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Lecture 13 – Digestive System,
Part II
Dr. Siddique
Introduction to Human Anatomy
East Los Angeles College
The Pharynx
• Oropharynx and laryngopharynx
– Passages for air and food
– Lined with stratified squamous epithelium
– External muscle layer
• Consists of superior, middle, and inferior pharyngeal
constrictors
The Esophagus
• Gross anatomy—muscular tube
– Begins as a continuation of the pharynx
– Joins the stomach inferior to the diaphragm
• Cardiac sphincter—closes lumen to prevent stomach
acid from entering esophagus
The Esophagus
• Microscopic anatomy
– Epithelium is stratified squamous epithelium
– When empty, mucosa and submucosa in
longitudinal folds
– Mucous glands—primarily compound
tubuloalveolar glands
– Muscularis externa
• Skeletal muscle first third of length
– Adventitia—most external layer
Microscopic Structure of the Esophagus
Mucosa
(contains a stratified
squamous epithelium)
Submucosa (areolar
connective tissue)
Lumen
Muscularis externa
Circular layer
Longitudinal layer
Adventitia (fibrous
connective tissue)
(a) Cross section through esophagus (5)
(b) Gastroesophageal
junction, longitudinal
section (85)
Figure 23.16
The Stomach
• Site where food is churned into chyme
• Secretion of pepsin begins protein digestion
– Functions under acidic conditions
• Food remains in stomach approximately 4
hours
• Regions of the stomach
– Cardiac region
– Fundus
– Body
– Pyloric region
The Stomach
Cardia
Fundus
Esophagus
Serosa
Muscularis externa
Longitudinal layer
Circular layer
Oblique layer
Body
Lumen
Lesser
curvature
Rugae of
mucosa
Greater
curvature
Duodenum
(a)
Pyloric
canal
Pyloric sphincter
(valve) at pylorus
Pyloric
antrum
Figure 23.17a
The Stomach
Fundus
Liver
(cut)
Body
Spleen
Lesser
curvature
Greater
curvature
(b)
Figure 23.17b
Microscopic Anatomy of the Stomach
• Muscularis has three layers
– Circular and longitudinal layers and oblique layer
• Epithelium is simple columnar epithelium
• Mucosa dotted with gastric pits
– Gastric glands—deep to gastric pits
Microscopic Anatomy of the Stomach
• Gastric glands of fundus and body
– Mucous neck cells
• Secrete a special mucus
– Parietal (oxyntic) cells
• Secrete hydrochloric acid and gastric intrinsic factor
– Chief (zymogenic) cells
• Secrete pepsinogen
– Pepsinogen is activated to pepsin when it encounters acid in
the gastric glands
The Stomach—Microscopic Anatomy
Gastric pits
Surface epithelium
(mucous cells)
Surface
epithelium
Gastric
pit
Mucosa
Submucosa (contains
submucosal plexus)
Mucous neck cells
Parietal cell
Gastric
gland
Lamina
propria
Muscularis
mucosae
Chief cell
Oblique layer
Circular layer
Muscularis externa
(contains myenteric
Longitudinal
plexus)
layer
Serosa
Stomach wall
(a) Layers of the stomach wall, longitudinal section
Pepsinogen
HCl
Enteroendocrine cell
(b) Enlarged view of gastric pits and gastric glands
Pepsin
Gastric pits
Mucus-secreting
cells
Surface mucous cell
Mucus neck cells
Mitochondria
Parietal cell
HCl secreting parietal cells
Gastric
gland
Chief cell
Enzyme secreting chief cells
Enteroendocrine
cell
(c) Location of the HCl-producing parietal cells and
pepsin-secreting chief cells in a gastric gland
Muscularis
mucosae
(d) Micrograph of the stomach mucosa, view similar to part (b) (115)
Figure 23.18
The Small Intestine—Gross Anatomy
• Longest portion of the alimentary canal
• Site of most enzymatic digestion and
absorption
• Three subdivisions
– Duodenum
– Jejunum
– Ileum
• Innervation
– Parasympathetic fibers from vagus nerve
– Sympathetic from thoracic splanchnic nerves
The Duodenum
• Receives digestive enzymes and bile
• Main pancreatic duct and common bile duct
enter duodenum
– Sphincters control entry of bile and pancreatic
juices
The Duodenum and Related Organs
Right and left
hepatic ducts
of liver
Common hepatic
duct
Cystic duct
Bile duct and sphincter
Accessory pancreatic duct
Mucosa
with folds
Gallbladder
Major duodenal
papilla
Hepatopancreatic
ampulla and
Duodenum
sphincter
Tail of pancreas
Pancreas
Jejunum
Main pancreatic duct and
sphincter
Head of pancreas
Figure 23.19
The Small Intestine—Microscopic
Anatomy
• Modifications for absorption
– Circular folds (plicae circulares)
• Transverse ridges of mucosa and submucosa
– Villi
• Finger-like projections of the mucosa
• Covered with simple columnar epithelium
– Microvilli
• Further increase surface area for absorption
Histology of the Intestinal Wall
• Absorptive cells
– Uptake digested nutrients
• Goblet cells
– Secrete mucus that lubricates chyme
• Enteroendocrine cells
– Secrete hormones
• Intestinal crypts
– Epithelial cells secrete intestinal juice
The Small Intestine—Structural
Features
Vein carrying
blood to
hepatic portal
vessel
Muscle
layers
Lumen
Microvilli
(brush
border)
Circular
folds
Absorptive
cells
Villi
Lacteal
Goblet
cell
Blood
capillaries
(a)
(b)
Mucosa
associated
lymphoid
tissue
Intestinal
crypt
Muscularis
mucosae
Duodenal
gland
Absorptive cells
Vilus
Goblet
cells
Villi
Enteroendocrine
cells
Venule
Lymphatic vessel
Submucosa
(c)
Intestinal crypt
Figure 23.20
The Large Intestine
• Digested residue contains few nutrients
• Small amount of digestion by bacteria
• Main functions
– Absorb water and electrolytes
• Mass peristaltic movements force feces
toward the rectum
Gross Anatomy of Large Intestine
• Subdivided into
– Cecum, vermiform appendix, colon, rectum,
anal canal
• Special features of large intestine
– Teniae coli
• Thickening of longitudinal muscularis
– Haustra
• Puckering created by teniae coli
– Epiploic appendages
• Fat-filled pouches of visceral peritoneum
Gross Anatomy of Large Intestine
• Cecum
– Blind pouch
– Beginning of large intestine
• Vermiform appendix
– Contains lymphoid tissue
– Neutralizes pathogens
• Colon
– Divided into distinct segments
• Ascending, transverse, descending, and sigmoid
colon
Gross Anatomy of Large Intestine
• Rectum
– Descends along the inferior half of the sacrum
• Anal canal
– The last subdivision of the large intestine
– Lined with stratified squamous epithelium
Gross Anatomy of Large Intestine
Left colic
(splenic) flexure
Transverse colon
Transverse
mesocolon
Epiploic
appendages
Superior
mesenteric artery
Descending colon
Right colic
(hepatic) flexure
Haustrum
Ascending colon
IIeum
Cut edge of
mesentery
IIeocecal valve
Teniae coli
Sigmoid colon
Cecum
Vermiform appendix
Rectum
Anal canal
External anal sphincter
(a)
Figure 23.21a
Gross Anatomy of Large Intestine
Rectal valve
Rectum
Hemorrhoidal
veins
Levator ani muscle
Anal canal
External anal
sphincter
Internal anal
sphincter
Anal columns
Anal valves
Pectinate line
Anal sinuses
Anus
(b)
Figure 23.21b
Microscopic Anatomy of Large
Intestine
•
•
•
•
Villi are absent
Contains numerous goblet cells
Intestinal crypts—simple tubular glands
Lined with simple columnar epithelial tissue
– Epithelium changes at anal canal
• Becomes stratified squamous epithelium
Mucosa of the Large Intestine
Absorptive cells
Lamina propria
Goblet cells
Intestinal crypts
Muscularis
mucosae
Figure 23.23
The Liver
• Largest gland in the body
– Performs over 500 functions
– Digestive function
• Bile production
• Stored in gall bladder
– Performs many metabolic functions
The Liver
Sternum
Nipple
Bare area
Liver
Falciform
ligament
Left lobe
of liver
Right lobe of liver
Gallbladder
Round
ligament
(ligamentum
teres)
Figure 23.24
Visceral Surface of the Liver
Lesser omentum
(in fissure)
Caudate lobe
of liver
Left lobe of liver
Porta hepatis
containing hepatic
artery (left) and
hepatic portal vein
(right)
Quadrate lobe
of liver
Ligamentum teres
Bare area
Sulcus for
inferior
vena cava
Hepatic
vein (cut)
Bile duct
(cut)
Right lobe
of liver
Gallbladder
(a)
Figure 23.25a
Visceral Surface of the Liver
Hepatic portal vein
Caudate
lobe
Hepatic veins
Inferior vena
cava
Bare area
Left lobe
Ligamentum
venosum in
fissure
Porta hepatis
Right hepatic
artery
Left hepatic artery
Right hepatic
duct
Left hepatic duct
Cystic duct
Common hepatic
duct
Gallbladder
Fissure
(b)
Falciform ligament
Ligamentum teres
Right lobe
Quadrate lobe
Figure 23.25b
Microscopic Anatomy of the Liver
• Some functions of hepatocytes
– Rough ER manufactures blood proteins
– Smooth ER produces bile salts, detoxifies
poisons
– Peroxisomes detoxify poisons (alcohol)
– Golgi apparatus packages secretory products
– Mitochondria provide energy for liver
processes
– Glycosomes store sugar
– Great capacity for regeneration
Microscopic Anatomy of Liver
(a)
(b)
Lobule
Central vein
Connective
tissue septum
Interlobular veins
(to hepatic vein)
Central vein
Sinusoids
Bile canaliculi
Plates of
hepatocytes
Bile duct (receives
bile from bile
canaliculi)
Fenestrated
lining (endothelial
cells) of sinusoids
Hepatic
macrophages in
sinusoid walls
Bile duct
Portal venule
Portal arteriole
Portal triad
Portal vein
(c)
Figure 23.26
The Gallbladder
• Stores and concentrates bile
• Expels bile into duodenum
– Bile emulsifies fats
• Cholecystokinin—released from
enteroendocrine cells in response to fatty
chyme
The Gallbladder
Right and left
hepatic ducts
of liver
Common hepatic
duct
Cystic duct
Bile duct and sphincter
Accessory pancreatic duct
Mucosa
with folds
Gallbladder
Major duodenal
papilla
Hepatopancreatic
ampulla and
Duodenum
sphincter
Tail of pancreas
Pancreas
Jejunum
Main pancreatic duct and
sphincter
Head of pancreas
Figure 23.19
The Pancreas
• Exocrine function
– Acinar cells make, store, and secrete pancreatic
enzymes
– Enzymes are activated in the duodenum
• Endocrine function
– Produces insulin and glucagon
– Regulates blood sugar
The Exocrine Pancreas: Histology
Diaphragm
Liver
Spleen
Pancreas
Tail
Body
Head
Duodenum
Acinar
cells
(b) Photomicrograph of the exocrine
acinar cells of the pancreas (160)
Small
duct
Acinar cells
(a) Dissection illustrating the pancreas and its
relationship to surrounding organs in the
superior abdomen
Basement
membrane
Zymogen
granules
Rough
endoplasmic
reticulum
(c) Illustration of the pancreatic acinar cells
Figure 23.27
Peptic Ulcers
• Are erosions of the mucosa of a region of the
alimentary canal
• Gastric ulcers
– Occur in pyloric region of the stomach
• Duodenal ulcers
– Occur in duodenum of the small intestine
Peptic Ulcers
• Caused by Helicobacter pylori
• H. pylori
– Acid-resistant
– Binds to gastric epithelium
• Induces oversecretion of acid and inflammation
Peptic Ulcers
Bacteria
Mucosa
layer of
stomach
(a) A gastric ulcer lesion
(b) H. Pylori bacteria
Figure 23.28
Disorders of the Digestive System
• Intestinal obstruction
– Mechanical obstructions
• Adhesions, tumors, or foreign objects
– Nonmechanical obstruction
• Halt in peristalsis
– Trauma
– Intestines touched during surgery
Disorders of the Digestive System
• Inflammatory bowel disease
– Inflammation of intestinal wall
• Crohn’s disease
• Ulcerative colitis
• Viral hepatitis
– Jaundice and flu-like symptoms
– Major types—A, B, C, and G
Disorders of the Digestive System
• Cystic fibrosis and the pancreas
– Pancreatic ducts become blocked with mucus
• Clogged ducts prevent pancreatic juices from entering
small intestine
• Leads to malabsorption of fats and other nutrients