The Digestive System
Chapter 23 – Lecture Notes
to accompany
Anatomy and Physiology: From Science to Life
textbook by
Gail Jenkins, Christopher Kemnitz, Gerard Tortora
Chapter Overview
23.1 Gastrointestinal (GI) Tract
23.2 Accessory Organs of the Head
23.3 Swallowing
23.4 Stomach
23.5 Accessory Organs of the Abdomen
23.6 Small Intestine
23.7 Large Intestine
23.8 Phases of Digestion
23.9 Food Molecules
23.10 Metabolism
Essential Terms
digestion
 process of mechanically or chemically breaking
down food
absorption
 passage of small molecules into blood and lymph
digestive system
 organs which carry out process of digestion and
absorption
metabolism
 all the chemical reactions of the body
Introduction
Digestive System
1.
2.
3.
4.
Composed of GI tract and accessory
organs
Breaks down ingested food for use by the
body
Digestion occurs by mechanical and
chemical mechanisms
Excretes waste products or feces through
process of defecation
Concept 23.1
Gastrointestinal (GI) Tract
GI Tract / Alimentary Canal







Continuous tube from mouth to anus
Mouth
Pharynx
Esophagus
Stomach
Small intestine
Large intestine
Accessory Digestive Organs







Provide mechanical and chemical mechanisms
to aid digestion
Teeth
Tongue
Salivary glands
Liver
Gallbladder
Pancreas
Figure 23.1
Functions of Digestive System
Ingestion
Secretion
Mixing and propulsion
1.
2.
3.
•
Digestion
4.
•
5.
6.
Motility
Mechanical and chemical
Absorption
Defecation
Layers of GI Tract

Same in all areas of GI tract

From deep to superficial:
Mucosa
Submucosa
Muscularis
Serosa




Figure 23.2
Layers of GI Tract

Mucosa

Epithelium


Lamina propria – areolar connective tissue



Type varies
MALT – mucus-associated lymphatic tissue
Muscularis mucosae – smooth muscle
Submucosa



Areolar connective tissue
Blood and lymphatic vessels
Neurons – submucosal plexus
Layers of GI Tract

Muscularis



Skeletal and smooth muscle
Neurons – myenteric plexus
Serosa


Areolar and simple squamous epithelium
Visceral peritoneum
Peritoneum





Mesothelium
Parietal peritoneum
Visceral peritoneum
Peritoneal cavity
Retroperitoneal
Figure 23.3a
Figure 23.3b
Figure 23.3c
Figure 23.3d
Folds of Peritoneum

Greater omentum


Falciform ligament



Liver to anterior abdominal wall
Lesser omentum
Mesentery


Adipose tissue
Small intestine to posterior abdominal wall
Mesocolon
Neural Innervation of GI Tract

Regulated by autonomic nervous system

Enteric division
 Myenteric plexus / plexus of Auerbach
 Submucosal plexus / plexus of Meissner
Able to function independently from rest of nervous system




Linked to CNS by extrinsic sympathetic and parasympathetic
nerves
Sympathetic nerves decrease GI secretions & motility
Parasympathetic nerves increase GI secretion and motility
Concept 23.2
Accessory Organs of the
Head
Mouth Parts of Digestive System

Mouth formed by several parts:

Cheeks
Lips / labia
Labial frenulum
Orbicularis
Vestibule
Oral cavity proper
Fauces
Hard and soft palate
Uvula
Palatoglossal and palatopharyngeal arch









Figure 23.4
Tongue






Skeletal muscle and mucous membrane
Helps form floor of oral cavity
Extrinsic muscles
Intrinsic muscles
Lingual frenulum
Papillae





Fungiform
Filiform
Circumvallate
Foliate
Lingual glands

Lingual lipase
Salivary Glands

Release saliva to oral cavity

3 pairs of salivary glands
Parotid
Submandibular
Sublingual



Composition of Saliva


99.5 % water
0.5% other solutes






Ions
Mucus
Immunoglobulin A
Enzymes
Salivation controlled by autonomic nervous
system
Stimulated by various mechanisms
Figure 23.5
Teeth
External regions

Crown
Root
Neck
1.
2.
3.
Internal components

Enamel
Dentin
1.
2.

Cementum
Pulp cavity
3.


PulpRoot canals
Apical foramen
Figure 23.6
Teeth









Dentitions
Deciduous teeth – first set
Permanent teeth – secondary
Carry out mechanical digestion by mastication
Creates bolus
Salivary amylase
Breakdown starch
Lingual lipase
Breakdown triglycerides
Figure 23.7
Table 23.1
Concept 23.3
Swallowing
Pharynx





Composed of skeletal muscle
Lined by mucous membrane
Nasopharynx
Oropharynx
Laryngopharynx
Esophagus

Collapsible muscular tube through esophageal
hiatus of diaphragm

Mucosa


Muscularis



Skeletal muscle
Upper and lower esophageal sphincter
Adventitia


Submucosa contains areolar connective tissue
Attaches esophagus to nearby structures
Secrets mucus and transports food
Figure 23.8
Deglutition


Stages of swallowing
Voluntary


Pharyngeal




Mouth to oropharynx
Deglutition center in medulla oblongata and pons
Closing of epiglottis
Involuntary
Esophageal


Involuntary
Peristaltic contractions
Figure 23.9a,b
Figure 23.9c
Table 23.2
Concept 23.4
Stomach
Stomach
Serves as mixing chamber and storage area for
ingested food
Rugae allow for increased volume
4 main regions
Cardia
Fundus
Body
Pylorus



1.
2.
3.
4.



Pyloric antrum and canal
Pyloric sphincter
Lesser and greater curvatures
Figure 23.10a
Stomach Histology
Mucosa
1.







Submucosa – areolar connective tissue
Muscularis
2.
3.

4.
Surface mucous cells
Lamina propria
Muscularis mucosae
Gastric glands and pits
Parietal cells
Chief cells
G cells
3 layers of smooth muscle
Serosa
Figure 23.11a
Figure 23.11b
Figure 23.11c
Mechanical and Chemical Digestion




Mixing waves caused by peristaltic movement
Chyme released in process of gastric emptying
Proton pumps bring H+ into the lumen
Carbonic anhydrase forms carbonic acid to
provide H+ and bicarbonate ions (HCO3-)
Figure 23.12
Mechanical and Chemical Digestion


Chemical digestion stimulated by nervous system
Parasympathetic neurons release acetylcholine



Pepsin begins digestion of proteins



Works with gastrin
HCl released in presence of histamine
Stomach protected by alkaline mucus secretion
Gastric lipase digests triglycerides
Few molecules absorbed by stomach

Water, ions, short-chain fatty acids, alcohol
Table 23.3 pt 1
Table 23.3 pt 2
Concept 23.5
Accessory Organs of the
Abdomen
Pancreas





Produces secretions to aid digestion
Head
Body
Tail
Pancreatic duct /duct of Wirsung


Hepatopancreatic ampulla
Sphincter of the heatopancreatic ampulla
(sphincter of (Oddi)


Regulates passage of pancreatic juice and bile
Accessory duct (duct of Santorini)
Figure 23.13a
Figure 23.13b
Figure 23.13c
Histology of Pancreas

Glandular epithelial cells


99% exocrine clusters
Secrete pancreatic juice


Fluid and enzymes
Pancreatic islets (islets of Langerhans)


1% endocrine cells
Hormones




Glucagon
Insulin
Somatostatin
Pancreatic polypeptide
Pancreatic Juice






1200-1500 mL/day
pH 7.1-8.2
Water
Salts
Sodium bicarbonate
Enzymes
 Pancreatic amylase
 Trypsin






Entereokinase
Chymotrypsin
Carboxypeptidase
Elastase
Pancreatic lipase
Ribonuclease and deoxyribonuclease
Liver and Gallbladder




Liver
Largest gland at 1.4 kg (~3 lb)
Gallbladder
Closely associated with liver
Anatomy of Liver

Right and left lobe separated by falciform
ligament
Quadrate lobe
Caudate lobe

Round ligament (ligamentum teres)




Remnant of umbilical vein
coronary ligaments
Histology of Liver

Lobule



Hepatocytes radiating from central vein
Sinusoids
Reticuloendothelial (Kupffer) cells

Stationary phagocytes
Figure 23.14a
Figure 23.14b
Figure 23.14c
Figure 23.14d
Bile Duct System








Bile secreted by hepatocytes
Bile canaliculi
Bile ducts
Right and left hepatic ducts
Common hepatic duct
Common bile duct
Gallbladder for temporary storage of bile
Cystic duct
Blood Supply of Liver


Hepatic artery provides oxygenated blood
Hepatic portal vein provides deoxygenated blood


Hepatic artery and vein carry blood to sinusoids



Nutrients, drugs, toxins, microbes
Substances exchanged by hepatocytes
Blood drains to central vein and eventually hepatic vein
Portal triad



Hepatic portal vein
Hepatic artery
Bile duct
Figure 23.15
Bile





800-1000 mL/day
pH 7.6 – 8.6
Water
Bile acids
Bile salts




Emulsification
Cholesterol
Lecithin
Bile pigments

Bilirubin

Stercobilin
Liver Functions







Metabolism of:
 Carbohydrates
 Lipids
 Proteins
Process drugs and hormones
Excrete bilirubin
Synthesize bile salts
Storage
 Glycogen
 Vtamins
 Minerals
Phagocytosis
Activate Vitamin D
Concept 23.6
Small Intestine
Small Intestine



Adapted for digestion and absorption
3 m (10 ft) living
6.5 m (21 ft) without muscle tone

Duodenum
Jejunum
Ileum

Ileocecal sphincter



Connection to large intestine
Figure 23.16a
Figure 23.16b
Histology of Small Intestine


Mucosa
Cell types




Absorptive
Goblet
Endocrine
Paneth


Lysozyme
Intestinal glands (crypts of Lieberkühn)

S cells


Hormone secretin
CCK cells

Hormone – cholecystokinin (CCK)
Figure 23.17a