Overview of Human Digestion

The human body has a monogastric digestive system, meaning it has one stomach chamber.

Digestion begins with the cephalic phase. During this phase, the brain signals the body to prepare for food intake, stimulating digestive secretions such as saliva and gastric juice.

Ingestion, the intake of food, happens in the oral cavity, also called the mouth.

The teeth mechanically break down large food particles while saliva from the salivary glands, which contains different enzymes like amylase and lipase, starts the process of chemical digestion.

Next, the tongue pushes the chewed, soft mass of food mixed with saliva into the pharynx, which opens into the esophagus. Through peristalsis, the rhythmic contraction of smooth muscles, the food mass moves in one direction down the esophagus and into the stomach.

The stomach is an acidic environment containing gastric juices, including key enzymes.

The lower esophageal sphincter at the junction between the esophagus and stomach prevents acidic stomach contents from damaging the esophagus.

As the stomach churns through the contraction and relaxation of smooth muscles, the contents turn into a mixture called chyme, which is partially digested food mixed with gastric juices.

Small amounts of chyme are then released by the pyloric sphincter toward the small intestine.

As chyme moves through the small intestine, nutrients are absorbed into the bloodstream by passing through the highly folded intestinal epithelial cell lining.

The remaining undigested material moves into the large intestine, where water is absorbed. The remaining waste material forms feces, which are stored in the rectum until excretion.