Anatomy of Gastrointestinal system

The gastrointestinal system comprises of the digestive tract and accessory organs. The digestive tract is a hollow muscular tube starting at the mouth, continuing through the pharynx, esophagus, stomach, intestines, rectum and ends at the anus. The accessory organs include the salivary gland, liver, pancreas and gall bladder, which secrete enzymes that help break down the food into nutrients. The food is propelled through the digestive system by peristaltic movements

The main function of the gastrointestinal tract is to break down the food consisting of protein, carbohydrates and fat into nutrients, which are absorbed into the body to provide energy. The wastes are excreted from the body as feces.

The oral cavity:

The oral cavity or mouth is responsible for intake of food. It consists of the

  • Tongue, which manipulates the food to get to the teeth. It also is able to sense taste, temperature and touch of the food, using sensors called papillae.
  • Palate helps push food to the teeth
  • Teeth mechanically chop the food

Chemical breakdown is done by the saliva

The salivary glands:

There are three pairs of salivary glands, parotid, sublingual and submandibular, which empty their secretion through ducts into the mouth. Salivation occurs due to taste, smell or appearance of food. Saliva helps to moisten the mouth and act as a lubricant. Saliva produces an enzyme called amylase, which help the first stage of the digestion process.

The esophagus:

The esophagus is a muscular tube that carries the food from the mouth to the stomach

The stomach:

The stomach is a J-shaped bag. The stomach function includes

  • Storage of food for about 4 hours
  • Mechanical breakdown of food by churning and mixing
  • Chemical breakdown by acids and enzymes
  • The acid destroys germs

The stomach produces a hormone called grehlin, which stimulates appetite

Small intestine:

The small intestine is made up of the:

  • Duodenum: into which pancreatic, gall bladder and liver secretions enter and digest the food
  • Jejunum: is where majority of digestion and absorption of nutrients occurs
  • Ileum: carries remnants of food to the caecum

The large intestine:

The large intestine consists of:

  • Appendix
  • Caecum
  • Ascending colon
  • Transverse colon
  • Descending colon
  • Sigmoid colon

The large intestine mainly absorbs water and passes on the undigested material to be excreted

Rectum:

The rectum holds the fecal matter before it is excreted through the anus. Thick bands of muscle called sphincter holds the feces in the rectum, till it is excreted. The glands secrete lubricant to enable feces to pass out smoothly. The main functions of the large intestine:

  • Accumulation of unabsorbed material to form feces
  • Digestion by bacteria
  • Resorption of water, salts, sugar and vitamins

Liver:

The liver is made up of 4 lobes and has several important functions:

  • It acts as a mechanical filter for blood from the intestines
  • It detoxifies the body by breaking down several metabolites like bilirubin and estrogen
  • It produces albumin and blood clotting factors
  • Produces bile and helps metabolism of nutrients
  • Bile produced by the liver enters the intestines and helps in digestion of lipids mainly

Gall bladder:

The gall bladder stores and thickens the bile secreted by the liver and empties it into the biliary system when required.

Pancreas:

The pancreas connects with the duodenum. It produces insulin, glucagon and other substances, which if deficient causes diabetes. It also produces enzymes to digest different components of food