In HA23, the wall of the gall bladder is much narrower than in HA21&22. This section was taken from the thinner wall of the gall bladder, where it protrudes into the peritoneum and is covered by mesothelium. At low magnification, you can identify the layers of the gall bladder. The epithelium (arrowhead) and the lamina propria (LP) compose the mucosa. The muscularis externa (ME) consists of a thin layer of circularly arranged smooth muscle. The serosa (S) consists of loose connective tissue and a mesothelium.