Functional Anatomy of the Digestive System Quiz

Gastrointestinal Tract Structure

• The GI tract is a long tube with an input (mouth) and output (anus) and specialized areas with direct input from associated organs (liver, pancreas, and gallbladder).
• Sphincters along the tract separate major sections, regulating the flow of food into the stomach and chyme out of the stomach and through the intestines.

Functional Anatomy of Digestive System

• The digestive system consists of the gastrointestinal tract (GI tract) and accessory organs that help in digestion and absorption.
• The GI tract is a tubular structure, approximately 30 feet long, extending from the mouth to the anus, with both ends open to the external environment.

Primary and Accessory Digestive Organs

• Primary digestive organs: mouth, pharynx, esophagus, stomach, small intestine, and large intestine, where actual digestion takes place.
• Accessory digestive organs: teeth, tongue, salivary glands, exocrine part of pancreas, liver, and gallbladder, which help primary digestive organs in digestion.

Mouth

• Mechanical digestion occurs through mastication (chewing), and chemical digestion begins on starch and lipids.
• Salivary glands secrete saliva, which buffers and digests food, and lubricates it for swallowing.

Esophagus

• The esophagus is a tube that passes through the chest and into the stomach, with relaxation of the upper esophageal sphincter allowing the bolus of food to enter.
• The lower esophageal sphincter (LES) relaxes to allow the bolus into the stomach.

Stomach

• The stomach is a pouch for food storage, secretion of digestive enzymes and hydrochloric acid (HCl), and mixing of food and digestive juices to make chyme.
• The pyloric sphincter regulates the entry of chyme into the small intestine.

Small Intestine

• The small intestine is composed of three sections: duodenum (∼1 foot long), jejunum (∼8 feet long), and ileum (∼10 feet long).
• Secretions from the liver, gallbladder, and pancreas enter the small intestine via the common bile duct and through the sphincter of Oddi.
• The small intestine has finger-like projections (villus brush border) that increase the surface area for absorption.
• There is only one layer of intestinal epithelial cells (enterocytes) between the lumen and the systemic blood supply.
• Enterocytes are vulnerable to the harsh environment of the gut lumen and need protection from intestinal buffers and mucus.

Digestion and Absorption in the Small Intestine

• The majority of digestion occurs in the jejunum by pancreatic enzymatic action.
• Absorption occurs along the small intestine, with most nutrients absorbed by the mid-jejunum.
• The terminal part of the ileum is the site of vitamin B12 absorption and recycling of bile.

Large Intestine

• The large intestine functions in dehydration of chyme to produce feces and storage.
• Chyme that remains in the tract leaves the small intestine through the ileocecal sphincter and moves into the large intestine.