The gastrointestinal tract organs form a continuous tube that includes the oral cavity, pharynx, esophagus, stomach, small intestine, large intestine, and anus. The accessory digestive organs assist in the digestion of food. accessory digestive organs that are not glands include teeth, tongue, and gallbladder. accessory digestive glands produce secretions that empty into the GI tract. the accessory digestive glands are the salivary glands, liver and pancreas.
The GI tract is a hollow tube composed of four tunics:
1.) The mucosa is the innermost tunic, which consists of an epithelium, an underlying lamina propria, and a
thin layer of muscularis mucosae.The epithelium is in contact with the contents within the lumen.The lamina propria is composed of
areolar connective tissue that contains small blood vessels and nerves.The muscularis mucosae is a
thin layer of smooth muscle deep to the lamina propria, which causes slight movements in the
mucosa by contracting.
The submucosa is composed of areolar and dense irregular connective tissue containing many large blood
vessels, lymph vessels, and nerves.The submucosal nerve plexus innervates the smooth muscle and glands of the mucosa and
submucosa.Peyer patches are mucosa-associated lymphatic tissue of the ileum, which are housed
in the lamina propria of the mucosa and the submucosa.
The muscularis contains two layers of smooth muscle.The smooth muscle cells of the muscularis are organized into the inner circular layer and the outer
longitudinal layer. The myenteric nerve plexus controls the contractions of the muscularis. The
enteric nervous system is comprised of both the submucosal nerve plexus and the myenteric nerve
plexus. The inner circular layer of the muscularis is greatly thickened at several locations along the
GI tract to form a sphincter. Peristalsis is the alternating contraction sequence of both layers of the
muscularis for the purpose of propelling materials through the GI tract. Mixing is the kneading
motion of the GI tract that lacks directional movement.The outermost tunic may be either an adventitia or a serosa.An adventitia is composed of areolar connective tissue with dispersed collagen and elastic fibers
and is found outside of the peritoneal cavity.
A serosa has the same composition as the adventitia,
but it is covered by a visceral peritoneum and is found within the peritoneal cavity.