What is the apical membrane of a plasma membrane?

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Discussion Overview

The discussion revolves around the definitions and distinctions between the apical and basolateral membranes of plasma membranes in cells, particularly in the context of epithelial tissue. Participants explore the orientation of these membranes and their relevance to cellular structure.

Discussion Character

  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions whether the apical membrane is oriented towards the inside of the cell (cytoplasm) or the outside.
  • Another participant clarifies that the basolateral membrane contacts the basement membrane, while the apical membrane faces the outside environment, using skin as an analogy.
  • A third participant seeks confirmation on whether the apical membrane is indeed the part facing outside the cell and asks about the basolateral membrane's orientation and the concept of the basement membrane.
  • A fourth participant explains that 'apical' and 'basolateral' apply to polarized cells and that in epithelial tissue, the apical surface faces the outside while the basolateral surface faces the inside (blood).

Areas of Agreement / Disagreement

Participants express varying levels of understanding regarding the definitions of apical and basolateral membranes. While some clarifications are provided, confusion remains about the terms and their applications, indicating that the discussion is not fully resolved.

Contextual Notes

Some participants express confusion about the definitions and relationships between apical, basolateral, and basement membranes, highlighting a need for clearer explanations or examples.

marc32123
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I keep coming across the word apical and basolateral membrane in my study of plasma membranes of cells. I am wondering if the apical membrane is towards the inside of the cell (cytoplasm) or towards the outside ?
 
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Neither, basolateral membrane means the membrane that is contacting the basement membrane, the apical is on the opposite side. Think of your skin: the membrane that faces the environment/outside is apical, the membrane facing the inside of your body is the basolateral side. The apical membrane of intestinal cells face the lumen.
 
So the part of the cell's membrane that is facing towards the outside of the cell is called the apical membrane? And apical surface would refer to that the apical membrane then right? Also, is the basolateral membrane the membrane that is facing towards the cytoplasm? And what is the basement membrane that you mentioned? I am really confused!
 
The terms 'apical' and 'basolateral' refer to adherent cells (as opposed to say, circulating blood cells) that have a 'polarized' structure: at the tissue level, the tissue constitutes a dividing surface between 'inside' and 'outside'- osteocytes and neurons are adherent but don't have an apical/basolateral side.

For example:
http://droualb.faculty.mjc.edu/Course%20Materials/Physiology%20101/Chapter%20Notes/Fall%202007/figure_18_15_labeled.jpg
http://droualb.faculty.mjc.edu/Course%20Materials/Physiology%20101/Chapter%20Notes/figure_04_23_labeled.jpg

For epithelial tissue, the side facing 'outside' is the apical surface, while the side facing 'inside' (the blood) is the basolateral surface.
 

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