Activity 1. The Food Journey
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How the food changes consistency and form
Given that the food we consume from the external environment is a large molecule and is difficult to be absorbed by our body tissues and cells, digestion is a crucial process. The gastrointestinal tract, along with a few accessory digestive organs, is the primary organ system responsible for breaking down these large food molecules into simpler forms.
As the food we eat enters the mouth, digestion readily occurs as the physical breakdown happens through mastication or chewing. In this phase, the teeth are the ones to assist in the physical breakdown of food, whereas secretion such as saliva containing salivary amylase and mucus turns these smaller pieces of food into a semi-solid paste called “bolus.” In this phase, chemical breakdown already takes place with the aid of salivary amylase that acts on starch, water that hydrates and dissolves the food, and mucus that lubricates the food and makes it easier to swallow.
As the food now takes the form of a bolus, it will now pass through the esophagus until it reaches the stomach, where the churning action through the aid of muscle contractions helps with the physical breakdown of the bolus into further smaller pieces. Meanwhile, the acids and enzymes secreted within the stomach help to chemically break down food into simpler forms. Now, as the bolus gets sheared into smaller pieces and acted upon by enzymes and acid, it will now turn into “chyme,” which is more fluid-like. At this point, it will now move down to the small intestine, where absorption of nutrients takes place until it reaches the large intestine, rectum, and anus for defecation.
2. How the body is able to absorb the nutrients from the foods we eat
As the chyme leaves the stomach, it reaches the small intestine, where most of the nutrients are absorbed. The villi, which are microscopic brush-like structures that line the small intestine, are the ones that grab the essential nutrients from the digested food that will be used by the cells. In addition, the villi contains lacteals which pull out macro and micronutrients from the food and direct them into the bloodstream. However, another process called diffusion diffuses water and water-soluble compounds (e.g., vitamins B & C, glucose, amino acids, and minerals) into the villi, which will then be transported into the bloodstream and into the cells throughout the body.
Meanwhile, fats and fat-soluble vitamins (e.g., vitamins A, D, E, and K), require more steps before reaching the bloodstream and the body cells. In this case, the liver releases bile acids that mix with the fats in the small intestine to convert them into fatty acids. Now, these fatty acids and fat-soluble vitamins are absorbed by the villi and lacteals, which then transport them into the liver for storage and only released to cells when needed. The fatty acids help build cell membranes, while fat-soluble vitamins keep the eyes, brain, heart, and bones healthy.
As the compounds now enter the bloodstream, the carrier proteins embedded in the cell membrane aid in the transport of these nutrients into the cell. And as the nutrients reach and enter the cells, they can now make energy (ATP), move muscles, pick up sensory information, and propel life.