Absorptive cells outnumber goblet cells 3:1 (Fig 13.13) (6). Mature absorptive cells absorb water and electrolytes; have numerous short, regularly spaced microvilli; and are joined by junctional complexes and lateral desmosomes. The intercellular spaces are variably dilated depending on the physiologic activity of the colon (5). A glycocalyx covers the microvilli on the luminal surface of the epithelial cells. Microvilli increase in number and elongate as the cells mature. Hairlike, loosely packed projections extend perpendicularly from the plasma membrane into the lumen and radiate from the microvilli. Small, round, 30- to 100-nm vesicles, called C bodies, are embedded among the filaments (7). Similar bodies are seen in the apical cytoplasm of mature absorptive cells. These are called R bodies and measure 106 to 250 nm in diameter. As the cells mature, there is a concomitant migration of the R bodies to the apex of the cell. The cytoplasmic microfilaments form a loose, stratified network that retains the same basic organization as that found in the small intestine (8). The apical cytoplasm contains a terminal web composed of microfilaments and core rootlets. Mitochondria, lipid droplets, lysosomes, apical vesicles, and round basally located nuclei are present in the cytoplasm (5). These cells secrete secretory component, which participates in the epithelial translocation of IgA as discussed in Chapter 6.

There are more goblet cells in the large intestine than in the small intestine. They are most abundant in the sigmoid colon and rectum, with approximately one goblet cell for every four columnar cells (Figs. 13.12 and 13.13). Their broad shape creates the false impression that they constitute the majority of the cells. As they differentiate, they migrate toward the mucosal surface and become progressively filled
with mucus granules. The nucleus is compressed into a small dense structure in the basal region of the cell. Mucus secretion occurs throughout the life span of the cell. The membrane-bound mucin granules migrate toward the apical surface of the cell, where they are released by exocytosis. As the cells become more distended with mucin, the microvilli become sparser. The lateral cell surfaces are interlocked by cytoplasmic processes. Junctional complexes are present at the cell apices, and desmosomes are located at various points along the lateral surfaces.