Chapter 24
Digestive System
24.5 Peritoneum
• Peritoneum
• Visceral: Covers organs
• Parietal: Covers interior surface of body
wall
• Retroperitoneal: Certain organs covered
by peritoneum on only one surface and
are considered behind the peritoneum;
e.g., kidneys, pancreas, duodenum
• Mesenteries: two layers of peritoneum with
thin layer of loose C.T. between
• Routes by which vessels and nerves pass
from body wall to organs
–Greater omentum: connects greater curvature of the stomach to the
transverse colon.
–Lesser omentum: connects lesser curvature of the stomach and the proximal
part of the duodenum to the liver and diaphragm.
–Transverse mesocolon, sigmoid mesocolon, mesoappendix.
•Ligaments
–Coronary: between liver and diaphragm
–Falciform: between liver and anterior abdominal wall
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Coronary ligament
Liver
Lesser omentum
Visceral peritoneum
Peritoneal cavity
Stomach
Pancreas (retroperitoneal)
Kidney (retroperitoneal)
Parietal peritoneum
Duodenum (retroperitoneal)
Greater omentum
Transverse mesocolon
Transverse colon
Omental bursa
Mesentery proper
Small intestine
Urinary bladder
(retroperitoneal)
(a) Medial view
Rectum (retroperitoneal)
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Liver
Falciform
ligament
Liver
Gallbladder
Stomach
Transverse
mesocolon
Transverse
colon
Mesentery
proper
Greater
omentum
Small
intestine
(b)
Anterior view
(c)
Anterior view
b-c: © McGraw-Hill Higher Education, Inc./Rebecca Gray, photographer/ Don Kincaid, dissections
Secretions of the Stomach
• Chyme: ingested food plus stomach secretions
• Mucus: surface and neck mucous cells
• Viscous and alkaline
• Protects from acidic chyme and enzyme pepsin
• Irritation of stomach mucosa causes greater mucus
• Intrinsic factor: parietal cells. Binds with vitamin B12 and helps
it to be absorbed. B12 necessary for DNA synthesis
• HCl: parietal cells
• Kills bacteria
• Stops carbohydrate digestion by inactivating salivary
amylase
• Denatures proteins
• Helps convert pepsinogen to pepsin
• Pepsinogen: packaged in zymogen granules released by
exocytosis. Pepsin catalyzes breaking of covalent bonds in
proteins
Movements of the Stomach
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Esophagus
• Combination of mixing
waves (80%) and
peristaltic waves (20%)
• Both esophageal and
pyloric sphincters are
closed.
1 A mixing wave initiated in the body
of the stomach progresses toward
the pyloric sphincter (pink arrows
directed inward).
Mixing
wave
Pyloric
sphincter
Chyme
1
Body of
stomach
Duodenum
2 The more fluid part of the chyme
is pushed toward the pyloric
sphincter (blue arrows), whereas
the more solid center of the chyme
squeezes past the peristaltic
constriction back toward the body
of the stomach (orange arrow).
2
More solid
chyme
Pyloric
part
More fluid
chyme
3 Peristaltic waves (purple
arrows) move in the same
direction and in the same way as
the mixing waves but are stronger.
4 Again, the more fluid part of the
chyme is pushed toward the
pyloric region (blue arrows),
whereas the more solid center of
the chyme squeezes past the
peristaltic constriction back
toward the body of the stomach
(orange arrow).
5 Peristaltic contractions force a
few milliliters of the mostly fluid
chyme through the pyloric opening
into the duodenum (small red arrows).
Most of the chyme, including the more
solid portion, is forced back toward
the body of the stomach for further
mixing (yellow arrow).
Peristaltic
wave
3
4
5
Secretions of the Small Intestine
• Fluid primarily composed of water, electrolytes and mucus.
• Mucus
• Protects against digestive enzymes and stomach acids
• Digestive enzymes: bound to the membranes of the
absorptive cells
• Disaccharidases: Break down disaccharides to
monosaccharides
• Peptidases: Hydrolyze peptide bonds
• Nucleases: Break down nucleic acids
• Duodenal glands
• Stimulated by vagus nerve, secretin, chemical or tactile
irritation of duodenal mucosa
Functions of the Liver
• Bile production: 600-1000 mL/day. Bile salts (bilirubin),
cholesterol, fats, fat-soluble hormones, lecithin
• Neutralizes and dilutes stomach acid
• Bile salts emulsify fats. Most are reabsorbed in the ileum.
• Secretin (from the duodenum) stimulates bile secretions,
increasing water and bicarbonate ion content of the bile
• Storage
• Glycogen, fat, vitamins, copper and iron. Hepatic portal
blood comes to liver from small intestine.
Functions of the Liver
• Nutrient interconversion
• Amino acids to energy producing compounds
• Hydroxylation of vitamin D. Vitamin D then travels to kidney
where it is hydroxylated again into its active form
• Detoxification
• Hepatocytes remove ammonia and convert to urea
• Phagocytosis
• Kupffer cells phagocytize worn-out and dying red and white
blood cells, some bacteria
• Synthesis
• Albumins, fibrinogen, globulins, heparin, clotting factors
24.12 Pancreas
• Pancreas both endocrine and exocrine
• Head, body and tail
• Endocrine: pancreatic islets. Produce
insulin, glucose, and somatostatin
• Exocrine: groups acini (grape-like
cluster) form lobules separated by
septa.
• Pancreatic duct joins common bile
duct and enters duodenum
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Common bile duct
Jejunum
Duodenum
Body of pancreas
Accessory
pancreatic
duct
Minor
duodenal
papilla
Pancreatic duct
Tail of pancreas
Hepatopancreatic
ampulla
Interlobular duct
Major
duodenal
papilla
Circular
folds
Head of
pancreas
(a) Anterior view
Pancreatic
islet
Acinar cells
(secrete enzymes)
Alpha cells
(secrete glucagon)
Beta cells
(secrete insulin)
Intercalated duct
Intralobular duct
Interlobular duct
Vein
To
pancreatic
duct
(b)
To
bloodstream
Lobule
Pancreatic Secretions
• Aqueous. Produced by columnar epithelium lining smaller ducts.
Na+, K+, HCO3-, water. Bicarbonate lowers pH inhibiting pepsin
and providing proper pH for enzymes
• Enzymatic portion:
• Trypsinogen
• Chymotrypsinogen
• Procarboxypeptidase
• Pancreatic amylase
• Pancreatic lipases
• Deoxyribonucleases and ribonucleases
Pancreatic Secretions
• Interaction of duodenal and pancreatic enzymes
• Enterokinase from the duodenal mucosa and attached to the
brush border activates trypsinogen to trypsin.
• Trypsin activates chymotrypsinogen to chymotrypsin.
• Trypsin activates procarboxypeptidase to carboxypeptidase.
• Trypsin, chymotrypsin, and carboxypeptidase digest proteins:
proteolytic.
• Pancreatic amylase continues digestion of starch.
• Pancreatic lipase digests lipids.
• Deoxyribonucleases and ribonucleases digest DNA and
ribonucleic acid, respectively.
Secretions of the Large Intestine
• Mucus provides protection
• Parasympathetic stimulation increases rate of goblet cell
secretion
• Pumps: bacteria produce acid and the following
remove acid from the epithelial cells that line the large
intestine
• Exchange of bicarbonate ions for chloride ions
• Exchange of sodium ions for hydrogen ions
• Bacterial actions produce gases (flatus) from particular
kinds of carbohydrates found in legumes and in
artificial sugars like sorbitol
• Bacteria produce vitamin K which is then absorbed
• Feces consists of water, undigested food (cellulose),
microorganisms, sloughed-off epithelial cells