number of transport proteins for that substance and their speed of function
What 2 factors determine the Tubular Maximum?
in PCT, glucose is coabsorbed with Na+ via SGLT-2. It is moved into the blood via GLUT-2.
How do the nephrons reabsorb glucose?
at 180mg/dL, glucose will get past the PCT and be lost in the urine
What is the renal threshold of glucose?
not filtered. if it happens to be filtered, receptor-mediated endocytosis removes it from the filtrate
How do the nephrons handle albumin-sized large (66000 MW) proteins?
filtered and reabsorbed from the filtrate via recept-med endocytosis
How do the nephrons handle growth hormone-sized small proteins?
filtered and converted to amino acid via luminal proteolysis for cotransport with Na+
How do the nephrons handle angiotensin-sized peptides (very small)?
larger proteins are digested via lyzosomes and their amino acids diffuse into the blood. small peptides are fully cleaved by peptidases in the lumen, cotransported into the cell and diffused into the blood.
What is the ultimate fate of peptides/proteins in the filtrate?
Organic Acid Transporters (OATs) bind and transport things from the blood and into the lumen of the PCT
How do the nephrons handle organic acids such as bile salts, fatty acids or drugs like penicillin?
it is excreted via an OAT, clinically useful to measure renal function. 5% is protein-bound but virtually all of the rest is secreted by healthy kidneys
What is the significance of Para-AminoHippuric Acid?
Organic Cation Transporters (OCTs) moves them from blood to cell, antiporter then moves cation into the lumen while taking an H+ into the cell
How do the nephrons handle organic cations like acetylcholine, creatinine, morphine and dopamine?
urea transporters in the PCT, also absorbed into interstitium in the collecting duct (helps absorb H2O)
How do the nephrons reabsorb urea?
OCT in the thin ascending loop of henle (found only in Juxtamedullary Nephrons!)
How do the nephrons excrete urea?
absorbs 60% of Na+ (and H2O/Cl-/K+). Na+/H+ antiporter handles most absorption. SGLT2, Na/amino acid cotransporter and other cotransporters also absorb Na+.
How much Na+ does the PCT absorb? How does it do this?
Cl- / HCO3 antiporter absorbs 60% of Cl-
How does the PCT handle Cl-?
absorbed and excreted in different parts of the nephron but mostly reabsorbed. diffuses via paracellular transport.
How do the nephrons handle K+?
40% if prot-bound so not freely filtered. reabsorbed in PCT and with hormonal control in DCT.
Describe the adventures of Ca++ in the nephron
Ca++ diffuses into the cell due to very low cellular concentration, binds to Calbindin to prevent interference with signalling / apoptosis, exported with Ca-ATPase or Na/Ca antiporter
Describe how nephron cells handle Calcium in the PCT lumen
only 10% protein-bound, Na-PO4 cotransporter in PCT is always close to saturation, excess PO4 excreted in urine
Describe how the nephrons handle phosphate
HCO3 is freely filtered while H+ is not
Why are we in danger of acidosis if they PCT doesn't reabsorb bicarbonate?
PCT uses carbonic anhydrase to convert CO2 and H2O to H+ and HCO3. Na/3 HCO3 cotransporter moves HCO3 into the blood. CO2 / H2O is regenerate when filtered HCO3 reacts with H+ in lumen. CO2 / H2O also diffuse into the blood.
How do the nephrons handle HCO3?
glutamine + H2O is broken down into NH4 and glutamate in the nephron cells. NH4 is moved into the PCT lumen. Another way to excrete H+.
How do the nephrons excrete NH4?
aquaporin-1 in both apical and basolateral membranes. H2O follows osmotic gradient.