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Digestion starts in the mouth as food is chewed and mixed with saliva. Once food is softened, it’s swallowed and on its way through the digestive tract.

Learn the structures of the upper digestive tract, including the mouth, esophagus, and stomach.

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Digestive Tract

Babies explore the world by putting things in their mouth. Whether it’s a rattle, toy, or the dog’s tail, there’s a good chance that if a baby can hold it in her hands, she’ll put it in her mouth. As young children, it becomes fun to explore different textures of food. Children take their time licking the smooth, creamy consistency of an ice cream cone and try to make the loudest crunch by chomping down on a potato chip.

As adults, we learn that the mouth is the gateway to good nutrition. Foods are roughly broken down in the mouth so they can be softened and passed down through the digestive tract, or gastrointestinal tract, which is the long continuous tube that breaks down food particles into small enough particles to pass into the bloodstream.In this lesson, we will look at the structures of the upper gastrointestinal tract including the mouth, pharynx, esophagus, and stomach.

Mouth

Your mouth is the area where food enters the digestive tract. It’s guarded by the lips or labia at the entrance and bordered by the cheeks on the sidewalls.If you put your tongue on the roof of your mouth, you’ll notice that it’s hard in the front but soft in the back. You’re feeling the hard palate and the soft palate, which combine to form the boundary between the mouth cavity and the nasal, or nose, cavity.

Did you ever hear of a baby being born with a cleft palate? That’s a condition in which the palate doesn’t form properly leaving an opening to the nasal cavity. When this happens, it can be hard for a baby to eat because food can pass from the mouth back through the nose, instead of continuing down the digestive tract.When you think of your tongue, you probably think about how it allows you to taste foods. The tongue does contain taste receptors, known as taste buds, but it also plays an important role in moving food around. Your tongue is a powerful muscle. When food enters your mouth, your tongue pushes it under your teeth, which are the bonelike structures that grind food into smaller pieces. The tongue also allows food to be mixed with saliva, which is produced from the salivary glands.

You have three pairs of salivary glands. One big set is located just in front of your ears. These are the glands that get inflamed in a child suffering from the mumps.

The other pairs are located below the tongue and jaw. Saliva contains enzymes that initiate the breakdown of carbohydrates. Saliva also makes the food mass slick and smooth. When the food is chewed up and moistened, your tongue pushes it to the back of your mouth so it can be swallowed.

Pharynx ; Esophagus

When food is swallowed, it passes into your pharynx, or throat, which is a common passageway for air, food, and fluids. When the air you breathe in enters the pharynx, it gets routed into your lungs. When you swallow food or drink something, it gets routed into your esophagus, which is the passageway that connects your pharynx with your stomach.

To make sure the air, food, and fluid go down the right road, your pharynx relies on the epiglottis, which is a flap of cartilage that covers the entrance to the windpipe. When you breathe, this flap stays open, allowing air to go into your lungs. When you swallow, your epiglottis tips over and closes the door to your windpipe until the food passes by.Once the food mass moves past this tricky area, it’s on its way down the esophagus. It’s pushed down by the rhythmic muscular contractions of the esophagus until it bumps into the lower esophageal sphincter, which is a ring of muscle that leads from the esophagus to the stomach.

The sphincter is not there to prevent food from entering the stomach. Its job is to close off after food passes through it to prevent the stomach contents from going backward and returning up the esophagus.

Stomach

Your stomach is a c-shaped structure that temporarily stores and breaks down food.

It’s located to the left side of your abdominal cavity. If you put your hand near the bottom of your ribs and off to the left a little bit, your hand is resting on top of your stomach.When it’s empty, your stomach is not a particularly big structure, but it can expand like a water balloon when it’s full. Your stomach is capable of holding about a gallon of food and fluid. This expansion is allowed because of rugae, which are large folds in the lining of the stomach that collapse inward as your stomach empties.You might want to think of your stomach as a temporary food warehouse and processing plant.

Food can stay here for up to six hours and is constantly being pushed around or churned thanks to the powerful muscles that crisscross throughout the stomach wall. Churning allows the food mass to be physically broken down, but food in the stomach is also chemically broken down.The lining of the stomach is dotted with pits that lead to gastric glands. These glands secrete gastric juices that help initiate the breakdown of protein, change the acidity of the contents, and prepare food nutrients for absorption later in the digestive tract.Once food has been sloshed around and sufficiently mixed with gastric juices, it’s ready to exit the stomach. But to do that, it must get permission from the pyloric sphincter, which is a ring of muscle that controls the passage of food out of the stomach. The pyloric sphincter runs a tight ship and only allows a little food to leave at a time.

This makes sure the small intestine, which is the next stop for your food mass, does not get overwhelmed.

Lesson Summary

Let’s review.Your digestive tract is the long continuous tube that breaks down food particles into small enough particles to pass into the bloodstream. Your mouth is the area where food enters the digestive tract. It’s bordered by the lips, cheeks, and palate. Your tongue plays an important role in moving food around so it can be grinded by your teeth and mixed with saliva from the salivary glands.

When food is swallowed, it passes into your pharynx, or throat, which is a common passageway for air, food, and fluids. Food and drinks get routed into your esophagus, which is the passageway that connects your pharynx with your stomach.Your stomach is a c-shaped structure that temporarily stores and breaks down food. Churning allows the food mass to be physically broken down, and gastric juices are secreted into the stomach to allow for chemical breakdown.

Food leaves the stomach through the pyloric sphincter, which is a ring of muscle that controls the passage of food out of the stomach.

Learning Outcomes

Study and review all portions of the lesson, then try to:

  • Convey knowledge of the purpose of the digestive tract
  • Name the organs that make up the digestive tract
  • Explain the work done by each of these organs

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