Health (Commonwealth Union) – Nutrient absorption is a complex and fascinating process that takes place in the digestive system, allowing the body to extract essential elements from the food we consume. From the moment food enters our mouths to its final transformation into usable nutrients, this journey involves intricate physiological processes. Many studies have indicated the variations in nutrition absorption to the way the food is consumed. Iron absorption generally increases when consumed with vitamin c such as the consumption of green salad leaves with lemon or lime.
The journey of nutrient absorption starts in the mouth with the mechanical and chemical breakdown of food. Chewing not only helps in breaking down food into smaller particles but also initiates the release of saliva containing enzymes like amylase, which begins the digestion of carbohydrates.
As the chewed food forms a bolus, it travels down the esophagus and enters the stomach. In the stomach, gastric juices containing hydrochloric acid and pepsin work to further break down the food into chyme – a semi-liquid mixture of partially digested food. This acidic environment sets the stage for the activation of digestive enzymes and the breakdown of proteins.
The majority of nutrient absorption takes place in the small intestine, a remarkable organ where the chyme is subjected to further digestion and nutrient extraction. The pancreas releases digestive enzymes, including amylase, lipase, and protease, into the small intestine to break down carbohydrates, fats, and proteins, respectively.
The liver also plays a crucial role in nutrient absorption by producing bile, which is stored in the gallbladder and released into the small intestine. Bile emulsifies fats, breaking them down into smaller droplets and facilitating their digestion by lipase. This process is essential for the absorption of fat-soluble vitamins like A, D, E, and K.
Microvilli, tiny finger-like projections on the surface of the small intestine, greatly increase the absorptive surface area. Each microvillus contains specialized transporters that facilitate the absorption of specific nutrients into the bloodstream. Carbohydrates are broken down into simple sugars (glucose, fructose, and galactose), proteins into amino acids, and fats into fatty acids and glycerol.
The small intestine absorbs simple sugars through specialized transporters in the microvilli. Glucose and galactose are absorbed through active transport, requiring energy, while fructose is absorbed through facilitated diffusion. Once inside the intestinal cells, these sugars enter the bloodstream and are transported to various tissues for energy.
Proteins are broken down into amino acids, dipeptides, and tripeptides in the small intestine. Specialized transporters facilitate the absorption of these breakdown products into the intestinal cells. Once inside, dipeptides and tripeptides are further broken down into amino acids, which are then transported into the bloodstream for distribution to various cells and tissues throughout the body.
Fats undergo a complex process of digestion and absorption. Bile emulsifies fat into smaller droplets, allowing lipase to break it down into fatty acids and glycerol. These components are then absorbed into the intestinal cells, where they are reassembled into triglycerides. The triglycerides, along with cholesterol and fat-soluble vitamins, are packaged into structures called chylomicrons and released into the lymphatic system. Eventually, they enter the bloodstream and travel to tissues where they are either used for energy or stored for later use.
Water-soluble vitamins, such as vitamin C and the B vitamins, are absorbed directly into the bloodstream through passive diffusion or active transport. Fat-soluble vitamins, as mentioned earlier, are absorbed along with dietary fats and transported through the lymphatic system.
Mineral absorption occurs through various mechanisms. Some minerals, like iron and calcium, are absorbed in the small intestine through active transport. Others, like zinc and magnesium, are absorbed through both active and passive mechanisms. The body tightly regulates mineral absorption to maintain balance and prevent deficiencies or excesses.
