Download Liver - Dr. Par Mohammadian

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prepared by
Barbara Heard,
Atlantic Cape Community
College
CHAPTER
23
The Digestive
System: Modified
by Dr. Par
Mohammadian
© Annie Leibovitz/Contact Press Images
© 2013 Pearson Education, Inc.
Digestive System
• Two groups of organs
1. Alimentary canal (gastrointestinal or GI tract/gut)
– Mouth to anus
– Digests food and absorbs fragments
• Organs: Mouth, pharynx, esophagus, stomach, small
intestine, and large intestine
2. Accessory organs
• Teeth, tongue, gallbladder, and
• Digestive glands
– Salivary glands
– Liver
– Pancreas
Figure 23.1 Alimentary canal and related accessory digestive organs.
Mouth (oral cavity)
Tongue*
Parotid gland
Sublingual gland
Submandibular gland
Salivary
glands*
Pharynx
Esophagus
Stomach
Pancreas*
(Spleen)
Liver*
Gallbladder*
Transverse colon
Small
intestine
Anus
Duodenum
Jejunum
Ileum
Descending colon
Ascending colon
Cecum
Sigmoid colon
Rectum
Appendix
Anal canal
Large
intestine
Digestive Processes
• Six essential
activities
• Ingestion
Ingestion
Mechanical
breakdown
• Chewing (mouth)
• Churning (stomach)
• Segmentation
(small intestine)
Digestion
• Propulsion
• Mechanical
breakdown
• Digestion
• Absorption
Food
Pharynx
Esophagus
Propulsion
• Swallowing
(oropharynx)
• Peristalsis
(esophagus,
stomach,
small intestine,
large intestine)
Stomach
Absorption
Lymph
vessel
Small
intestine
Large
intestine
Blood
vessel
Mainly H2O
Feces
• Defecation
Defecation
Anus
Figure 23.3 Peristalsis and segmentation.
From
mouth
Peristalsis: Adjacent segments of
alimentary tract organs alternately contract and
relax, moving food along the tract distally.
Segmentation: Nonadjacent segments
of alimentary tract organs alternately contract
and relax, moving food forward then backward.
Food mixing and slow food propulsion occur.
Peritoneum and Peritoneal Cavity
• Peritoneum - serous membrane of abdominal cavity
– Visceral peritoneum on external surface of most digestive
organs
– Parietal peritoneum lines body wall
• Peritoneal cavity
– Between two peritoneums
– Fluid lubricates mobile organs
• Mesentery - double layer of peritoneum – fanlike
– Routes for blood vessels, lymphatics, and nerves
– Holds organs in place; stores fat
• Retroperitoneal organs posterior to peritoneum (pancreas, duodenum)
• Intraperitoneal (peritoneal) organs surrounded by peritoneum (parts of
the large intestine)
Blood Supply: Splanchnic Circulation
• Branches of aorta serving digestive organs
– Hepatic, splenic, and left gastric arteries
– Inferior and superior mesenteric arteries
• Hepatic portal circulation
– Drains nutrient-rich blood from digestive
organs
– Delivers it to the liver for processing
Histology of the Alimentary Canal
• Four basic layers (tunics)
– Mucosa
– Submucosa
– Muscularis externa
– Serosa
Intrinsic nerve plexuses
• Myenteric nerve plexus
• Submucosal nerve plexus
Glands in
submucosa
Mucosa
• Epithelium
• Lamina propria
• Muscularis
mucosae
Submucosa
Muscularis externa
• Longitudinal muscle
• Circular muscle
Mesentery
Nerve
Artery
Gland in mucosa
Vein
Duct of gland outside
Lymphatic vessel
alimentary canal
Serosa
• Epithelium
(mesothelium)
• Connective tissue
Lumen
Mucosa-associated
lymphoid tissue
Mucosa
• Lines lumen
• Functions – different layers perform 1 or all 3
– Secretes mucus, digestive enzymes, and
hormones
– Absorbs end products of digestion
– Protects against infectious disease
• Three sublayers:
– epithelium,
– lamina propria, and
– muscularis mucosae
Mucosa
• Epithelium
– Simple columnar epithelium and mucus-secreting cells
(most of tract)
• Mucus
– Protects digestive organs from enzymes
– Eases food passage
– May secrete enzymes and hormones (e.g., in stomach and
small intestine)
• Lamina propria
– Loose areolar connective tissue
– Capillaries for nourishment and absorption
– Lymphoid follicles: Defend against microorganisms
• Muscularis mucosae: smooth muscle  local movements of
mucosa
Submucosa
• Submucosa
– Areolar connective tissue
– Blood and lymphatic vessels, lymphoid follicles,
and submucosal nerve plexus
Muscularis Externa
• Muscularis externa
– Responsible for segmentation and peristalsis
– Inner circular and outer longitudinal layers
• Circular layer thickens in some areas  sphincters
• Myenteric nerve plexus between two muscle layers
Serosa
• Visceral peritoneum
– Areolar connective tissue covered with
mesothelium in most organs
– Replaced by fibrous adventitia in esophagus
– Retroperitoneal organs have both an
adventitia and serosa
Figure 23.6 Basic structure of the alimentary canal.
Intrinsic nerve plexuses
• Myenteric nerve plexus
• Submucosal nerve plexus
Glands in
submucosa
Mucosa
• Epithelium
• Lamina propria
• Muscularis
mucosae
Submucosa
Muscularis externa
• Longitudinal muscle
• Circular muscle
Mesentery
Nerve
Artery
Gland in mucosa
Vein
Duct of gland outside
Lymphatic vessel
alimentary canal
Serosa
• Epithelium
(mesothelium)
• Connective tissue
Lumen
Mucosa-associated
lymphoid tissue
Functional
Anatomy: Mouth
• Oral (buccal) cavity
– Bounded by lips,
cheeks, palate,
and tongue
– Oral orifice is
anterior opening
– Lined with
stratified
squamous
epithelium
Soft
palate
Palatoglossal
arch
Uvula
Hard
palate
Oral cavity
Palatine
tonsil
Tongue
Oropharynx
Lingual tonsil
Epiglottis
Hyoid bone
Laryngopharynx
Esophagus
Trachea
Sagittal section of the oral cavity and pharynx
Lips and Cheeks
• Contain orbicularis oris and buccinator
muscles
• Oral vestibule - recess internal to lips
(labia) and cheeks, external to teeth and
gums
• Oral cavity proper lies within teeth and
gums
• Labial frenulum - median attachment of
each lip to gum
Figure 23.7b Anatomy of the oral cavity (mouth).
Upper lip
Gingivae
(gums)
Palatine
raphe
Hard
palate
Soft
palate
Uvula
Palatine
tonsil
Superior
labial
frenulum
Palatoglossal
arch
Palatopharyngeal
arch
Posterior wall
of oropharynx
Tongue
Sublingual
fold with
openings of
sublingual
ducts
Lingual frenulum
Opening of
Submandibular
duct
Gingivae (gums)
Oral vestibule
Lower lip
Anterior view
Inferior labial
frenulum
Palate
• Hard palate - palatine bones and palatine
processes of maxillae
– Slightly corrugated to help create friction
against tongue
• Soft palate - fold formed mostly of skeletal
muscle
– Closes off nasopharynx during swallowing
– Uvula projects downward from its free edge
Tongue
•
Skeletal muscle
•
Functions include
– Repositioning and mixing food during chewing
– Formation of bolus
– Initiation of swallowing, speech, and taste
•
Intrinsic muscles change shape of tongue
•
Extrinsic muscles alter tongue's position
•
Lingual frenulum: attachment to floor of mouth
•
Surface bears papillae
– Filiform—whitish, give the tongue roughness and provide friction; do not
contain taste buds
– Fungiform—reddish, scattered over tongue; contain taste buds
– Vallate (circumvallate)—V-shaped row in back of tongue; contain taste buds
– Foliate—on lateral aspects of posterior tongue; contain taste buds that
function primarily in infants and children
Epiglottis
•
•
Lingual lipase
– Secreted by
serous cells
beneath foliate
and vallate
papillae secrete
– Fat-digesting
enzyme
functional in
stomach
Terminal sulcus
marks division
between
– Body - anterior
2/3 residing in
oral cavity
– Root - posterior
third residing in
oropharynx
– Just posterior to
vallate papillae
Palatopharyngeal
arch
Palatine tonsil
Lingual tonsil
Palatoglossal
arch
Terminal sulcus
Foliate papillae
Vallate papilla
Medial sulcus
of the tongue
Dorsum of tongue
Fungiform papilla
Filiform papilla
Salivary Glands
• Major salivary glands
– Produce most saliva; lie outside oral cavity
– Parotid
– Submandibular
– Sublingual
• Minor salivary glands
– Scattered throughout oral cavity; augment
slightly
•
Function of saliva
– Cleanses mouth
– Dissolves food chemicals for taste
– Moistens food; compacts into bolus
– Begins breakdown of starch with enzymes
Salivary Glands
• Parotid gland
– Anterior to ear; external to masseter muscle
– Parotid duct opens into oral vestibule next to
second upper molar
– Mumps is inflammation of parotid glands
• Submandibular gland
– Medial to body of mandible
– Duct opens at base of lingual frenulum
• Sublingual gland
– Anterior to submandibular gland under tongue
– Opens via 10–12 ducts into floor of mouth
Figure 23.9 The salivary glands.
Tongue
Teeth
Ducts of
sublingual
gland
Frenulum
of tongue
Sublingual
gland
Parotid
gland
Parotid duct
Masseter muscle
Body of mandible
(cut)
Posterior belly of
digastric muscle
Mylohyoid
muscle (cut)
Submandibular
duct
Anterior belly of
digastric muscle
Submandibular
gland
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Mucous cells Serous cells
forming demilunes
Salivary Glands
• Two types of secretory cells
– Serous cells
• Watery, enzymes, ions, bit of mucin
– Mucous cells
• Mucus
• Parotid, submandibular glands mostly
serous; sublingual mostly mucous
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Teeth
• Tear and grind food for digestion
• Primary and permanent dentitions formed
by age 21
• 20 deciduous teeth erupt (6–24 months of
age)
– Roots resorbed, teeth fall out (6–12 years of
age) as permanent teeth develop
• 32 permanent teeth
– All but third molars in by end of adolescence
• Third molars at 17–25, or may not erupt
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Classes of Teeth
• Incisors
– Chisel shaped for cutting
• Canines
– Fanglike teeth that tear or pierce
• Premolars (bicuspids)
– Broad crowns, rounded cusps – grind/crush
• Molars
– Broad crowns, rounded cusps – best grinders
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Figure 23.10 Human dentition.
Incisors
Central (6–8 mo)
Lateral (8–10 mo)
Canine (eyetooth)
(16–20 mo)
Molars
First molar
(10–15 mo)
Second molar
(about 2 yr)
Deciduous
(milk) teeth
Incisors
Central (7 yr)
Lateral (8 yr)
Canine (eyetooth)
(11 yr)
Premolars
(bicuspids)
First premolar
(11 yr)
Second premolar
(12–13 yr)
Molars
First molar (6–7 yr)
Second molar
(12–13 yr)
Third molar
(wisdom tooth)
(17–25 yr)
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Permanent
teeth
Figure 23.11 Longitudinal section of a canine tooth within its bony socket (alveolus).
Enamel
Dentin
Crown
Neck
Dentinal
tubules
Pulp cavity
(contains
blood vessels
and nerves)
Gingival
sulcus
Gingiva
(gum)
Cement
Root
Root canal
Periodontal
ligament
Apical
foramen
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Bone
Esophagus
• Flat muscular tube from laryngopharynx to
stomach
• Pierces diaphragm at esophageal hiatus
• Joins stomach at cardial orifice
• Gastroesophageal (cardiac) sphincter
• Surrounds cardial orifice
•
•
•
•
Esophageal mucosa contains stratified squamous epithelium
– Changes to simple columnar at stomach
Esophageal glands in submucosa secrete mucus to aid in bolus movement
Muscularis externa - skeletal superiorly; mixed in middle; smooth inferiorly
Adventitia instead of serosa
Stomach: Gross Anatomy
• In upper left quadrant; temporary storage;
digestion of bolus to chyme
• Cardial part (cardia)
– Surrounds cardial orifice
• Fundus
– Dome-shaped region beneath diaphragm
• Body
– Midportion
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Cardia
Fundus
Esophagus
Muscularis
externa
• Longitudinal layer
• Circular layer
• Oblique layer
•
Pyloric part
– Antrum (superior
portion)  pyloric
canal  pylorus
– Pylorus continuous
with duodenum
through pyloric
valve (sphincter
controlling
stomach emptying)
Duodenum
Serosa
Body
Lumen
Lesser
curvature
Rugae
of
Mucosa
(extend
s when
we eat
to 1
gallon)
Greater
curvature
Pyloric sphincter
(valve) at pylorus
Pyloric
canal
Pyloric
antrum
Figure 23.14b Anatomy of the stomach.
Liver
(cut)
Fundus
Body
Spleen
Lesser
curvature
Greater
curvature
Stomach: Gross Anatomy
• Greater curvature - convex lateral
surface
• Lesser curvature - concave medial
surface
• Mesenteries tether stomach
– Lesser omentum
• From liver to lesser curvature
– Greater omentum – contains fat deposits &
lymph nodes
• Greater curvature  over small intestine  spleen
& transverse colon  mesocolon
Figure 23.30a Mesenteries of the abdominal digestive organs.
Falciform ligament
Liver
Gallbladder
Spleen
Stomach
Ligamentum teres
Greater omentum
Small intestine
Cecum
Figure 23.30b Mesenteries of the abdominal digestive organs.
Liver
Gallbladder
Lesser omentum
Stomach
Duodenum
Transverse colon
Small intestine
Cecum
Urinary bladder
Figure 23.30c Mesenteries of the abdominal digestive organs.
Greater omentum
Transverse colon
Transverse
mesocolon
Descending colon
Jejunum
Mesentery
Sigmoid
mesocolon
Sigmoid colon
Ileum
Stomach: Gross Anatomy
• ANS nerve supply
– Sympathetic from thoracic splanchnic nerves
via celiac plexus
– Parasympathetic via vagus nerve
• Blood supply
– Celiac trunk (gastric and splenic branches)
– Veins of hepatic portal system
• Four tunics
• Muscularis and
mucosa modified
– Muscularis externa
• Three layers of
smooth muscle
• Inner oblique layer
allows stomach to
churn, mix, move,
and physically break
down food
Surface
epithelium
Mucosa
Lamina
propria
Muscularis
mucosae
Submucosa
(contains
submucosal
Oblique
plexus)
layer
Muscularis
Circular
externa
layer
(contains
Longitudinal
myenteric
layer
plexus)
Stomach wall
Serosa
Layers of the stomach wall
Stomach: Microscopic Anatomy
• Mucosa
– Simple columnar epithelium composed of
mucous cells
• Secrete two-layer coat of alkaline mucus
– Surface layer traps bicarbonate-rich fluid beneath it
– Dotted with gastric pits  gastric glands
• Gastric glands produce gastric juice
Microscopic Anatomy of the Stomach
Epithelial lining is composed of:
– Goblet cells that produce a coat of alkaline mucus
- The mucous surface layer traps a bicarbonaterich fluid beneath it
– Gastric pits contain gastric glands that secrete gastric
juice, mucus, and gastrin
Gastric glands of the fundus and body have a variety of
secretory cells
– Mucous neck cells – secrete acid mucus
– Parietal cells – secrete HCl
Figure 23.15b Microscopic anatomy of the stomach.
Gastric pits
Surface epithelium
(mucous cells)
Gastric
pit
Mucous neck cells
Parietal cell
Gastric
gland
Chief cell
Enteroendocrine cell
Enlarged view of gastric pits and
gastric glands
Small Intestine: Gross Anatomy
• Major organ of digestion and absorption
• 2-4 m long; from pyloric sphincter to
ileocecal valve
• Subdivisions
– Duodenum (retroperitoneal)
– Jejunum (attached posteriorly by mesentery)
– Ileum (attached posteriorly by mesentery)
Figure 23.1 Alimentary canal and related accessory digestive organs.
Mouth (oral cavity)
Tongue*
Parotid gland
Sublingual gland
Submandibular gland
Salivary
glands*
Pharynx
Esophagus
Stomach
Pancreas*
(Spleen)
Liver*
Gallbladder*
Transverse colon
Small
intestine
Anus
Duodenum
Jejunum
Ileum
Descending colon
Ascending colon
Cecum
Sigmoid colon
Rectum
Appendix
Anal canal
Large
intestine
Duodenum
• Curves around head of pancreas; shortest part – 25 cm
• Bile duct (from liver) and main pancreatic duct (from pancreas)
– Join at hepatopancreatic ampulla
– Enter duodenum at major duodenal papilla
– Entry controlled by hepatopancreatic sphincter
• Jejunum
– Extends from duodenum to ileum
– About 2.5 m long
• Ileum
– Joins large intestine at ileocecal valve
– About 3.6 m long
Figure 23.21 The duodenum of the small intestine, and related organs.
Right and left
hepatic ducts
of liver
Cystic duct
Common hepatic duct
Bile duct and sphincter
Accessory pancreatic duct
Mucosa
with folds
Tail of pancreas
Pancreas
Jejunum
Gallbladder
Major duodenal
papilla
Hepatopancreatic
ampulla and sphincter
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Main pancreatic duct and sphincter
Duodenum
Head of pancreas
Gross Anatomy of Small Intestine
• Vagus nerve (parasympathetic) and
sympathetics from thoracic splanchnic
nerves serve small intestine
• Superior mesenteric artery brings blood
supply
• Veins (carrying nutrient-rich blood) drain
into superior mesenteric veins  hepatic
portal vein  liver
Structural Modifications
• Increase surface area of proximal part for nutrient absorption
– Circular folds (plicae circulares)
– Villi
– Microvilli
• Circular folds
– Permanent folds (~1 cm deep) that force chyme
to slowly spiral through lumen  more nutrient
absorption
• Villi
– Extensions (~1 mm high) of mucosa with capillary
bed and lacteal for absorption
• Microvilli (brush border) – contain enzymes
for carbohydrate and protein digestion
Small Intestine: Microscopic Anatomy
Mucosa
• Peyer's patches protect especially distal
part against bacteria
– May protrude into submucosa
• B lymphocytes leave intestine, enter
blood, protect intestinal lamina propria with
their IgA
• Duodenal (Brunner's) glands of the
duodenum secrete alkaline mucus to
neutralize acidic chyme
The Liver and Gallbladder
• Accessory organs
• Liver
– Many functions; only digestive function  bile
production
• Bile – fat emulsifier
• Gallbladder
– Chief function  bile storage
Liver
• Largest gland in body
• Four lobes—right, left, caudate, and quadrate
• Falciform ligament
– Separates larger right and smaller left lobes
– Suspends liver from diaphragm and anterior
abdominal wall
• Round ligament (ligamentum teres)
– Remnant of fetal umbilical vein along free edge of
falciform ligament
Figure 23.24a Gross anatomy of the human liver.
Sternum
Nipple
Bare area
Liver
Falciform
ligament
Left lobe of
liver
Right lobe of liver
Gallbladder
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Round ligament
(ligamentum
teres)
Figure 23.24b Gross anatomy of the human liver.
Lesser
omentum
(in fissure)
Left lobe
of liver
Porta hepatis
containing
hepatic
artery (left)
and hepatic
portal vein
(right)
Quadrate
lobe of liver
Ligamentum
teres
Bare area
Caudate lobe
of liver
Sulcus for
inferior
vena cava
Hepatic vein
(cut)
Bile duct
(cut)
Right lobe
of liver
Gallbladder
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Liver: Associated Structures
• Lesser omentum anchors liver to stomach
• Hepatic artery and vein enter at porta
hepatis
• Bile ducts
– Common hepatic duct leaves liver
– Cystic duct connects to gallbladder
– Bile duct formed by union of common hepatic
and cystic ducts
Figure 23.21 The duodenum of the small intestine, and related organs.
Right and left
hepatic ducts
of liver
Cystic duct
Common hepatic duct
Bile duct and sphincter
Accessory pancreatic duct
Mucosa
with folds
Tail of pancreas
Pancreas
Jejunum
Gallbladder
Major duodenal
papilla
Hepatopancreatic
ampulla and sphincter
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Main pancreatic duct and sphincter
Duodenum
Head of pancreas
Liver: Microscopic Anatomy
• Liver lobules
– Hexagonal structural and functional units
– Composed of plates of hepatocytes (liver cells)
• Filter and process nutrient-rich blood
– Central vein in longitudinal axis
Figure 23.25a–b Microscopic anatomy of the liver.
Lobule
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Central Connective
vein tissue septum
Liver: Microscopic Anatomy
• Portal triad at each corner of lobule
– Branch of hepatic artery supplies oxygen
– Branch of hepatic portal vein brings nutrient-rich blood
– Bile duct receives bile from bile canaliculi
• Liver sinusoids - leaky capillaries between
hepatic plates
• Stellate macrophages (hepatic macrophages
or Kupffer cells) in liver sinusoids remove debris
& old RBCs
Figure 23.25c Microscopic anatomy of the liver.
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
Stellate macrophages
in sinusoid walls
Portal vein
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Bile duct
Portal venule
Portal arteriole
Portal triad
Liver: Microscopic Anatomy
• Hepatocytes – increased rough & smooth ER, Golgi,
peroxisomes, mitochondria
• Hepatocyte functions
– Process bloodborne nutrients
– Store fat-soluble vitamins
– Perform detoxification
– Produce ~900 ml bile per day
• Regenerative capacity
– Restores full size in 6-12 months after 80% removal
– Injury  hepatocytes  growth factors  endothelial
cell proliferation
Bile
• Yellow-green, alkaline solution containing
– Bile salts - cholesterol derivatives that function in
fat emulsification and absorption
– Bilirubin - pigment formed from heme
• Bacteria break down in intestine to stercobilin  brown
color of feces
– Cholesterol, triglycerides, phospholipids, and
electrolytes
• Enterohepatic circulation
– Recycles bile salts
– Bile salts  duodenum  reabsorbed from ileum
 hepatic portal blood  liver  secreted into bile
The Gallbladder
• Thin-walled muscular sac on ventral surface of liver
• Stores and concentrates bile by absorbing water and ions
• Muscular contractions release bile via cystic duct, which
flows into bile duct
• High cholesterol; too few bile salts  gallstones (biliary
calculi)
– Obstruct flow of bile from gallbladder
• May cause obstructive jaundice
– Gallbladder contracts against sharp crystals  pain
– Treated with drugs, ultrasound vibrations (lithotripsy),
laser vaporization, surgery
Pancreas
• Location
– Mostly retroperitoneal, deep to greater curvature of
stomach
– Head encircled by duodenum; tail abuts spleen
• Endocrine function
– Pancreatic islets secrete insulin and glucagon
• Exocrine function
– Acini (clusters of secretory cells) secrete
pancreatic juice
• To duodenum via main pancreatic duct
• Zymogen granules of acini cells contain proenzymes
Figure 23.26a Structure of the enzyme-producing tissue of the pancreas.
Small
duct
Acinar cell
Basement
membrane
Zymogen
granules
Rough
endoplasmic
reticulum
Duct cell
One acinus
Figure 23.26b Structure of the enzyme-producing tissue of the pancreas.
Acinar cells
Pancreatic
duct
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Pancreatic Juice
•
•
•
•
1200 – 1500 ml/day
Watery alkaline solution (pH 8) neutralizes chyme
Electrolytes (primarily HCO3–)
Enzymes
– Amylase, lipases, nucleases secreted in active form but
require ions or bile for optimal activity
– Proteases secreted in inactive form
• Protease activation in duodenum
– Trypsinogen activated to trypsin by brush border enzyme
enteropeptidase
– Procarboxypeptidase and chymotrypsinogen activated by
trypsin
Figure 23.27 Activation of pancreatic proteases in the small intestine.
Stomach
Pancreas
Epithelial
cells
Membrane-bound
enteropeptidase
Trypsinogen
(inactive)
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Trypsin
Chymotrypsinogen
(inactive)
Chymotrypsin
Procarboxypeptidase
(inactive)
Carboxypeptidase
Large Intestine
• Unique features
– Teniae coli
• Three bands of longitudinal smooth muscle in muscularis
– Haustra
• Pocketlike sacs caused by tone of teniae coli
– Epiploic appendages
• Fat-filled pouches of visceral peritoneum
• Regions
– Cecum
– Appendix
– Colon
– Rectum
– Anal canal
Figure 23.29a Gross anatomy of the large intestine.
Left colic
(splenic) flexure
Right colic
(hepatic) flexure
Transverse
mesocolon
Transverse colon
Epiploic
appendages
Superior
mesenteric artery
Descending colon
Haustrum
Ascending colon
IIeum
Cut edge of
mesentery
IIeocecal valve
Tenia coli
Sigmoid colon
Cecum
Appendix
Rectum
Anal canal
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External anal sphincter
Subdivisions of the Large Intestine
• Cecum – first part of large intestine
• Appendix – masses of lymphoid tissue
– Part of MALT (Mucosa-Associated Lymphoid
Tissue) of immune system
– Bacterial storehouse  recolonizes gut when
necessary
– Twisted  enteric bacteria accumulate and
multiply
Colon
• Retroperitoneal except for transverse and
sigmoid regions
• Ascending colon (right side – to level of
right kidney)  right colic (hepatic)
flexure 
• Transverse colon  left colic (splenic)
flexure 
• Descending colon (left side) 
• Sigmoid colon in pelvis  rectum
Figure 23.30c Mesenteries of the abdominal digestive organs.
Greater omentum
Transverse colon
Transverse
mesocolon
Descending colon
Jejunum
Mesentery
Sigmoid
mesocolon
Sigmoid colon
Ileum
© 2013 Pearson Education, Inc.
Figure 23.30d Mesenteries of the abdominal digestive organs.
Liver
Lesser omentum
Pancreas
Stomach
Duodenum
Transverse mesocolon
Transverse colon
Mesentery
Greater omentum
Jejunum
Ileum
Visceral peritoneum
Parietal peritoneum
Urinary bladder
Rectum
© 2013 Pearson Education, Inc.
Rectum and Anus
• Rectum
– Three rectal valves stop feces from being
passed with gas (flatus)
• Anal canal
– Last segment of large intestine
– Opens to body exterior at anus
• Sphincters
– Internal anal sphincter—smooth muscle
– External anal sphincter—skeletal muscle
Figure 23.29b Gross anatomy of the large intestine.
Rectal valve
Rectum
Hemorrhoidal
veins
Levator ani muscle
Anal canal
External anal
sphincter
Internal anal
sphincter
Anal columns
Pectinate line
Anal sinuses
Anus