Briefly explain the processes of nutrient absorption and nutrient circulation

Answer 1

When the process of digestion is complete, nutrients are ready to be absorbed. Nutrient absorption is the movement of nutrients from the lumen of the gastrointestinal (GI) tract into either the blood or the lymph. Although some nutrient absorption takes place through the lining of the stomach, the vast majority of nutrients are absorbed in the small intestine.In the small intestine, microvilli move in a sweeping action to trap and pull nutrients toward the enterocytes that line each villus. During absorption, nutrients move into and out of these cells by both passive and active transport mechanisms. Once absorbed, nutrients enter either the blood or lymphatic circulatory system.Once food has been digested and nutrients have been absorbed, the body's next task is to transport the nutrients throughout the body. This is accomplished by the veins and arteries that comprise the blood circulatory system and the lymphatic vessels that comprise the lymphatic circulatory system. These extensive systems both deliver the nutrients to where they are needed in the body, and aid in the elimination of waste products generated by cells.Upon absorption, water-soluble nutrients enter the bloodstream through the capillaries contained within each villus. Once they reach the bloodstream, water soluble nutrients circulate directly to the liver, giving it first access to the nutrient-rich blood as it leaves the small intestine. The liver then regulates the use of the nutrients to suit the body's needs. Small amounts of some nutrients are stored in the liver, but most either undergo chemical modification or are released directly into blood, and circulated to where they are needed in the body. The lymphatic system also plays an important role in the circulation of fat-soluble nutrients (mostly lipids and some fat-soluble vitamins) away from the GI tract. Each villus contains a lymphatic vessel-a lacteal-through which the nutrients are absorbed. Each lacteal connects to a larger network of lymphatic vessels that circulate a translucent liquid called lymph. Though the circulatory route of the lymphatic system initially bypasses the liver, it eventually empties into the bloodstream where nutrients can be taken up and used by cells.