Two way digestive system
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Human digestive system
The human digestive system consists of the gastrointestinal tract plus the accessory organs of digestion (the tongue, salivary glands, pancreas, liver, and gallbladder). Digestion involves the breakdown of food into smaller and smaller components, until they can be absorbed and assimilated into the body. The process of digestion has three stages: the cephalic phase, the gastric phase, and the intestinal phase.
The first stage, the cephalic phase of digestion, begins with secretions from gastric glands in response to the sight and smell of food. This stage includes the mechanical breakdown of food by chewing, and the chemical breakdown by digestive enzymes, that takes place in the mouth. Saliva contains the digestive enzymes amylase, and lingual lipase, secreted by the salivary and serous glands on the tongue. Chewing, in which the food is mixed with saliva, begins the mechanical process of digestion. This produces a bolus which is swallowed down the esophagus to enter the stomach.
The second stage of digestion begins in the stomach with the gastric phase. Here the food is further broken down by mixing with gastric acid until it passes into the duodenum, the first part of the small intestine.
The third stage begins in the duodenum with the intestinal phase, where partially digested food is mixed with a number of enzymes produced by the pancreas. Digestion is helped by the chewing of food carried out by the muscles of mastication, the tongue, and the teeth, and also by the contractions of peristalsis, and segmentation. Gastric acid, and the production of mucus in the stomach, are essential for the continuation of digestion.
Peristalsis is the rhythmic contraction of muscles that begins in the esophagus and continues along the wall of the stomach and the rest of the gastrointestinal tract. This initially results in the production of chyme which when fully broken down in the small intestine is absorbed as chyle into the lymphatic system. Most of the digestion of food takes place in the small intestine. Water and some minerals are reabsorbed back into the blood in the colon of the large intestine. The waste products of digestion (feces) are defecated from the rectum via the anus.
What is the digestive system?
The digestive system is made up of the gastrointestinal tract—also called the GI tract or digestive tract—and the liver, pancreas, and gallbladder. The GI tract is a series of hollow organs joined in a long, twisting tube from the mouth to the anus. The hollow organs that make up the GI tract are the mouth, esophagus, stomach, small intestine, large intestine, and anus. The liver, pancreas, and gallbladder are the solid organs of the digestive system.
The small intestine has three parts. The first part is called the duodenum. The jejunum is in the middle and the ileum is at the end. The large intestine includes the appendix, cecum, colon, and rectum. The appendix is a finger-shaped pouch attached to the cecum. The cecum is the first part of the large intestine. The colon is next. The rectum is the end of the large intestine.
Bacteria in your GI tract, also called gut flora or microbiome, help with digestion. Parts of your nervous and circulatory NIH external link systems also help. Working together, nerves, hormones, bacteria, blood, and the organs of your digestive system digest the foods and liquids you eat or drink each day.
Why is digestion important?
Digestion is important because your body needs nutrients from food and drink to work properly and stay healthy. Proteins, fats, carbohydrates, vitamins NIH external link, minerals NIH external link, and water are nutrients. Your digestive system breaks nutrients into parts small enough for your body to absorb and use for energy, growth, and cell repair.
- Proteins break into amino acids
- Fats break into fatty acids and glycerol
- Carbohydrates break into simple sugars
Organs of the Digestive System
Several organs make up the digestive system. Every organ has a role in breaking down food and managing the waste material.
The digestive organs, in the order in which food travels through them, are:
Mouth: Digestion starts at the very beginning, with food being chewed in the mouth.
Food is broken down into smaller pieces and the saliva in the mouth begins digesting it. An enzyme in saliva called amylase breaks down certain starches down into the smaller sugars, maltose, and dextrin.
Esophagus: The esophagus is a tube inside the throat, behind the windpipe.
After food is chewed and swallowed, it travels down through the esophagus to the stomach. The muscles in the esophagus contract to move food along, which is called peristalsis.
Stomach: After the food is deposited in the stomach, the digestive process continues.
The food is mixed with the acids and enzymes that are secreted from the stomach wall. After the food is thoroughly broken down, it’s moved along into the small intestine.
Small Intestine: The small intestine is a long tube where most of the vitamins and nutrients are absorbed from food into the bloodstream.
More enzymes are added into the small intestine as the food moves through to help facilitate the process. The small intestine is composed of three parts:
- Duodenum
- Jejunum
- Ileum
Large Intestine: After moving through the small intestine, the food is now partially digested and mostly in a liquid form as it passes through a sphincter called the ileocecal valve and enters the large intestine.
The large intestine is where much of the water is absorbed from the waste material. By the time the stool reaches the end of the large intestine, it’s in a more solid form. The sections of the large intestine are called:
- Cecum
- Ascending colon
- Transverse colon
- Descending colon
- Sigmoid colon
Rectum: At the end of the large intestine is the rectum, a reservoir that holds stool until it can be passed out of the body.
When the rectum becomes full of stool, it gives off a signal to the brain that it’s time to go to the bathroom.
Anus: The anus has two sphincters that serve to hold stool inside the body until it is time to pass it. When you consciously relax your external sphincter, the stool can then leave the body.
The digestive tract forms one long tube through the body, all the way from the mouth to the anus (with some sphincters between organs to keep things moving in the right direction).
What Is the Order of Digestive System?
You may know about some of the solid and hollow organs included in the digestive system, but not many have complete information about them. Now let’s get a closer look:
1st Stop – The Mouth
When you start chewing something, your salivary glands start producing saliva to lubricate your food. Your break down your food and your tongue mixes it up with saliva. There are three pairs of salivary glands in your mouth – the sublingual, parotid and submandibular glands. These glands produce up to a liter of saliva every day.
2nd Stop – The Esophagus
Your tongue, teeth and saliva will turn your food into a soft, round mass that will make it easy to swallow. There are muscles in your throat and mouth used to push food to your esophagus, which is the tube connecting your stomach with your throat. The esophagus also has muscles that create synchronized waves to propel your food into your stomach. It works in a systematic way – the muscles behind the round mass of food you have in the esophagus will contract to push it forward and the muscles ahead of it will relax to make it easy for your food to travel to your stomach. When your food reaches the lower end of the esophagus, a muscular valve, called the lower esophageal sphincter, feels the pressure from the food and opens up to let what you eat enter your stomach.
3rd Stop – The Stomach
You have powerful muscles in your stomach that help to break down your food into smaller pieces. The digestive glands in your stomach will also produce enzymes and stomach acid. The combination of stomach acid and enzymes turn the food into a paste called chyme. Your stomach muscles will then contract to push the chyme towards your small intestine. The food will enter the small intestine through a valve called the pylorus. The pylorus releases a small amount of food at a time.
4th Stop – Small Intestine
Small intestine comes next in the order of digestive system. The digestion will continue even when your food has entered your duodenum, the first section of your small intestine. A variety of digestive juices released by liver, pancreas and gallbladder will enter your small intestine for complete digestion of food. Pancreas produces enzymes to break down carbohydrates, proteins and fats, whereas the liver produces bile to digest fats. The wall of your small intestine also secretes other juices for digestion. The food will then move into the second section of your small intestine where it will turn into smaller molecules of nutrients. After that, it moves into the final portion of your small intestine where the remaining nutrients are absorbed.
5th Stop – The Large Intestine
After the absorption of nutrients in the final section of your small intestine, there remains a combination of water, electrolytes and waste products, such as dead cells and plant fiber. This waste enters your large intestine (colon), which is a 5-7 feet long muscular tube connecting your small intestine to the rectum. The waste moves through your colon by means of peristalsis. It enters your large intestine in a liquid state but then converts into solid form because the water is absorbed in the colon. Stool goes in the S-shaped colon and enters into the rectum once or twice a day. The rectum is an 8-inch chamber connecting your colon to your anus. It receives stool form the colon and holds it until evacuation happens.
