There are four main stages along the digestive tract. The first is the mouth, which cuts and chews food into small chunks. The second is the stomach, where food is churned into a liquid called chyme. Inside the small intestine, the chyme is broken down into nutrients that can be absorbed and carried to the body’s cells. Finally, anything not used enters the large intestine, where it dries out to become faeces.
Mouth
The mouth is the beginning of the digestive tract. In fact, digestion starts here as soon as you take the first bite of a meal. Food is chewed up inside the mouth.
Parotid gland
This is the largest salivary gland. In humans, the two parotid glands are present on either side of the mouth and in front of both ears. They are the largest of the salivary glands. Each parotid is wrapped around the mandibular ramus, and secretes serous saliva through the parotid duct into the mouth, to facilitate mastication and swallowing and to begin the digestion of starches.
Teeth
The teeth grind down food, making it easier to swallow. Teeth are like bones, but they are a lot stronger. They have four tissues: enamel, dentin, cementum, and pulp.
Epiglottis
The epiglottis is a flexible flap at the superior end of the larynx in the throat. It acts as a switch between the larynx and the esophagus to permit air to enter the airway to the lungs and food to pass into the gastrointestinal tract. A flap of cartilage stops food or liquid entering the trachea (windpipe) during swallowing.
Tongue
Food moves to the back of the mouth where the tongue helps push it down the throat. When you’re ready to swallow, the tongue pushes a tiny bit of mushed-up food called a bolus toward the back of your throat and into the opening of your esophagus, the second part of the digestive tract.
Pharynx
The pharynx, or throat, connects the mouth to the oesophagus. Branching off the pharynx is the esophagus, which carries food to your stomach, and your trachea or windpipe, which carries air to your lungs.
Salivary glands
These glands release saliva into the mouth during chewing. It also helps break down carbohydrates (with salivary amylase, formerly known as ptyalin) and lubricates the passage of food down from the oro-pharynx to the esophagus to the stomach.
Oesophagus
Muscles in this tube push swallowed food from the throat to the stomach. When you swallow food, the walls of the oesophagus squeeze together (contract). This moves the food down the oesophagus to the stomach.
Liver
The liver has many functions, but two of its main functions within the digestive system are to make and secrete bile, and to cleanse and purify the blood coming from the small intestine containing the nutrients just absorbed.
Stomach
Food is churned by muscle contractions and broken down by acid juices into creamy chyme. When it leaves the stomach, food is the consistency of a liquid or paste. From there the food moves to the small intestine.
Gallbladder
The gallbladder is a pear-shaped reservoir that sits just under the liver and stores bile. Bile is made in the liver then if it needs to be stored travels to the gallbladder through a channel called the cystic duct. A green fluid, called bile, is released by the gallbladder to help break down fatty foods.
Pancreas
The pancreas releases enzymes, which help to digest food, into the small intestine. These enzymes break down protein, fat, and carbohydrates from the food we eat.
Small intestine
Most digestion takes place in the small intestine, where nutrients are absorbed by the bloodstream. The small intestine continues the process of breaking down food by using enzymes released by the pancreas and bile from the liver. Bile is a compound that aids in the digestion of fat and eliminates waste products from the blood.
Ascending colon
This is the first part of the large intestine. It is usually located on the right side of the body, extending from the cecum upward. Although the colon is a continuous structure, the piece that is considered the ascending colon ends where the colon bends, just below the liver and gallbladder.
Large intestine
Watery waste from the small intestine is absorbed into the large intestine to form faeces. The ileocecal valve of the ileum (small intestine) passes material into the large intestine at the cecum. Material passes through the ascending, transverse, descending and sigmoid portions of the colon, and finally into the rectum. From the rectum, the waste is expelled from the body.
Descending colon
This is the last part of the large intestine. Its function is to reabsorb fluids and process waste products from the body and prepare for its elimination. The colon consists of four parts: descending colon, ascending colon, transverse colon, and sigmoid colon.
Appendix
The appendix sits at the junction of the small intestine and large intestine. It’s a thin tube about four inches long. Normally, the appendix sits in the lower right abdomen. Digestive bacteria are stored here in case levels in the intestines need topping up.
Rectum
The rectum is an 8-inch chamber that connects the colon to the anus. This muscular chamber holds and expels faeces.
Anus
The anus is the last part of the digestive tract. It consists of the pelvic floor muscles and the two anal sphincters (internal and external muscles). Faeces leave through this opening at the end of the digestive tract.
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