The caecum is part of the digestive tract. It is the first part of the large intestine that digesting food enters after leaving the small intestine, and is shaped like a sac. Separating the caecum from the small intestine is the ileocecal valve, also called Bauhin's valve, and the appendix protrudes from the lower part of the caecum.
As part of the large intestine, the caecum creates a space for liquids to empty into from the small intestine. During digestion, the small intestine absorbs nutrients from solid foods, and passes the solid waste products and liquid into the large intestine for absorption into the body. The caecum acts as a receptacle for the liquid products passed into the large intestine.
More than just a reservoir for liquids, the caecum is responsible for the absorption of salts and electrolytes into the body from liquids. The muscle tissue of the caecum contracts, causing the liquid products to churn. This churning extracts salts and electrolytes, such as sodium and potassium. These salts are then absorbed into the mucus membrane of the caecum. Humans lose salts and electrolytes as they sweat, and must replace these nutrients to carry electrical charges between cells. The caecum separates these salts from the liquids consumed and absorbs them into the body.
Another important function of the caecum is to lubricate the solid waste that passes into the large intestine, mixing this waste with mucus. A thick mucus membrane lines the caecum, and produces the mucus necessary to lubricate the solid waste. The large intestine extracts liquid from the waste products, making it necessary for the mucus to lubricate the solid waste and allow it to pass through the rest of the large intestine.
The caecum is also responsible for breaking down the cellulose fibres from digesting plant matter. Animals, both herbivores and omnivores, take in cellulose when eating plants. Bacteria and enzymes in the caecum of these animals cause fermentation that breaks down cellulose fibres, which then allows the rest of the large intestine to digest the nutrients from cellulose.
Caecum in Animals
The caecum functions differently in various animal species. Though most vertebrates' digestive systems include a caecum, carnivores such as tigers and wolves have either a very small caecum, or it is nonexistent. Since these animals do not consume plant matter, the caecum is unnecessary. The caecum of herbivores is much larger than the caecum of omnivores. These animals consume more cellulose and water, making a larger caecum necessary for effective digestion.