Breakdown of the Food into Carbohydrates, Fats, and Proteins
According to the main ingredients of a pizza with cheese, onion, and pepperoni, there would be the following possible amounts of protein, fats, and carbohydrates for the average pizza size.
- Proteins: cheese contributes about 30 grams, onion contributes about 1 gram, pepperoni contributes 40 grams;
- Fats: the cheese is about 50 grams, the onion about 0.1 grams, and the pepperoni about 100 grams;
- Carbohydrates: the cheese is roughly 5 grams, the onion about 9 grams, and the pepperoni has no weight (0 grams).
Digestion Processes and Hormonal Mechanisms
Cephalic Phase
The cephalic phase of digestion begins when the medulla oblongata receives information about the product’s appearance. Activation of the nuclei of the vagus nerve leads to the secretion of histamine by the cells of the stomach. Histamine induces gastrin release in the antral region, activating gastric juice secretion (Blaker et al., 2022). During oral ingestion, carbohydrates are partially broken down by salivary alpha-amylase. Most likely due to the high-fat content of the pizza, some of it can be broken down into triglycerides in the oral cavity; however, proteins will never be digested in the mouth.
Gastric Phase
Secretion of acetylcholine by the primary cells of the stomach leads to secretin secretion by the S cells. Stretching of these cells leads to an even greater secretion of gastrin, which acts on the parietal cells. As a consequence, the concentration of hydrochloric acid increases due to its stimulation by histamine (Blaker et al., 2022). During the gastric phase, high concentrations of hydrochloric acid prevent the breakdown of carbohydrates but activate pepsinogen into pepsin, which coagulates proteins, and partial protein hydrolysis occurs. Small amounts of triglycerides are digested by gastric lipase.
Intestinal Phase
The intestinal phase is associated with the evacuation of chyme into the duodenum. In particular, cholecystokinin promotes pancreatic secretion. In the duodenum, starch is broken down to glucose by pancreatic amylase; sucrose and lactase in the small intestine break down sucrose and lactose (Blaker et al., 2022). Small intestinal lipase is the primary enzyme for digesting triglycerides. Pancreatic trypsin and chymotrypsin break down proteins into amino acids. Pizza digestion will occur primarily in the small intestine, based on the above.
Reference
Blaker, W., Bowers, J., Barlow, M., Hortsch, M., Bradshaw, E., Tallman, K., Campbell, B., Tarapore, R., Jablanovic, B., Dobbins, P., Shmaefsky, B., Christie-Pope, B., Sizemore, D., Culver, M., McLaughlin, D., Maring, B., Dukehart, P., Dentel, S., Tattersall, E. … Elf, P. (2022). Chapter 23: The digestive system. Anatomy and physiology. OpenStax. Web.