Download Chapter 23

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
 Type

varies
Lamina propria – areolar connective tissue
 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


Adipose tissue
Falciform ligament

Liver to anterior abdominal wall
Lesser omentum
 Mesentery



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
1.
2.
3.

Crown
Root
Neck
Internal components
1.
2.
Enamel
Dentin

3.
Cementum
Pulp cavity


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



1.
2.
3.
4.
Serves as mixing chamber and storage area for
ingested food
Rugae allow for increased volume
4 main regions
Cardia
Fundus
Body
Pylorus



Pyloric antrum and canal
Pyloric sphincter
Lesser and greater curvatures
Figure 23.10a
Stomach Histology
1.
Mucosa







2.
3.
Submucosa – areolar connective tissue
Muscularis

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:







Process drugs and hormones
Excrete bilirubin
Synthesize bile salts
Storage





Carbohydrates
Lipids
Proteins
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