Another cell type, parietal cells, secrete hydrogen and chloride ions, which combine in the lumen to form hydrochloric acid, the primary acidic component of the stomach juices. Hydrochloric acid helps to convert the inactive pepsinogen to pepsin. The highly-acidic environment also kills many microorganisms in the food and, combined with the action of the enzyme pepsin, results in the hydrolysis of protein in the food.
Chemical digestion is facilitated by the churning action of the stomach. Contraction and relaxation of smooth muscles mixes the stomach contents about every 20 minutes. The partially-digested food and gastric juice mixture is called chyme.
Chyme passes from the stomach to the small intestine. Further protein digestion takes place in the small intestine.
Gastric emptying occurs within two to six hours after a meal. Only a small amount of chyme is released into the small intestine at a time.
The movement of chyme from the stomach into the small intestine is regulated by the pyloric sphincter. Learning Objectives Describe the parts of the digestive system from the oral cavity through the stomach. Key Points Mechanical and chemical digestion begin in the mouth with the chewing of food and the release of saliva, which starts carbohydrate digestion. The epiglottis covers the trachea so the bolus ball of chewed food does not go down into the trachea or lungs, but rather into the esophagus.
The tongue positions the bolus for swallowing and then peristalsis pushes the bolus down the esophagus into the stomach. In the stomach, acids and enzymes are secreted to break down food into its nutrient components. The churning of the stomach helps to mix the digestive juices with the food, turning it into a substance called chyme. Key Terms bolus : a round mass of something, especially of chewed food in the mouth or alimentary canal peristalsis : the rhythmic, wave-like contraction and relaxation of muscles which propagates in a wave down a muscular tube pepsin : a digestive enzyme that chemically digests, or breaks down, proteins into shorter chains of amino acids chyme : the thick semifluid mass of partly digested food that is passed from the stomach to the duodenum.
Parts of the Digestive System The vertebrate digestive system is designed to facilitate the transformation of food matter into the nutrient components that sustain organisms. Digestive system and its function How does digestion work - animation Why is digestion important?
How does food move through the GI tract? How do digestive juices in each organ of the GI tract break down food? What happens to the digested food molecules? How is the digestive process controlled? When you're finished, you take a last drink of milk, wipe your mouth, and head to your next class.
In a few minutes you're thinking about the capital of Oregon or your science fair project. You've completely forgotten about that pizza lunch you just ate. But it's still in your stomach — sort of like a science experiment that happens all the time!
Your digestive say: dye-JES-tiv system started working even before you took the first bite of your pizza. And the digestive system will be busy at work on your chewed-up lunch for the next few hours — or sometimes days, depending upon what you've eaten.
This process, called digestion , allows your body to get the nutrients and energy it needs from the food you eat. So let's find out what's happening to that pizza, orange, and milk. Even before you eat, when you smell a tasty food, see it, or think about it, digestion begins. Saliva say: suh-LYE-vuh , or spit , begins to form in your mouth. When you do eat, the saliva breaks down the chemicals in the food a bit, which helps make the food mushy and easy to swallow.
Your tongue helps out, pushing the food around while you chew with your teeth. When you're ready to swallow, the tongue pushes a tiny bit of mushed-up food called a bolus say: BO-luss toward the back of your throat and into the opening of your esophagus, the second part of the digestive tract.
The esophagus say: ih-SOF-eh-guss is like a stretchy pipe that's about 10 inches 25 centimeters long. It moves food from the back of your throat to your stomach. But also at the back of your throat is your windpipe, which allows air to come in and out of your body. When you swallow a small ball of mushed-up food or liquids, a special flap called the epiglottis say: ep-ih-GLOT-iss flops down over the opening of your windpipe to make sure the food enters the esophagus and not the windpipe.
If you've ever drunk something too fast, started to cough, and heard someone say that your drink "went down the wrong way," the person meant that it went down your windpipe by mistake. This happens when the epiglottis doesn't have enough time to flop down, and you cough involuntarily without thinking about it to clear your windpipe.
Once food has entered the esophagus, it doesn't just drop right into your stomach. Instead, muscles in the walls of the esophagus move in a wavy way to slowly squeeze the food through the esophagus. This takes about 2 or 3 seconds.
Your stomach, which is attached to the end of the esophagus, is a stretchy sack shaped like the letter J. It has three important jobs:.
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