Anatomy 403: GI System Study Notes

• Provides study notes for Anatomy 403 Exam 4

GI System Anatomy Overview

• Digestive System (DS) is a muscular tube with accessory structures, made of the Gastrointestinal Tract and Accessory digestive organs
• Gastrointestinal Tract (GIT) includes the Oral cavity, pharynx, esophagus, stomach, small intestine, and large intestine
• Accessory digestive organs include the Teeth, tongue, salivary glands, gall bladder, liver, and pancreas

Function Overview

• Mouth: Functions in biting, chewing, and swallowing (mechanical and chemical digestion)
• Pharynx and esophagus primarily transport food
• Stomach facilitates mechanical disruption, absorption of water and alcohol, and chemical digestion
• Small Intestine (SI) is the main site for chemical/mechanical digestion and absorption
• Large Intestine (LI) primarily serves as a waste storage site and absorbs some electrolytes and vitamins (B &K)
• Rectum/anus is responsible for defecation

Body Innervation

• Parasympathetic innervation occurs via CN 3,7, 9, 10 (10 for proximal gut) and S2-S4 (pelvic splanchnic nerves, PS to distal gut)
• Sympathetic innervation involves the chain, synapsing near target organs (splanchnic) via celiac or inferior mesenteric ganglion

Layers of the GI Tract Wall

• Mucosal layer (luminal): includes epithelium, lamina propria, and muscularis mucosae
• Submucosal layer is a supportive CT layer with a large neurovascular supply, containing a specialized enteric nervous system
• Muscularis layer has an internal circular layer and an external longitudinal layer
• Serosa layer acts as a "saran wrap"

The Peritoneum

• The peritoneum is a double-layer serous membrane lining the entire cavity, comprising the parietal and visceral layers
• Parietal layer: Lines the abdominopelvic wall and folds back, forming a mesentery Mesentery supports intestines, prevents twisting, stores fat, and provides a pathway for blood vessels and nerves
• "The" Mesentery anchors small intestine to the abdominal wall
• Omentum: Two layers of peritoneum connecting the stomach to another organ Greater Omentum (inferior): connects the greater curvature of the stomach and the transverse colon Lesser Omentum (superior): connects the lesser curvature of the stomach and duodenum to the liver
• Peritoneal Ligaments: Two layers of peritoneum that connect organ to body wall or to another organ
• Visceral layer: Lines the abdominal organs within the peritoneum

Intra- vs. Retroperitoneal

• Intra: Viscera within the visceral peritoneum, just "poking" in
• Retro: Outside of the peritoneum; can be secondarily retroperitoneal
• SAD PUCKER helps remember the retroperitoneal organs: Suprarenal glands, Aorta (and IVC), Duodenum, Pancreas, Ureters, Colon, Kidneys, Esophagus, Rectum
• Peritonitis - acute inflammation of the peritoneum caused by contamination or rupture of abdominal organs

Oral Cavity

• Lined with non-keratinized stratified epithelium, it heals quickly to withstand abrasion from chewing food
• Anterior boundary: Lips (orbicularis oris mm.) with a mucous membrane on the inner surface Lips attach to the gums via labial frenulum
• Lateral boundary: Cheeks (buccinator mm.) keep food out of the oral vestibule and are covered by mucous membrane
• Superior boundary: Palates(hard = maxillary bone & soft = skeletal mm.)
• Inferior boundary: Tongue (mylohyoid m. = floor of mouth)
• Anterior 2/3 is in the oral cavity anchored by the lingual frenulum, with the posterior 1/3 in the oropharynx Nasopharynx, oropharynx
• Oral vestibule is the space between the cheeks and the teeth, and the oral cavity proper is the space within the teeth

Features

• Tonsils Palatine tonsils are located laterally, and lingual tonsils are at the root of the tongue
• Tongue Terminal sulcus: Junction between the anterior 2/3 and posterior 1/3 Foramen cecum: Middle of the terminal sulcus; where the thyroid gland starts in development Attachment of tongue muscles is to the hyoid bone inferiorly/posteriorly and to the internal aspect of the mandible anteriorly
• Papillae (4 types) Filiform: Most abundant, cone-shaped, smallest, provide friction, NO TASTE Fungiform: Mushroom-shaped, well vascularized, has taste buds present in the front 2/3 and have cranial nerve 7 Vallate: 12 large papillae, inverted "V" shape at the back of the tongue, has taste buds, cranial nerve 9 Foliate Sweet, salty, sour, bitter, umami are the tastes. Taste bud structures: gustatory hairs/pores/taste cells, supporting cells, basal cells, sensory nerve fibers (CN7 and CN9)

Innervation

• Efferent (motor) Hypoglossal nerve mostly (CN 12; inferior to lingual nerve) Vagus nerve (CN10); only serves motor of the pharynx palatoglosssus m.) AFFERENT (sensory)
• Front 2/3 Taste by facial nerve (CN7, chorda tympani n. does PS); general sensation by lingual nerve (CN V3; internal most aspect between teeth and tongue)
• Back 1/3 → Taste and general sensory from glossopharyngeal nerve (CN9), Vagus n. (CN10)
• Lingual artery (branch of external carotid) travels in this space and supplies the back of the tongue Travels deep to muscle that forms base of tongue posteriorly (hyoglossus m.)

Teeth

Division

• Adult teeth (32 total), four types → 8 incisors, 4 canines, 8 premolars, 12 molars
• Numbering begins in the upper right (so wisdom teeth are 1,16,17,32) Divide mouth into 4 quadrants, ratio is 2:1:2:3 (incisor: canine: premolar: molar) juvenile/deciduous/primary teeth (20 total;, 8 incisors, 4 canines, 8 molars)

Structure

• Pulp cavity center of tooth, receives blood vessels & nerves from the root canal supports the tooth
• Dentin non-living bony matrix of tooth, largest portion, surrounded by enamel
• Enamel above gum line, hardest biological substance, made of calcium phosphate crystals(Vitamin D and Calcium) Alveolar process bone that the tooth lives in Apex = inferior most aspect of the root of tooth

Issues with Teeth

• Gingivitis bacterial infection of gums
• Plaque sticky matrix on surface of teeth made by bacteria, called tartar if hardens
• Cavity acid product of bacteria wears away at enamel

Epiglottis

• Seals off the larynx when swallowing and is connected to the root of the tongue by the median glossoepiglottic fold

Salivary Glands

• Fluid = saliva General information pH = 7, 1-1.5 L/day produced Composition: mostly water, immunoglobulin A, lysozyme, ions, amylase (enzyme breaks down sugars), mucus Function: cleanse mouth, antibacterial, begin sugar digestion, aids in chewing and swallowing 2 types INTRINSIC inside oral cavity Tiny lips, cheeks, palate, tongue (labial, buccal, palatal, lingual glands)

Extrinsic Salivary Glands

• Largest, mumps = when these get infected with myxovirus Parotid (Stensen's) Duct → connected to oral cavity, makes wateriest saliva Served PS by the glossopharyngeal nerve (CN9)
• Submandibular Beneath mandible, Pac-man shaped Submandibular (Wharton's) Ducts Served PS by the facial nerve (CN7) via chordae tympani
• Sublingual Under the tongue Many small ducts rather than 1 main duct (Rivinus' Ducts) Served PS by the facial nerve (CN7) via chordae tympani

Submandibular Ganglion

• Preganglionic PS from chorda tympani n. (CN 7), accompanying lingual n. (CN V) from infratemporal fossae
• Postganglionic PS to submandibular and sublingual glands, secretomotor to submandibular and sublingual glands

Pharynx

• Nasopharynx → oropharynx → laryngopharynx
• Muscles and innervation of the pharynx: Superior, middle, inferior constrictors
• Stylopharyngeus m separates superior from middle pharyngeal constrictor Efferent: PS by Vagus Nerve (CN10) Affectantby 3 nerves: Nasopharynx - V2Oropharynx - CN9 Laryngopharynx - CN10

Physiology of Swallowing

• (1) Voluntary Phase Tongue pushes food to the back of the oral cavity (2) Involuntary Phase (pharyngeal stage) Breathing stops, airways close, soft palate/ uvula lift, epiglottis is bent over airway as larynx lifts Upper sphincter relaxes when larynx is lifted peristalsis pushes food down Circular fibers move the bolus forward, Longitudinal fibers in front of bolus shorten the distance Lower sphincter relaxes as food approaches, allowing entry into the stomach

Esophagus

• Continuation of the pharynx, anterior to the spinal column, but posterior to the airway
• Upper esophageal sphincter at the top of esophagus
• Lower esophageal sphincter is just above the entrance to the stomach
• Circular and longitudinal muscle fibers for moving a food bolus towards the stomach PS innervation - Vagus Nerve (CN 10), Sympathetic

Gastro-Esophageal Junction

• GERD - if the sphincter is insufficient and some stomach acid gets into the esophagus Hernias Sliding the stomach circumferentially pops out of the diaphragm Paraoesophageal hiatus hernia only to one side

Stomach Anatomy

LUQ of the abdomen

• 3 muscle layers (muscularis externa) Outer = longitudinal, Middle = circular, Inner = oblique Main regions: Cardiac part (where esophagus meets stomach), fundus (holds air), body, pyloric part, greater and lesser Omentum, hepatoduodenal ligament (part of lesser Omentum), and rugae (mucosa and submucosa; when stomach is empty) Cephalic Phase Cephalic Phase stomach getting ready Cerebral cortex stimulate PS nervous system Vagus nerve increases stomach muscle and glandular activity Mechanical Digestion mixing waves 15-25 Gentle mixing waves turn it into chyme, more vigorous waves travel, Intense waves open it Chemical Digestion
• specialized cell types: Parietal cells → secrete HCI Chief cells → secrete pepsin Mucous cells → protect stomach walls.
• Protein digestion
• HCl denatures transforms into pepsin breaks peptide bonds
• Fat digestion gastric lipase splits triglycerides in milk fat, absorption = water, electrolytes, some drugs, alcohol

Nerves of the Stomach

• Blood supply to the gut, Foregut is served by the celiac trunk- its 3 branches are... Left gastric a. Left Meets with R. gastric along lesser curvature, splenic a., and the common hepatic a. Gastroduodenal a. greater curvature of the stomach Midgut served by SMA Hindgut served by IMA Inferior mesenteric artery
• Venous drainage IMV and SMV both drain into the Splenic vein → hepatic portal V

Nerves and Vomiting

Sensory input from medulla causes stomach contraction Small Intestine Basics convoluted tube 12ft, diameter = 2.5 cm, function = digestion and absorption

Regions

• Duodenum (most superior part; 10 in long), 3 accessory organs Pancreas (pancreatic duct), Gall Bladder (cystic duct), Liver (hepatic duct Structure Brunner's Glands-makes alkaline 2nd part Ducts

• Jejunum (middle portion): HAS CIRCULAR, ABSORPTION OCCURS

• Ileum: SMOOTH INSIDE terminates valve

Intestine Structure

Peyer's patches: lymph cells 4 (3 tunics, Microvillincrease SA (200m^2

• Large Intestine Basics 5ft, has regions Transverse, etc.,functions- forms indigestible, - absorption
• Ascending, - descending, Sigmoid segments Sma - Transverse
• Descending
• Anal canal Stratified classification
• Contraction
• Epithelial appendage
• Accessory GI Organs
• • Liver-
• • -common is greatest.
• • • bile
• • Gallbladder
• • • stored etc. Mal functions