Laxative action. Artwork of a laxative to treat constipation, in the large intestine, or colon. Constipation involves infrequent or difficult passing of faeces. The arrows show a clear laxative (at upper right) acting on the intestinal mucosa, or lining (pink). Laxatives make the faeces easier to expel through lubrication or by increasing the amount of water the faeces absorb. The mucosa is highly folded and pitted with openings (at upper right) to create a larger surface for water absorption. Most laxatives work by temporarily interfering with this absorption. Below the mucosa is the muscularis externa (red & light pink), a layer of smooth muscle.