Absorption Across the Epithelium
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Questions and Answers

What is the primary mechanism driving the UNIDIRECTIONAL TRANSPORT of substances across a cellular sheet in Victorian Transport?

  • Simple diffusion across the cellular membrane
  • Active transport on one side and diffusion on the opposite side (correct)
  • Osmosis through the cell membrane
  • Facilitated diffusion on both sides of the cell

What role do the Solute Carrier (SLC) transporters play in the process of absorption across the epithelium?

  • Secondary active transport for entry of substances into the cell (correct)
  • Efflux transport to remove substances from the cell
  • Facilitated diffusion at both sides of the cell
  • Simple diffusion assisting with passive transport

How does temperature affect the absorption process across the epithelium?

  • It has no significant effect on absorption rates.
  • Higher temperatures increase the rate of diffusion. (correct)
  • Temperature only affects facilitated diffusion and not active transport.
  • Higher temperatures decrease the rate of diffusion.

Which of the following correctly describes a factor that influences absorption across the epithelium?

<p>The presence of competing substances in the epithelium (A), The concentration of solute in the bloodstream (B), The type of drug being absorbed (D)</p> Signup and view all the answers

What distinguishes ATP-binding cassette (ABC) transporters from Solute Carrier (SLC) transporters?

<p>ABCs are involved in efflux transport, while SLCs primarily handle influx transport. (A)</p> Signup and view all the answers

What effect does emphysema have on oxygen diffusion in the lungs?

<p>It reduces the rate of oxygen diffusion due to less surface area. (A)</p> Signup and view all the answers

How does pneumonia impact the diffusion distance for oxygen absorption?

<p>It prolongs absorption time due to increased diffusion distance. (C)</p> Signup and view all the answers

What is the role of P-glycoprotein in drug absorption?

<p>It extrudes some drugs back to the intestinal lumen, reducing their absorption. (D)</p> Signup and view all the answers

What factor influences the absorption speed of a drug based on its molecular properties?

<p>The drug's size and molecular weight. (A)</p> Signup and view all the answers

How does stomach acidity affect the absorption of acid-labile drugs?

<p>It can impair their absorption, necessitating enteric-coated formulations. (C)</p> Signup and view all the answers

Flashcards

Victorian Transport

Transport across an entire epithelial sheet, involving movement through both cell membranes and the intracellular space.

Solute carrier (SLC) superfamily

A superfamily of membrane proteins that facilitate the entry of substances into cells via secondary active transport or facilitated diffusion.

ATP-binding cassette (ABC) superfamily

A superfamily of membrane proteins that actively pump substances out of cells, requiring energy from ATP.

Transcellular transport

The process by which a substance moves across an epithelial sheet, from one side to the other, through the cells.

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Factors influencing absorption

The absorption rate of a substance across an epithelium can be affected by factors such as temperature and surface area.

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Surface Area for Diffusion

The total surface area available for a substance to cross a membrane. A larger surface area allows for faster absorption.

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Diffusion Distance

The distance a substance must travel to cross a membrane. A shorter distance allows for faster absorption.

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Size and Molecular Weight

The rate at which a substance moves across a membrane is affected by its size and mass. Smaller molecules and lighter substances tend to cross membranes faster.

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Drug Ionization

Drugs can exist in either an ionized (water-soluble) or a non-ionized (lipid-soluble) form. Non-ionized drugs are more easily absorbed across cell membranes.

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Efflux Transporters

Certain transporters in the intestines can pump some drugs back into the gut, decreasing their absorption. These efflux transporters can affect drug dosage.

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Study Notes

Absorption Across the Epithelium

  • Victorian transport describes substance movement across entire epithelial sheets, not just cell membranes.
  • This occurs in various tissues including intestines, renal tubules, exocrine glands, gallbladder, choroid plexus, and placenta.
  • Transport involves active transport across one side of a cell, followed by either simple or facilitated diffusion across the opposite side.
  • This unidirectional transport is achieved by different transporter families on opposite cell faces.
  • Solute carriers (SLCs) facilitate influx in secondary active or facilitated transport.
  • ATP-binding cassette (ABC) transporters facilitate efflux in active transport.
  • Examples include absorption from the intestine to blood, from blood to bile, across kidney tubules, and from blood to other body cells.

Factors Influencing Absorption

  • Physiological factors influence absorption rate:

    • Temperature: higher temperatures increase diffusion rates.
    • Surface area: larger surface areas allow faster absorption.
    • Diffusion distance: shorter distances facilitate quicker absorption.

  • Pharmacological considerations:

    • Stomach acidity affects acid-labile drugs, potentially impacting absorption. This may necessitate enteric-coated tablets.
    • Gastrointestinal motility affects drug absorption. Drugs might be taken on an empty stomach to optimize absorption.
    • Presence of efflux transporters, such as P-glycoprotein, can reduce drug absorption. Dosage adjustments might be needed with concurrent inhibitors of P-glycoprotein.

  • Factors related to the substance itself:

    • Size and molecular weight: smaller substances absorb more quickly.
    • Ionization: non-ionized (lipophilic) drugs absorb more easily across cell membranes than ionized (hydrophilic) drugs. Ionization depends on the drug's pKa and the surrounding pH.

  • Drug interactions: Cardiac glycosides like digoxin can have interactions with other drugs impacting P-glycoprotein-mediated transport, affecting absorption and elimination.

  • Examples include macrolide antibiotics (e.g., erythromycin) and anti-epileptic drugs (e.g., carbamazepine), which can affect Digoxin absorption in terms of increasing absorption or eliminating it in urine.

Applications of Victorian Transport Info

  • Ezetimibe inhibits cholesterol transport.
  • Gliflozins block glucose reabsorption in the kidneys, lowering blood sugar levels.

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Absorption Across the Epithelium PDF

Description

This quiz covers the mechanisms of absorption across epithelial tissues, focusing on Victorian transport. Explore key concepts such as active transport, facilitated diffusion, and the role of various transporter families. Test your knowledge on how physiological factors like temperature affect absorption rates.

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