The portion of the membrane that faces the lumen is called the apical membrane.
Membrane is the lipid bilayer that surrounds the cell on its outer surface. The membrane serves various functions like: protection, cell shape and integrity and regulate the traffic of molecules across the membrane. It is semi-permeable in nature.
Lumen is the hollow portion present inside any organ or tube like the artery or intestine. It is a Latin word that means 'an opening'. The lumen of different organs served various purposes. However, the major function is the transport of substances like air, nutrients, waste materials, immune cells, hormones, etc.
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