N3 Anatomy and Physiology AY 2024-2025

How does the food change in consistency and form?
In the course of the digestion process , food changes in consistency and form as it traverses in our body. The first stage of change occurs in the mouth—an area in which the first step of digestion occurs—chewing or the mechanical breakdown of food. Food would not be able to travel down the esophagus as a 'solid' whole therefore our oral cavity—teeth, tongue and saliva (composed of salivary enzymes) breakdown the food into a much more simpler substance called the bolus. 

Before acquiring 'bolus' the food is ripped, torn and broken down by the teeth mechanically along with the help of saliva which chemically breaks down the food into a bolus through the presence of water and enzymes, thus hydrolysis, as indicated in the material below.

After so, the food travels down to the esophagus for it to reach the stomach—where the second stage of change occurs through churning. Churning is simply the process of mixing bolus with gastric juices in the stomach to break it down into a much more simpler substance called the 'Chyme.' In a much more simpler aspect, churning can be associated with a fruit blender—In a blender we have our solids (food) and liquids (gastric juices, waters, enzymes, etc.) once we start the blender, our end product is a liquid like substance that appears to be simpler and much more 'passable' than the bolus which we now call the chyme. In line with that, along with churning, hydrolysis also plays a significant role in the transition of bolus to chyme. 

Moreover, chyme also changes into a 'stool' or 'feces once its nutrients has been absorbed by the intestines—this is also another stage of a change in appearance wherein chyme turns into a solid-like structure that we pass down during defecation. 

Summary: 
Food changes in:
1. Chewing in the oral cavity: Food becomes bolus 
2. Churning in the stomach: Bolus becomes Chyme 
3. Absorption in the intestines: Chyme becomes Stool or Feces.

How could the body absorb the nutrients from the foods we eat? 
After food changes into bolus in the oral cavity and chyme in the stomach as mentioned above. Chyme travels to the small and large intestine for absorption of nutrients.

In the small intestine (composed of: Duodenum, Jejunum, Ileum) absorption takes place through the help of its lining called the 'small intestinal mucosa' which exhibits villi that not only helps propel food but also in absorbing nutrients (vitamins and minerals) by increasing the surface area of the intestine. Furthermore, the small intestine mostly absorbs the nutrients of the chyme as compared to the large intestine, and the absorbed nutrients are taken back to the blood stream.

After going through the small intestine, the chyme travels to the large intestine where water and electrolytes are absorbed for it to transform into what we know as 'feces.'

The main difference between the small intestine and large intestine is that, small intestine absorbs most of the nutrients such as vitamins and minerals while large intestine is mostly responsible for the last stages of absorption and takes in water and electrolytes in order to solidify the chyme and turn it into feces. 

SUMMARY: 
How does the body absorb the nutrients from the foods we eat? 
1. Small intestine: Absorption of most nutrients (vitamins and minerals) from the chyme
2. Large intestine: Last stage of absorption (absorbs water and electrolytes), turns chyme into feces