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Digestive System - Coggle Diagram
Digestive System
Small Intestine
Humans have two intestines, the small intestine and the large intestine.
In the small intestine, more chemicals and enzymes are added to the mix to finish the process of digestion. A small organ called the gall bladder secretes bile into the small intestine.
The small intestine is also in charge of absorbing digested proteins into the blood stream. To do this, the small intestine is lined with epithelial cells covered with millions of tiny structures called microvilli. Microvilli look like tiny fingers, and are equipped with surface proteins to transport sugars and proteins through their cell walls.
The small intestine is called “small” because it is thinner than the large intestines. Despite its name, the small intestine is usually over 13 feet (4 meters). The large intestine, however, is only about 5 feet (1.5 m) long.
Bile helps prepare fat to be absorbed into the blood. It also neutralizes the acid from the stomach.
The pancreas, another small organ near the small intestine, secretes a mixture of enzymes called pancreatic juice. The pancreatic juice is full of enzymes that break down carbohydrates and proteins.
The small intestine itself also secretes its own enzymes for breaking down carbohydrates into individual sugar molecules.
The reason why mirovilli are shaped like fingers is to increase their surface area, or the amount of their cell surface that is in contact with the food. If you were to pour sugar into a bowl and press the back of your fingers down onto it, some of the sugar would be stuck to them. If you push your fingers in, you’ll pick up more sugar because it will stick to all the sides of each finger. Microvilli increase the surface area of the intestine in the same way. From the microvilli and the epithelial cells, the nutrients are transported into the blood and the rest of the body.
Stomach
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The stomach is like a sack surrounded by muscles. The stomach contains gastric acid and powerful enzymes for breaking down the food.
Muscles around the stomach work to thoroughly mix and churn the mixture of food, acid, and enzymes. The food is then pushed through another sphincter into the small intestine.
Gastric acid adjusts the chemical reaction between the food and the enzymes to the proper pH. One of the most important enzymes is pepsin. The “pep” in pepsin is the same as in the word “peptide,” as in “polypeptide.” Pepsin is a powerful enzyme that cuts apart the bonds that hold proteins together, releasing the individual amino acids in the polypeptide chains.
Sphincters are muscles that act like doorways within the body. It’s the lower esophageal sphincter’s job to let food from the esophagus in, but not let the acids from the stomach out. After the sphincter opens and the food is pushed through, the sphincter closes.
Large Intestine
Muscles around the small intestine gradually squeeze the digested food into the large intestine. The job of the large intestine is to absorb water from the digested food and form anything left into feces.
The microvilli in the small intestine can only absorb small molecules like sugars and proteins. Large molecules like cellulose, also called fiber, cannot be broken down small enough to be absorbed.
Feces are stored in the rectum, then pushed out of the body through the anal sphincter.
The First Bite
Digestion begins as soon as you take a bite of food with your mouth. As you chew your food, you begin to break it down into smaller and smaller pieces. Your front teeth, called incisors, cut hard pieces in half. Your back teeth, the molars, then grind your food up into small pieces. Your tongue helps to push the food around while all of this is taking place and form it into a small ball called a bolus.
While your teeth are doing the heavy duty work, the epithelial cells in your mouth begin to secrete saliva and enzymes. Saliva helps to keep the food moist and lubricated in your mouth and after you swallow. The enzymes, such as amylase, begin to break down the food. Other organisms, such as starfish, can digest food outside of their bodies. A similar thing happens in your mouth.
Swallowing
The next step in digestion is swallowing. When we swallow, food is pushed into a muscular tube called the esophagus. Animals have two tubes connected to their mouths. The trachea, or windpipe, goes to the lungs, and the esophagus to the stomach. When you swallow, muscles close the opening to your trachea to prevent food from going towards your lungs. Choking happens when food enters your trachea.
Once you swallow, the food does not fall down the esophagus. Muscles in the esophagus work to push the food toward your stomach. This is why astronauts are able to eat in outer space. If gravity was involved in dropping the food into our stomachs, astronauts would be in trouble.