Metabolism test 1 Quick overall note Utilize the hand drawn pathways she posted on blackboard to aid through the step processes The ones she drew will be what she tests on Other than that I hope my guide really helps you grasp the concepts and understand things she said in class Good Luck The Gastrointestinal tract is the basically the pathway for ingested food The tract starts in the mouth and ends in the large intestine Mouth pharynx esophagus stomach small intestine and large intestine The function of the GI tract is primarily digestion and absorption Digestion is the hydrolysis of energy nutrients Absorption is a passage of simple molecules across the gut wall into blood or lymph fats The GI tract is also responsible for many other things elimination large intestine protect the body white blood cells metabolic processes Before talking about how the GI tract works we need to discuss the anatomy of the system There are 4 layers of the GI tract and some have layers within them I will break the layers down for us 1 The innermost layer consists of 3 layers and it is known as the mucosa layer a The first layer is the epithelium This includes glandular tissue and is contact with food This layer has epithelial cells along with exocrine ducts to secrete mucus and endocrine glands hormones to the blood b The second layer is known as the lamina propria and it is the vascular layer that is in contact with the epithelium and contains mucosal glands c The final 3rd layer of this 1st layer is the lingoid muscularis mucosa and it is a thin double layer of smooth muscle where white blood cells are located 2 Submucosa This is layer is made of connective tissue and is known as the network of nerves submucosal plexus This layer is responsible for blood flow and the movement of mucosa 3 Muscularis propria externa This is a layer of muscle with another network of nerves mysenteric plexus to play a role in motility peristalsis These inner layers of muscles are circular while the outer layer is longitudinal 4 Serosa This layer is covered by the visceral peritoneum to protect the GI tract and is highly vascular containing blood vessels lymphatics and nerves Esophagus The esophagus is a 10 muscular tube that connects the back of the mouth to the stomach It moves food via peristalsis The esophagus is designed by sphincters to complete this peristalsis They work by staying constricted until food is swallowed and then they relax to let the food through Then they constrict again to keep food from coming back up The upper sphincter is made of voluntary muscle and the lower sphincter muscle is made of smooth circular muscle GERD Gastrointestinal Esophagus Reflux Disease This is due to reflux of digestive juices from stomach into esophagus This is due to a weak gastroesophageal sphincter LES The pain can be relieved by antacids alka seltzer Also Histamine H2 blockers and proton pump inhibitors could prevent it Heartburn is negative result of this Stomach The stomach is the region of the GI tract after the esophagus connected by the gastroesophagel sphincter LES This area of the body holds 1 2 oz before eating and then can fold open rugae to hold 30 60 oz The stomach digests foods by mechanical digestion by diagnol muscle and gastric secretions It takes roughly 2 6 hours for food to pass through There are 4 regions of the stomach containing glands and cells within the regions 1 Cardia region after LES containing cardiac glands 2 Fundus hump at the top of the stomach next to the cardia 3 Body also known as the bis region It contains oxyntic glands 4 Antrum pyloric region end of the stomach Contain pyloric sphincter for chyme acid food to enter duodenum of the small intestine Cells within the gland are Neck mucus bicarbonate and mucus Parietal oxyntic HCl and Intrensic Factor IF cannot absorb B12 without Chief zymogenic pepsinogen zymogenic means inactive Enteroendocrine hormones There is some digestion in the stomach Lipids have a limited hydrolysis via lingual gastric lipase Protein has some hydrolysis to smaller polypeptides peptones via pepsin Pepsin is considered an endopeptidase meaning it can break interior bonds Carbs aren t digested so much there is still some digestion going on for carbs from the amylase in the bolus when entering the stomach but is inactivated by HCl Regulation of Gastric Secretions up some So this next part was very confusing during lecture let s see if I can clear things Chief cells mainly in the response of acetylcholine secrete pepsinogen Pepsinogen is a zymogen meaning it is an inactive protein digesting enzyme Pepsinogen can be activated by HCl to make pepsin Once pepsin has been made newly made pepsinogen can be activated by HCl or pepsin autocatalytic HCl is released by parietal oxyntic cells and it used to activate pepsinogen kill microorganisms and denature tertiary and quaternary proteins so pepsin can digest them A few things regulate HCl release by parietal cells Gastrin a peptide hormone released by G cell it is released by the presence of a protein or by GRP in the response of acetylcholine Acetylcholine released by vagus nerve in response to stomach distension can stimulate the release of gastin via GRP or binding on gastrin cells It may also bind straight to parietal cells to release HCl Histamine is a vasoactive amine produced by mast enterochromaffin cells which are released by the vagus nerve and gastrin o Identically to acetylcholine and gastrin Histamine can bind straight to parietal cells Somatostatin an inhibiting hormone which is released by the stomach intestine and pancreatic cells o ACH inhibits its release while H stimulates it So when pH gets so low this is released to stop the process There are some factors affecting the gastric emptying The increased volume of food can speed up the rate of emptying The composition of food Carbs are the fastest pro fat the slowest and Hormones that delay gastric emptying motility CCK Secretin and soluble fiber delays GIP and peptide YY Oral Cavity Now that we know what the GI tract looks like we can talk more about the GI tract itself and how it digests food and absorbs nutrients Digestion begins in the oral cavity where saliva contains enzymes The enzymes that begin in the mouth are salivary amylase carbs and lingual lipase milk fat Lingual lipase is located on the back of the tongue and is very important in infants since most of their meals are consisted with milk This will decrease with age One thing to know about
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