The stomach is an important organ of the digestive system that sits between the esophagus and the small intestine. It is responsible for producing digestive enzymes and gastric acid to facilitate digestion.
When chewed food enters the stomach through the esophagus, the stomach will produce pepsin and gastric acid. Gastric acid can kill the bacteria and maintain a pH level of 2 to support the function of pepsin. With the help of the contraction of the gastric wall, the food is broken down into chyme. The stomach can hold about one litre of food.
The band of smooth muscle between the stomach and small intestine is called pyloric sphincter, which acts as a valve that controls the flow of chyme from the stomach to the duodenum.
The small intestine located between the stomach and the large intestine is responsible for absorption, and consists of three parts, namely the duodenum, jejunum and ileum.
The bile and pancreatic juice run from the pancreatic duct work in synergy in the duodenum. The digestive enzymes in the pancreatic juice not only break down the protein in the chyme and emulsify the fat, but also turn carbohydrates into glucose and neutralize the gastric acid.
The villi covering the jejunum further absorb the glucose, amino acid and fatty acid into to the blood vessels.
Like jejunum, the ileum is also covered with villi and mainly absorbs Vitamin B12, cholic acid and other nutrients.
The importance of gastric juice is always overlooked. In fact, the digestive fluid secreted by the stomach plays a key role in the digestive process. Imbalanced secretion of gastric juice not only hurts the digestive system, but may also cause damage of esophageal, gastric and duodenal mucosa. Hence, we should never underestimate its importance to our health.
Gastric juice is the highly acidic digestive fluid (pH 1.0-1.5) secreted by the gastric mucosal glands. It mainly contains gastric acid (hydrochloric acid), pepsin, rennet and a small amount of lipase, mucus and electrolytes. About 1,500ml to 2,500ml of gastric juice is produced per day.
- Gastric acid is an antibacterial agent that can suppress bacterial growth in the digestive system and prevent gastrointestinal diseases.
- Gastric acid can activate the pepsin to break down proteins.
- It also regulates the pH level of the body fluids and electrolyte metabolism.
The three phases of gastric acid secretion :
- Before a meal, the presentation, smell, taste or a vision of food will stimulate the cerebral cortex and promote gastric acid secretion.
- The food entering the stomach will directly stimulate the gastric glands to secrete gastric juice. The secretion will be further promoted by the parasympathetic nervous system and digestive tract hormones.
- When the food enters the small intestine, the secretion will be reduced.
1. Food：
Foods that stimulate gastric juice secretion, such as fruits, tea and a small amount of alcoholic drinks.
Foods that suppress gastric juice secretion, such as fat; excessive consumption of greasy foods will cause indigestion.
2. Emotion：
Being nervous, emotional or worried may stimulate the cerebral cortex and affect gastric juice secretion.
3. Endocrine system：
Corticosteroids can promote the generation of gastric acid and pepsin.
Meanwhile, we should not underestimate the destructive power of gastric acid. While it can kill bacteria and break down proteins in food, it can also damage the gastric wall and duodenal tissues. Experts found that damaged digestive tract mucosa does not occur on the mucosa that is not in contact with gastric acid, while animal tests have proven that it can be caused by continuous excessive acid secretion. It has also been clinically proven that patients with achlorhydria (e.g. pernicious anemia) are spared from damaged digestive tract mucosa, highlighting the close relationship between gastric acid and damaged digestive tract mucosa. Fortunately, there are some natural protective mechanisms in our body:
- The epithelial cells on the gastric and duodenal mucosa have adipoid-rich cell membranes that can protect the tissues against the excess gastric acid entering the mucosa through the epithelial cells.
- The mucus covering the mucosa can minimize the direct contact of mucosa and gastric acid. It can also absorb and neutralize the gastric juice.
- The self-regulation of gastric acid secretion: When the pH value in antrum and duodenum is too acidic (~pH 1.5), the gastric acid secretion will be suppressed by the gastrointestinal hormones (secretion) or nervous reflex.
These protective mechanisms can protect the gastrointestinal mucosa, but they can be undermined by a number of factors, causing different gastrointestinal problems. These adverse factors include:
| Bad eating habits | Irregular eating schedule Imbalanced diet Consumption of irritating foods or drinks, such as coffee, chilies and curry Consumption of heavy or greasy foods Consumption of foods or drinks that are too cold or too hot |
| Emotional problems | Anxiety Extreme emotional distress Overworriedness Stress |
| Irregular lifestyle | Overwork Irregular sleep schedule Insomnia |
| Bad habits | Smoking and drinking |
| Inappropriate use of drugs | E.g. aspirin, non-steroidal analgesic anti-inflammatory drugs, steroids and certain antibiotics |
| Pathogens | Such as Helicobacter pylori |
| Patients with certain diseases | Patients with emphysema, liver diseases or rheumatoid arthritis |
| Genetic factor | People with hereditary gastrointestinal disorders are more vulnerable to gastrointestinal diseases; Blood Type O |
These factors can stimulate the secretion of gastric acid or damage the gastrointestinal protective mechanisms, causing gastrointestinal diseases.
