1. How does the food change in consistency and form?
The process of food changing in consistency and form is primarily facilitated by the digestive system. Digestion is a complex and coordinated series of events that begins in the mouth and continues through the digestive tract. In the mouth, mechanical digestion starts with the chewing of food, breaking it down into smaller pieces and mixing it with saliva, which contains enzymes like amylase that initiate the chemical breakdown of carbohydrates. The partially broken down food, now referred to as bolus, travels down the esophagus through peristalsis—a series of coordinated muscular contractions.
Upon reaching the stomach, the bolus encounters gastric juices containing enzymes and hydrochloric acid. This environment promotes further mechanical churning and chemical digestion, transforming the bolus into a semi-liquid mixture called chyme.The chyme then progresses through the small intestine, where the majority of nutrient absorption occurs. Here, pancreatic enzymes and bile aid in breaking down proteins, fats, and carbohydrates into simpler molecules for absorption. The absorbed nutrients enter the bloodstream and are transported to cells throughout the body. The undigested residue moves into the large intestine, where water absorption occurs, solidifying the remaining material into feces. Finally, the formed feces are expelled from the body through the rectum and anus during the process of elimination. Overall, the digestive process involves the mechanical and chemical breakdown of food, transforming it into a consistency suitable for nutrient absorption and waste elimination.
2. How could the body absorb the nutrients from the foods we eat?
The process of nutrient absorption in the human body involves a series of coordinated mechanisms within the digestive system to ensure the assimilation of macronutrients, micronutrients, vitamins, and minerals.
The small intestine, a key player in nutrient absorption, features villi and microvilli on its surface, maximizing the absorptive area. As chyme traverses the small intestine, digestive enzymes and bile continue the breakdown of proteins into amino acids, fats into fatty acids and glycerol, and carbohydrates into monosaccharides. Absorptive cells on the villi actively transport these simpler molecules into the bloodstream. Amino acids and monosaccharides enter directly, while fatty acids are reassembled into triglycerides and packaged into chylomicrons, which enter the lymphatic system before reaching the bloodstream.
Simultaneously, water-soluble vitamins are absorbed with water during passive absorption, while fat-soluble vitamins are absorbed along with dietary fats, forming micelles that are transported into the lymphatic system or bloodstream. Essential minerals, regulated by various transporters, undergo active and passive transport mechanisms for absorption, contributing to overall health.
The large intestine, or colon, primarily absorbs water and electrolytes from the remaining indigestible material after nutrient absorption in the small intestine. While the large intestine absorbs some vitamins produced by bacteria in the colon (such as vitamin K and some B vitamins), the overall contribution of the large intestine to nutrient absorption is relatively minor compared to the small intestine.
Once absorbed, these nutrients are transported through the bloodstream to cells and tissues throughout the body. Their vital roles include supporting energy production, contributing to bone health, participating in biochemical reactions, and fortifying the immune system. The efficiency of this complex process is paramount for maintaining optimal health and preventing nutrient deficiencies. In summary, the digestive system orchestrates a symphony of processes to transform ingested food into a myriad of nutrients essential for the body's diverse functions, with the small intestine serving as the central hub for nutrient assimilation.
Reference/s:
Tortora, G. J., & Derrickson, B. H. (2017). Tortora’s Principles of Anatomy & Physiology. Wiley.
Begum, J. (2023, May 5). The Digestive System. WebMD. https://www.webmd.com/digestive-disorders/digestive-system
How Does the Body Absorb Nutrients? (2020). National Institute of Diabetes and Digestive and Kidney Diseases. https://www.niddk.nih.gov/health-information/digestive-diseases/digestive-system-how-it-works#:~:text=The%20small%20intestine%20absorbs%20most,intestinal%20lining%20into%20your%20bloodstream.
How does your body turn food into the poo | Human digestion system in human beings. (2020, December 10). [Video]. Dandelion Medical Animation. https://www.youtube.com/watch?v=HXrl37BC3QU
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