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Most digested molecules of food, as well as water and minerals, are absorbed through the small intestine. The mucosa of the small intestine contains many folds that are covered with tiny fingerlike projections called villi. In turn, the villi are covered with microscopic projections called microvilli. These structures create a vast surface area through which nutrients can be absorbed. Specialized cells allow absorbed materials to cross the mucosa into the blood, where they are carried off in the bloodstream to other parts of the body for storage or further chemical change. This part of the process varies with different types of nutrients
After traveling through the esophagus and esophageal sphincter, bolus enters the stomach. The stomach is known to be the “temporary storage unit for food (Wiley 2013).” While in the stomach, bolus is mixed with secretions from the stomach that are highly acidic. Once mixed, the bolus becomes chyme. Chyme is a mixture of incompletely digested food and stomach secretions. Some absorption does occur in the stomach, however, absorption mainly occurs in the small intestine. The stomach wall contains two layers of muscle, and in the lining of the stomach there are gastric pits with gastric glands that secrete gastric juice. Gastric juice contains water, mucus, hydrochloric acid, and pepsinogen. Gastric juice is stimulated and secreted by a hormone called Gastrin. Gastrin is secreted once food has entered the stomach and is signaled by the stretching of local nerves(Wiley 2013). Pepsinogen is also produced by the gastric glands, is a part of gastric juice, and is an enzyme that kills bacteria present in food. Pepsinogen is activated to form pepsin through the stomach acids, which breaks proteins into shorter chains of amino acids, therefore, assisting in digestion (Wiley 2013). Once the chyme has moved through the stomach it passes through the pyloric sphincter then enters the Small Intestine. Food remains in the stomach for roughly 4 to 5 hours before it is completely emptied. The pyloric sphincter helps to regulate the rate food empties from the stomach. When one eats a high-fat meal, chyme may stay in the stomach for a longer period of time because the gastrointestinal motility is slowed down by the release of certain hormones. Other aspects that could slow the emptying of the stomach are exercise, sadness, or fear (Wiley 2013). (Postlethwaite)
The process in which materials are moved across a membrane caused by the presence of a concentration gradient. Materials move from high concentrations to low concentrations (Singer).
Uses carrier proteins to move materials across a concentration gradient (Singer).
Uses energy and protein pumps to move materials in and out of the plasma membrane (Singer). Great example is the sodium/potassium pump
3.3.3 The circulatory systemEdit
When glucose is absorbed, it enters the bloodstream. The concentration of glucose in the bloodstream is regulated by the liver and hormones that are secreted by the pancreas. It is pumped by the heart (Whitney 82).
Materials that are absorbed through the small intestine enter the lymph. One way route for fluid from the tissue spaces to enter the blood (Whitney 84).