N3 Anatomy and Physiology AY 2023-2024

As food enters the mouth or the oral cavity, it gets chewed (physical breakdown of food) and it turns into a paste called “bolus” due to its mixture with the saliva, hence it is easier to swallow. Chloride ions in the saliva activate the salivary amylase that contains enzymes indicating chemical digestion as it breaks down starch into sugars. Passing through the esophagus, the bolus enters the stomach, churning and the activity of enzymes and acid  then occurs which further breaks down food and makes what was initially a paste into a liquid substance (melted down) which is called the "chyme". Then entering the small intestine starting from the duodenum, where nutrition from food gets absorbed. Then, it gets passed through the large intestine which absorbs water, ions, and vitamin K. Lastly, as the time comes where the digested food gets expelled through the anus its form is now in a waste matter (solid state), which is called “feces.”

It is known that the absorption of the nutrients from food happens in the small intestine. absorption of materials occurs via diffusion, facilitated diffusion, osmosis, and active transport. First, entering the small intestine as “chyme,” enzymes (amylase) break down complex carbohydrates, bile breaks down fat, triglycerides are broken down into fatty acids, and monoglycerides by the pancreatic amylase. Peptides are also converted into amino acids. As these move to the jejunum, what was initially broken down gets absorbed by the villi and microvilli structure. Any undigested or unabsorbed material (mostly water) left in the small intestine passes on to the large intestine for absorption.