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VI. Small Intestine & Associated Organs …
B. Liver = largest gland in the body
1. Gross Anatomy
a. 4 lobes:
• Right– anterior surface
• Left on Anterior surface
Sternum
Nipple
Liver
Bare area
Falciform
ligament
Left lobe of liver
Right lobe
of liver
Gallbladder
(a)
Round ligament
(ligamentum
teres)
B. Liver … a. Lobes …
• Caudate small, seen mainly posterosuperiorly; nest to V. Cava
• Quadrate small and mainly seen posteroinferiorly below Left
Lobe and next to gallbladder(“q” like “g”)
b. Ligaments
• Falciform Ligament: separates Right & Left lobes
anteriorly and suspends liver from diaphragm
• Round ligament (ligamentum teres) – remnant of umbilical
vein
Sternum
Bare area
Liver
Right lobe
of liver
Gallbladder
(a)
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Falciform
ligament
Left lobe of liver
Round ligament
(ligamentum
teres)
c. Ducts
• Bile Duct (Common Bile Duct)
• Common Hepatic Ducts
• Cystic Duct
• R&L
Hepatic
Right and left
hepatic ducts
of liver
Cystic duct
Common hepatic duct
Bile duct
Gallbladder
(bile storage)
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Pancreas
Jejunum
d. Blood Vessels
• Hepatic Artery
• Hepatic Portal Vein
• Hepatic Vein
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
(b)
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Bare area
Caudate lobe
of liver
Sulcus for
inferior
vena cava
Hepatic vein
(cut)
Bile duct (cut)
Right lobe of
liver
Gallbladder
2. Microscopic Anatomy of Liver
a. Liver lobules = hexagonal structural and functional units
• Hepatocytes
• Many rough & smooth ER, Golgi, peroxisomes
• Functions: produce bile (900 ml per day)
• Process nutrients from blood (glucose  glycogen, …)
• Store fat soluble vitamins
• Detoxification (nitrogen from amino acids/ammonia 
urea, …)
• Central vein drains
filtered blood to
Portal Triad
Hepatic Veins
Plates of
Hepatocytes
LOBULE
Central
2. Microscopic Anatomy of Liver …
b. Portal triad = bile duct, arteriole (from hepatic artery),
hepatic venule (from portal vein) – both blood vessels
branch into sinusoids: Blood flows toward central vein, bile
toward triad
c. Liver sinusoids = leaky capillaries between hepatic plates
• Carry oxygenated blood and nutrient rich/oxygen poor
blood
Portal Triad
Plates of
Hepatocytes
Central
2. Microscopic Anatomy …
d. Kupffer cells (hepatic macrophages) in sinusoid walls
e. Bile canaliculi feed bile ducts
f. High regeneration capacity: from high blood flow, 80%
removed  regenerates
Bile canaliculi
Plates of
Hepatocytes
Sinusoids
g. Bile
• Function: Fat emulsifier
• Particularly Bile Salts
• Bile Composition:
• Bile Salts (acids derived from cholesterol)
• Pigments: bilirubin– break down product of RBCs
• Cholesterol
• Phospholipids
• Bile Salts Recycled:
reabsorbed in ileum
then Enterohepatic
Circulation—
Hepatic Portal Vein
 Liver  new bile
g. Bile …
• Health: Excess cholesterol can crystallize = gallstones
• Control bile production
• Secretin: released from intestinal cells exposed to fats
stimulate Liver.
• Recycled bile salts: as increase and recycle back to
liver = major stimuli to liver for increased bile production
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C. The Gallbladder
• Muscular sac with Cystic
Duct to Bile Duct
• Function:
Stores/concentrates (10-20
times) & releases bile
• Control:
• Cholecytokinin (CCK)
major stimulus: released
from duodenum when
acidic fatty chyme enters
duodenum
Gallbladder
• Causes contraction
• Vagus nerve– minor
stimulus
• No digestion if: Hepatopancreatic Sphincter closed—bile
backs up into gallbladder & is stored
D. Pancreas
• Parts: Head, tail, Main Duct
• Location:
• deep to greater curvature of stomach
• Head encircled by duodenum; tail abuts
spleen
• Exocrine function: Pancreatic Juice
• Acini = round cluster of secretory cells that
secrete enzymes; enzymes need alkalinity
Pancreas
• Duct cells secrete bicarbonate: neutralizes
stomach acid to pH of 8; cuboidal
Small duct
Acinar cells
Tail
Head of
Pancreas
Pancreas
Islets
Acinar
cells
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Pancreas
Acinar cells
Pancreatic Duct,
branch
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Pancreatic Juice …
Exocrine Function …
• Enzymes: Pancreas secretes enzymes for all 4 major
Biochemical groups (food molecules)
• Amylase, Lipases, Nucleases
• secreted active; optimal activity with bile & ions
• Proteases = secreted inactive (activated in duodenum)
• Control: Secretin target Duct cells AND
Cholecystokinin targets acinar cells
Epithelial
cells
1 of many brush
border enzymes
Membrane-bound
enteropeptidase
Trypsinogen
Trypsin
(inactive)
Chymotrypsin
Chymotrypsinogen
(inactive)
Carboxypeptidase
Procarboxypeptidase
(inactive)
• Pancreas Endocrine Function: hormones insulin &
glucagon from cells in the Islets of Langerhans
Acinar
cells
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E. Regulation of Bile & Pancreatic Secretion
and Entry into the Sm. Intest.
Stimulatory events
Cephalic
phase
Gastric
phase
1 Sight and thought
of food
Cerebral cortex
Conditioned reflex
2 Stimulation of
taste and smell
receptors
Hypothalamus
and medulla
oblongata
1 Stomach
distension
activates
stretch
receptors
Vagovagal
reflexes
Intestinal Phase
1 Presence of low
pH, partially digested
foods, fats, or
hypertonic solution
in duodenum when
stomach begins to
empty
Stimulate
Inhibit
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Medulla
Vagus
nerve
Vagus
nerve
Local
reflexes
2 Food chemicals
(especially peptides and
caffeine) and rising pH
activate chemoreceptors
Intestinal
phase
Inhibitory events
G cells
Intestinal
(enteric)
gastrin
release
to blood
Gastrin
release
to blood
Lack of
stimulatory
impulses to
parasympathetic
center
Cerebral
cortex
Gastrin
secretion
declines
G cells
Overrides
parasympathetic
controls
Sympathetic
nervous
system
activation
1
1
2
Stomach
secretory
activity
Enterogastric
reflex
Brief
effect
Processing in
Small IntestineFigure 23.17
Local
reflexes
Vagal
nuclei
in medulla
Pyloric
sphincter
Release of intestinal
hormones (secretin,
cholecystokinin, vasoactive
intestinal peptide)
1 Distension
of duodenum;
presence of
fatty, acidic,
hypertonic
chyme, and/or
irritants in
the duodenum
2 Distension;
presence of
fatty, acidic,
partially
digested food
in the
duodenum
E. Regulation of Bile & Pancreatic Secretion and
Entry into the Small Intestine
Continuation after intestinal phase of Stomach:
1. Cholecystokinin & Secretin released
• Stimulus = Chyme entering Duodenum
• CCK & Secretin potentiate (syngergistic)one another
2. Hormones  Blood
3. Hepatopancreatic Sphincter
relaxes (CCK)
4. Pancreatic Juice secreted
(CCK & Secretin)
5. Liver produces more bile
(Secretin, Bile Salts)
6. Gallbladder contracts (CCK)
7. Secretions enter Duodenum
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8. Absorption across ample surface area
(circular folds, villi, microvilli)
• Breakdown products of carbohydrate
protein, fat, & nucleic acid digestion
9. Peristalsis: occurs after most
nutrients have been absorbed;
10. Ileocecal Sphincter relaxes
• Next Meal, increased stomach
activity  increased segmentation
in Ileum
• Gastrin from stomach relaxes
ileocecal sphincter remaining
substances move into Lg. Intestine
• Sm. Intestine is emptied
START ALL OVER AGAIN WITH CYCLE
VII. Large Intestine
A. Gross Anatomy
1. Parts = Colon, Cecum, appendix, Rectum, & Anal Canal
2. Gross Anatomy
• Teniae coli – Reduction of the 3 bands of longitudinal
smooth muscle in muscularis to a thin band
Transverse
colon
Haustrum
Ascending
colon
IIeum
IIeocecal
valve
Cecum
Rectum
Vermiform appendix Anal canal
Epiploic
appendages
Descending
colon
Teniae coli
Sigmoid
colon
VII. Large Intestine …
2. Gross Anatomy
• Haustra - pocketlike sacs caused by tone of teniae
coli
• Epiploic appendages - fat-filled pouches of visceral
peritoneum
a) Veriform
Appendix
Transverse
colon
Haustrum
Ascending
colon
IIeum
IIeocecal
valve
Cecum
Rectum
Vermiform appendix Anal canal
Epiploic
appendages
Descending
colon
Teniae coli
Sigmoid
colon
b. Cecum
c. Colon
• Ascending Colon
• Right Colic (Hepatic) Flexure
• Transverse Colon
• Left Colic (Splenic) Flexure
• Descending Colon
• Sigmoid Colon
d. Rectum & Anal Canal
• 3 rectal valves stop feces
from being passed with gas
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d. Rectum and
Anus …
• Rectum …
• Well-developed
muscularis
Rectum
Rectal valve
Hemorrhoidal
veins
• Anal Canal
• Internal anal sphincter—
smooth muscle
• External anal sphincter—
skeletal muscle
Anal
canal
B. Bacterial Flora
• Enter from small intestine or anus
• Ferment indigestible carbs
• Release irritating acids and gases
• Synthesize B complex vitamins and vitamin K
C. Microscopic Anatomy
1. Mucosa
• Simple Columnar ET w/ many Goblet Cells
• Stratified Squamous in Anal Canal
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Colon
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D. Functions of the Large Intestine
• Vitamins, water, and
electrolytes reclaimed
• Major function = propel
feces to anus
• Slow segmentation by
haustra gradually move
contents distally
• Gastrocolic reflex = food in
stomach causes 3-4 mass
peristaltic waves thru colon
per day
PART 3
Physiology of Digestion and Absorption
I. Carbohydrates: Polysaccharides 
disaccharides & Monosaccharides
II. PROTEINS:
III. Lipids
IV. Nucleic Acids
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END
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Review Questions
The digestive function of the liver is to produce
_______
bile which functions in the chemical
lipids
digestion of _________.
Liver _________
lobules are the functional units of the
liver which contain a central vein and peripheral
portal __________
with what 3 components?
triads
arteriole, hepatic venule,
and bile duct
Review Questions
CCK stimulates the release of pancreatic enzymes
________
contraction of the gall bladder while ________
secretin
and __________
stimulates the release of bicarbonate
__________ - rich pancreatic
chyme from the
secretion to neutralize acidic _________
stomach.
proteins
Enzymes that break down __________
must be activated
in the duodenum.
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Review Questions
Motilin is released during the ‘fasting state’ by
_________
the __________
duodenum and initiates the ___________
migrating
motility complex that gradually moves residues to
large intestine
the _________
____________.
Conscious control of defecation is via relaxation of
external anal sphincter.
the ___________
Review Questions
Amylase, lactase, and sucrase (among others) are
enzymes that help break down carbohydrates
___________.
active
Amino acids are absorbed from the lumen via __________
transport.
emulsified by bile salts, then travel as
Fats are first _________
micelles between microvilli, and are finally converted to
________
chylomicrons in the absorptive cells before being
_____________
lacteals as part of the lymph.
carried away in the ________
1
Chyme in
duodenum =
release of
cholecystokinin
(CCK) + secretin
from duodenal
enteroendocrine
cells.
Bile and Pancreatic Juice
Regulation
Figure 23.28, step 1
1
Chyme entering duodenum
causes release of
cholecystokinin
(CCK) and
secretin from
duodenal
enteroendocrine
cells.
2
CCK (red
dots) and
secretin (yellow
dots) enter the
bloodstream.
CCK =
secretion of
enzyme-rich
pancreatic juice.
Secretin =
secretion of
HCO3–-rich
pancreatic juice.
CCK and
secretin
potentiate
one another
3
Figure 23.28, step 3
1
Chyme entering duodenum
causes release of
cholecystokinin
(CCK) and
secretin from
duodenal
enteroendocrine
cells.
4
Bile salts
returning from
ileum +
secretin = liver
produces bile
more rapidly.
2
CCK (red
dots) and
secretin (yellow
dots) enter the
bloodstream.
3
CCK induces
secretion of
enzyme-rich
pancreatic juice.
Secretin causes
secretion of
HCO3–-rich
pancreatic juice.
Figure 23.28, step 4
1
Chyme entering duodenum
causes release of
cholecystokinin
(CCK) and
secretin from
duodenal
enteroendocrine
cells.
2
CCK (red
dots) and
secretin (yellow
dots) enter the
bloodstream.
3
CCK induces
secretion of
enzyme-rich
pancreatic juice.
Secretin causes
secretion of
HCO3–-rich
pancreatic juice.
4
Bile salts and,
to a lesser extent,
secretin
transported via
bloodstream
stimulate liver to
produce bile
more rapidly.
5
CCK also =
gallbladder
contracts +
hepatopancreatic
sphincter
relaxes; bile
enters
duodenum.
Figure 23.28, step 5
1
Chyme entering duodenum
causes release of
cholecystokinin
(CCK) and
secretin from
duodenal
enteroendocrine
cells.
2
CCK (red
dots) and
secretin (yellow
dots) enter the
bloodstream.
3
CCK induces
secretion of
enzyme-rich
pancreatic juice.
Secretin causes
secretion of
HCO3–-rich
pancreatic juice.
4
Bile salts and,
to a lesser extent,
secretin
transported via
bloodstream
stimulate liver to
produce bile
more rapidly.
5
CCK (via
bloodstream)
causes
gallbladder to
contract and
hepatopancreatic
sphincter to
relax; bile enters
duodenum.
6
Cephalic and
gastric phases,
vagal nerve
causes weak
contractions of
gallbladder.
Figure 23.28, step 6
Carbohydrate digestion
Foodstuff
Enzyme(s)
and source
Site of
action
Starch and disaccharides
Oligosaccharides
and disaccharides
Lactose Maltose Sucrose
Galactose Glucose Fructose
Salivary
amylase
Pancreatic
amylase
Brush border
enzymes in
small intestine
(dextrinase, glucoamylase, lactase,
maltase, and sucrase)
Mouth
Small
intestine
Path of absorption
• Glucose/galactose
absorbed via
cotransport w/ Na+.
• Fructose passes via
facilitated diffusion.
• All
Small
intestine
monosaccharides
leave epithelia via
facilitated diffusion,
enter capillary blood in
villi, and transported to
liver via hepatic portal
vein.
Lumen of
intestine
Amino acids of protein fragments
Brush border enzymes
Apical membrane (microvilli)
Pancreatic
proteases
1
Proteins digested to amino
acids by pancreatic proteases
(trypsin, chymotrypsin, carboxypeptidase) + brush border
enzymes (carboxypeptidase,
aminopeptidase, dipeptidase).
Na+
Na+
Absorptive
epithelial
cell
2
amino acids absorbed by
active transport into absorptive
cells.
Amino
acid
carrier
Active transport
Passive transport
3
Capillary
Amino acids leave villus by
facilitated diffusion, enter
capillary via intercellular clefts.
Figure 23.33
Protein digestion
Foodstuff
Protein
Large polypeptides
Small polypeptides,
small peptides
Amino acids
(some dipeptides
and tripeptides)
Enzyme(s)
and source
Pepsin
(stomach glands)
in presence
of HCl
Pancreatic
enzymes
(trypsin, chymotrypsin,
carboxypeptidase)
Brush border
enzymes
(aminopeptidase,
carboxypeptidase,
and dipeptidase)
Site of
action
Path of absorption
• Amino acids are absorbed
by cotransport with
Stomach
sodium ions.
• Some dipeptides and
tripeptides are absorbed
via cotransport with H++
Small
and hydrolyzed to amino
intestine
acids within the cells.
• Amino acids leave the
epithelial cells by
Small
facilitated diffusion, enter
intestine
the capillary blood in the
villi, and are transported
to the liver via the hepatic
portal vein.
Figure 23.32 (2 of 4)
Fat digestion
Foodstuff
Enzyme(s)
and source
Unemulsified
fats
Emulsification by
the detergent
action of bile
salts ducted
in from the liver
Pancreatic
lipases
Monoglycerides Glycerol
and fatty acids
and
fatty acids
Site of
action
Path of absorption
• Fatty acids and monoglycerides
enter the intestinal cells via
diffusion.
Small
intestine • Fatty acids and monoglycerides
are recombined to form
triglycerides and then
combined with other lipids and
proteins within the cells, and
the resulting chylomicrons are
Small
extruded by exocytosis.
intestine
• The chylomicrons enter the
lacteals of the villi and are
transported to the systemic
circulation via the lymph in the
thoracic duct.
• Some short-chain fatty acids
are absorbed, move into the
capillary blood in the villi by
diffusion, and are transported
to the liver via the hepatic
portal vein.
Figure 23.32 (3 of 4)
Nucleic acid digestion
Foodstuff
Enzyme(s)
and source
Site of
action
Nucleic acids
Pentose sugars,
N-containing bases,
phosphate ions
Path of absorption
• Enter
Pancreatic ribonuclease and
deoxyribonuclease
Brush border
enzymes
(nucleosidases
and phosphatases)
Small
intestine
intestinal cells
by active transport via
membrane carriers.
Small • Absorbed
intestine capillaries,
into villi
transported
to liver via hepatic
portal vein.
Figure 23.32 (4 of 4)
E. Regulation of Bile & Pancreatic Secretion and Entry into the Sm. Intest.
Regulation of Gastric Secretion-- REVIEW
Stimulatory events
Cephalic
phase
Gastric
phase
1 Sight and thought
of food
Cerebral cortex
Conditioned reflex
2 Stimulation of
taste and smell
receptors
Hypothalamus
and medulla
oblongata
1 Stomach
distension
activates
stretch
receptors
Vagovagal
reflexes
1 Presence of low
pH, partially digested
foods, fats, or
hypertonic solution
in duodenum when
stomach begins to
empty
Stimulate
Inhibit
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Medulla
Vagus
nerve
Vagus
nerve
Local
reflexes
2 Food chemicals
(especially peptides and
caffeine) and rising pH
activate chemoreceptors
Intestinal
phase
Inhibitory events
G cells
Intestinal
(enteric)
gastrin
release
to blood
Gastrin
release
to blood
Lack of
stimulatory
impulses to
parasympathetic
center
Cerebral
cortex
Gastrin
secretion
declines
G cells
Overrides
parasympathetic
controls
Sympathetic
nervous
system
activation
1 Loss of
appetite,
depression
1 Excessive
acidity
(pH <2)
in stomach
2 Emotional
upset
Stomach
secretory
activity
Enterogastric
reflex
Brief
effect
Processing in
Small IntestineFigure 23.17
Local
reflexes
Vagal
nuclei
in medulla
Pyloric
sphincter
Release of intestinal
hormones (secretin,
cholecystokinin, vasoactive
intestinal peptide)
1 Distension
of duodenum;
presence of
fatty, acidic,
hypertonic
chyme, and/or
irritants in
the duodenum
2 Distension;
presence of
fatty, acidic,
partially
digested food
in the
duodenum
F. Digestion in the Small Intestine
1. Overall Function: finish digestion/absorb nutrients & water
2. Hypertonic Chyme moved slowly into Duodenum from
stomach via slow peristalsis (3ml)
• Chyme = acidic and hypertonic w/ partially digested
carbohydrates/proteins & undigested fats
• Pancreatic juices neutralize chime & make it isotonic
3. Segmentation Mixes chime w/ bile & pancreatic secretions
and moves chime slowly towards Ileum