Anatomy of the Digestive System Anatomy & Physiology Chapter 25

Function Altering the chemical & physical composition of food so that it can be absorbed & used by body cells (digestion)

Organs of the Digestive System Mouth Oropharynx Esophagus Stomach Duodenum Jejunum Ileum Large Intestine Cecum Colon Ascending colon Transverse colon Descending colon Sigmoid colon Rectum Anal Canal Accessory Organs Salivary glands Parotid Submandibular Sublingual Tongue Teeth Liver Gallbladder Pancreas Vermiform appendix

Walls of the Gastrointestinal (GI)Tract Tube with 4 layers of tissue Mucosa Submucosa Muscularis Serosa

Mucosa Inner most layer Made of 3 layers of epithelium, connective tissue & smooth muscle

Submucosa Thicker than mucosal layer Connective tissue layer that contains glands, blood vessels, nerve plexus (Meissner plexus)

Muscularis Thick layer of muscle tissue Inner layer of circular smooth muscle Outer layer of longitudinal smooth muscle Myenteric plexus between the muscular layers

Serosa Outermost layer Made of connective tissue & peritoneum (visceral layer) Layer of peritoneum that lines the abdominal cavity= parietal layer Mesentery is the fold of membrane that connects the parietal & visceral layer of peritoneum

Mouth (Oral cavity) Lips Cheek Tongue Hard & Soft Palates

Lips Surround the orifice of the mouth & form anterior boundary Covered by skin externally & mucous membrane internally Philtrum: shallow vertical groove that marks the midline of upper lip

Cheeks Form lateral boundaries, continuous with lips, lined by mucous membranes Formed in large part by buccinator muscle

Hard & Soft Palates Hard palate: consists of 4 bones: 2 maxillae & 2 palatines Soft palate: partition between mouth & nasopharynx Uvula: small cone shaped process extending from soft palate

Tongue Intrinsic muscle: changes in size & shape of tongue; important for mastication (chewing) Extrinsic muscle: origin outside the tongue; important for deglutition (swallowing) & talking 3 parts: root, body, tip

Papillae Vallate: large, form an inverted V on posterior part of tongue; 10-14; taste buds on lateral aspect Fungiform: taste buds on lateral aspect; mostly on sides & tips of tongue Filiform: no taste buds, over anterior 2/3 of tongue; whitish appearance

Lingual Frenulum Fold of mucous membrane on the undersurface of the tongue that anchors the tongue to the floor of mouth

Salivary glands Three pairs: Secrete about 1 L of saliva/day Parotid Submandibular Sublingual Secrete about 1 L of saliva/day

Parotid Glands Largest Between skin & masseter muscle in front of & below the ear Produce a serous (watery) type of saliva

Submandibular glands Mixed gland-contain both serous & mucus-producing elements Located below mandibular angle

Sublingual glands Smallest Under the mucous membrane covering the floor of the mouth Produce only a mucous type of saliva

Tooth 3 main parts Tooth suspended in place by periodontal membrane Crown: exposed portion, covered by enamel Neck: area surrounded by gingiva Root: area that fits into jaw Tooth suspended in place by periodontal membrane

Tooth structure Dentin: makes up greatest portion of tooth shell, covered by enamel on crown & cementum in neck & root Dentin contains a pulp cavity consisting of vessels & nerves

Type of teeth Deciduous teeth (baby): 20; erupt from 6 mos. to 20 mos. Permanent teeth: 32

Pharynx Food now called a bolus leaves mouth & enters oropharynx Food does not go thru nasopharynx

Esophagus Collapsible tube, posterior to trachea Mucosa: stratified squamous epithelium to resist abrasion Muscularis: striated in upper third, smooth in lower third

Sphincters of esophagus Upper esophageal sphincter: helps prevent air from entering during respiration Lower esophageal sphincter (cardiac sphincter): between stomach & esophagus

Stomach Three divisions: Fundus: enlarged portion to left & above opening of esophagus Body & Pylorus

Sphincter of Stomach Pyloric sphincter: controls opening of pylorus to duodenum

Gastric mucosa Folds (rugae) with depressions (gastric pits) Gastric glands are located below the level of the pits

Gastric glands Chief cells: secrete enzymes 3 major secretory cells: Chief cells: secrete enzymes Parietal cells: secrete HCl & intrinsic factor (binds to Vitamin B12 to protect it) Endocrine cells: secrete ghrelin (stimulates hypothalamus to increase appetite) & gastrin (regulates gastric function)

Gastric muscle Made of 3 layers instead of 2

Functions of stomach Reservoir Secretes gastric juice to aid in digestion Churns food Secretes intrinsic factor Absorption-small amounts Produces hormones Protects by destroying pathogens

Small intestine Main site of digestion & absorption 3 divisions: Duodenum Jejunum Ileum

Wall of Small Intestine Has circular folds (plicae) with many tiny projections (villi) Each villus contains vessels & lacteal Epithelial cells on surface of villi have microvilli which form a brush border which increases surface area

Goblet cells Large numbers of mucus secreting goblet cells on villi & in crypts Crypts serve as area of rapid mitotic division & at base of crypts secretory cells produce an enzyme that is thought to inhibit bacterial growth

Large Intestine Cecum: blind pouch Colon Divisions: Cecum: blind pouch Colon Ascending colon: right side, ileum attaches at junction of cecum & ascending colon Transverse colon: from hepatic flexure to splenic flexure Descending colon: left side Sigmoid colon: S shaped Rectum: terminal inch is anal canal

Wall of Large Intestine Intestinal mucus glands which produce mucus to lubricate feces Longitudinal muscle fibers form strips called taeniae coli & circular muscles are grouped into rings that produce pouches, haustra

Vermiform appendix Wormlike tubular organ, communicates with cecum

Peritoneum Large continuous sheet of serous membrane that lines the walls of abdominal cavity & forms outer serous coat of organs Mesentery: fan shaped projection of peritoneum encloses the jejunum & ileum Greater omentum: continuation of serosa of stomach to transverse colon Lesser omentum: from liver to lesser curvature of stomach

Liver Largest gland in body 2 lobes separated by falciform ligament: Left lobe (about 1/6) Right lobe

Hepatic lobules anatomical units of liver Branch of hepatic vein through center of each lobule Outer corners of lobules are the branches of hepatic artery, portal vein, hepatic duct

Bile ducts Small bile ducts join to form right & left hepatic duct which join to form hepatic duct which merges with cystic duct from gallbladder to form common bile duct which opens into duodenum at major duodenal papilla

Functions of liver Detoxify substances Secrete bile Metabolism of foods Store several substances Produces plasma proteins & site of hematopoiesis during fetal development

Gallbladder Pear shaped on underside of liver Serous, muscular & mucosal layer Functions: stores, concentrates & ejects bile

Pancreas In curve of duodenum, extending behind stomach Exocrine gland (most) Acinar cells: secrete enzymes through pancreatic duct that empties into duodenum Endocrine gland-Islets Alpha cells: produce glucagon Beta cells: produce insulin

Image Citations Slide 6: Brunner’s glands, 2/28/07, http://w3.ouhsc.edu/histology/Text%20Sections/Lower%20GI.html Slide 25: Lower esophageal sphincter, 3/13/07, http://hopkins-gi.nts.jhu.edu/pages/latin/templates/index.cfm?pg=disease1&organ=1&disease=13&lang_id=1 Slide 38: The human vermiform appendix, 3/13/07, http://www.talkorigins.org/faqs/vestiges/appendix.html