What is the apical membrane of a plasma membrane?

[marc32123]

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 ?

 

[Monique]

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.

 

[marc32123]

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!

 

[Andy Resnick]

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.