Question

Think of the meal you ate last night for dinner (if you do not eat dinners, think of what you had for lunch). Discuss in detail what happens to the food you ate in your mouth, stomach, small intestine, and large intestine. Was your dinner high in protein? Fats? Did it contain any carbohydrates? Fiber? Where were these nutrients digested chemically? Where do you think your dinner spent the most time and why? Be as specific (to your meal) as possible.

Answer 1

The dinner was high in protein and contained fats, carbohydrates, and low fiber. The process of digestion is explained below:-

The digestion process is regulated by 6 mechanisms that are ingestion, propulsion, mechanical digestion, chemical digestion, absorption and the last one is defecation. Ingestion is the first process of digestion which is defined as the entry of the good to the GI tract via the mouth. Inside the mouth, the food is properly chewed and gets dissolve with saliva that has enzymes helping in the breakdown of the carbohydrate present in the food and digests some lipids. The food is masticated with the help of teeth and converted into a bolus in the mouth. Teeth are a special feature of the mouth that performs a function of chewing the food before swallowing. The surface area can be raised while chewing the food and permits the bolus to be formed.

Food is withdrawn from the mouth when the tongue and the pharyngeal muscles move it into the food pipe. This process of swallowing until the defecation process is an example of propulsion that is the movement of the food via the GI tract. It consists of both the unforced process of swallowing and the forced process of peristalsis. Peristalsis consists of interspersed waves of opening and closing of the GI tracts wall of the smooth muscles that move the food. These waves help in dissolving the food with the digestive juices. This action is so strong that the solid and the liquid we swallow enters the stomach even if we are standing on our head.

The process of digestion has both physical and chemical processes wherein the physical digestion of the food is made so smaller to raise the surface area and his mobility. It consists of the mastication or chewing process and also the movement of the tongue to split the food into the smaller piece and dissolve it with the saliva. The physical stirring of the food in the stomach acts to split it apart and give it more surface area for the digestive juices thereby forming an acidic soup known as chyme. The process of segmentation occurs in the small intestine which comprises the opening of the circular muscle of the alimentary canal. These contractions separate some parts of the intestine by transporting the content to and from, breaking them, and dissolving the contents. This movement of to and from in the luminal intestine allows the segmentation process to dissolve the food with digestive juices and encourages the absorption process.

In the next process which is chemical digestion, the food starts from the mouth enzymes break down the complex food molecules into the chemical building blocks like breaking proteins into amino acids. This process is completed in the small intestine. Food that splits is of no use unless it plays a role in providing nutrients or entering the bloodstream of the body and this takes place by the process of absorption which occurs in the small intestine. Here most of the nutrients are absorbed from the lumen of the GI tract into the bloodstream. At last, the defecation process takes place where the undigested food is excreted out in the form of the feces.

The digestion is a catabolic process in which large pieces of food are broken down into small absorbable forms of food by the digestive enzymes like salivary amylase, lipase, trypsin, nucleases, etc.

The action of some digestive enzymes is shown in the table below:-

Biomolecules	Digestion	Reactions
Carbohydrates	Starch is a polysaccharide whose digestion starts in the mouth by the enzyme, salivary amylase. Starch is broken down into a disaccharide (maltose) in the small intestine by the enzyme, pancreatic amylase present in the pancreatic juice. The maltose is further broken down into glucose by the enzyme maltase.
Fats	The fat molecules are broken down into glycerol and fatty acids in the small intestine by the enzyme, lipase present in the pancreatic juice that is secreted by the pancreas after they have been emulsified into fat droplets by the bile salts.
Proteins	The digestion of proteins into peptides begins in the stomach in the presence of the enzyme pepsin that is produced by the gastric glands. Protein is further broken down into peptides in the small intestine by the enzyme trypsin present in the pancreatic juice that is secreted by the pancreas. The enzyme peptidases secreted by the small intestine converts the peptides into amino acids in the small intestine.
Nucleic Acids	The digestion of nucleic acid takes place in the small intestine. RNA and DNA are broken down into nucleotides in the presence of the enzyme nuclease which is secreted by the pancreas. The nucleotides are further broken down into sugar and phosphate by the enzyme nucleosidases which is secreted by the small intestine.

The dinner spent the most time in the large intestine.