 |
| This article is part ofa series on |
| Anatomical terminology |
|---|
Ahistological scope ofanatomical terminology describes structure, layout and position more precisely and mitigates ambiguity. An internationally accepted lexicon isTerminologia Histologica.
Epithelial cells line body surfaces, and are described according to their shape, with three principal shapes: squamous, columnar, and cuboidal.
Endothelium refers to cells that line the interior surface ofblood vessels andlymphatic vessels,[1] forming an interface between circulatingblood orlymph in thelumen and the rest of the vessel wall. It is a thin layer of simple, or single-layered,squamous cells calledendothelial cells. Endothelial cells in direct contact with blood are called vascular endothelial cells, whereas those in direct contact with lymph are known as lymphatic endothelial cells.
Epithelium can be arranged in a single layer of cells described as "simple", or more than one layer, described as "stratified". By layer, epithelium is classed as either simple epithelium, only one cell thick (unilayered) or stratified epithelium asstratified squamous epithelium,stratified cuboidal epithelium, andstratified columnar epithelium that are two or more cells thick (multi-layered),[2][3] and both types of layering can be made up of any of the cell shapes.[4] However, when taller simple columnar epithelial cells are viewed in cross section showing several nuclei appearing at different heights, they can be confused with stratified epithelia. This kind of epithelium is therefore described aspseudostratified columnar epithelium.[5]
Transitional epithelium has cells that can change from squamous to cuboidal, depending on the amount of tension on the epithelium.[6]
Amucous membrane ormucosa is amembrane that lines various cavities in the body and covers the surface of internal organs. It consists of one or more layers ofepithelial cells overlying a layer ofloose connective tissue. It is mostly ofendodermal origin and is continuous with the skin at variousbody openings such as theeyes,ears,inside the nose,inside the mouth,lip, theurethral opening and theanus. Some mucous membranes secretemucus, a thick protective fluid. The function of the membrane is to stoppathogens and dirt from entering the body and to prevent bodily tissues from becoming dehydrated.
Thesubmucosa consists of a dense and irregular layer of connective tissue withblood vessels, lymphatics, and nerves branching into the mucosa and muscular layer. It contains thesubmucous plexus, andenteric nervous plexus, situated on the inner surface of the muscular layer.[7]: 263
Themuscular layer (also known as themuscularis propria[8] ) consists of two layers of muscle, the inner and outer layer. The muscle of the inner layer is arranged in circular rings around the tract, whereas the muscle of the outer layer is arranged longitudinally. The stomach has an extra layer, an inner oblique muscular layer.[7]: 263 Between the two muscle layers are themyenteric or Auerbach's plexus. This controls peristalsis. Activity is initiated by the pacemaker cells (interstitial cells of Cajal). The gut has intrinsic peristaltic activity (basal electrical rhythm) due to its self-contained enteric nervous system. The rate can of course be modulated by the rest of theautonomic nervous system.
The layers are not truly longitudinal or circular, rather the layers of muscle are helical with different pitches. The inner circular is helical with a steep pitch and the outer longitudinal is helical with a much shallower pitch.
The hollow inner part of a body organ (such as thegastrointestinal tract) or tube (such as anartery) is called thelumen. The side of a cell facing the lumen is called theapical surface; the opposite side, facing away from the lumen is thebasolateral surface, which faces instead towards theinterstitium, and away from the lumen.