The hepatic portal vein transports absorbed food from the small intestine to the liver. Absorption Absorption is the movement of digested food molecules through the wall of the intestine into the blood or lymph. Each villus has a network of capillaries and fine lymphatic vessels called lacteals close to its surface.
The epithelial cells of the villi transport nutrients from the lumen of the intestine into these capillaries amino acids and carbohydrates and lacteals lipids. The absorbed substances are transported via the blood vessels to different organs of the body where they are used to build complex substances, such as the proteins required by our body. The food that remains undigested and unabsorbed passes into the large intestine. Absorption of the majority of nutrients takes place in the jejunum, with the following notable exceptions:.
Section of duodenum : Section of duodenum with villi at the top layer. Glucose, amino acids, fats, and vitamins are absorbed in the small intestine via the action of hormones and electrolytes.
During breastfeeding, the lactase enzyme breaks down lactose milk sugar. However, lactase production ceases after weaning in most populations, so adults in those populations experience gastric discomfort or distress when eating dairy products.
The small intestine is where most chemical digestion occurs. Most of the digestive enzymes that act in the small intestine are secreted by the pancreas and enter the small intestine via the pancreatic duct.
The enzymes enter the small intestine in response to the hormone cholecystokinin, which is produced in the small intestine in response to the presence of nutrients. The hormone secretin also causes bicarbonate to be released into the small intestine from the pancreas in order to neutralize the potentially harmful acid that comes from the stomach.
Small intestine : This image shows the position of the small intestine in the gastrointestinal tract. Brush border enzymes take over from there. The most important brush border enzymes are dextrinase and glucoamylase that further break down oligosaccharides.
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