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BIOL 255 SI, Molly Unit 5B/C – Digestion pt. 2, 12/2/16 1) Swallowing referred to as deglutition, and in the pharyngeal-esophageal phase is controlled by the medulla and the lower pons. 2) As the bolus move down the esophagus in an action referred to as peristalsis, the first valve or sphincter it moves through to get into the stomach is the cardiac or lower esophageal sphincter. 3) In the stomach chemical digestion of proteins begins and food is churned, and converted to chyme. ***Greater Omentum from greater curvature/ lesser omentum from lesser curvature*** ****TALK ABOUT #5 AFTER THE REST**** Epithelial lining contain goblet cells that produce alkaline mucus to protecting epithelial lining from digesting itself. Whereas, the glands of stomach which are the gastric glands of fundus and body contain mucous neck cells that secrete acid mucus, and the parietal cells that secrete HCl and intrinsic factor for Vitamin B12 absorption along with chief cells that produce pepsinogen which is activated to pepsin by the HCl in stomach and pepsin itself, in which protein is digested into polypeptides and finally enteroendocrine cells that secrete the hormones into the blood. 4) The functions of the Stomach are to hold ingested food, digest food, physically and chemically, to deliver chyme to small intestine, enzymatically digests proteins with pepsin and secrete intrinsic factor required for vitamin B12 absorption. 5) Small intestine, in which most absorption takes place, run from the pyloric sphincter to the ileocecal valve and have three subdivisions: the first is the duodenum, the middle portion is the jejunum, and the last portion is the ileum, which joins with the large intestine at the ileocecal valve. 6) The right and left hepatic ducts merge and become the common hepatic duct, the cystic duct merges with the common hepatic duct and become the common bile duct, which merge with the main pancreatic duct at the hepatopancreatic ampulla which empties into the duodenum, this is controlled by the sphincter of Oddi. Also the accessory pancreatic duct empties directly into the duodenum, anterior to the hepatopancreatic ampulla. 7) The inner surface of the small intestines contains plicae circulares which are deep circular folds of mucosa and submucosa which increase surface area 10 fold, which are made up of villi that are fingerlike extensions of mucosa into lumen which also increase surface area 10 fold and finally microvilli which are tiny projections of absorptive mucosal cells’ plasma membranes into lumen which also increases surface area 10 fold. 8) Hepatocytes’ functions include: production of bile, processing bloodborne nutrients, storage of fat-soluble vitamins and detoxification. Secreted bile flows in bile canaliculi between hepatocytes toward bile ducts in portal triads. 9) The small intestines is the site where most chemical digestion occurs and virtually all nutrient are absorbed. 10) Large Intestine have 3 unique features: the teniae coli which is three bands of longitudinal smooth muscle in muscularis, along with the haustra which are pocket-like sacs caused by muscle tone of teniae coli, and finally the epiploic appendages that are fat-filled pouches of visceral peritoneum which store energy for future use. 11) The functions of the normal flora of the large intestines are to colonize the colon, inhibit potential pathogens, ferment indigestible carbohydrates which release irritating acids and gases (flatus) and synthesize B complex vitamins and vitamin K. 12) The process of defecation starts with the fecal distension of rectal walls which stimulates the rectal wall contraction that relaxes internal anal sphincter that is composed of smooth muscle and is under involuntary control. This then stimulates the Nervous System controlling the voluntary control aspects of defecation and when you are ready you perform the Valsalva maneuver which involves the contraction of diaphragm, the abdominal wall muscles and closing of the glottis, and then finally relaxation of external anal sphincter results in defecation. 13) During the embryonic development of the digestive system by the 3rd week an endoderm fold becomes the foregut and hindgut. The mouth and anal openings are formed of mucosa from the endoderm; while all muscularis is formed from the mesoderm; but the oral cavity and anus are formed from ectoderm. During the 8th week the accessory organs bud from endoderm, and their connections become ducts.