Digestive System: Alimentary Canal and Accessory Digestive Organs | KN 252, Study notes of Kinesiology

Download Digestive System: Alimentary Canal and Accessory Digestive Organs | KN 252 and more Study notes Kinesiology in PDF only on Docsity! *Intraparitoneal organs – organs that are hanging inside cavity *Retroperitoneal organs – organs pushed back against posterior wall *Mucosa  submucosa  muscularis externa  serosa/adventitia Digestive System: Alimentary canal and Accessory Digestive Organs [W11 – Lecture 1]  Alimentary tract – continuous muscular digestive tube that runs through the body; digests food and absorbs digestive fragments o Histology: same 4 layers from esophagus to rectum  (1) Mucosa – simple columnar epithelial lining with an underlying supportive connective tissue called lamina propria; (innermost layer)  Lamina propria – connective tissue that supports the epithelium (under epithelium) o It has glands and lymphatic nodules (cluster of lymphs) to fight out invaders  Muscularis mucosa – thin layer of smooth muscle, separates mucosa from submucosa  Lumen – opening through which food passes; lined by the epithelium of mucosa  Oral cavity, esophagus, and anal canal are lined with stratified squamous epithelium o Stratified makes it more durable (good for chewing)  (2) Submucosa – connective tissue layer just outside the mucosa  Submucosal plexus – ANS fibers that controls peristalsis  Contains nerve fibers , blood vessels, lymphatic vessels, lymph nodules, and glands o The glands connect via a duct to the lumen  (3) Muscularis externa – double layer of smooth muscle  Myenteric plexus – ANS nerve fibers that controls peristalsis  Longitudinal muscle – outer layer  Circular muscle – inner layer  The muscularis externa of upper part of esophagus is formed by skeletal muscle  In stomach, there is an additional “oblique layer” (three layers of muscularis externa)  (4) Serosa– simple squamous epithelium that covers organ within abdominal cavity (smooth)  Visceral peritoneum – simple squamous layer that covers the organ and continues as parietal peritoneum  Parietal peritoneum – lines wall within abdominal cavity  Peritoneal cavity – space between visceral and parietal peritoneum o Serous fluid – small amount of fluid in cavity that lubricates the organs so they can move easily within abdominal cavity o Mesentary – the double layer of peritoneum that suspends into peritoneal cavity  (4) Adventitia – loose connective tissue that holds organs against posterior abdominal wall  Covers sides of organ that lies against posterior abdominal wall (doesn’t lie within peritoneal cavity) (rough irregularly arranged layer)  It’s a fusion of visceral and parietal layer (undistinguishable)  Accessory digestive organs – organs connected by ducts and lie outside of GI tract o These organs produce variety of secretions that contribute to breakdown of food  Salivary glands, liver, pancreas, gall bladder *Parotid, submandibular and sublingual glands are all exocrine *Styloglossus and hyoglossus fuse Oral cavity/mouth – entire cavity lined with stratified squamous epithelium (very thick and durable)  Labia/lips – surrounded by orbicularis oris [anterior] o Orbicularis oris muscle – muscle of facial expression that helps keep mouth closed when chewing  Cheek – formed by a muscle called buccinator [lateral] o Buccinator muscle – keeps cheek firm against teeth and hold food within chewing surfaces of teeth o Orbicularis oris and buccinator are muscles of facial expression and innervated by facial nerve  Tongue – composed of skeletal muscles that are innervated by the hypoglossal nerve o Tongue movement mixes food with saliva and helps to push food in swallowing o Intrinsic muscles ~ change shape of tongue but not position o Extrinsic muscles ~ move tongue position: protrude, side to side, retract (originates off external bone)  Genioglossus – protrudes and depresses tongue; fan shaped muscle (forms most of the bulk)  Originates from anterior portion of mandible and inserts on to dorsum of tongue  Styloglossus – retracts tongue and helps with swallowing; short muscle  Originates from styloid process & inserts into side/inferior aspect of tongue  Hyoglossus – depresses and retracts tongue; square muscle  Originates from hyoid bone and inserts into side/inferior aspect of tongue  Palate – hard palate and soft palate forms roof of the mouth (floor of nasal cavity) o Hard palate – formed by maxilla and palatine bones (anterior portion of palate) o Soft palate – formed by skeletal muscle and ends at uvula; it’s covered with mucosa  Uvula – goes upward to close nasopharynx when food is swallowed so food goes to esophagus  Glossopharyngeal (CNIX) carries sensory information; vagus (CNX) controls the muscle  Teeth – masticate/chew food to help with swallowing and digestion; 2 sets: deciduous and permanent o Alveolar sockets – within maxilla and mandible, the teeth lie in these sockets o Deciduous (baby teeth) – 20 primary teeth that fall out and replaced by permanent teeth o Permanent – 32 secondary teeth (upper and lower teeth)  Incisors – four teeth in center; two central incisors and two lateral incisors [4]  Canine – next to lateral [2]  Premolars/bicuspids – two teeth next to canine; first and second premolar [4]  Molars – three teeth next to premolars; first, second and third molar [6]  Wisdom tooth – the third molar tooth (17-25 years) Accessory glands – help with digestion  Salivary glands – produce and secrete saliva; [controlled by ANS] o Saliva – ease swallowing and begins digestion and facilitates sense of taste  Saliva is delivered to oral cavity via ducts from glands o Extrinsic salivary glands – 3 pairs of glands that lie outside of oral cavity  Parotid gland – anterior to ear; innervated by the glossopharyngeal [PNS and SNS]  Parotid duct – crosses gland and pierces the buccinator muscle to enter the mouth near the upper second molar (secretes more watery material)  Accessory parotid gland – a small portion of glandular tissue attached to duct  Parasympathetic nervous system increases the release of saliva  Sympathetic nervous system secretes mucous like secretions making mouth sticky  Submandibular gland – under the mandible (size of large grapes); innervated by facial nerve  Their ducts lie under mucosa and open anteriorly at base of tongue  Submandibular duct – opens into papilla just below the tongue and anterior part of mouth (crosses over sublingual gland) o Secretions from submandibular gland squirt out from tongue when yummy food is being thought off (secretions are primarily mucous)  Sublingual gland – under the tongue/mucosa (triangular shaped); innervated by facial nerve  10-12 small glands that secrete mostly mucous and some serous o Buccal glands – small intrinsic glands that are scattered throughout mucosa of oral cavity SUBMANDIBULAR GLAN ESOPHAGUS go & @ Sees x an — ££ 7 F { m2 ? 5 : f me, ——————+ 1 2 PIAS. 7 os _ ‘ - mw RAN oD at \ & rr { y yk SH *there is a sphincter located in bile duct and hepatopancreatic ampulla Stomach – distal to the esophagus; lies in upper left quadrant of abdomen [W11 – Lecture 2]  The stomach’s volume is 50mL in its empty state, but it can expand to hold 3-4 gallons of content  Oblique layer –additional layer formed by the increased muscularis externa; this enhances gastric motility o Gastric motility – ability of stomach to move the substances within it to enhance digestion  Greater curvature – outer curve o Greater omentum – a double layer of peritoneum extending off the stomach and used as fat storage  Lesser curvature – inner curve on upper surface of stomach o Lesser omentum – peritoneum off of lesser curvature to attach stomach to posterior abdominal wall  Rugae – many folds of the mucosa inside the stomach’s lumen; rugae flattens when stomach distends  Cardiac region – area where esophagus enters and where cardiac sphincter is located  Fundus – domed part at superior aspect of stomach (extends above cardiac region)  Body – mid-portion or main portion of stomach  Pyloric region – area that approaches small intestine or duodenum; it is at distal end of stomach o Pyloric antrum – entrance to the area o Pyloric canal – narrower part of pyloric region o Pyloric sphincter (valve) – very thick layer of smooth muscle that does not allow content in stomach to enter duodenum [anatomical sphincter]  It allows entry into duodenum after a considerable amount of digestion occurs  Stomach wall’s mucosa is lined with simple columnar epithelium o Surface mucous cells/goblet cells – cells closest to the surface epithelium of stomach  They produce an alkaline coat of mucous to protect stomach from its acid content o Mucous neck cells – cells located in area where a distinction is made from gastric pits and glands  As the epithelium invaginates (folds), it forms these pits and glands o Parietal cells – secrete HCl and intrinsic factor (located in gastric gland)  Intrinsic factor – helps with absorption of B12 o Chief cells – secrete pepsinogen; occupies majority of gastric glands (located in gastric gland)  Pepsinogen – is the precursor of pepsin which is involved in protein digestion o Enteroendocrine cells – release hormones in lamina propria (few located in gastric gland)  These hormones (gastrin) are picked up by blood vessels within lamina propria and distributed to other areas of digestive system to help with digestion and motility Small intestine – major digestive organ, almost all nutrients absorbed here; consists of duodenum, jejunum, and ileum  Plicae circulares – circular folds of mucosa and submucosa that increase absorptive surface area of small intestine (more abundant in duodenum and less in ileum)  Duodenum – c-shaped first part of small intestine (shortest part of small intestine) o Starts at pyloric region of stomach and hooks back behind the stomach o Two important accessory glands empty into small intestine via ducts: liver and pancreas  Pancreatic duct – duct from pancreas that joins the bile duct  Bile duct – duct from liver and gall bladder  Cystic duct – duct from gall bladder that joins the “common hepatic duct” o Hepatopancreatic ampulla – the dilated portion after the pancreatic & bile duct join  The joining happens outside the wall of duodenum  Major duodenual papilla – a bump inside the lumen created by the large duct pushing through duodenum wall o Brunner’s glands – secrete an abundance of mucous to line lumen of duodenum to protect the walls from the acidic content received from stomach  The glands are within the connective tissue of submucosa  Jejunum – second part of small intestine (8 feet in upper left quadrant)  Ileum – third part (12 feet in lower right quadrant); there are lymphatic nodules within the wall of lumen o Ileocecal junction – where the ileum and cecum meet (the junction of ileum and cecum) o Lymphatic nodules ~ structures important for response of immune system to any foreign substance She uses bile duct and hepatic duct interchangeably. The bile ultimately empties into bile duct  Mesentary – suspends the jejunum and ileum in the peritoneal cavity o Intraparitoneal – organs hung in abdominal cavity by mesentary o Retroperitoneal – lies behind peritoneal cavity (the mesentary holding it is gone)  Serosa lines the side that faces cavity; adventitia lines the side where mesentery is lost  Wall of small intestine has three structures that increase amount of surface area o Plicae circulares – large circular folds of mucosa and submucosa that form wall of small intestine  The folds increase absorption by increasing the surface area o Villi – small folds of mucosa that covers the plicae circulares of small intestine  Mucosa contains the epithelium and lamina propria  Central lacteal – enters into each villi and absorbs fat; part of lymphatic system o Microvilli – on the surface of each of simple columnar cells (in the cell membrane of villi) o Intestinal gland – small “dipping” of epithelium  There are some goblet cells, absorptive cells and endocrine cells located in these glands Liver – an accessory gland that contains 4 lobes; located in upper right quadrant of abdomen  Liver – largest accessory gland in body weighing about 3 pounds  Right lobe – rounded part; Left lobe – narrower part  Caudate lobe – most posterior near the inferior vena cava (caudate means tail)  Quadrate lobe – square shaped, located immediately to left of gall bladder  Falciform ligament – thin connective tissue layer of mesentary; divides the right and left lobe  Round ligament of liver – thicken band that runs along inferior end of falciform ligament; o “Round ligament of liver” is a remnant of umbilical vein  Right/left hepatic ducts – comes from the right and left lobe and joins together o Common hepatic duct – the duct formed once the right and left hepatic ducts join o Cystic duct – comes from gall bladder, it joins the common hepatic duct o Bile duct – duct form once the common hepatic duct and cystic duct o Main pancreatic duct – joins the bile duct at hepatopancreatic ampulla  Porta hepatis – the area where bile duct, artery, and vein enter/exits from liver o Order from left to right: bile duct  hepatic portal vein  artery o Epiploic foramen – the space behind the three structures  Microscopic structure of the liver o Hepatocytes – liver cells that synthesize bile [square shaped cells]  Cords of liver cells divide the liver into functional lobules  Canaliculi – small tubules where the bile is released into; bile travels outward  The canaliculi come together and deliver it to the bile duct (via hepatic duct);  The liver can directly release bile to the duodenum o Portal triad – a branch of hepatic artery, portal vein, and bile duct at each corner of lobules  Central vein – blood from artery and vein flows into this; at the center of each of the lobules  Blood from artery and vein mix and travel inward to central vein o Artery brings oxygenated blood to help maintain tissue of liver o Vein brings deoxygenated blood containing substances absorbed from intestines  These substances will be absorbed or detoxified  Bile flows outward through canaliculi o Hepatic vein – takes blood from central vein and empties it into inferior vena cava o Sinusoids – dilated capillaries within the liver where blood flows through Gall bladder – stores bile; small sac on inferior side of liver  Bile – digests fats; manufactured in the liver and stored in the gall bladder; transports via the ducts o When bile is needed for digestion, “CCK” (a hormone) stimulates contraction of gall bladder which releases bile into cystic duct, which empties into bile duct, which empties into the duodenum. Ducts emptying into Duoednum hr —  Microscopic structure of the liver  VERMIFORM APPENDIX HAUSTRA TENIA COLI EPIPLOIC APPENDAGES o Intestinal phase – starts once food enters duodenum ; has excitatory & inhibitory phase  Excitatory phase – while pH > 3,duodenum stimulates gastric secretions and stimulates vagus nerve to increase gastric motility  This phase starts when “initial gastric chyme” (food) enters duodenum  While pH > 3.0  a stimulation causes small intestines to secrete “enteric gastrin hormone”; and simultaneously the stimulation causes vagus nerve to continue to stimulate gastric motility o This results an increase in gastric secretions and muscular contractions o Enteric gastrin hormone – causes stomach to increase gastric secretions  pH of duodenum lumen is usually 5-6 (pH of stomach is 2.0) o The food entering is very acidic, and mixes with fluids in duodenum lumen  Inhibitory phase – when pH < 3, the duodenum decreases its stimulation to stomach and vagus nerve and starts to secrete two different hormones [reversal process]  When pH < 3.0  enteric gastrin hormone decreases  the intestines now secrete “secretin” and “cholecystokinin”  this causes change in nervous input  Simultaneously, when pH < 3.0  vagus nerve stimulation decreases  sympathetic activity increases which shuts down muscular contraction  pyloric sphincter closes  Overall, when pH < 3.0, gastric secretions and muscular contractions decrease o The pH decreases because the acidic chyme mixes with fluids in small intestines  Like a titration  Stomach mixes ingested food and turns it into chyme o Stomach is capable of filling up by expanding  the rugae flattens as stomach expands o Chyme – food stuffs mixed with digestive juices o Pepsinogen is secreted by chief cells which are converted to pepsin in the stomach  Is activated when it comes into contact with HCl [pH < 3] o Stomach slowly empties its content into small intestine (takes 3-4 hours for an average meal) Physiology of Digestion ~ Small Intestine [W11 – Lecture 4]  Plicae circulares – permanent circular folds of mucosa and submucosa o Villi – 1mm projections of mucosa; consist of absorptive, goblet and endocrine cells  Absorptive cells – columnar in shape and contain microvilli on part of plasma membrane that is exposed to lumen (columnar/cuboidal implies absorption)  Microvilli – increase surface area through which material can be absorbed  Goblet cells – secretes mucus  Mucus protects cells of small intestine from the high pH of chyme  Endocrine cells – secretes secretin, cholecystokinin, and enteric gastrin into blood stream  Enteric gastrin has same effect on stomach as gastrin, but it is secreted from the intestines, not the stomach. Physiology of Digestion ~ Liver (4 lobes)  Liver, pancreas, & gall bladder are lined up together because they transport fluid to duodenum through ducts o Liver and gall bladder work together as a single unit. Pancreas works independently  Bile – emulsifies fat, it’s a “cholesterol derivative” synthesized by liver; its components are salts and bilirubin o Bilirubin – pigments from heme portion of broken down RBC  Liver stores nutrients: fats, proteins, vitamins, and lots of glycogen  Liver is a detoxifier o Useful when drinking alcohol, because it breaks down alcohol and turn it into something harmless o Liver also detoxifies and metabolizes good/bad drugs (this is built into the treatment of the drug)  Liver synthesizes proteins: clotting proteins, anticoagulation proteins, proteins that breakdown clot etc.  Liver is involved in defense o Kupffer cells – macrophages that line sinusoidal capillaries in the liver  The kupffer cells destroy unwanted material; if spleen is absent, the liver is primary destroyer Physiology of Digestion ~ Gall bladder (lies on inferior surface of liver)  Gall bladder – primary function is to store bile (40-70mL); it contracts after a meal to release bile o Liver secretes bile into right/left hepatic duct  common hepatic duct  cystic duct or bile duct  Sphincter of oddi – contracts which forces the bile back up the cystic duct into the gall bladder o It’s possible to live without gall bladder, but diarrhea may occur after a fat containing meal Physiology of Digestion ~ Pancreas  Pancreas – has endocrine and exocrine function o Acinar cells – exocrine portion that form cluster of cells  These cells produce different enzymes needed to digest different organic compounds  Acini – the large lobule formed by the cluster of cells o Secretions  Aqueous component – watery material that consists of bicarbonate; this component is secreted by the cells that line the duct and is combined with the enzymatic component  Bicarbonate – a base that slowly raises pH of chyme  Enzymatic component – secreted by acinar cells  Proteolytic enzymes – digests proteins o Trypsin, Chymotrypsin, and Carboxypeptidase  Pancreatic amylase – digests carbohydrates  Pancreatic lipase – digests lipids/fats  Ribonuclease – digests nucleic acids (DNA/RNA found in animal/plant product) Intestinal phase Process of Digestion – Small Intestine  Vagus nerve – stimulates the entire digestive process o Vagus nerve stimulates secretion of hormones, peristalsis, and segmentation in small intestine o When pH < 3.0, the vagus output decreases and sympathetic stimulation will temporarily increase  This happens so the pyloric sphincter can close and give duodenum time to process material  Mechanical processes: segmentation and peristalsis o Segmentation – mixing chyme back and forth by squeezing; most common movement  This allows enzymes, bicarbonate, bile and other fluids to mix with chyme  This continues until most of the food has been digested and absorbed o Peristalsis – propels chyme down tube; longitudinal movement (after segmentation)  Chemical processes: hormones and digestive juices o Duodenum contains endocrine cells that secrete: secretin, cholecystokinin, and enteric gastrin o During “excitatory phase”, acidic chyme enters duodenum & pH > 3[basic condition]  In this phase (pH > 3), enteric gastrin is released from duodenum and enters blood stream and stimulates stomach to continue to release gastric secretions and continue motility  Enteric gastrin – hormone that stimulates gastric secretions o same function as gastrin o During “inhibitory phase”, pH < 3[acidic condition]  CCK & secretin are released into blood stream; they target pancreas, liver, & gall bladder  Hormones targeting pancreas  Secretin – stimulates pancreas to secrete watery bicarbonate (aqueous component) o The bicarbonate will neutralize the acid in the lumen of duodenum o Bicarbonate is released by the “cells that line the duct”  Cholecystokinin (CCK) – stimulates acinar cells to secrete pancreatic enzymes  Hormones targeting liver and gall bladder  Secretin – stimulates bile secretion from liver  Cholecystokinin (CCK) – stimulates gallbladder contraction to release stored bile  End result o Chyme is mixed with bicarbonate and enzymes  Bicarbonate – a base that slowly raises pH of chyme o Enzymes breakdown each organic nutrient into its component building blocks o This cycle is repeated for each new bolus (ball) of chyme  Excitatory phase  inhibitory phase  excitatory phase  inhibitory phase [around & around]  Absorption occurs in remainder of small intestine o As the chyme is propelled through peristalsis from duodenum  jejunum  ileum, there is continued mixing and absorption o Vitamin B12 is absorbed in distal portion of ilium with intrinsic factor  Intrinsic factor – synthesized/secreted by parietal cells of stomach