Proximal Tubular Dysfunctions and Disorders of Water Balance Flashcards
How is the PT designed for large reabsorption?
The epithelial cells have microvilli (brush border) and basolateral surface is thrown into folds: both enhance surface area
T or F. Proximal tubular cells are reach in mitochondria which are needed to provide sufficient energy for the reabsorption
T. ISCHEMIA is bad here
What are the parts of the PT (structurally)?
First 2/3: proximal convoluted tubule (PCT)
Remaining 1/3: proximal straight tubule (parse recta). In turn, parse recta has cortical and medullarly segments
What are the parts of the PT (functionally)?
Some differences in transporter proteins):
- S1- initial short segment of PCT
- S2- remaining PCT and cortical parse recta
- S3- medullary parse recta
What are the main functions of the PT?
Reabsorption of filtered water, electrolytes, and organic compounds
Secretion of organic compounds including some drugs (S2, S3 segments)
Hormonal function: final pathway in the synthesis of calcitriol
How much Na is reabsorbed in the PT?
Water?
K+?
55-65% (Na+ and water)
K+- 65%
How much Pi is reabsorbed in the PT?
Calcium?
Glucose?
Urea?
80-95%
60%
100%
50%
What are some pathways of reabsorption in the PT?
1) transcellular (through the PT epithelium to the ISF)
2) paracellular (through junctions to the ISF)
Passive diffusion typically requires what?
an electrochemical gradient of some kind
What is reabsorption in the tubular cells from the PT lumen driven by?
The electrochemical gradient created by the basolateral Na-K ATPase.
What does the basolateral Na-K ATPase do specifically?
transports 3Na+ to the ISF and 2K+ into the tubular cell
What things are typically coupled to Na+ as it is reabsorbed into the tubular cell via the electrochemical gradient formed by the basolateral Na-K ATPase?
sugars, AAs, phosphate, glucose in symport (or H+ into the tubular lumen in antiport)
this is called 2ndary active transport
How is the K+ brought into the cell by the BL Na/K ATPase removed back to the ISF?
by passive transport couple to a negative ion (usually Cl-)
What is the basis of glomerulotubular balance?
The intrinsic ability of the tubules to increase their reabsorption rate in response to increased tubular load (increased tubular inflow).
all segments have this capability
What things decrease the net reabsorption of sodium and water?
Arterial pressure (Pressure natriuresis): increase in peritubular capillary hydrostatic pressure reduces the net reabsorption of sodium and water
diuretics, hypoaldosteronism
What hormones regulate PT reabsorption?
Angiotensin II: regulates NaCl and water re-absorption and H+ excretion
Parathyroid hormone and FGF23- regulate Pi excretion