The cells that line the surface of the colon and the glands are principally absorptive cells (AC) and goblet cells (GC). The absorptive cells have a thin striated border that is evident where the arrows show the opening of the glands. Interspersed among the absorptive cells are the goblet cells (GC). As the absorptive cells are followed into the glands, they become fewer, whereas the tudinal layer (ME[l] ) is substantially thinner than the circular layer (ME[c] ) except in three locations where the longitudinal layer of smooth muscle is present as a thick band. One of these thick bands, called a tenia coli (TC ), is shown in this figure. Because the colon is cross-sectioned, the tenia coli is also cross-sectioned. The three teniae coli extend along the length of the large intestine as far as, but not into, the rectum.
The submucosa consists of a rather dense irregular connective tissue. It contains the larger blood vessels (BV ) and areas of adipose tissue (see A in figure below).
ally, the lumen of the glands is narrow except in the deepest part of the gland, where it is often slightly dilated (asterisks, lower left figure). Between the glands (Gl) is a lamina propria (LP) that contains considerable numbers of lymphocytes and other cells of the immune system. Two rectangles mark areas of the mucosa that are examined at higher magnification in figures below.
show rounded nuclei; however, other smooth muscle cells appear as more or less rounded eosinophilic areas. These smooth muscle cells have been cut in cross section. Just above these cross-sectioned smooth muscle cells are others that have been cut longitudinally; they display elongate nuclei and elongate strands of eosinophilic cytoplasm.
goblet cells increase in number. Other cells in the gland are enteroendocrine cells, not easily identified in routine H&E–stained paraffin sections, and, in the deep part of the gland, undifferentiated cells of the replicative zone, derived from the stem cells in the base of the crypt. The undifferentiated cells are readily identified if they are undergoing division, by virtue of the mitotic figures (M) they display (see figure on left).
KEY A, adipose tissue AC, absorptive cells BV, blood vessels GC, goblet cells GI, intestinal glands LP, lamina propria M, mitotic figures ME, muscularis externa ME(c), circular layer of muscularis externa ME(l), longitudinal layer of muscularis externa MM, muscularis mucosae Muc, mucosa S, serosa SubM, submucosa TC, tenia coli arrowheads, smooth muscle cells showing rounded nuclei arrows, opening of intestinal glands asterisks, lumen of intestinal glands