Inside a Human's Stomach: The Process of Digestion

Dec 28, 2011
Stetson Thacker

Digestive System - Gray's Anatomy

A summary of the complex process of digestion in humans, beginning with the ingestion of food and ending in its degradation, absorption, and excretion.

All organisms need energy to live. There are two ways that organisms can garner energy: producing it themselves or by consuming the producers. The latter is the way in which humans garner energy; however, this is not a simple process. When we consume other organisms we have to break down what we take in so that it can be utilized by our bodies. The digestive system is responsible for this energy-gleaning process.

The Process of Digestion

After food is taken into the body by the mouth, it is chewed so that the surface area of the food particles is increased. The increase in surface area of the food allows for preliminary enzymes in saliva such as salivary amylase to degrade the food particles more effectively. The food is then shaped into a ball called a bolus, which passes through the pharynx into the esophagus. The esophagus moves the bolus of food down to the stomach by rhythmic, wavelike contractions of the smooth muscles in the esophagus; this process is called peristalsis.

In the Stomach

When food reaches the stomach it is mixed with gastric juice, an amalgam of digestive enzymes and hydrochloric acid, HCl. The stomach accomplishes several different tasks in the digestive process: storage, mixing, physical breakdown, chemical breakdown, and controlled release. The stomach stores food when a larger amount is ingested than can be broken down — the stomach can store from two to four liters of food material. As mentioned above, the stomach mixes food with gastric juices and this mixing created a thick, creamy substance called chyme. The physical breakdown occurs because the stomach muscles churn the contents of the stomach. The chemical breakdown occurs because HCl causes ingested proteins to denature and activates enzymes called pepsins, which further breakdown proteins. Finally, the stomach moves the chyme into the small intestines by controlled release of the chyme through the pyloric sphincter.

The Intestines

The first 25 centimeters of the small intestine is called the duodenum, which is a source of several important enzymes: aminopeptidase, maltase, lactase, and phosphatase. These enzymes continue to digest the contents of the chyme. Aminopeptidase breaks down proteins; maltase and lactase break down sugars; and phosphatase breaks down nucleotides. These are not the only active enzymes and chemicals participating in the digestion that occurs in the duodenum because both the pancreas and liver add enzymes and bile, respectively.

After the digestion that occurs in the duodenum, the remaining six meters of the small intestines absorb the broken down products into fingerlike projections called villi and microvilli. The absorbed nutrients are then transferred to the circulatory and lymphatic system where they can be of use to the body.

The waste from the small intestines is then transferred to the large intestines, which reabsorb water into the body so that homeostasis can be maintained. This creates solid waste in the large intestines that is called feces. Feces are stored at the end of the large intestine, which is an area called the rectum. Finally, the feces are excreted through the anus. Although the excretion of waste is not a task of the digestive system, it is intrinsically linked to it by the intestines.