Digestive System PDF

Digestive System Edie Sperling, PhD(c), DPT, OCS COMP-NW  General Features of the Gastrointestinal System, aka Alimentary Canal  Diges&ve System Head region taught in Overview Head &...

Digestive System Edie Sperling, PhD(c), DPT, OCS COMP-NW  General Features of the Gastrointestinal System, aka Alimentary Canal  Diges&ve System Head region taught in Overview Head & Neck We will cover items in the following categories: Esophagus Alimentary Canal Liver Stomach Accessory Organs Gallbladder Pancreas Small intesJne Alimentary canal is a con&nuous tube, from oral cavity to anus, where food is Appendix Large IntesJne brought in, prepared, digested, nutrients Rectum absorbed, and waste eliminated. Anus Accessory organs are the organs that assist in diges&on of the food.  Organs of the Digestive System I. Alimentary Canal: ConJnuous Tube, in order, cranial to caudal Oral Cavity Pharynx Esophagus Stomach Small intesJne Large intesJne Rectum Anal Canal II. Accessory Organs: AssisJng in digesJon, or in post-digesJve funcJon Salivary Glands Pancreas Liver Gall Bladder Functions of the Digestive System MasJcaJon (Chewing) DegluJJon (Swallowing) Peristalsis (Propulsive movement) DigesJon (Chemical breakdown of nutrients) AbsorpJon (Moving nutrients into bloodstream) EliminaJon (Passage of undigested maQer) Organization of the alimentary canal (inner to outer) Mucosa Mucosa = inner lining of the gut; this Epithelium with glands term is ubiquitous and used EVERYWHERE Lamina Propria (Areolar CT) Muscularis Mucosae Submucosa (Dense irregular CT) Muscularis externa (smooth M.) Muscular part; responsible for Inner (circular) muscle layer peristalsis, sphincters Myenteric nerve plexus Outer (longitudinal) muscle layer Serosa/advenJJa Schema&c of ExtraintesJnal gland (e.g., Inner circular layer layers in the pancreas) Muscularis externa Myenteric plexus alimentary canal Outer longitudinal layer Mucosal epithelium Mucosal glands Mucosa Lamina Propria Muscularis Mucosae Mesentery Submucosal plexus Dense irregular CT Submucosa Submucosal glands Small arteries and veins Smooth muscle structure and function Single elongated cell, no stria&ons Single nucleus Communica&ng junc&ons, external lamina stretched AcJn Slaments contracted Acts as a unit: when one muscle cell contracts, the en&re mass contracts.  One cell outlined to show its general appearance It is oPen hard to see the separa&on between individual cells. Nuclei are typically elongated; when the cell is contracted, the nucleus is twisted, some&mes called a “Corkscrew nucleus.  Peristalsis—Rhythmic contrac&on of smooth muscles causing movement of Peristalsis starts with relaxa&on of the smooth bolus. Red—contract Blue--relax muscle ahead of (i.e., distal or caudal to) the food bolus. Bolus Smooth muscle in front of (cranial to) the bolus contracts, and this Cranial Caudal contrac&on propagates distally to force the bolus distally. This is a Bolus housekeeping func&on of the intes&nal smooth muscle and is done with liYle or no input from the nervous system.  Mesente ries Tubes of the GI tract are held in place by mesenteries Mesenteries consist of parietal peritoneum, arteries, veins, lymph ducts, autonomic nerves, and adipose Jssue and aQach some organs to our internal body walls Most organs are free in the abdominal cavity, but a few of the organs are aTxed to body wall (duodenum, appendix, ascending and descending colon, sigmoid colon). When they are aTxed they are behind the peritoneum which lines the abdomen, and are therefore called retroperitoneal Alimentary Canal Organs are aYached to The purpose of a mesentery is to do the the posterior body wall (vertebrae, aorta following: & IVC) by a mesentery—a sheet of 1) Allow the organ to be peritoneal membranes plus fat and so free for mo&on (e.g. peristalsis) much more! Gut 2) Supply it with arteries, Lumen veins, nerves, and lympha&cs Visceral peritoneum Gut Inside are tube Fat Veins Parietal mesenteric Arteries peritoneum Autonomic Mesentery nerves Lymph nodes Parietal peritoneum Mesentery  Alimentary Canal: Oral Cavity, Pharynx and Esophagus  Oral Cavity DigesJon starts in the mouth (oral cavity) Teeth help to mechanical digest food by breaking it down into smaller pieces Saliva also helps to dampen and break down food Amylase, an enzyme in saliva, begins to chemically digest carbohydrates Chewing and swallowing are very complex acJons, involving a balance of the muscles of masJcaJon (chewing), jaw mobility and stability, head and neck posture, salivary glands, teeth placement and health, motor and sensory nerves, and tongue moJons The tongue, soW and hard palates, teeth, and muscles of masJcaJon all act together to form a bolus, or lump of food, which is then swallowed The pharynx is the passageway and SoW Palate 1. Nasopharynx associated structures of the nose and mouth down to the larynx (vocal cords) 2. Oropharynx and consists of three Tongue parts, labeled here 1, 2, 3 3. Laryngopharynx: split between airway and “foodway” Epiglo`s 6 Esophagus The epiglo[s is a piece of carJlage which automaJcally closes over our airway (trachea) when we swallow  Esophagus—a muscular tube Collapsed when not in use. Same layers as rest of alimentary canal. StraJSed squamous epithelium (not keraJnized, same as inside of mouth and of pharynx) Muscular layer—Srst 1/3, all skeletal muscle; second 1/3, mixed; last 1/3, all smooth muscle. Sends food bolus to stomach by peristalsis.  Arises out of Esophagus and pharynx Trachea its transit Esophagus through the medias&num The Srst inch of the esophagus is in the neck. The bulk of the esophagus is traveling in the thorax. Esophagus Only the last inch of the esophagus is in the abdomen. Penetrates diaphragm Aorta at T-10 level Frank NeQer, M.D. Alimentary Canal: Stomach  Histology of the stomach Mucosa: Simple branched glands, lamina Parietal cells (make propria (areolar HCl, intrinsic factor) Jssue), muscularis mucosae Submucosa: Chief cells (make Dense enzymes) irregular CT Muscularis Gland from externa: mucosa. Smooth muscle.  The Stomach: Bag of Acid—and its func&ons 1. The stomach receives food from esophagus, mixes it up and stores it, to be passed on. 2. The stomach produces hydrochloric acid (HCl), primarily to eliminate bacteria. 3. It produces the enzyme Pepsin (pH optimum ~3.0, acidic) to break down proteins into smaller peptides, and a lipase, to break down triglycerides to a glycerol and fatty acid. 4. It produces Intrinsic Factor for absorption of vitamin B-12 5. In churns up the food, mixing it and helping to break it up somewhat. 6. Stores gasses to be eliminated by reverse peristalsis through the esophagus (Eructation—a belch). 7. Note: one can survive without the stomach, but you have to a) chew your food up very well, and b) take daily Vitamin B-12 shots. Alimentary Canal: Small Intestine  First 10 inches– Duodenum Second part: Jejunum most of digesJon occurs here Third part: Ileum Duodenum; structure Duodenal bulb Pyloric sphincter and (frst part) func&on Duodenum (second part) Pancreas Greater duodenal papilla (hepato- pancrea&c duct) Jejunum Duodenum: fourth part Duodenum: third part. Superior mesenteric artery and vein  Duodenum First part receives acidic chyme from stomach. Alkaline mucus protects Srst part of duodenum from acid. Second part receives: Pancrea&c duct(s) (bicarbonate; bucers acidity, digesJve enzymes to break down food into consJtuent monomers) Bile duct(s) from gall bladder (bile for lipid digesJon) Third part crosses right to leW Fourth part empJes into jejunum, pH-neutral chyme now SomeJmes an accessory pancreaJc duct  Small Small intes&ne— Intes&ne Jejunoileum—is a con&nuous tube; Jejunum; upper, they gradually more leP transi&on from one to another. Ileum; lower, more right The small intes&ne is not so much coiled as it is folded.  Contrasted X-ray of small IntesJne following barium swallow. Jejunum: looks fucy because of Circular folds (plicae large circular circulares) of folds. jejunum. They gradually become Ileum; looks much smaller as you smooth because of go down the ileum. very small circular folds. Next slide Mucosa Small Gut Surface Villus Histo Increase surface epithelium area Mucosa and what it is composed of in the Mucosa small intes&ne. —full thickness Plica circularis Submucosa Circular Regenera&ve muscle cells Nerve ganglia Replenish epithelial Longitudinal Muscularis cells. muscle Mucosae Jejunum You can tell Epithelium this is Jejunum by Mucosa the height of the villi. Ileum Villus has shorter villi. Colon has no villi. Gland Circular Muscular layer  Lipid diges&on Bile emulsiSes fats so the enzymes can reach them. Pancrea&c lipase breaks down triglyceride into a glycerol and free faQy acids  Carbohydrate diges&on Amylase breaks down starch into small di-and tri-saccharides of glucose (e.g., maltose) in mouth, stomach, and small intesJne Maltase enzyme (on microvilli) break maltose into glucose, which can be directly absorbed. Sucrase enzyme (also on microvilli) break sucrose (table sugar) into glucose and fructose. Lactase enzyme (also on microvilli) break lactose (milk sugar) into glucose and galactose. Absence of enzyme is cause of lactose intolerance. End result is monosaccharide (glucose or fructose) which is absorbed through the epithelial cells into underlying capillaries.  Protein diges&on Trypsin breaks proteins into small fragments called pepJdes. CarboxypepJdase breaks pepJdes into individual amino acids or di/tri pepJdes. On microvilli, there are two more enzymes to break down pepJdes into amino acids. AWer digesJon, amino acids and di/tri pepJdes are absorbed.  Absorp&on of nutrients: H2O soluble Lipids Gut Lumen Nutrient Microvilli Absorp&on Green: Absorp&on of Goblet Cell: Lipids and lipid- Makes soluble vitamins Mucus Blue: absorp&on of water-soluble nutrients: amino acids, glucose, minerals, vitamins. Absorp&on: To blood capillaries to lymph ducts Lamina Propria Space Alimentary Canal: Large Intestine  Large Intestine Starts at cecum—small sac (1 to 6 inches), closed-end, rudimentary fermentaJon sac. EmpJes into ascending colon. Appendix—narrow tube, several inches long, serves for accumulaJon of lymphocytes. EmpJes into cecum. Colon—long tube, with four parts: ascending, transverse, descending, sigmoid. Serves for water/electrolyte absorpJon. EmpJes into rectum. Rectum—usually empty; holds feces unJl eliminaJon. EmpJes through anal canal.  Large Intes&ne Transverse colon. No diges&on Ascending colon. Descending occurs in the colon colon, Cecum although water and Appendix salts are s&ll Sigmoid colon absorbed. Rectum. Dreamstime royalty-free stock image http://www.dreamstime.com/royalty-free-stock-image-intestines-image1928197 6 Real life large LeP colic hexure intes&ne Transverse colon Right colic hexure Intraperitoneal Ascending colon Descending colon Retroperitoneal Retroperitoneal Terminal ileum Sigmoid colon Intraperitoneal Cecum Intraperitoneal  Superior mesenteric A. Jejunal bbr. Middle colic A. Inferior mesenteric R. Colic A. A. L. Colic A. Ileocolic A. Superior rectal A. Sigmoidal AA. Accessory Organs of Digestion  Accessory organs of diges&on 1. Salivary glands 2. Liver 3. Gallbladder 4. Pancreas Liver The liver, a vital (life- sustaining) organ, resides In the upper right quadrant of the abdomen. Anatomically one of the most boring organs of the body. Physiologically, it is one of the most complex.  Liver Position in the abdomen Diaphragm The liver is spread out, most of it being on the right but carrying over to the leW side. A part of it in the center is not protected by the ribcage. The liver is very soW and so diTcult to palpate; if it can be easily palpated as a solid mass, parJcularly below the right margin of the ribs, there is a good chance of something wrong, like cirrhosis  Liver Func&ons Manufacture of most blood proteins. Manufacture of bile, in part using bilirubin from spleen (byproduct of RBC breakdown). RegulaJon of blood sugar in correlaJon with pancreas. DetoxiScaJon of ingested toxins, including ethanol (alcohol); also acects oral medicaJons Venous drainage of liver All internal veins drain to the Hepatic Veins which drain directly into Inferior Vena Cava and into the heart IVC  Posterior end Right anatomic LeP anatomic lobe of liver lobe of liver Hepa&c portal vein ;Hepa&c aa. Common Hepa&c bile duct Gallbladder Anterior end  Portal Vein The blood entering the portal vein is draining from all the veins in the digesJve system and spleen. ALL veins of alimentary canal, pancreas, and spleen go into the liver! These veins coalesce into a single portal vein, which then distributes its blood TO the liver. The slightly lower oxygen of the portal venous blood mixes with high- oxygen arterial blood entering the liver. The blood collected nutrients in the alimentary canal and now delivers them for storage in the liver  Gall Bladder Receives bile produced in liver Concentrates bile by removing water Stores bile for release At appropriate signal, secretes bile through common bile duct into duodenum for break-down of fats Note, if liver can not produce bile, the bilirubin will not be taken from the bloodstream to form bile. It remains in the blood stream. This results in jaundice, which shows up cutaneously as an overall greenish color—and it makes the sclera of the eye bright yellow  Pancreas TWO important funcJons: (1) Exocrine gland: produces substances that secrete to duodenum as part of the digesJve process: Bicarbonate Trypsin Amylase Lipase (2) Endocrine gland: Produces hormones in cells called pancreaJc islets, scaQered throughout pancreas Produces insulin (lowers blood glucose) and glucagon (raises blood glucose) Produces somatostaJn for control of hormones it produces More about this in the Endocrine lecture Note—endocrine parts (pancrea&c islets) are scaYered throughout the pancreas. Histology of the pancreas; scaYered ducts and islets, most of volume taken up by exocrine glands. Pancrea&c exocrine duct Islet of Langerhans (one of three seen in this Seld) Pancrea&c exocrine gland (basically seen everywhere) Pancrea&c artery & vein.