Gall Bladder,
The gall bladder is a specialized portion of the bile duct. The gall bladder is shaped like a small sack to store bile, it has an absorptive epithelial lining to concentrate bile, and it has a muscular wall to expel bile.
In its absorptive function, the gall bladder epithelium is a highly exaggerated striated duct, as is the functionally similar epithelium of the proximal tubule of the kidney.
Inflammation of the gall bladder is a fairly common problem. For an image of cholecystitis, see WebPath or Milikowski & Berman's Color Atlas of Basic Histopathology, p. 308.
Historical note: The Greek name for gall bladder is cholecyst, from chole, bile + cyst, bladder. The Greek root chole also appears in the word choleric, hot-tempered, irascible, "bilious". This word is derived from the ancient medical theory that temperament, along with all other aspects of health and disease, is governed by the balance among four humours, allied to the deeper philosophical belief in four elements of fire, water, air and earth. The four humours are gall (= chole) or yellow bile from the gall bladder, black bile (= melan + chole) from the spleen, blood (Latin sanguis), and phlegm or mucus. Along with choleric, the modern words melancholy (pensive, depressive), sanguine (confident, cheerful), and phlegmatic (sluggish, stolid) complete the set of terms for humour-based temperaments.
Without
due care, a section of the gall bladder could easily be mistaken for
one of small intestine. Therefore, the gall
bladder provides an excellent opportunity to observe how various details can
serve to distinguish organs which otherwise appear superficially similar.
Since the gall bladder is really just a glandular duct, its structure
is much simpler than that of intestine.
- The gall bladder has a wrinkled mucosa, with sections across the wrinkles resembling villi. However, in sections of gall bladder the wrinkles always appear attached to the wall and sometimes form arches. In contrast, in sections of intestine, finger-shaped villi occasionally have the appearance of separate "islands", cut off from the wall.
- The mucosa of the gall bladder, unlike that of the intestine, has no crypts.
- The epithelial lining of the gall bladder consists of simple columnar cells specialized for absorption, with an apical brush border of microvilli, very similar to intestinal absorptive cells. However, unlike intestinal epithelium, gall bladder epithelium includes only this single cell type; it has no goblet cells.
- Like the intestine, the gall bladder has a muscular outer wall. However, the muscular wall of the gall bladder is not organized into distinct circular and longitudinal layers, unlike the muscularis externa of the intestine. The gall bladder has no muscularis mucosae, and no distinct submucosa.