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  • A person had roti and dal for his lunch Trace the changes in those during its passage through the alimentary canal

A person had roti and dal for his lunch. Trace the changes in those during its passage through the alimentary canal.

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Let us first determine what nutrients had the man is taken. Roti mainly consists of carbohydrates and fibres, whereas dal contains protein. It may also contain fat due to the addition of oil during cooking.
Thus, the trajectory of the diet would be as follows:

a) Oral Cavity: Saliva is mixed with food, making it a semi-solid paste, which is easier to digest. Moreover, the enzyme, salivary amylase in saliva digests starch. The starch of food is converted into maltose during this process.
b) Oesophagus: No digestion occurs inside the oesophagus.
c) Stomach: Food, once it reaches the stomach, is further churned into an even finer paste. Hydrochloric acid is mixed with the food, which kills germs in the food, if any, as well as it provides acidic pH for optimum activity of pepsin. Partial digestion of protein begins in the stomach. Here, the protein present in dal is converted by pepsin into peptones and proteases.
d) Small intestine: Pancreatic juices flow till here. They contain pancreatic amylase which converts polysaccharides into disaccharides. This step further processes the carbohydrates from the roti. Chymotrypsin further breaks peptones and proteoses into dipeptides. Intestinal juice contains various enzymes, which help in the digestion of all the nutrients. The dipeptides are broken down into Amino acids by the enzyme Dipeptidases. Maltose breaks into glucose with the help of Maltase. Lactose breaks into glucose and galactose with the help of lactase. Sucrose breaks into glucose and fructose with the help of Sucrase. The di and monoglycerides are broken down into fatty acids and glycerol with the help of Lipases.

Once all the nutrients are finally converted into their simpler forms, they get absorbed by the walls of the small intestine. After that, the remaining undigested food is sent to the large intestine and is passed on to the rectum.

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