Mangiarua - Tubular Reabsorption Flashcards
Is glucose normally excreted in urine?
No
Diffusion between cells
Paracellular
Diffusion across the cell
Transcellular (luminal membrane or basolateral membrane)
Requires an electrochemical gradient and carriers
Exhibits specificity, saturability, and competition
Downhill transport
Facilitated diffusion
The entire overall process of glucose reabsorption depends ultimately on the ________- pump in the basolateral membrane
primary active Na K ATPase
Limit to the amount of material the active transport systems in the renal tubule can transport per unit of time
Due to saturation of carriers
Transport Maximum (Tm)
Transport max rate of Glucose
375mg/min
The appearance of glucose in the urine before the Tm is reached
Splay
Reasons for splay
A carrier mediated mechanism shows kinetics similar to those of enzyme systems so that maximal activity is substrate-dependent
Not all nephrons have the same Tm for glucose
Describes the mass flows of filtration, reabsorption, and excretion of glucose over the range of plasma glucose concentrations
Glucose titration curve
Plasma concentration at which glucose first appears in the urine.
Threshold
Renal plasma threshold for glucose?
180-200 mg / 100mL
This will be when glucose is seen in the urine clinically
Glucose clearance occurs when ?
Flitered load of glucose is increased
Tubular reabsorptive transport max for glucose is reached
Very high levels of plasma glucose ______ all reabsoprtion of xylose
Blocks
Affinity of membrane carriers for glucose is ______ than that for xylose
Much higher
Renal glycosuria is ?
Glucose in urine as a result of a defective or missing transport mechanism
(Tg = 0 or very low)
Are glucose transporters intact in diabetes mellitus?
Yes, glucosuria is due to elevated plasma glucose concentrations, not faulty transporters
What can cause glucosuria in pregnancy ?
Increased GFR (glomerular hyperfiltration)
[renal blood flow can increase by 40% due to gestational hormones]
Normal clearance of amino acids ?
0
Viscous drag
Lining of pore retards forward movement in glomerusu
Does normal urine contain protein?
No
What three things cause a filtration of proteins to be absent or small
Steric hindrance
Viscous drag
Electrical hindrance
How does reabsorption of small linear polypeptides occur?
They are catabolized to AA’s by peptidases in the luminal membrane of the Proximal Tubule and then AA’s are actively reabsorbed
Protein bound calcium filters, true or fals?
False
What happens to plasma calcium concentration in acidosis ?
More H+ are buffered by plasma proteins, so bound calcium is displaced from proteins and [Ca] increases
What happens to [Ca++] in alkalosis ?
The release of H+ from plasma proteins causes the plasma [K++] to decreases
Hypocalcemic tetany possible
A ________ of [Ca] causes a release of parathyroid hormone ?
Decrease
This causes increased calcium reabsorption in the kidney and increases [Ca++]ecf
High plasma Ca levels ______ PTH
Suppress
What protein does calcium bind to in the distal tubule to form a complex that is able to diffuse across the basolateral membrane
Calbindin
Water is reabsorbed and everything that is dissolved in the water is reabsorbed with it
Solvent drag
___ % of phosphate is actively reabsorbed
Out of the 90% that is filtered
90
