The large intestine absorbs the water left in any undigested food matter and passes unused waste material from the body. It also absorbs important vitamins like vitamin K, B12, riboflavin, and thiamine and it houses friendly bacteria that produce other vitamins and perform other helpful functions.
The mucosa of the large intestine secretes bicarbonates to reduce acidity in the gut and serves as a protective barrier against infection. The large intestine also contains lymphoid tissue that produces antibodies that protect the body from harmful bacteria. The large intestine is approximately 5 feet long and consists of the cecum, colon and rectum. The cecum is a pouch that connects the small intestine with the colon of the large intestine. A valve in the cecum called the ileocecal valve controls the movement of undigested food, vitamins and water into the colon.
The colon is the largest part of the large intestine. The colon absorbs water to form stool, absorbs vitamins, secretes bicarbonates to neutralize acidity and produces antibodies. It consists of the ascending colon, transverse colon, descending colon and sigmoid colon.
The rectum receives stool from the sigmoid colon and stores it until the stool is expelled from the body through the anus.