22. Renal Tubular Function and Physiology Flashcards
What is tubular reabsorption?
Solutes and water are removed from tubular fluid and transported into the blood
What is the function of tubular reabsorption?
Maintains homeostasis of blood volume, pressure, pH and osmolarity
What is tubular secretion?
Transport of solutes from interstitium into tubular lumen
Clears substrates from blood
Name 5 things secreted into filtrate
K+ H+ NH4+ Creatinine Urea
What type of epithelium is found in the PCT and thick limb of loop of henle?
Cuboidal
What are important features of the tubular cells in the PCT?
Microvilli to increase surface area for absorption
Mitochondria for active reabsorption
What type of epithelium is found in the thin limb of loop of henle?
Squamous
What are tight junctions?
Contact between neighbouring cells on the luminal surface
Transmembrane proteins form bonds with their same type on the other cell
What proteins are found in tight junctions?
Occludins
Claudins
Junctional Adhesion Molecule
What is functional polarity?
Epithelial cells express different transport proteins on their apical and basolateral sides
Allows for directional transport of solutes
Which aquaporin is found in the PCT and DLoH?
1
Which aquaporins are found in the DCT and CD?
2,3,4
How is Na reabsorbed in the early PCT?
Na/K pump maintains electrochemical gradient for Na+ absorption across apical membrane
Na+ exchanged with H+ to re-enter cell
HCO3- reabsorbed with Na+
How is Cl reabsorbed in the late PCT?
Cl- builds up in filtrate
Late PCT is permeable to Cl-
Reabsorbed passively through paracellular pathway
How is glucose reabsorbed in the early PCT?
Dependent on energy of Na/K
Enters through Na+/glucose co-transporter (SGLT-2)
Exits cell via GLUT 2
Name a gliflozin
Dapaglifozin
How do gliflozins work?
Target SGLT2
Increases amount of glucose excreted
Lowers blood glucose in diabetics
How is protein reabsorbed in the PCT?
Receptor mediated endocytosis
Proteins are degraded in intracellular lysosomes
AAs exit via basolateral transporters
What does glycosuria with normoglycaemia indicate?
Decreased tubular resorptive capacity
What are 2 reasons for glycosuria with normoglycaemia?
Pregnancy
Falconi syndrome
What are the 3 types of proteinuria?
Glomerular (damage causes more protein to be filtered)
Tubular (alterations in reabsorption)
Overload (increase plasma low weight proteins)
How are AAs reabsorbed in the PCT?
Na+ coupled secondary active transport
Small amounts of passive reabsorption
Separate carriers on apical and basolateral membranes for different types of AAs
How is HCO3- reabsorbed in the PCT?
Filtered HCO3- can’t cross the apical membrane due to its charge
Combines with H+ to produce carbonic acid, breaks down into CO2 and water
CO2 crosses membrane, recombines with water to produce HCO3-
HCO3- crosses basolateral membrane via a Na+/HCO3- symporter
How are organic ions secreted in the PCT?
Through multiple different transporters
Multiple Drug Resistance Protein, p-glycoprotein, Organic Acid Transporters, Organic Cation Transporters
