1. How does the food change in consistency and form?
The food that enters the digestive system changes in consistency and form as it is met with different processes from different organs in the system:
A. Mouth Digestion: Through chewing or mastication by the mouth, food is torn and minimized into smaller pieces which we call bolus that allows the food material to be swallowed and move down the esophagus. Also in the mouth, chemical digestion occurs when salivary glands secrete salivary amylase to break down large starch macromolecules into simple sugar molecules.
B. Stomach Processing: The food then enters the stomach that contains gastric juices which mixes with the bolus. This further breaks down the food into a more liquid phase called chyme.
C. Small Intestine Digestion & Absorption: Into the next station from the stomach, chyme enters the small intestine and is met with enzymes from the pancreas and bile which emulsifies fat that is produced by the liver and stored by the gallbladder. This is the phase where the food matter is in its smallest form, thus allowing the process of absorption to take place.
D. Large Intestine Absorption: As nutrients in the small intestine and water, electrolytes, and vitamins in the large intestine are absorbed, the food that entered the digestive system takes form into solid phase called feces.
Phases of food as it goes through the digestive system: Food → Bolus → Chyme → Feces
2. How could the body absorb the nutrients from the foods we eat?
The body absorbs nutrients from the food that we eat through several organs in our digestive system:
A. Stomach: The stomach absorbs alcohol, aspirin and other lipid-soluble drugs, and some water as the epithelial cells of the stomach are impermeable to most materials.
B. Small Intestine: The small intestine absorbs nutrients. Simple sugars and amino acids, which the enzymes in the intestinal wall have broken down from carbohydrates and proteins, respectively, enter the bloodstream via active transport and facilitated diffusion. Fats are emulsified by the bile salts, broken down to fatty acids, taken into epithelial cells and assembled as triglycerides, and transported away from the site of absorption as chylomicrons via the lymphatic system. Fat-soluble vitamins A, D, E, K are absorbed with fats, water-soluble vitamins and minerals are absorbed by diffusion or highly specialized transport mechanisms. Nutrients enter the liver in the blood for processing or travel via the lymphatic system to ensure efficient distribution of nutrients to the body.
C. Large Intestine: Electrolytes, vitamins, and water are absorbed in the large intestine, in which as chyme propel through the rectum, it becomes more solid in structure and transforms into fecal form. The undigested material is formed into feces and deemed of no use by the body, thus eliminated through the anus.