Question

For your given bite of food, outline or use a flow chart to show what happens to this piece as it moves down the digestive tract. Take notes in your laboratory journal about how this bite is processed in the digestive tract. Mention key enzymes, describe mechanical and chemical digestion, and discuss absorption of nutrients and removal of wastes.

Answer 1

Answer: Mouth (amylase digest carbohydrates), esophagus, stomach (digestion of proteins by pepsine), small intestine (digestion of fats, proteins and carbohydrate by pancreatic enzymes and bile), large intestine (it receives the indigestible substances, absorbs the water and leaves the waste products called feces, peristalsis helps move stool into the rectum and feces are expelled from the body through the rectum and anus). Insulin facilitates glucose uptake by the cells and glucagon turns glycogen into glucose.

Explanation:

The gastrointestinal tract is a series of hollow organs joined together in a tube from the mouth to the anus. The organs found there are the mouth, esophagus, stomach, small intestine, large intestine and anus. The liver, pancreas and gallbladder are the solid organs of the digestive tract that also have important functions during digestion.

Digestion is important because the organism needs nutrients to function properly. (carbohydrates, proteins, fats, vitamins). So, the digestive system breaks down nutrients into small parts so that the body can transport and absorb them. During digestion, carbohydrates are broken down into simple sugars, proteins into amino acids and fats into fatty acids and glycerol.

The digestion of food begins in the mouth, where the food is chewed. The saliva possesses enzymes that already begin with the degradation of starches and sugars. The two most important proteins in saliva are amylase (produced by parotid glands) and mucin (produced by sublingual and submandibular glands). When the person swallows, the tongue pushes the food down the throat and the epiglottis folds over the windpipe to prevent choking and so the food passes into the esophagus. The food bolus then passes through the esophagus, where a process called peristalsis takes place to transport the food.

Then the food reaches the stomach, where the upper muscle in the stomach relaxes (esophageal sphincter) to allow the food to enter and the lower muscle of the stomach mixes the food with the digestive juice. This sphincter remains closed to prevent the content in the stomach from flowing back into the esophagus. Protein digestion begins in the stomach with the action of pepsin and continues in the small intestine with pancreatic enzymes such as trypsin (produced in the pancreas), chemotrypsin, aminopeptidases and carboxypeptidases. So, the stomach acid and enzymes act there, which are molecules created by our body that are responsible for breaking down the polymers present in food into smaller molecules so that they can be easily absorbed.

The food then passes into the small intestine and is transported along the small intestine by peristaltic movements. There, fats, proteins and carbohydrates are digested. The small intestine has three parts: duodenum, jejunum and ileum. The pancreas produces pancreatic juice and the liver produces bile, and these two juices are discharged into the small intestine. Bile helps to dissolve fats, which facilitates their assimilation. Meanwhile, the pancreatic juice completes the digestion of proteins and sugars, a process that began in the stomach, together with the intestinal juice produced by the walls of the small intestine. Once the food has been digested, its components must pass into the blood to be distributed to all the organs of the body. The inner walls of the small intestine has intestinal villi which are irrigated internally by blood vessels and they are responsible for the absorption of water and nutrients into the bloodstream. So, when the digestive enzymes have dissociated the large molecules into small components, the products are absorbed by the wall of the intestine.  The mucosa of the small intestine also secretes the hormone secretin, which stimulates the pancreas to produce digestive enzymes.

Finally, the large intestine is involved, where bacteria (microbiota) in the large intestine can also chemically break down food. The large intestine includes the appendix, cecum, colon and rectum and it receives the indigestible substances from the small intestine, absorbs the water and leaves the waste products called feces. The colon, is the last structure to process food. Peristalsis helps move stool into the rectum and feces are expelled from the body through the rectum and anus.

After digestion, glucose will be available as a source of energy. Once it begins to circulate in the bloodstream, it will need the help of a hormone called insulin to enter the cells and provide them with the energy they need. Insulin is a peptide hormone secreted by the β cells of the pancreatic islets of Langerhans and it helps cellular glucose uptake by signaling cells to take in glucose from the blood. If the body has enough energy. On the other hand, glucagon turns a type of stored sugar called glycogen into glucose, which goes from the liver into your blood to provide energy.