04-02-07, Digestive system notes

Also see the 03-29-07 anatomy and physiology notes on the digestive system (36 megabytes).

The digestive system has the job to break down food and absorb nutrients. Once the digestive system breaks down the food, it is absorbed for nourishment. You can demonstrate digestion via eating (yeah, this is serious).

The digestive system can be broken down into two sections: the alimentary canal (gastrointestinal tract) and the digestive accessory organs. The gastrointestinal tract is an open-ended tube that food passes through. This food gets digested and absorbed on the way.

The regions are the oral cavity, etc. etc. stomach, small intestine, large intestine, and so on. The oral cavity is a place where the teeth provide for mastication. Food is mixed with saliva and is rolled into a bolus, a ball of food and saliva. The tongue and teeth are accessory organs in the mouth.

The salivary glands are important to the early stagtes of digestive. Small ducts secrete saliva from the salivary glands. The saliva contains enzymes and other substances. Saliva is responsible for digestion of carbohydrates. The swallowing (or deluteititon) of bolus moves the bolus to the pharynx (throat).

The pharynx is connected to the oral cavity and propels the food to the rest of the throat. The tonsils provide for infectious-fighting agents so that bacteria in food can be neutralized. The esophagus is where food goes down. The esophagus is the tube that transports the bolus directly to the stomach. The esophogaus drops the food through the gastroesophageal sphincter, a passageway to the stomach.

The stomach has gastric juices. The bolus is converted to chyme. When the bolus reaches the stomach, the bolus is stored, and then the stomach begins a chemical breakdown of proteins inside the food. The chyme is a disgusting, creamy paste of semi-digested food, and is in the stomach where protein-digestion begins.

The first part of the intestine is the small intestine. The chyme passes into the small intestine through the pyloric sphincter. The small intestine is the longest part of the intestines, it's responsible for the absorption of proteins, lipids, fats, and seven liters of the nine liters of water that it comes across. The small intestine can be broken up into three regions: the duoden, the jejunum, and the ileum.

The duodenum is the first part of the small intestine. It receives the bile and other juices, like from the liver, gallbladder and the pancreas. The jujenum is the next section of the small intestine and is about eight feet long. The ileum is the smallest section and ends at the ileocecal valve. The illeocecal valve opens up to let food to go into the large intestine and keeps food from backtracking, kind of like the valves in the heart. The ileum is 12 feet long.

The large intestine forms the terminal end of the gastrointestinal tract. The large intestine is wide, but is only five feet long. The large intestine absorbs 90% of the remaining water from the indigestible food. That's lots of water. When too little water is absorbed, we get diarrhea, and when there's too much, it's constipation.

The secum, the colon, and the rectum is the parts of the large intestine. The first part is the cecum, which is continuous with the ileum but separated by the ileocceal valve. There is the appendix, which has lymphatic tissue. Fecal matter builds up and becomes trapped in the appendix, and at this point the appendix becomes infected and inflamed, appendicitis. The colon forms a rectangular-like frame around the small intestines. The side of the large intestinal frame, extends out of the cecum and is known as the ascending colon. The left part of the abdominal cavity is the descending colon. The part near the rectum is the sigmoid colon.

The end of the rectum is the anal canal which has muscular sphincters which controls the defecation process near the anus.

There are six accessory organs in the digestive process: the teeth, the tongue, and the salivary glands. The teeth and most of the tongue are found in the oral cavity. The extrinsic salivary glands are found in or just outside of the oral cavity and connected to the mouth via ducts. There is also: the liver, the gallbladder, and the pancreas, which are all associated with the duodenum.

The liver is the large gland in the body, with four lobes and weighs maybe three pounds, to the right of the midline in the body. It produces bile, which is full of salt, pigments and liquids. Bile helps the body break down fat.

The gallbladder is another accessory organ. It's a green ,four-inch long muscular sac near the liver. The gallbladder is like a bile-storage center. It stores excess bile, and then concentrates bile by absorbing water out of it, and then delivers bile to the small intestine, to the cystic duct, which connects with the bile duct, which forms the common bile duct, which leads to the heapto-pancreatic duct to go to the duodenum.

The pancreas cooks up most of the enzymes needed for digestion. The pancreas produces hormones and enzymes. The pancreas is a yellow-ish, tadpole-like gland, and it creates pancreatic juice, which leads to the haptopancreatic duct which goes to the duodenum.