Peristalsis mixes the bolus with gastric secretions containing hydrochloric acid (HCl), hormones and digestive enzymes to produce a thick slurry called chyme. Digestion in the StomachĪs the bolus approaches the stomach, a ring-like muscle called the lower esophageal sphincter relaxes, allowing the chewed food to enter. The passage of the bolus through the esophagus to the stomach occurs by peristalsis, a series of wave-like muscle contractions. You voluntarily swallow it, but the rest of the digestion-absorption process is involuntary. The mass of chewed sandwich is called a bolus. Before your food passes from the mouth and down your esophagus, salivary amylase, an enzyme in saliva, begins to digest the starch in your bread. This chewing reduces the size of the food particles and mixes them with saliva for easier swallowing. Once you take a bite of your sandwich, you’ve initiated mechanical digestion. This anticipation stimulates the secretion of saliva in the mouth and gastric juices in the stomach. When you see and smell food and even start thinking about eating, the brain readies the digestive tract for nourishment. This is the cephalic phase of digestion, which is stimulated by the parasympathetic nervous system. That’s because digestion actually begins in the brain. The hungrier you are and the more you crave that sandwich, the more you will salivate. If you really want that sandwich, you may notice that you’re salivating. In front of you is a turkey and cheese sandwich with lettuce, onion, red bell pepper, mustard and mayonnaise on multi-grain bread. Undigested and compacted material enters the rectum for temporary storage before being eliminated through the anus.Let’s examine the journey that a sandwich (or any piece of food) takes as it makes its way through the digestive tract. As the material slowly moves down, undigested material is compacted and absorption of water and electrolytes takes place. Other important chemical compounds such as vitamin K are also produced by this bacterial action. These are used as an energy source for the bacteria and the cells lining the large intestine. The bacteria are able to ferment some of the undigested material, producing short-chain fatty acids. Also present is a system of vessels known as a lacteal, which absorbs fat nutrients and carries them to the circulatory system.Īt the end of the ileum, a muscular structure controls the release of undigested material into the first part of the large intestine – the caecum.įrom here, peristaltic movements push the undigested material down the large intestine and allow it to mix with the large bacterial population present. They play an important role in absorbing the breakdown products of digestion.Įach villus has a rich blood supply, allowing nutrients to be readily absorbed and transported to the liver. These increase the surface area of the small intestine. The inside of the jejunum and ileum are lined with tiny finger-like projections called villi. Folds in the wall of the jejunum greatly increase its surface area, allowing for ready absorption of the products of digestion. ![]() The next section of the small intestine is the jejunum, about 2.5 m long. Chemical breakdown of carbohydrate, protein and fats into smaller absorbable molecules takes place. These allow enzyme-rich pancreatic juice and bile to be released and mixed with the chyme. The duodenum is only 25 cm long, but most of the digestion takes place in this region.Īlso opening into the duodenum are ducts from the pancreas and the gall bladder. This action further breaks up the food particles, forming a milky fluid known as chyme.Īt the bottom of the stomach, a muscular valve controls the release of chyme into the first part of the small intestine called the duodenum. Peristaltic movements of the stomach wall mix and churn the food with the gastric juices. The lining of the stomach produces gastric juices that contain protein-digesting enzymes. ![]() At the end of the oesophagus, the food empties into the upper portion of the stomach. Saliva contains the starch-digesting enzyme amylase and a slippery protein called mucin that helps to lubricate the food particles for easier swallowing.Īs food is swallowed, it enters the oesophagus and is moved downwards by wavelike muscular contractions called peristalsis. Chewing breaks down food particles and mixes them with saliva.
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