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15 Cards in this Set
- Front
- Back
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Define isotonic, hypertonic, hypotonic.
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Isotonic - osmotic pressure of soltion on the outside is the same as inside
Hypertonic - osmotic pressure is greater on the outside Hypotonic - osmotic pressure is less on the outside |
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In cells, is hydrostatic pressure important?
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No, its negligible. Only osmotic pressure is important
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Why does a 1 molar solution of sucrose have half the osmotic pressure of 1 molar solution of NaCl?
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NaCl dissociates to form two molecules, effectively having double the concentration of sucrose
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What are aquaporins?
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These are water channels, which are very specific for water.
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What are the two possible reasons a cell stays at constant volume?
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Either it is
1. Impermeable to water 2. Isotonic with extracellular fluid |
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How does ADH function in relation to thirst?
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When you get thirsty, your brain releases ADH (vasopresin). This binds to epithelial cells in the kidney. This causes the epithelial cell to express more aquaporins
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What is the pump leak hypothesis?
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Na and K reach a steady state in the cell by the combination of pumps and channels for these ions
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What does inhibition of the Na K pump cause?
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This causes the pump to swell. This is because much more Na will enter the cell the potassium will leave, making the cell have a higher concentration of solute than the solution. Water will rush in, causing swelling
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What happens when a cell enters a hypotonic solution for a long time? What happens with hypertonic solutions?
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Initially, it swells. Over time, it returns to its normal volume. It does this by dumping K, Cl, amino acids, sugars, and other molecules, in order to become isotonic with the solution.
Cells in a hypertonic solutions initially shrunk, but they eventually upregular Na 2 Cl K transporters, which allows them to take in ions and become isotonic. There is also a Na+ myoinositol cotransporter which gets upregulated. This is regulated by a Na+ response element |
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What pathway does water take to pass across epithelia?
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It takes a transcellular route
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How do you absorb water and ions across an epithelium where the solution is isotonic?
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Put a Na H exchange protein, and a Cl HCo3 exchange protein in the apical side of the cell. (Bicarbonate will take up the protons, to form carbonic acid and water) This will cause NaCl to enter the cell from the lumen. Put a N K pump and a Cl channel in the basolateral side of the cell.
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What is local osmosis?
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Local osmosis is a theoy that explains how water is absorbed across an epithelium. The ion transporters are located along one region of the lateral membrane, between two epithelial cells. As the epithelial cells pump out ions, the ion concentration of this area becomes very high. This creates a local osmotic effect, causing water to flow out of the epithelial cell across the length of the lateral membrane. By the time the water leaves the region, it is isotonic with the other side of the epithelium
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How does cholera toxin work?
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Cholera toxin binds a intestinal epithelial cell. This causes changes in cAMP, which lead to the activation of Cl- receptors. Chloride leaves the cell, water follows, and you end up with too much water leaving the cell into the intestine, causing secretory diarrhea
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How does oral rehydration therapy work?
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There are glucose Na+ sodium transporters which absorb glucose and Na+ into the epithelium of the intestine. In oral rehydration therapy, you give patients pedialyte, a mixture of salt and sugar. Na+ and Gluose are absorbed into the intestines via the Na glucose transporter. Water follows ions and glucose into the cell, increasing the reabsorption of water
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What happens if you poison the sodium pump in a membrane that is supposed to absorb water?
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Water follows ions, so if ions cant move, then water cant be absorbed either
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