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EXAMS 1 and 2Metabolism 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 arelocated. 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 tocomplete 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. Thisis 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. StomachThe 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 theregions.1. Cardia- region after LES containing cardiac glands2. Fundus- hump at the top of the stomach next to the cardia3. 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- hormonesThere 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 SecretionsSo this next part was very confusing during lecture, let’s see if I can clear things up some! 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 soluble fiber delays.- Hormones that delay gastric emptying/motility: CCK, Secretin, and GIP, and peptide YY. Oral CavityNow 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


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FSU HUN 3224 - EXAMS 1 and 2

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