCT)
- Apical cation transport is fueled by Na+/K+/ATPase pump.
- Resulting sodium gradient drives H+ out of the cell via the ____________________.
- Apical OCTN proteins move small cations out of the cell in exchange for H+ while larger cations are transported out via _____________ transporter
- Cations are transported across basolateral membrane, via passive diffusion or _____________, along concentration gradients.
Example Cation?
- Apical cation transport is fueled by Na+/K+/ATPase pump.
- Resulting sodium gradient drives H+ out of the cell by the Sodium Hydrogen Antiporter (NHE3).
- Apical OCTN proteins move small cations out of the cell in exchange for H+. Larger cations transported out via MDR1 ATPase transporter.
- Cations are transported across basolateral membrane, via passive diffusion or via OCT 1,2,3, along concentration gradients.
Example: Creatine
________________:amount of solute delivered to the tubule per minute that just saturates its transport process
Transfer or Transport Maximum (Tm) ~380mg/min
Co-infusion of ________ w/ penicillin (BOTH ____) reduces penicillin excretion extending its biological half-life.
Co-infusion of Hippurates w/ penicillin (BOTH ANIONS) reduces penicillin excretion extending its biological half-life.
Why does elevated plasma levels of one cation (or anion) inhibit secretion of the other?
Because organic cations (and anions) compete for the same secretory pathways both reabsorption and secretory transport processes can become saturated i.e. tubular maximum-limited (Tm) systems
____________ is particularly critical for the excretion of anions and cations extensively bound to plasma proteins and not filterable at renal corpuscle
PCT secretion is particularly critical for the excretion of anions and cations extensively bound to plasma proteins and not filterable at renal corpuscle
How are most proteins reabsorbed from the urine?
Receptor-mediated endocytosis (aka Pinocytosis)
This mechanism reabsorbs virtually all the proteins filtered, and hence the urine is essentially protein free in the healthy kidney