1. How does the food change in consistency and form?
First, from the oral cavity, food is shredded, cut, and ground which turns it into a smaller, more digestible substance called bolus. It is even aided by the salivary amylase that carbohydrates can already be digested from the start. This gives the food a viscous yet fluid-like consistency compared to when it entered as starches were already digested by the salivary amylase. Next, as it goes down to the stomach, gastric juices will then start to break down protein while also turning the food into a pulp semi-liquid consistency (chyme). It will also not be fully watery while in the stomach as water absorption already starts here. As it goes to the small intestine, most of its proteins, lipids, and other components will be broken down by the pancreatic juice, while the liver will emulsify all the fat content, making the chyme more fluid as it goes through the GI tract. The bile released by the gallbladder as it goes to the small intestine will also help in emulsifying fat, which makes them turn into smaller droplets, making the food a more digestible, liquid consistency. As it finally reaches the small intestines, 90% of its nutrients will be absorbed, including the water, which will now turn the digested food into a semi-solid consistency. When it reaches the large intestine, as it reaches the ascending colon, it will be around the same consistency as it entered, and as it progresses through the right hepatic flexure and transverse colon, the food will be more solid-like and will be a more firm form of waste as it reaches the descending and sigmoid colon until the rectum. This will now be the feces to be excreted.
2. How could the body absorb the nutrients from the foods we eat?
The body will need to digest the food to be able to gain access to the nutrients available from the food. This starts from the salivary amylase, which breaks down the carbohydrates, then to the stomach, where the food is turned into chyme, where most of its components are churned once mixed with gastric juice. Some nutrients are absorbed here, like alcohol, aspirin and other lipid-soluble drugs, and water, which is made possible by the epithelial cells of the stomach. However, since these cells are impermeable to most materials, only small amounts of nutrients are absorbed. After contributions of pancreatic juices and bile, as the food (chyme) reaches the small intestines, its villi and microvilli assist in absorbing and excreting, and 90% of the nutrients from food are absorbed by the body once finished going through the small intestines. The rest of the nutrients, like water and electrolytes, are then absorbed in the large intestine to complete the nutrient absorption.