Under the microscope, the layers of the gallbladder wall can be seen. The gallbladder wall's innermost surface is lined by a single layer of columnar cells with an apical brush border of microvilli, very similar to intestinal absorptive cells. Underneath the epithelia is an underlying lamina propria, muscularis, perimuscular layer and serosa. Unlike elsewhere in the intestinal tract, the gallbladder does not have a muscularis mucosae, and the muscular fibres are not arranged in distinct layers. In greater detail, the layers are:
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- The epithelium is the innermost layer of the gallbladder, and is of simple columnar type. Underneath the epithelia is a lamina propria: together, these two layers are known as the mucosa.
- The submucosa is a thin layer of loose connective tissue with smaller blood vessels. It contains many elastin fibres, lymphatics, and in the neck of the gallbladder, glands which secrete mucous. The lymphatics of this layer help to drain water when the bile is concentrated, and the mucous glands may create a surface that protects the wall of the biliary tree.
- The muscularis, a layer of smooth muscular tissue. The interspersed muscle fibres lie in longitudinal, oblique and transverse directions, and are not arranged in separate layers. The muscle fibres here contract to expel bile from the gallbladder.
- The perimuscular ("around the muscle") fibrous tissue, another layer of connective tissue
- The serosa is a thick layer that covers the outer gallbladder, and is continuous with peritoneum, which lines the abdominal cavity. The serosa contains layer blood vessels and lymphatics.