Tympanic membrane retraction Tympanic membrane retraction Tympanic membrane retraction describes a condition in which a part of the eardrum lies deeper within the ear than its normal position. The eardrum comprises two parts, the pars tensa, which is the main part of the eardrum, and the pars flaccida, which is a smaller part of the eardrum located above the pars tensa. Either or both of these parts may become retracted. The retracted segment of eardrum is often known as a retraction pocket. The terms "atelectasis" or sometimes "adhesive otitis media" can be used to describe retraction of a large area of the pars
Semipermeable membrane the rate and the permeability. Many natural and synthetic materials thicker than a membrane are also semipermeable. One example of this is the thin film on the inside of the egg. Note that a semipermeable membrane is not the same as a selectively permeable membrane. Semipermeable membrane describes a membrane that allows some particles to pass through (by size), whereas the selectively permeable membrane "chooses" what passes through (size is not a factor). An example of a biological semi-permeable membrane is the lipid bilayer, on which is based on the plasma membrane that surrounds all biological cells. A group of