Involuntary weight loss exceeding 10 pounds or 5% of body weight over a period of a few months is cause for concern. Tests are done based on the person's symptoms and findings on physical examination.
Fluid Mosaic Model. A model of membrane structure; according to this model, membranes are composed of a double layer of phospholipids in which various proteins are embedded. The phospholipid bilayer is a somewhat fluid matrix that allows the movement of proteins within it.hospholipid Bilayer. A double layer of phospholipids that forms the basis of all cellular membranes. The phospholipids heads, which are hydrophilic, face the water of extracellular fluid or the cytoplasm; the tails, which are hydrophobic, are buried in the middle of the bilayer.
Cell membranes are composed of a bimolecular layer of phospholipids and cholesterol, with hydrophilic and hydrophobic regions. Peripheral proteins move along the surfaces and integral proteins are embedded in the lipid bilayer. Some integral proteins extend through both layers (transmembrane proteins). Many of these are glycoproteins with surface carbohydrate units. The cell membrane is the site of the sodium ion pump which maintains cell volume by pumping sodium out of the cell. The outer plasma membrane is permeable to ions, but not to larger molecules. It is also the site for hormone-receptor and cell signal interaction.