Pepsin 

Pepsin is a digestive enzyme that plays a crucial role in breaking down proteins in the stomach. It is produced by the stomach lining as an inactive precursor called pepsinogen, which is then activated to pepsin by the acidic environment of the stomach (specifically, hydrochloric acid). Once activated, pepsin begins to break down proteins into smaller peptides, which are further digested in the small intestine.

1.0Stomach

• The stomach lies below the diaphragm in the upper left region of the abdominal cavity. The beginning portion of the stomach that is attached to the esophagus is called the cardiac region. 
• The portion of the stomach that balloons over the cardiac portion are called the fundic region, or fundus. 
• The central part of the stomach is called the body, and the narrow portion that is connected to the small intestine is called the pyloric region or pylorus. 
• A sphincter called the pyloric sphincter controls substances from the pyloric region of the stomach into the small intestine. 

Functions of the stomach 

• Receive food from the esophagus, mix food with gastric juice. 
• Start protein digestion.
• Move food into the small intestine. 

Cells  of the Gastric gland in Stomach

• It is found in the fundus and body of the stomach and composed of the following cells:
• Mucous cells - Produce alkaline mucous, which protects the stomach wall itself from being damaged by the acid.
• Parietal cells. Produce HCL – hydrochloric acid, which makes the stomach content acidic.
• Chief cells. Produce enzymes, mostly pepsinogen.
• G-cells. Produce Gastrin hormone.
• D-cells. Secrete Somatostatin. 

2.0pH of Pepsin

• Pepsin is most active in a highly acidic environment, with an optimal pH range of about 1.5 to 2.5. 
• This low pH is provided by the hydrochloric acid (HCl) present in the stomach. 
• At this acidic pH, pepsin is able to efficiently break down proteins into smaller peptides.
• If the pH rises above this range (for example, if the stomach becomes less acidic), pepsin's activity decreases significantly. 
• At a pH above 5.0, pepsin becomes inactive, and at an even higher pH, it can denature, meaning it loses its structure and function. 
• This is why pepsin is specifically suited to function in the stomach, where the acidic environment supports its enzymatic activity.

3.0Uses of Pepsin

Pepsin is primarily used for its role in protein digestion within the body, but it also has several applications outside of its natural function. Here are the key uses of pepsin:

• Protein Digestion: Pepsin is crucial for breaking down dietary proteins into peptides in the stomach, which are then further digested into amino acids in the small intestine. This process is essential for the body to absorb and utilize proteins from food.
• Supplements: Pepsin is sometimes included in digestive enzyme supplements, particularly for individuals with low stomach acid (hypochlorhydria) or those who have difficulty digesting proteins.
• Biochemical Research: In laboratory settings, pepsin is used to digest proteins in studies related to protein structure and function. It is also used to prepare peptide fragments for further analysis, such as mass spectrometry.
• Food Industry: Pepsin is used in the food industry for the production of protein hydrolysates, which are used in various food products, such as flavorings and nutritional supplements.
• Leather Industry: Pepsin is utilized in the leather industry to help break down unwanted proteins in animal hides during the tanning process, improving the quality of the final leather product.

4.0Functions of pepsin in the stomach

1. Production and Activation:

• Pepsinogen Secretion: Pepsin is secreted by the cells in the lining of the stomach, specifically by the chief cells, in an inactive form called pepsinogen.
• Activation by Stomach Acid: When pepsinogen is released into the stomach, it encounters hydrochloric acid (HCl), which is produced by the parietal cells in the stomach lining. The acidic environment (with a pH of around 1.5 to 2.5) triggers the conversion of pepsinogen into its active form, pepsin.

2. Protein Digestion:

• Breaking Down Proteins: Once activated, pepsin starts breaking down the long chains of amino acids that make up proteins. It specifically targets peptide bonds, which are the links between amino acids in proteins. This breakdown process results in smaller fragments called peptides.
• Further Digestion: The peptides produced by pepsin action are then passed into the small intestine, where other enzymes continue the digestion process, breaking them down into individual amino acids that the body can absorb and use.

3. Optimal Environment:

• Acidic pH: Pepsin functions optimally in a highly acidic environment, which is why it is most active in the stomach, where the pH is very low. Outside of this acidic environment, pepsin becomes inactive.

4. Importance in Digestion:

• Essential for Protein Digestion: Pepsin is crucial for the digestion of dietary proteins, such as those found in meat, eggs, and dairy products. Without it, the body would not be able to efficiently break down these proteins into absorbable nutrients, leading to potential nutritional deficiencies.

5. Protection of the Stomach Lining:

• Mucus Barrier: The stomach lining produces a thick layer of mucus to protect itself from the acidic environment and the activity of pepsin. Without this protection, pepsin could damage the stomach's own tissues.