Term
| Why are tight junctions important for maintaining polarity? |
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Definition
| They prevent migration of proteins between the apical and basolateral parts of cell. |
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Term
| How does sodium get transported from the lumen to an epithelial cell and then from the epithelial cell to the serosa? |
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Definition
Sodium can enter an epithelial cell either through ion channels or the Na+-Glucose cotransporter. Both of these methods involve sodium going down its electrochemical gradient into the cell.
Sodium exits the cell through the Na+/K+ ATPase. Here sodium gets pumped up against its electrochemical gradient. |
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Term
| What are examples of co-transporters in the apical membrane? Explain how this is relevant for glucose transport. |
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Definition
The Na+-Amino Acid and the Na+-Cl- transporters are examples of co-transporters.
Glucose is transported across the membrane in the Na+-Glucose co-transporter. This is an example of secondary active transport because sodium going down its electrochemical gradient drives the glucose transport. |
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Term
| What are some examples of countertransporters found in the apical membrane of epithelial cells? |
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Definition
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Term
| What is the driving force behind water absorption? |
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Definition
| When Na+ and other solutes get transported into the cell (through ion channels or transporters) they decrease the concentration of water inside the cell. This affects the gradient and causes water to flow into the cell. |
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Term
| What is the driving force behind water secretion? |
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Definition
| In the basolateral area of the cell, transporters (like Na+/K+ ATPase) transport solutes out of the cell. This raises the concentration of water inside the cell and now the gradient favors water secretion out of the cell. |
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Term
| What is solvent drag and how does it relate to leaky and tight junctions? |
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Definition
Solvent drag is when water can drag ions with it whenever it flows somewhere. As water moves in/out ions can follow.
This is more important in leaky junctions because the ions are allowed to pass through the spaces. It becomes less important as the junctions become tighter. |
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Term
| What are amiloride, thiazide, and furosemide examples of? |
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Definition
| Drugs that block co-transporters in the apical membrane. They are diuretics. |
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