Continued from: Digestive diet. How it works. Part I
The stomach when empty is about the size of your hands held palm to palm. Its walls are much thicker than any other part of the digestive tract. The stomach is designed to knead and churn the food with the gastric digestive juices, which are secreted by the millions of glands lining the stomach wall. These gastric juices are mainly comprised of the enzymes pepsin and hydrochloric acid, which are responsible for the breakdown of proteins. Rennin, which is secreted in less quantity, coagulates or curdles certain types of foods (such as the caseinogen of milk solids) so that they can be exposed for a longer period of time to the action of the digestive juices. Another important enzyme present in the gastric juices is pepsinogen, which terminates the action of the saliva. Together with hydrochloric acid, it also destroys germs which might be present in the food. The amount of gastric juices secreted depends on the amount of food consumed as well as the person’s appetite. Tasteless, monotonous food produces little gastric juices, whereas pleasant, tasteful food encourages abundant secretions of these juices. However, on an average several litres a day are utilized. An average meal requires about 800 cc of gastric juices to be secreted from the stomach walls. This is not all released during meals; about 200 cc are secreted while eating and the remainder during the subsequent time that the food remains in the stomach.
The Digestive System
Given figures denote time taken for first particles of food eaten to reach that point
The length of time that solid food stays in the stomach varies from two to six hours, depending on the nature of the food. Fats are more difficult than proteins and carbohydrates, and therefore remain in the stomach longer. Water and other liquids do not stay in the stomach for more than a few minutes. They pass almost immediately into the small intestine and are quickly absorbed into the bloodstream.
From the stomach the food gradually passes into the small intestine through the pyloric valve in a semi-liquid form called chyme. The first section of the small intestine is called the duodenum. Within the duodenum further digestive juices are mixed with the food from various glands within the gastrointestinal system. The pancreas is the most important of these glands. The pancreatic secretions contain powerful enzymes including amylase, lipase and trypsin which are capable of digesting all types of foodstuffs – proteins, fats and carbohydrates. The pancreas does not function properly unless the food has already been sufficiently mixed with hydrochloric acid from the stomach. This is why some people who secrete insufficient hydrochloric acid fail to digest their food properly. About 600 cc of pancreatic juices are used every day.
Another important gland in the digestive system is the liver, which is the biggest single gland in the body. It is primarily concerned with the storage of food after it has been absorbed by the blood. It changes and stores the food in the form of glycogen. When energy or nutrition is required in any part of the body, the glycogen is converted into glucose (blood sugar) and discharged into the bloodstream for distribution. It also aids the pancreatic juice, lipase, in breaking down the fats. It performs this function by producing a clear, golden-coloured liquid called bile which is stored in the gallbladder, where it becomes more concentrated. This liquid not only aids the pancreatic juices but also helps to keep the food moving in the small intestine by stimulating the peristalsis.
Continue to: Digestive diet. How it works. Part III