Digestion of Food in an Animal with a Simple Stomach

In a monogastric digestive system, food is chewed, swallowed, and enters a low-pH stomach where protein disassembly begins. From there, the food enters the small intestine where energy is digested and absorbed. Enzymes from the liver and pancreas assist in small intestine digestion. Protein breakdown and absorption occur here too. After the small intestine extracts available nutrients, the feed passes through the large intestine where water is absorbed from the digested feed before faeces are excreted. Notice that there are no digestive structures that are capable of digesting high-fibre feeds like hay. Thus, neither carnivores nor omnivores can extract nutrients from these feedstuffs.

Click here to view a video that explains the fetal pig's digestive structure.

Digestion in the Stomach

In farm animals with a simple stomach, such as the pig and dog the following enzymes help with the digestion of food:

Pepsin: The cells of the mucosa of the stomach secrete the enzyme pepsin for protein digestion. Before pepsin can have any proteolytic effect, it has to be activated by the presence of hydrochloric acid. The activated pepsin then breaks down proteins into peptides. Food does not, however, stay in the stomach long enough for this process to be completed and enzymes in the small intestine have to complete this process.

Lipase: Only small quantities are found in the stomach juices. This is an enzyme that breaks down fats into fatty acids.

Hydrochloric acid (HCI): Activates pepsin and rennin and curdles milk.

Digestion in the Small Intestine

Pancreatic juice: The following enzymes are the most important ones formed/produced by the pancreas:

Trypsinogen: This is changed to trypsin by enterokinase, which is secreted by the small intestine. Trypsin breaks down protein into peptides and amino acids. Before trypsin can react, the medium in which it is dissolved must be alkaline and the proteins must be digested to a certain stage.

Pancreatic Lipase: This enzyme hydrolyses fats to fatty acids and glycerol. Most of the fat is absorbed in this form in the small intestine.

Pancreatic Amylase: This breaks down carbohydrates to maltose. The presence of bile possibly improves the action of amylase.

Intestinal Juice: Intestinal secretions also contain various enzymes, which, as is the case in the previous group, are responsible for the final steps in the digestion of:

• Proteins and peptides to amino acids,
• Compound sugars to glucose and fructose.