The Biological Process of Digestion

The Mouth Cavity and Pharynx

The mouth cavity contains the teeth and tongue. Dentition is made up of hard parts embedded in the jaw and covered by dental enamel. The tongue is a powerful muscle that contains taste receptors. The pharynx is a cavity common to both the digestive and respiratory systems.

The Esophagus and Stomach

The esophagus is a muscular conduit that connects the pharynx to the stomach. Regarding the digestive tract, the stomach is a widening of the tract that binds to the esophagus through a valve called the pylorus.

The Small and Large Intestines

The Small Intestine

The small intestine is a tube bending over 6 meters in many loops. It is divided into three regions: the duodenum, the jejunum, and the ileum.

The Large Intestine

The large intestine is a tube wider and shorter than the small intestine, measuring approximately 1.5 meters. It consists of three regions: the cecum (blind sac), the U-shaped colon, and the rectum, which is the end of the digestive tube.

Digestive Glands and Enzymes

Digestive glands are organs that develop digestive juices and discharge them within the digestive tract. These liquid digestive juices contain enzymes, which are protein molecules that speed up chemical reactions.

Types of Digestive Glands

• Gastric glands: Located in the walls of the stomach.
• Intestinal glands: Located in the bowel movements of the digestive tract.
• Salivary glands: Located under the tongue.
• Pancreas: Located below the stomach; it produces pancreatic juice.
• Liver: A large gland that produces bile, which contains bile salts.

The Stages of the Digestion Process

Digestion is a set of mechanical and chemical transformations leading to the liquefaction of food. This process involves the following stages:

• Ingestion: Food is taken in by the mouth. Solid foods are crushed by the teeth and insalivated. Saliva contains enzymes that begin the chemical digestion of carbohydrates. After mastication, the food becomes a bolus, which reaches the stomach through the pharynx and esophagus.
• Stomach Digestion: In the stomach, mechanical fragmentation of the food continues through peristaltic movements. The food loses its appearance and becomes chyme.
• Intestinal Digestion: In the small intestine, the chyme is mixed by peristalsis. Mucus serves a protective function. Pancreatic juice contains digestive enzymes capable of chemically digesting glucids. Bile does not contain digestive enzymes but acts like a powerful detergent. Intestinal juice is composed of digestive enzymes to complete the final stages of digestion for carbohydrates, protein molecules, and lipids, forming a liquid called chyle.

Nutrient Absorption

After digestion, absorption occurs. This is the process of nutrients passing from the small intestine into the blood and lymph.