The key difference between protein digestion in stomach and small intestine is that protein digestion in the stomach takes place by pepsin and hydrochloric acid while protein digestion in the small intestine takes place by trypsin and chymotrypsin secreted by the pancreas.
Food that we consume is subject to chemical and mechanical digestion in the digestive system. Once the food is digested, the nutrients are absorbed into our bloodstream through the small intestine. Protein digestion takes place in two stages: in the stomach and in the first part of the small intestine (duodenum) by proteases. In the stomach, pepsin breaks down proteins into amino acids and oligopeptides. Further digestion of oligopeptides into amino acids, dipeptides and tripeptides takes place in the small intestine by pancreatic enzymes.
CONTENTS
1. Overview and Key Difference
2. What is Protein Digestion in the Stomach
3. What is Protein Digestion in the Small Intestine
4. Similarities Between Protein Digestion in Stomach and Small Intestine
5. Side by Side Comparison – Protein Digestion in Stomach vs Small Intestine in Tabular Form
6. Summary
What is Protein Digestion in the Stomach?
Protein digestion begins in the stomach. It is the first stage or preparation stage of protein digestion. When food reaches the stomach, it stimulates G cells of the mucosa of the gastric antrum and proximal duodenum, which secrete hormones into the bloodstream. Hormones stimulate the production and secretion of hydrochloric acid into the stomach. Gastric juice, due to its low pH, activates pepsin in order to digest proteins into amino acids.
Figure 01: Protein Digestion
Pepsin is the first enzyme involved in protein digestion in the stomach. Pepsin hydrolyses 10-20% of the proteins in the meal. As a result, a mixture of peptides and amino acids are produced in the stomach. Further digestion of peptides happens in the first part of the small intestine by the enzymes secreted by the pancreas.
What is Protein Digestion in the Small Intestine?
Protein digestion in the small intestine is the second or final stage of digestion of proteins in food. When the gastric content reaches the duodenum, the acidity of the content stimulates S cells to produce and release the hormone secretin into the bloodstream. Hormones stimulate the secretion of alkaline pancreatic juice in order to neutralize gastric content into neutral pH. Moreover, amino acids in the gastric content stimulate the exocrine pancreas to secrete a juice rich in trypsinogen, chymotrypsinogen and proelastase. They are inactive precursors – the zymogens. These zymogens are then activated into trypsin and chymotrypsin and carry out further digestion of proteins in the duodenum. These enzymes cleave proteins into polypeptides and then finally into amino acids.
What are the Similarities Between Protein Digestion in Stomach and Small Intestine?
- Protein digestion in the stomach and small intestine are the two stages of protein digestion.
- Enzymes catalyze both stages.
What is the Difference Between Protein Digestion in Stomach and Small Intestine?
Protein digestion in the stomach is the first stage of protein digestion which is catalyzed by pepsin. In contrast, protein digestion in the small intestine is the second stage of protein digestion which is catalyzed by trypsin and chymotrypsin. So, this is the key difference between protein digestion in stomach and small intestine.
Moreover, in the stomach, protein digestion happens in an acidic environment while in the small intestine, protein digestion happens in a neutral environment.
Below infographic shows more details of the difference between protein digestion in stomach and small intestine.
Summary – Protein Digestion in Stomach vs Small Intestine
Protein digestion in the stomach is catalyzed by HCl and pepsin while protein digestion in the small intestine is catalyzed by two enzymes called chymotrypsin and trypsin. Thus, this is the key difference between protein digestion in stomach and small intestine. Protein digestion in the stomach takes place under acidic environment while protein digestion in the small intestine takes place under a neutral environment.
Reference:
1. Calabrese, Allison, et al. “Protein Digestion and Absorption.” Human Nutrition DEPRECATED, Available here.
2. “Protein Digestion In The Stomach And Small Intestine”. Tuscany Diet, 2020, Available here.
Image Courtesy:
1. “2429 Digestion of Proteins (Physiology)” By OpenStax College – Anatomy & Physiology, Connexions Web site, Jun 19, 2013 (CC BY 3.0) via Commons Wikimedia