The Gastrointestinal System

Anatomy of the Digestive System

This lesson introduces the structures and functions of the digestive system.

The following are the functions of the digestive system:

  1. Take in food.
  2. Break down food.
  3. Absorb digested molecules.
  4. Provide nutrients.
  5. Eliminate wastes.

The digestive system consists of the digestive tract, which is a tube extending from the mouth to the anus, and the associated organs, which secrete fluids into the digestive tract. The term gastrointestinal tract technically refers to only the stomach and intestines.

The Path of Food

Food takes the path outlined below as it moves through the body.

The oral cavity, or the mouth, is the first part of the digestive system. It is bounded by the lips and cheeks and contains the teeth and tongue. Its primary function is to masticate, or chew, and moisten the food.

The pharynx, or throat, connects the mouth to the esophagus.

Gastrointestinal System Anatomy

Stomach Diagram

The esophagus is a muscular tube about 25 centimeters long. Food travels down it to the cardiac sphincter of the stomach.

The stomach is an enlarged segment of the digestive tract.
The opening of the stomach is the cardiac sphincter.
The muscular layer of the stomach is different from other regions because it has folds called rugae that increase the surface area.
The exit of the stomach is the pyloric sphincter.

The small intestine is about 6 meters long and consists of three parts: duodenum, jejunum, and ileum.

  • The duodenum has more villi (finger-like projections), has a larger diameter, and is thicker than the other two parts.
  • This increases the surface area in the duodenum, which allows for more absorption of nutrients.
  • The small intestine is the primary site for diffusion of nutrients into the blood.

The large intestine consists of the cecum, colon, rectum, and anal canal. The cecum is located where the small and large intestine meet.

  • The colon is about 1.5 to 1.8 meters long and consists of four parts: the ascending, transverse, descending, and sigmoid colon.
  • The primary function of the large intestine is to compress the waste and collect any excess water that can be recycled.
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