Term
•Prevent movement between cells
•Prevent the passage of molecules & ions through the space between cells to maintain the polarity of the cell
•Stops the movement of proteins
What has these functions? |
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Definition
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Term
Explain the vectorial transport of sodium from the lumen of an epithelium to the serosa
• Sodium enters into the cell via diffusion due to its electrochemical gradient
o ENaC = epithelial Na+ channel is what it is called in the kidney
Blocked by Amiloride
• Na+ cannot enter down its concentration gradient so more Na+ will be outside
• This will speed up the Na+/Glucose & Na+/Amino Acid cotransporter
oThis affects the carbohydrates
• Uses Na+/K+ pump to enter into the serosa (THIS is exclusively located on basolateral side of all epithelial cells) |
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Name two cotransporters and two countertransporters found in the apical membrane of epithelial
cells, and describe how glucose is reabsorbed using one of these mechanisms:
•Cotransporters: Na+/Glucose (answer to Q)
Na+/Amino Acid
Na+/K+/2Cl- (BLOCKED by furosemide, which is a LOOP diuretic; (found in the loop of henle))
K+/Cl-
•Countertransporters: 3Na+/Ca2+
Na+/H+
Cl-/HCO3-
• Na+/Glucose is a secondary active transport that moves from the apical side into the cell (“uphill transport”)
• Buildup of glucose in cell will cause it to diffuse down its concentration gradient via facilitated diffusion (carrier protein is GLUT1, GLUT2)
•Glucose concentration in lumen is low because you are NOT eating all the time.
oWhen you are eating, Na+/Glucose transporter takes over |
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| Glucose and AAs leave the basolateral membrane by what mechanism? |
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Explain the forces responsible for water absorption and secretion.
• Absorption: Na+/Glucose enters into the cell & water will follow due to osmotic pressure
o The oncotic pressure (due to albumin) will cause water to enter into the blood
• Secretion: Na+/K+/2Cl- cotransporter pulls H2O into the cell from the blood
o K+/Cl- cotransporter will extrude H2O from cell into the lumen
o Water gets through via aquaporins in epithelial cells |
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Definition
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Epithelia are generally divided into “tight” or “leaky” categories. In which kind of epithelia would solvent drag play a greater role, and explain why.
• Solvent drag plays a greater role in “leaky” epithelia, since ions are able to pass through intercellular spaces
• In paracellular, if you have leaky epithelia, water will go through & whatever is in water will be dragged
• In transcellular, water will not drag because water will not flow freely
• Water diffusion occurs through channels in the plasma membrane & it is driven by its osmotic gradients. Dissolved solutes in the H2O are also carried along with it, in a process known as solvent drag
• This accounts for a significant amount of solute reabsorption across the proximal tubule
• Proximal tubule side is leaky. This is where you have the “leakiest” tight junctions
Leaky ----------------------------Tight
Proximal--------------------------Collecting Duct
Duodenum--------------------------Colon |
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Definition
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