The digestive system has the function of breaking down food to retrieve nutrients and minerals for use such as energy and filter out waste. Major organs include the intestines (small and big), stomach, esophagus, liver, mouth, gallbladder, pancreas, etc. Functional units include muscles and sphincters, muscular layer modified into ring-like valves at junctions in segments of digestive tube.
The small intestine is an organ responsible for digestion and absorption of nutrients from food. It is the longest section of the alimentary canal, with a small diameter. The first 25 centimeters of the intestine is the duodenum. Acid chyme from the stomach mixes with the digestive juices from the liver, pancreas, gallbladder, and gland cells of the intestinal wall. The pancreas creates hydrolytic enzymes and a solution of alkaline with bicarbonate, acting as a buffer to balance the acidity in stomach chyme.
The pancreatic juices include protein digesting enzymes that are activated once located in the duodenum’s extracellular space. The liver produces bile, a mix of substances stored in the gallbladder. Bile has no enzymes but bile salts which are detergents that help with fat digestion and absorption. It also has pigments from red blood cell death from the liver. The lining of the duodenum is called the brush border, and it is a source of digestive enzymes secreted into the lumen. Digestion finished early in the intestine while the chyme is in the duodenum and the last parts of the small intestine are called the jejunum and ileum focusing on absorption of the water and nutrients. Peristalsis is the rhythmic waves of contraction by muscles in the digestive tract that help with breaking down and moving food down the canal.
Nutrients in the lumen are absorbed mostly in the small intestine. It has a large surface area with large circular folds in the lining having villi, which are finger like projections. Each epithelial cell of the villi have microscopic micro-villi, projecting into the lumen. The micro-villi increases the rate of absorption. At each villi core is a net of microscopic capillaries and a vessel of the lymphatic system called a lacteal. Nutrients are absorbed in the epithelium in the intestine and then the capillaries and lacteals.
Written By: Neil 6/18/2019