Describe how digestion is controlled in the stomach. You should include a discussion of the enzymes and other secretions involved and both neural and hormonal control.
Digestion is the chemical break down of food in to smaller particles. This is done to allow absorption in the body, which is then used an energy fuel.
The digestion process involves the mixing of food with a number of digestive juices. This is done in the digestive tract, where larger molecules of food are broken down into smaller molecules. One of the main functions of the stomach is to break down large fat and protein molecules in food so that it can be easily absorbed in the small intestine. In order for this process to happen the stomach releases a number of gastric juices, which contain hydrochloric acid and a number of other digestive enzymes. The acidic juices vary from pH 1-3; these are used to kill the bacteria in food.
The whole process of digestion begins in the mouth and is finished in the small intestine.
The digestion process is important because, once the larger molecules are broken down to smaller molecules it is then ready to build and nourish cells and provide energy.
The digestive tract consists of the mouth, oesophagus, stomach, small intestine and large intestine. Within these organs is a lining called the mucosa. The mucosa lining in the stomach, small intestine and mouth contains small glands that produce juices that help food to be digested.
The muscular wall of the stomach works vigorously in mixing food with gastric juices that produces a mixture known as chyme. The walls of the stomach consist of strong muscles that mix and churn the food that has entered the stomach. The walls of the stomach are lining filled, which are filled with tiny glands; the glands secrete gastric juices such as water and enzymes, which help in the food to be digested in the stomach.
The stomach consists of three layers, the inner most layers being the mucosa, submucosa, muscularis externa and the outermost layer being the serosa. The mucosa is where the stomach acid is secreted in the stomach. The mucus that is present protects the stomach from HCL and pepsin.
The submucosa consists of connective tissues, which separate the mucosa from the muscularis externa. The muscularis externa has three layers of smooth muscle, which are responsible for mixing materials that have come into the stomach with the digestive enzymes and that move through the stomach. The outermost layer serosa is a layer of connective tissue that connects the lining of the abdominal cavity.
The main hormones that function and manage the digestive system are created and released by cells in the mucosa layer of the stomach and small intestine. The hormones that are released in the blood of the digestive tract pass through to the heart and return to the digestive system, where they stimulate digestive juices.
The three main hormones that control digestion are gastrin, secretin and cholecystokinin. However, there are additional hormones in the digestive system that control appetite, these are gherlin and peptide YY both of which are produced in the absence of food. Both hormones work on the brain to help adjust the intake of food for energy.
Gastrin is a hormone, which stimulates the stomach to secrete gastric juices. When gastrin is present in the blood it stimulates the production of pepsinogen that is converted to pepsin, which digests proteins.
Hydrochloric acid is involved in converting pepsinogen to pepsin.
Pepsin breaks protein down further to peptides. Hydrochloric acid is important in maintaining the pH of the stomach and can dissolve food and kill any microorganisms.
The digestive system is also controlled by nerve regulators, which help the actions of the digestive system. There are two types of nerve regulators, first of which is the extrinsic nerve. The extrinsic nerve comes to the digestive system from the brain. It releases acetylcholine and adrenaline. The second nerve regulator is the intrinsic nerve, which is made up of very thick network fixed in the walls of the stomach and small intestines. The intrinsic nerve acts when the walls of the stomach and small intestines are stretched by food.
Enzymes in the stomach work to break down food particles into smaller particles. Pepsin is an enzyme in the stomach that breaks down most of the protein in the food that has been digested. Pepsin is chemically converted from the inactive pepsinogen, which is secreted in many forms by the peptic and mucous cells in the stomach.
The inactive form only turns to active pepsin as soon as it comes into contact with hydrochloric acid in the stomach.
In the digestion process there are almost 22 different types of enzymes involved. Enzymes become active as soon as the food is entered through the mouth. The salivary amylase is available in the salvia of the mouth.
The hormones that control digestion are gastrin, secretin and cholecystokinin. Gastrin is a hormone that produces an acid in the stomach that is used for dissolving and digesting foods. Gastrin is also used for normal cell growth in the lining of the stomach, colon and small intestines. The secretin hormone is when the pancreas signals out a digestive juice rich in bicarbonate, which helps neutralise stomach acid. Secretin is also known to stimulate the stomach to produce pepsin, which is used to digest protein, and used in the liver to produce bile. The cholecystokinin also known as the CCK hormone is used in the pancreas to produce an enzyme of the pancreatic juice and is used to empty the gallbladder. CCK promotes normal cell growth in the pancreas,