What Happens When We Eat
The digestion of food
To become part of the body, food must be digested and absorbed.
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Digestion is the process by which food is broken into its components in the mouth, stomach, and small intestine with the help of digestive enzymes and fluids. Enzymes are substances that speed up food's breaking down to help the body absorb the nutrients. Enzymes also perform other functions in the body.
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Nutrients such as carbohydrates, fats, and proteins must be broken into components before they can be absorbed from the stomach or small intestines into the blood. Water, vitamins, and minerals need not be broken down further.
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Before the body can use any nutrients present in food, the nutrients must pass through the walls of the stomach or intestines into the body's tissues; this process is called absorption.
Much digestion occurs in the small intestines, so nutrients such as carbohydrates, fats, and proteins can be absorbed. Nutrients are then transported in the blood through the body to the cells.
Metabolism
Metabolism refers to all the biochemical processes by which nutrients support life. Within each cell, metabolism takes place. Metabolism is divided into two parts: the building up of substances and the breaking down of substances.
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Within each cell, nutrients such as glucose are split into smaller units to release energy. The energy is used to make heat to maintain body temperature or perform work within the cell. Substances such as proteins are built from their building blocks in every cell.
What Happens When We Eat, the Food Journey
Once we have eaten food, the food goes on a journey through the gastrointestinal tract, also called the GI tract or digestive tract. The gastrointestinal tract (GI) is a series of hollow organs joined in a long and twisting tube from the mouth to the anus. The hollow organs that comprise the GI tract are the mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum, and anus.
The digestive system consists of the GI tract and solid organs like the liver, pancreas, and gallbladder. The ingested food is digested to extract nutrients and absorb energy, and the waste is expelled at the anus as feces. The gastrointestinal tract is so busy that the cells lining it are replaced every few days.
Digestion in Mouth- Formation of Bolus
The digestive system starts with the mouth. Your tongue and teeth help with chewing. It moves food around the mouth during chewing. Your teeth grind and break down food. Chewing is necessary because it breaks up the food into smaller pieces to be swallowed.
Saliva is a fluid secreted into the mouth from the salivary glands, contains important digestive enzymes, and lubricates the food so that it may pass readily down the esophagus. Digestive enzymes help break down food into forms of nutrients that the body can use. The tongue rolls the chewed food into a ball to be swallowed. This ball is called a bolus.
Digestion in Esophagus and Stomach- Formation of Chyme
When swallowed, food enters the pharynx and then the esophagus, a muscular tube about ten inches long that leads to the stomach. Food is propelled down the esophagus by peristalsis, the rhythmic contractions of muscles in the wall of the esophagus. Peristalsis also helps break up food into smaller particles. Food then passes from the esophagus into the stomach.
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The stomach is a muscular sac that holds about four cups of food when full. The stomach makes an enzyme that helps in protein digestion and an acid that destroys harmful bacteria. The stomach has the strongest muscles and thickest walls of all the organs in the digestive tract.
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The food now has a semi-liquid consistency called chyme and is passed into the first part of the small intestine in small amounts. Liquids leave the stomach faster than solids, and carbohydrates and protein foods leave faster than fatty foods. The stomach absorbs few nutrients, but it does absorb alcohol. It takes 1.5 to 4 hours for the stomach to empty after eating.