A close up of an eye showing the capillaries. The definition of a capillary is a small blood vessel that is part of the network of the small arteries and small veins, or an extremely thin tube through which nothing thicker than a human hair can pass.
Phospholipid bilayer. Definition. noun. The two layers of phospholipids arranged in such a way that their hydrophobic tails are projecting inwards while their polar head groups are projecting on the outside surfaces. Supplement. This arrangement of phospholipids in bilayer is used to describe the cell membranes of many animal and plant cells. The two layers of phospholipids are arranged in a way that their hydrophobic tails are projecting to the interior whereas their hydrophilic heads are projecting the exterior.
This fluid lipid bilayer cross section is made up entirely of phosphatidylcholine. The three main structures phospholipids form in solution; the liposome (a closed bilayer), the micelle and the bilayer. The lipid bilayer is a thin polar membrane made of two layers of lipid molecules. These membranes are flat sheets that form a continuous barrier around all cells. The cell membranes of almost all living organisms and many viruses are made of a lipid bilayer, as are the membranes surrounding the cell nucleus and other sub-cellular structures.