How does the food change in consistency and form?
As food travels through the digestive system, the following changes occur due to the breakdown of such nutriment into smaller particles that could aid in digestion/absorption of important substances:
1. Upon ingestion of food, mastication/chewing mechanically breaks it down into smaller bite-sized pieces to form bolus (a mass of food that is solft and easy to swallow). This is also a result of the chemical breakdown caused by saliva from salivary glands, introducing salivary amylase (to break down starch) and lingual lipase (to break down dietary triglycerides/lipids) for yielding simpler sugars or fatty acids.
2. When the food enters the stomach, it proceeds in continuation of digestion of starch, triglycerides, and proteins, contributing to the formation of chyme (semi-liquid form). It is also mixed with HCI and pepsin (agents for protein digestion) making it highly acidic and viscous.
3. After peristalisis and food is pushed into the small intestines, brush border enzymes (helpful in the breakdown of carbohydrates/sugars) aid in the food becoming simple, absorbable units. Bile and pancreatic juices are added from the pancreas as well to break down macronutrients into their molecular forms.
4. As it is pushed into the large intestines, there is still material for the intestines to reabsorb water, electrolytes, and broken-down amino acids to acquire vitamins. This leads to the material's hardened state called feces.
How could the body absorb the nutrients from the foods we eat?
Chemical breakdown, starting from the mouth, denatures or simplifies complex molecules by the addition of enzymes, gastric juices, and other chemical compositions (stated in the first question) capable of reducing them to their absorbable, molecular forms of monosaccharides/polysaccharides, nucleic acids, amino acids, peptides, fatty acids, and, especially, the nutrients and minerals. Through absorption, the following transports occur:
1. Carbohydrates to monosaccharides/polysaccharides: active transport and facilitated diffusion into the bloodstream
2. protein to peptides to amino acids: active transport into the bloodstream
3. nucleic acids: denatured by acidic environment and absorbed through active transport and facilitated diffusion into the bloodstream
4. fatty acids: transported by the lymphatic system then enter the bloodstream
5. minerals and vitamins: It depends if water-soluble (diffusion) or fat-soluble (absorbed with other fats). It may require other transport mechanisms based on the needs of the body.
6. Water: osmosis