-
How does the food change in consistency and form?
Digestion causes the food to break down into smaller molecules that the body's cells can use, changing the food's consistency and form. Mechanical digestion in the mouth occurs when food is masticated—managed by the tongue, ground by the teeth, and combined with saliva. Consequently, the food is reduced to a bolus—a soft, flexible, and easily ingested mass. The mucus is secreted by the esophagus, which transports the bolus into the stomach. After going through waves of peristalsis, propulsion, and retropulsion, the stomach's contents and gastric juice combine to form chyme, a soupy liquid. Chyme, which contains partially digested proteins, lipids, and carbohydrates, travels from the stomach into the small intestine. Chyme becomes solid or semisolid due to water absorption and is referred to as feces after remaining in the large intestine for three to ten hours. Fecal material is forced from the sigmoid colon into the rectum by mass peristaltic movements, which continue until the feces are expelled through the anus.
-
How could the body absorb the nutrients from the foods we eat?
The small intestine is responsible for 90% of all nutrient absorption, with the stomach and large intestine carrying out the remaining 10%. Since most substances cannot pass through stomach epithelial cells, mucous cells in the stomach are only able to absorb a small amount of nutrients (such as water, ions, and short-chain fatty acids). Osmosis, active transport, facilitated diffusion, and diffusion account for the majority of absorption that takes place in the small intestine. The combined action of intestinal juice, bile, and pancreatic juice completes the digestion of lipids, proteins, and carbohydrates. Water is also absorbed, along with vitamins and electrolytes. Anything that remains unprocessed or unabsorbed in the small intestine moves on to the large intestine. Because of its absorption capacity, the large intestine plays a crucial role in preserving the body's water balance. Additionally, ions such as sodium and chloride as well as certain vitamins are absorbed in the large intestine.