Digestive System

The digestive system is responsible for processing and extracting nutrients from the food we eat to provide energy and support bodily functions. Its main functions include ingestion, digestion, absorption, motility, secretion, and elimination. Ingestion involves taking in food through the mouth, followed by digestion where food is broken down into smaller molecules.

Absorption occurs when nutrients are absorbed into the bloodstream, while motility helps move food through the digestive tract. Secretion involves releasing enzymes and other substances for digestion. Finally, elimination occurs when waste products are removed from the body as faeces. The digestive system plays a crucial role in maintaining overall health and well-being.

The digestive system includes a group of organs and structures necessary for good digestion to take place. 

• Mouth: The mouth is the beginning of the digestive system. Food is prepared in the mouth to make it easier to digest. Even before eating, in the presence of food, the salivary glands in the mouth are activated and begin to produce saliva. Saliva mixes with food so the body can make better use of its nutrients. Teeth help break up food to optimise digestion. When swallowing, the tongue pushes the food down the throat and it begins its journey through the digestive system. 

• Oesophagus: When food is swallowed, it passes through a tube of muscular tissue that leads to the stomach. This muscular tube is the oesophagus which performs contraction movements known as peristalsis. These movements of the oesophagus push food towards the stomach. Between the oesophagus and the stomach is a ring that acts as a sphincter. The function of the lower esophageal sphincter is to prevent food from flowing back from the stomach into the oesophagus. When the lower esophageal sphincter fails or is weak, gastroesophageal reflux occurs due to the return of gastric contents into the oesophagus. 

• Stomach: The stomach is a hollow organ also made of muscle tissue. It is shaped like a bean and is characterised by producing stomach enzymes to mix with food and continue breaking it down. When stomach acid breaks down food enough, it continues its journey through the digestive system. 

• Small intestines: When leaving the stomach, food passes through the small intestine. The first portion of the small intestine is the duodenum where they are mixed with bile from the gallbladder. Also in the duodenum, the exocrine pancreas releases an acid to continue the breakdown of food. Throughout the entire digestive tract, peristaltic movements occur to propel food forward on its way through the digestive tract.

Also, peristalsis helps digestive juices mix better with food to break it down. 

After the food has been mixed with digestive enzymes in the duodenum, it is propelled towards the jejunum and ileum, which are the lower part of the small intestine and whose main function is to absorb all the nutrients from the food. Nutrients from food such as vitamins, minerals, proteins, fats, and carbohydrates pass into the blood to be distributed throughout the body. 

• Large intestines: Also known as the colon, is a muscular tube that is responsible for absorbing water and processing food waste. Food passes through the colon for final absorption before formation of faeces and then it is propelled to the rectum for elimination  

• Rectum: The rectum receives faeces from the colon, and this is where a signal is sent to the brain letting it know to have a bowel movement.  

• Anus: The anorectal canal and the anus is the last portion of the digestive tract through which faeces leave the body. 

• Pancreas: The pancreas has a portion known as the exocrine pancreas which is responsible for producing substances that break down proteins, gases, and carbohydrates. In addition, the insulin produced by the endocrine pancreas allows the body to use the sugar in food as a source of energy. 

• Liver: Produces a substance known as bile which is stored in the gallbladder to be released in the small intestine. Bile from the liver helps digest food. 

• Intestinal microbiota: The billions of intestinal bacteria that make up the bacterial flora. They are attached to the intestinal walls. The intestinal microbiota is involved in metabolic activities, the absorption of nutrients, and in the defence of the body against harmful intestinal microorganisms. 

• Gallbladder: The gallbladder is a small organ located beneath the liver that stores and concentrates bile produced by the liver. When we consume fatty foods, the gallbladder releases bile into the small intestine to aid in the digestion and absorption of fats.

• Stomach acids: The primary stomach acid is hydrochloric acid (HCl), which is produced by the cells lining the stomach walls. Other important substances in the stomach include pepsin, an enzyme responsible for protein digestion, and mucus, which helps protect the stomach lining from the corrosive effects of stomach acid.