Anatomy & PhysiologyChapter 25

Anatomy of the Digestive System

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:

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

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 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 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