Chapter 11, Problem 1RQ

What are the main functions of the stomach? What roles do enzymes and hormones play?

Summary Introduction

To determine: The main functions of the stomach.

Introduction: The digestive system consists of a collection of organs that help in the digestion of food materials and converts them into basic energy-rich molecules for supplying them to the entire body. The ingested complex nutrients are broken down into simpler molecules and are absorbed into the blood along with the electrolytes and water.

Explanation of Solution

Stomach is a major organ present in the digestive system. It is a hollow organ that produces different proteins and enzymes for breaking down food into simpler compounds. Stomach is a muscular sac that can expand and acts as a reservoir for the food and fluid. It can hold up to 1 to 1.5 L of fluid and food. The food from the esophagus is received by the stomach.

Gastric acids and digestive enzymes for the digestion of food are secreted in the stomach. The process of secretion requires five different types of secretory cell made up of gastric epithelium.

The two general functional activities of the stomach are as follows:

1. 1. Chyme formation: The stomach mixes and churns food with the produced juices to form chyme.
2. 2. Stimulates the protein digesting enzymes: It is important for facilitating the chemical digestion or denaturation of proteins. The hydrochloric acid (HCl) produced by the parietal cells activated the digestive enzyme.

Other functions of stomach are as follows:

• Stomach produces intrinsic factor. The production of intrinsic factor (a glycoprotein) is essential for the absorption of vitamin B₁₂ in the ileum.
• Delivery of chyme into the duodenum for further absorption process.
• Absorption of some fat-soluble substances like alcohol or aspirin.
• Low pH of the stomach possesses antimicrobial functions that inhibit the growth of microbes in the stomach.

Summary Introduction

To determine: The roles that enzymes and hormones play in digestion.

Introduction: The digestive system consists of a collection of organs that help in the digestion of food materials and converts them into basic energy-rich molecules for supplying them to the entire body. The ingested complex nutrients are broken down into simpler molecules and are absorbed into the blood along with the electrolytes and water.

Explanation of Solution

The roles that enzymes and hormones play in digestion are as follows:

• Gastrin hormone:Gastrin is a peptide hormone produced by enteroendocrine cells (G cells) present in the stomach lining and upper small intestine. Gastrin stimulates the gastric acid secretion by activating the gastric parietal. This helps the stomach to breakdown the proteins and absorbs certain vitamins. Gastrin stimulates the growth of mucosal cells in the acid-secreting part of the stomach.
• Pepsin: Pepsin is one of the major digestive enzymes that are produced in the stomach of many animals including humans. The gastric gland present in the stomach secretes hydrochloric acid that activates pepsinogen into pepsin. All the proteolytic enzymes are secreted as inactivated precursor primarily because, in stomach, proteolytic enzymes would destroy the proteins within the cells that produce them. In addition to this, the proteolytic enzymes would digest the linings of the digestive tract and destroy the cells present in the main and accessory ducts of the digestive system when it passes through it.