The Digestion Process
Your digestive system basically consists of a long tube that runs all the way through you (Called the alimentary canal) and a few accessory organs that make digestive juices.
It starts with the mouth, which opens into your esophagus, which takes food to your stomach, which is followed by the small intestine, the large intestine, and finally the Anus. The Liver and the Pancreas both secret their digestive juices into the upper portion of the small intestine. Watch the video to the right for a quick tour! |
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An overview of the digestive process
Digestion basically involves three main processes: digestion, absorption, and excretion.
- Digestion is the process of breaking our food molecules down into smaller and smaller pieces, eventually winding up with the building blocks of macro-molecules, amino acids, monosaccharides (simple sugars), fatty acids, and nucleic acids. This takes place in your mouth, stomach, and small intestine.
- Absorption: Remember that as food passes through your alimentary canal, it is not in you yet. It is in the tube that runs through you, your donut hole. Absorption is the process of actually getting the food in your body. This happens when the small molecules left from digestion are absorbed through the wall of the intestine, into your blood stream, and then pumped all around your body. This mostly takes place in the small intestine.
- Excretion: The final step is excretion, where your body rids itself of wastes and things in your food it could not break down. We are pretty familiar with where this occurs, but it does not happen until the large intestine has reabsorbed much of the water in the waste and has used some bacteria to help us get a few last nutrients and vitamins from our food.
An overview of the digestive system organs (from Web MD)
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. Chewing breaks the food into pieces that are more easily digested, while saliva mixes with food to begin the process of breaking it down into a form your body can absorb and use.
Throat and Esophagus
Also called the pharynx, the throat is the next destination for food you've eaten. From here, food travels to the esophagus or swallowing tube. When we swallow what we are really doing is closing a "trap door" in our throat called the epiglottis.This sends food down the esophagus and prevents food from going down the trachea (or windpipe) and in to our lungs.
The esophagus is a muscular tube extending from the pharynx at the back of the throat to the stomach. By means of a series of contractions, called peristalsis, the esophagus delivers food to the stomach. Just before the connection to the stomach there is a "zone of high pressure," called the lower esophageal sphincter; this is a "valve" meant to keep food from passing backwards into the esophagus.
Stomach
The stomach is a sac-like organ with strong muscular walls. In addition to holding the food, it's also a mixer and grinder. The stomach secretes acid and powerful enzymes that continue the process of breaking down the food. When it leaves the stomach, food is the consistency of a liquid or paste. From there the food moves to the small intestine.
Small Intestine
Made up of three segments, the duodenum, jejunum, and ileum, the small intestine is a long tube loosely coiled in the abdomen (spread out, it would be more than 20 feet long). 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. Peristalsis (contractions) is also at work in this organ, moving food through and mixing it up with digestive secretions. The duodenum is largely responsible for continuing the process of breaking down food, with the jejunum and ileum being mainly responsible for the absorption of nutrients into the bloodstream.
Pancreas
Among other functions, the oblong pancreas secretes enzymes into the small intestine. These enzymes break down protein (proteases), fat (lipases), and carbohydrates (amylases) from the food we eat. The Pancreas also secretes insulin, which regulates the absorption of blood sugar and the storage of fat.
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. Bile is a digestive juice that is especially important in the digestion of fats. The bile helps to emulsify fats, which basically means it breaks fat molecules, which don't dissolve well in water, into much smaller pieces.
Gallbladder
The gallbladder is a pear-shaped reservoir that sits just under the liver and stores bile. Bile is made in the liver then travels to the gallbladder through a channel called the cystic duct. During a meal, the gallbladder contracts, sending bile to the small intestine. Once the nutrients have been absorbed and the leftover liquid has passed through the small intestine, what is left of the food you ate is handed over to the large intestine, or colon.
Large Intestine (colon)
The colon is a 5- to 6-foot-long muscular tube that connects the small intestine to the rectum (the last part of the large intestine). Stool, or waste left over from the digestive process, is passed through the colon by means of peristalsis (contractions), first in a liquid state and ultimately in solid form as the water is removed from the stool. A stool is stored in the colon until a "mass movement" empties it into the rectum once or twice a day. It normally takes about 36 hours for stool to get through the colon. The stool itself is mostly food debris and bacteria. These bacteria perform several useful functions, such as synthesizing various vitamins, processing waste products and food particles, and protecting against harmful bacteria. When the descending colon becomes full of stool, or feces, it empties its contents into the rectum to begin the process of elimination.
Rectum
The rectum (Latin for "straight") is an 8-inch chamber that connects the colon to the anus. It is the rectum's job to receive stool from the colon, to let you know there is stool to be evacuated, and to hold the stool until evacuation happens. When anything (gas or stool) comes into the rectum, sensors send a message to the brain. The brain then decides if the rectal contents can be released or not. If they can, the sphincters (muscles) relax and the rectum contracts, expelling its contents. If the contents cannot be expelled, the sphincters contract and the rectum accommodates, so that the sensation temporarily goes away.
Read more here
Or check out this interactive from National Geographic.
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. Chewing breaks the food into pieces that are more easily digested, while saliva mixes with food to begin the process of breaking it down into a form your body can absorb and use.
Throat and Esophagus
Also called the pharynx, the throat is the next destination for food you've eaten. From here, food travels to the esophagus or swallowing tube. When we swallow what we are really doing is closing a "trap door" in our throat called the epiglottis.This sends food down the esophagus and prevents food from going down the trachea (or windpipe) and in to our lungs.
The esophagus is a muscular tube extending from the pharynx at the back of the throat to the stomach. By means of a series of contractions, called peristalsis, the esophagus delivers food to the stomach. Just before the connection to the stomach there is a "zone of high pressure," called the lower esophageal sphincter; this is a "valve" meant to keep food from passing backwards into the esophagus.
Stomach
The stomach is a sac-like organ with strong muscular walls. In addition to holding the food, it's also a mixer and grinder. The stomach secretes acid and powerful enzymes that continue the process of breaking down the food. When it leaves the stomach, food is the consistency of a liquid or paste. From there the food moves to the small intestine.
Small Intestine
Made up of three segments, the duodenum, jejunum, and ileum, the small intestine is a long tube loosely coiled in the abdomen (spread out, it would be more than 20 feet long). 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. Peristalsis (contractions) is also at work in this organ, moving food through and mixing it up with digestive secretions. The duodenum is largely responsible for continuing the process of breaking down food, with the jejunum and ileum being mainly responsible for the absorption of nutrients into the bloodstream.
Pancreas
Among other functions, the oblong pancreas secretes enzymes into the small intestine. These enzymes break down protein (proteases), fat (lipases), and carbohydrates (amylases) from the food we eat. The Pancreas also secretes insulin, which regulates the absorption of blood sugar and the storage of fat.
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. Bile is a digestive juice that is especially important in the digestion of fats. The bile helps to emulsify fats, which basically means it breaks fat molecules, which don't dissolve well in water, into much smaller pieces.
Gallbladder
The gallbladder is a pear-shaped reservoir that sits just under the liver and stores bile. Bile is made in the liver then travels to the gallbladder through a channel called the cystic duct. During a meal, the gallbladder contracts, sending bile to the small intestine. Once the nutrients have been absorbed and the leftover liquid has passed through the small intestine, what is left of the food you ate is handed over to the large intestine, or colon.
Large Intestine (colon)
The colon is a 5- to 6-foot-long muscular tube that connects the small intestine to the rectum (the last part of the large intestine). Stool, or waste left over from the digestive process, is passed through the colon by means of peristalsis (contractions), first in a liquid state and ultimately in solid form as the water is removed from the stool. A stool is stored in the colon until a "mass movement" empties it into the rectum once or twice a day. It normally takes about 36 hours for stool to get through the colon. The stool itself is mostly food debris and bacteria. These bacteria perform several useful functions, such as synthesizing various vitamins, processing waste products and food particles, and protecting against harmful bacteria. When the descending colon becomes full of stool, or feces, it empties its contents into the rectum to begin the process of elimination.
Rectum
The rectum (Latin for "straight") is an 8-inch chamber that connects the colon to the anus. It is the rectum's job to receive stool from the colon, to let you know there is stool to be evacuated, and to hold the stool until evacuation happens. When anything (gas or stool) comes into the rectum, sensors send a message to the brain. The brain then decides if the rectal contents can be released or not. If they can, the sphincters (muscles) relax and the rectum contracts, expelling its contents. If the contents cannot be expelled, the sphincters contract and the rectum accommodates, so that the sensation temporarily goes away.
Read more here
Or check out this interactive from National Geographic.
Want to know more about individual organs? Or get another overview of the whole system? Watch the videos below:
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Radiolab: Guts
In class, we will listen to the first five minutes of the Radiolab: Guts! Podcast as an intro to digestion. If it interests you, check out the rest of the podcast by clicking on the link! The hour long podcast is broken into three sections: The first checks out how we first learned about how the stomach works, the second looks at all of the micro-organisms that live inside us and help us digest things, and the third looks at what can happen when you gut stops working!