Chapter 25 - The Digestive System

Digestive System Functions

Ingestion, motility, secretion, digestion (mechanical and chemical), absorption, and elimination

GI Tract Organs

Form a continuous tube; Oral cavity and pharynx, esophagus and stomach, small intestine, large intestine and anus

Accessory Organs

salivary glands, liver, pancreas, teeth and tongue, and gallbladder

GI Tract Organs Tunics

mucosa, submucosa, muscularis, adventitia

Mucosa

simple columnar epithelium allowing for secretion and absorption; lamina propria is composed of areolar tissue, small blood vessels and nerves; smooth muscle deep to lamina propria is muscularis mucosae

Submucosa

areolar and DICT; submucosal nerve plexus innervates smooth muscles and glands; houses mucosa-asociated lymphatic tissue which prevents ingested microbes from crossing GI tract wall;

Muscularis

Functions to mix and propel contents within GI Tract; Inner Circular Layer of smooth muscle cells which constricts lumen; outer longitudinal layer shortens tube; Myenteric nerve plexus contains axons and ganglia between layers that control contractions; enteric nervous system detects changes in tract wall and chemical makeup of lumen content

Mixing

backwards and forward motion that lacks directional movement; blends ingested materials with secretions

Propulsion

directional movement of materials through GI tract; occurs by Peristalsis (sequential contraction of muscularis causes GI wall to move like a wave)

Adventita

also called serosa; outermost tunic; adventitia is areolar CT found outside the peritoneal cavity; Serosa is completely covered by visceral peritoneum

Intraperitoneal Organs

completely surrounded by visceral peritoneum; includes stomach, most of SI and parts of LI

Retroperitoneal Organs

lie directly against posterior abdominal wall; only anterolateral portions covered with peritoneum; includes most of duodenum, pancreas, Colon, and rectum

Mesentery

double layer of peritoneum; supports, suspends and stabilizes intraperitoneal GI organs;

Greater Omentum

extends inferiorly from inferolateral stomach; covers most abdominal organs; accumulates large amounts of adipose tissue

Falciform Ligament

attaches the liver to the internal surface of anterior abdominal wall

Mesentary Proper

fan-shaped fold of peritoneum; suspends most of small intestine form posterior abdominal wall

Mesocolon

fold of peritoneum; attaches part of large intestine to posterior abdominal wall; several distinct sections named for portion of colon suspended

Mastication

mechanical digestion chewing; controlled by nuclei in medulla and pons

Deglutition

Swallowing

Oral Cavity

mechanical digestion begins; saliva is secreted from salivary glands in response to food; salivary amylase initiates digestion of starch; forms bolus

Mouth

entrance to the GI Tract; made of vestibule and oral cavity proper

Vestibule

space between gum, lips, cheeks

Oral Cavity Proper

lies central to the teeth, leads posteriorly into oropharynx

Cheeks

Contain buccinator muscles; compress cheeks to hold solid material while chewing

Lips

formed by orbicularis oris muscle; reddish hue from superficial blood vessels and reduced keratin; internal surfaces attach to gingivae

Labial Frenulum

mucosa fold in the midline of lips

Tongue

primarily from skeletal muscle with extrinsic and intrinsic muscles; papillae involved with taste; attaches to floor by lingual frenulum; manipulates and mixes materials during chewing; important functions in swallowing and speech

Lingual Frenulum

Attaches tongue to the floor of mouth;

Palate

roof of oral cavity; separates oral cavity from nasal cavity; soft palate is posterior third; Hard palate is anterior 2/3; palatine processes of maxillae and palatine bone

Uvula

Conical projection from posterior soft palate; elevates with soft palate during swallowing; closes off posterior entrance to nasopharynx

Fauces

opening between oral cavity and oropharynx; palatine tonsils housed between arches (early line of defense against foreign antigens)

Palatoglossal and Palatopharyngeal Arches

Palatoglossal arch is anterior; palatopharyngeal arch is posterior

Intrinsic Salivary Glands

unicellular; continuously release secretions independent of food; contains lingual lipase

Extrinsic salivary glands

produce most saliva; parotid, submandibular, and sublingual glands

Parotid Salivary Glands

anterior to ear; conducted through parotid duct to oral cavity; infection causes mumps

Submandibular Salivary Glands

inferior to oral cavity floor; 60-70% of saliva; submandibular duct opens to floor

Sublingual Salivary Glands

inferior to tongue; contribute only 3-5% of saliva

Dental Alveoli

sockets within alveolar processes

Gomphosis Joint

roots, dental alveoli, periodontal ligament

Dentin

primary mass of tooth; harder than bone

Enamel

forms crown; calcium phosphate crystals (hardest substance in the body)

Cementum

hardened material ensheathing root

Deciduous Teeth

20 baby teeth that erupt between 6 and 30 months

Permanent teeth

32 teeth that replace deciduous teeth; 3rd molars appear in late teens or 20s

Incisors

front 4 teeth

Canine

Sharp teeth

Molars

2 premolars on each side and 3 sets of molars

Bolus

Ingested materials mixed with saliva in the mouth

Chyme

formed from mixing in the stomach

Feces

produced in the large intestine and eliminated through the anus

Pharynx

funnel-shaped muscular passageway for air and food; 3 skeletal muscle pairs (pharyngeal constrictors); lined with nonkeratinized stratified squamous epithelium

Oropharynx

middle pharyngeal region; posterior to oral cavity; passageway for both food and air; lined by nonkeratinized stratified squamous epithelium

Laryngopharynx

inferior, narrow region of pharynx; posterior to the larynx; both food and air; lined by nonkeratinized stratified squamous epithelium

Esophagus

lubricated by mucus secretions; 4 tunics (mucosa, submucosa, muscularis, and serosa)

Esophageal Hiatus

opening in diaphragm

Superior and Inferior esophageal sphincter

not strong enough by itself to stop stomach contents from regurgitating

Stomach Greater Curvature

Larger convex inferiolateral surface

Stomach Lesser Curvature

smaller concave superomedial surface

Gastric Folds

found on internal stomach lining when stomach empty; allows stomach to expand with food; returns to normal when empty

Cardia

where stomach meets esophagus

Fundus

dome-shaped region superior and lateral to esophageal connection

Body

largest region of stomach, inferior to cardiac orifice and extends to pylorus

Pyloris

funnel-shaped pouch forming terminal region of stomach

Pyloric Sphincter

ring of circular smooth muscle surrounding pyloric orifice; regulates entry of material into duodenum

Small Intestine

3 continuous regions: most chemical digestion and absorption happens here

Duodenum

continuous with jejunum at duodenojejunal flexure; mostly retroperitoneal; Upper GI Tract

Jejunum

2/5 of total length of small intestine; primary region for chemical digestion and nutrient absorption; intraperitoneal and suspended by mesentery proper

Ileum

3/5 of small intestine; distal end terminates at iloceal valve; continues absorption of digested material

Circular Folds

internal folds of mucosal and submucosal tunics of small intestine; increase surface area for nutrient absorption; slow movement of chyme; less in ileum

Villi

most numerous in jejunum; epithelium covers lamina propria;

Lacteal

lymphatic capillary within villus; responsible for absorbing lipids and lipid-soluble vitamins

Microvilli

extensions of plasma membrane of simple columnar epithelial cells

Gastroileal Reflex

ileum contracts, ileocecal sphincter and cecum relaxes; moves contents from ileum to cecum in repose to food in stomach

Biliary Tree

network of ducts draining left and right lobes of liver; extends inferiorly to the duodenum

Hepatic ducts

left and right hepatic ducts merge to form the common hepatic duct

Cystic Duct

Duct connecting gallbladder to common hepatic duct

Common Bile Duct

formed from common hepatic duct and cystic duct

Accessory Pancreatic duct

small amount of pancreatic juice entering the duodenum; penetrates duodenal wall at minor duodenal papilla

Liver

immediately inferior to diaphragm; produces bile

Liver lobes

4 partially separated lobes; right lobe is larger than left lobe; quadrate and caudate lobes visible on the posterior

Liver Round Ligament

remnant of fetal umbilical vein; found in inferior free edge of falciform ligament

Falciform Ligament

peritoneal fold that secures liver to anterior abdominal wall; separates right and left lobesI

Inferior Vena Cava

seen on posterior view

Ligamentum Venosum

remnant of ductus venosus in embryo

Porta Hepatis

blood, lymph vessels, bile ducts, nerves, enter and leave the liver

Central Vein

at center of each lobule, drains blood from lobule, passes from portal triads through hepatic sinusoids to central vein;

Hepatic artery

carries oxygenated blood to liver

Hepatic Veins

empty into inferior vena cava

Hepatic Portal Vein

carries deoxygenated blood from capillary of GI tract, spleen, and pancreas to liver; blood mixes as passes through hepatic lobules

Bile

secreted by liver; contains water, bicarbonate ions, bile salts and pigments, etc; bile salts and lecithin help mechanically digest lipids

Gallbladder

3 tunics (mucosa, muscularis, serosa); sphincter valve controls flow in and out of gallbladder; stores bile

Pancreas

produces and secretes insulin and glucagon; pancreatic juice assists with digestive activity; retroperitoneal;

Large Intestine

absorbs water and electrolytes from digested material; compacted into feces; stores feces until eliminated through defecation

Cecum

first portion of large intestine; intraperitoneal

Vermiform Appendix

harbors beneficial bacteria; lined by lymphocyte-filled lymphatic nodules; intraperitoneal

Colon

Ascending and descending are retroperitoneal; transverse and sigmoid are intraperitoneal

Rectum

thick transverse folds are rectal valves; retroperitoneal

Anal Canal

lined by stratified squamous epithelium; ridges are columns; depressions are sinuses;

Internal anal sphincter

involuntary smooth muscle at base of anal canal

External Anal sphincter

voluntary skeletal muscle; normally closed