Answers:
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How does the food change in consistency and form?
Chewing, or mastication, plays a significant role in mechanical digestion in the mouth. It involves manipulating food with the tongue, grinding it with the teeth, and mixing it with saliva. This process results in the food being transformed into a soft, flexible, and easily swallowed mass known as a bolus. The presence of water in saliva allows food molecules to dissolve, which is essential for enzymes to react with them. In the mouth, two enzymes, salivary amylase and lingual lipase, contribute to chemical digestion. The salivary glands secrete salivary amylase, which initiates the breakdown of starch.
Bacteria activity in the lumen is responsible for the final stage of digestion in the colon. The glands in the large intestine secrete mucus, but they do not produce enzymes. Remaining carbohydrates are fermented by bacteria, leading to the release of gasses that contribute to flatulence. Proteins are converted into amino acids and undergo further breakdown. Certain byproducts contribute to the odor of feces, while others are absorbed and processed by the liver. Bilirubin is decomposed by bacteria, resulting in the production of pigments like stercobilin, which give feces their brown color. The absorption of essential vitamins such as B vitamins and vitamin K for normal metabolism takes place in the colon. Bacteria also play a role in the breakdown of chyme, aiding in its elimination process.
After 3-10 hours in the large intestine, chyme transforms into solid or semisolid matter known as feces, primarily due to water absorption. Feces contains water, inorganic salts, epithelial cells shed from the GI tract's mucosa, bacteria, byproducts of bacterial breakdown, undigested materials, and indigestible components of food.
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How could the body absorb the nutrients from the foods we eat?
The body uses these five mechanisms to absorb the nutrients from the food we eat:
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Chewing and the introduction of enzymes in your mouth: The moment a bite is taken, digestion begins. Food is broken up into bite-sized pieces by teeth. Salivary amylase, an enzyme found in saliva, breaks down the chemical structure of food.
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Churning and mixing with acid (gastric juice) in your stomach: It proceeds further into the stomach, where powerful acid further breaks down food. As food is ready to enter the small intestine, it is combined and perturbed by peristaltic motion, a rhythmic movement of the digestive system.
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Contact and absorption in your small intestine—your nutrient absorption center: With its unique features known as villi, the small intestine is a key organ for the extraction of nutrients from digested food, including glucose, fatty acids, amino acids, vitamins, and minerals. Villi function as tiny combs, expanding the small intestine's surface area to facilitate effective nutrition absorption. Hundreds of thousands of villi, which are made up of lymphatic and capillary tubes beneath a thin layer of tissue, are involved in this process. Diffusion, which carries water and water-soluble substances (such as glucose, amino acids, water-soluble vitamins, and minerals) past obstacles like the villi, is an essential part of this absorption process. Finally, these nutrients are delivered to the bloodstream, where they are utilized by cells all over the body for different physiological processes.
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Entrance into the bloodstream: After being absorbed into the bloodstream, nutrients still need to enter cells in order to power vital functions. Every cell controls the flow of materials because its cellular membrane, which is composed of fatty acids, protects it. Certain substances—like water—enter cells with ease, while others need help. Nutrients from the bloodstream are made easier to enter by proteins in the cellular membrane acting as ushers. Vitamins, lipids, amino acids, and glucose are all transported into cells with the help of carrier proteins. Once within, nutrients have a variety of functions. For example, they supply minerals that facilitate muscular contraction, support nerve cells in processing sensory data, and function as amino acid building blocks for DNA. In instance, glucose is essential for the synthesis of ATP, the energy that powers cells.
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Carrier proteins bringing nutrients into your cells: The brain uses a protective mechanism called the blood-brain barrier (BBB) to prevent damage while the small intestine effectively absorbs nutrients for cell distribution. The BBB, which is made up of capillaries and vessels, only allows the tiniest molecules to flow through. Specialized transport proteins are needed to allow larger molecules to enter. Crucial for brain fuel, glucose crosses the BBB with ease. It is also easily traversed by fatty acids, which are essential for brain function and of which omega-3s nourish developing brains. In order to make neurotransmitters, which control mood and the nervous system, amino acids must bind to carrier molecules. While vitamins B6 and B12 and vitamin C both require carriers to permeate the blood-brain barrier and deliver helpful chemicals to the brain, other nutrients do not.
References:
Tortora, G. J., & Nielsen, M. T. (2021). Principles of human anatomy. Wiley.
Sydney Sprouse. (2022). Your Guide to How Nutrients are Absorbed by the Body. Retrieved from https://askthescientists.com/nutrient-absorption/