The human digestive system breaks down food from larger
molecules into smaller components that can be used by the cells as sources of
energy and to build and repair tissues. The digestion process itself involves complex
mechanical and chemical action that requires energy. The digestive system
consists of two main components: the digestive tract-which starts from the
mouth and ended up in the anus, and internal organs that are not part of the digestive
tract, but play important roles in food digestion.
Parts of the digestive system
The components of the digestive tract are the mouth, pharynx,
esophagus, stomach, small intestines, large intestines, rectum, and the anus. These
hollow organs are lined with a mucosal layer that contains glands that produce protective
mucus, acid, and digestive juices. The pancreas is an organ that produce
enzymes that help break down the food. Besides producing digestive enzymes, the
liver also serves functions related to detoxification, metabolism, and energy storage.
The gallbladder stores bile acid until it is needed in the intestines.
Food passes from the mouth through the esophagus into the
stomach where acid and digestive enzymes break it down before it passes to the
small intestines. In the small intestines, most of the digestion process takes
place and food components are absorbed. The remnants of the food passed to the large
intestines and the indigestible components are expelled through the anus.Mouth and pharynx
The mouth is the start of the digestive tract. Chewing is a
mechanical process that breaks down food into smaller pieces. Salivary glands
produces saliva that contains enzymes that starts to break down food
chemically. However, because food only stays in your mouth for a short time,
the enzymatic reaction is minimal. It is still important to chew properly and
not swallow too quickly, though. Doing this will ensure the subsequent digestion
process runs more smoothly as the food travel down the pharynx (throat) to the
esophagus.
Esophagus
The esophagus connects the pharynx to the stomach. It is a
tube lined with muscle tissue that propels the food by contractive movements
called peristaltic. There is no enzymatic process that takes place in the
esophagus. At the lower end, there is a ‘gate’ called the lower esophageal
sphincter that prevents food from going backwards into the esophagus.
Stomach
Also known as the gaster, the stomach is a round sac-like structure
that holds the food for mechanical and chemical processing. It mixes up the
food with acid and enzymes that continue breaking down the food. Gastric acid kills
the majority of bacteria that got eaten, but our stomach is protected against
it by the mucosal layer. When it leaves the stomach into the first part of the
small intestines, the food will be in paste-like form. The stomach emptying
rate depends on the type of food we eat. Carbohydrates spend the least amount
of time in the stomach, protein stays longer, and fats the longest.
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| Anatomy of digestive system |
Small intestines
The small intestine is a very long tube that is coiled inside
the abdomen. Spread out, the length of our small intestines will reach over 20 feet
long. It is made up of three parts: the duodenum, jejunum, and ileum. With the
help of pancreatic enzymes and bile from the liver, the small intestine
continues the process of breaking down food as it mixes everything up by
peristaltic contractions. Usually after the food passed the duodenum, it is
already broken down into small molecules that are ready to be absorbed in the jejunum
and ileum into the bloodstream. Once the nutrients have been absorbed, the
leftover liquid passed into the large intestine.
Large intestines
Also known as the colon, the large intestine is a 5 feet long
tube that extends from the end of ileum to the rectum. It is made up of four
parts: the ascending colon, the transverse colon, the descending colon, and the
sigmoid. The undigested leftovers of food are passed through the colon and excess
water is reabsorbed from them. The stool, which consists mainly of debris,
fiber, and bacteria, is accumulated inside the sigmoid colon until a bowel
movement empties it into the rectum.
Rectum
The rectum connects the colon to the anus. When the rectum
receives the stool from the sigmoid colon, you will feel a sensation that
prepares you for stool evacuation. Sensors from the rectal mucosa signal the
brain which then decides whether or not it’s okay to release the rectal content.
If the brain allows, the sphincter muscle relaxes and the stool will be
propelled into the anus.
Anus
The anus is the end of the digestive tract. It is made up of
internal and external sphincters and supported by the pelvic muscular tissue.
The sphincters control the evacuation process so we don’t defecate when we’re
not supposed to. The pelvic floor muscle supports the sphincter function by
creating an angle between the rectum and the anus that holds the stool inside.
As mentioned before, besides the digestive track, some internal
organs play an important role in digestion. They are the pancreas, the liver
and gallbladder.
Pancreas
The pancreas secretes enzymes that break down protein, fat,
and carbohydrates from the food we eat. Besides producing enzymes, the pancreas
also serves an endocrine function-that is, producing hormones. The alpha and
beta cells of the pancreas respectively produces glucagon and insulin that act
against each other to control blood sugar level.
Liver and gallbladder
The liver produces bile which then stored inside the
gallbladder. The bile is a compound that helps to the digest fat and eliminates
waste products from the blood. During a meal, especially a fatty one, the gallbladder
contracts and sends bile to the small intestine. The liver also serves to
detoxify the things we digest. Nutrient-rich blood from the small intestines
flows to the liver through a blood vessel called the portal vein where it is
cleansed from metabolic wastes.
Other articles on how your body works:
- The cardiovascular or circulatory system is made up of two components: the heart and the blood vessels. Read more about how your cardiovascular system works
- The human respiratory system consists of a complex set of organs and tissues designed to capture oxygen from the environment and transport the it into the lungs. Read more about how your respiratory system works
- Everyone experience pain at some point of their life. Pain is the most common reason for physician consultation in the United States. Read more about physiology and psychology of pain
