N3 Anatomy and Physiology (1st Sem AY 2022-2023)

1. How the food changes consistency and form
Our food changes in consistency and form with the help of different enzymes and structures in our digestive system. Two main mechanisms aid the breakdown of food: mechanical and chemical digestion. Mechanical digestion is the physical breakdown of food to make smaller pieces. On the other hand, chemical digestion is the breakdown of large food molecules into small molecules. This is usually done with the help of different enzymes in our digestive tract.

From the mouth, chewing and hydrolysis, which are food's physical and chemical breakdowns, form the bolus. The bolus is a sphere of digested food that can be passed on to the esophagus. From the esophagus, the bolus will be propelled to the stomach through peristalsis. In the stomach, churning and hydrolysis happen. The bolus is further broken down into a more fluid substance, which is now called chyme. The chyme will be passed on to the small intestines, wherein chemical digestion happens. Different enzymes, like bile, are mixed into the chyme to further break it down in the duodenum, while more breaking down happens in the other parts of the intestines. The chyme will now be passed on to the large intestines, where water, ions, and vitamin K absorption happens. From there, it will be passed on to the rectum, where the undigested food will be stored until it is time to expel it. The food that is in the rectum is now called feces. And when it is expelled, it will come out through the anus.

2. How the body was able to absorb the nutrients from the foods we eat.
Most of the absorption of nutrients happens in the small intestine. Its length provides a large surface area for absorption to occur. Other structures, such as circular folds, villi, and microvilli, adds to the surface area. Therefore, the small intestine's structure itself makes it a very effective place for absorption. Aside from that, in the mucosa layer of the small intestine, absorptive cells can be found. These cells digest and absorb nutrients in the chyme.

Aside from that, absorption also happens in our stomach and large intestines. The stomach also absorbs some starch, triglycerides, and proteins. At the same time, the large intestine absorbs water, ions, and vitamin K.

References:
Raja Narayan [Khan Academy Medicine]. (2014, May 15). Meet the gastrointestinal tract! | Gastrointestinal system physiology | NCLEX-RN | Khan Academy [Video]. YouTube. https://www.youtube.com/watch?v=Oh_Pt_UrtEE

Tortora GJ & Derrickson B. (2014). Chapter 24-25 An Introduction to the Human Body.
Principles of Anatomy and Physiology. John Wiley & Sons, Inc. 14 edition. Pp 967-1023.