Physio 4 Flashcards
secretion
the movement of solutes from the circulation via the peritubular capillaries across the epithelial cell tubule into the tubular fluid
what is urine formed by?
formed by the solutes and the water NOT reabsorbed as well as solutes secreted into the tubular fluid
two methods of renal epithelial transport
transcellular and paracellular
transcellular transport
depends on solute specific transporters in the apical membrane facing the tubular fluid in the lumen and in the basolateral membrane facing the peritubular space and capillaries. Na/K ATPase are on the basolateral membrane.
secondary active transport
transduce energy stored in the electrochem gradient of one solute into the energy in the formation of a gradient of a second solute
paracellular transport
passive and driven by a transepithelial solute electrochem gradient. depends on the tightness, or solute-specific resistance to transport of the intercellular junctions. movement of water may entrain the solute movement through solvent drag, which contributes to transtubular solute reabsorption or secretion
tubular reabsorption of a solute may result from:
- active transport at the luminal membrane and passive transport at the baolateral membrane
- passive transport at luminal and active transport at basolateral
tubular secretion of a solute may result from
- active transport at basolateral and passive transport at luminal
- passive at basolateral, and active at lumenal
what does the handling of glucose by nephron include?
filtration and reabsorption, but NOT secretion. amount of glucose in the urine is a function only of the amount filtered and the amount reabsorbed. first tubular segment of the nephron (proximal tubule) does this
filtered load
amount of solute filtered at the glomerulus and is quantified as the product of solute concentration in the glomerular filtrate times the GFR.
Tm
tubular reabsorptive maximum defining the maximum solute reabsorptive rate or capacity for tubular solute reabsorption
what is the clearance of glucose when you have normal blood glucose?
- this is because it’s all being reabsorbed. UV/P. U is 0, so the clearance is 0
glucose transporter on lumenal membrane
Na+ / glucose cotransporters mediate concentrative accumulation of glucose into the cell. stoichiometry is 1 or 2 to 1, resulting in net positive charge transfer
glucose transporter on basolateral membrane
passive efflux of intracellular glucose mediated by facilitated diffusion (uniporter)
phosphate reabsorption
proximal tubular phosphate reabsorption increases with increasing filtered load of phosphate and approaches a tubular maximum where the process of transcellular phosphate transport becomes saturated and the rate of phosphate reabsorption becomes maximal and constant
phosphate reabsorption on the lumenal membrane
Na+ / PO4 cotransporter. 2 or 3 to 1 stoichiometry, resulting in net positive charge transfer with each PO4 transported
phosphate reabsorption on the basolateral membrane
passive efflux of intracellular PO4 mediated by facilitated diffusion
things that get secreted
foreign drugs and toxins, things metabolized by the kidney for excretion by the kidney, things metabolized by the liver, and things regulated in the blood (H+ and K+ concentration)
renal handling of p-aminohippuric acid
exogenous, nonmetabolizable prototype organic anion used to study renal organic anion secretion. secreted into tubular fluid but not reabsorbed. amount of PAH excreted in the urine is a function of the amount filtered as well as the amount secreted by the tubule
transport of PAH on the basolateral membrane
Na / Dicarboxylate cotransporter mediates concentrative accumulation of dicarboxylate inside the cell.
an organic anion antiporter mediates exchange of ketoglutarate for extracellular PAH. 1 to 1 ratio in stoichiometry.
transport of PAH on the lumenal membrane
efflux of intracellular PAH occurs by facilitated diffusion or anion gradient driven antiport
what does clearance of PAH measure
renal plasma flow.
renal handling of salicylate
active and passive transport help with secretion. reabsorption occurs by passive proces of nonionic diffusion across distal nephron. decreases with increased tubular fluid pH and flow, and vice versa
reabsorption
movement of filtered solutes and water from the tubular fluid across the epithelial cell tubule into peritubular capillaries and the circulation
