Figure 1529

Diagram of different forms of immunoglobulin A (IgA). This drawing shows the monomer of IgA (top). The dimer of IgA is a product of the plasma cell and contains a J chain (J) connecting two monomers (middle). The secretory component (SC), a product of the epithelial cells, is added to the dimer to form secretory IgA (slgA, bottom).

apical plasma membrane, where it is released into the lumen as secretory IgA (slgA). This process of synthesis and secretion of IgA is essentially identical to that which occurs in the more distal parts of the gastrointestinal tract, where slgA is transported across the absorptive columnar epithelium of the small intestine and colon.

Saliva contains water, various proteins, and electrolytes

Saliva contains chiefly water, proteins and glycoproteins (enzymes and antibodies), and electrolytes. It has a high potassium concentration that is approximately 7 times that of blood, a sodium concentration approximately one tenth that of blood, a bicarbonate concentration approximately 3 times that of blood, and significant amounts of calcium, phosphorus, chloride, thiocyanate, and urea. Lysozyme and «-amylase are the principal enzymes present (see Table 15.1).

monomer IgA (7S)

secretory IgA (11S)

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