Chapter 25— The Digestive
System
25-1
Ch. 25 Study Guide
1. Critically read 25.3 (stomach), 25.4 (liver,
gallbladder, and pancreas), 25.5 (small
intestine); pp. 977-995
2. Comprehend Terminology (those in bold)
3. Study-- Figure questions, Think About It
questions, and Before You Go On (sectionending) questions
4. Do end-of-chapter questions:
– Testing Your Recall— 1-4, 6, 9, 10, 15-17
– True or False– 1, 3-10
– Testing Your Comprehension– 2, 5
25-2
I. Stomach (25.3)—
A. Introduction and gross
anatomy
25-3
§ Introduction-- the stomach
1. Location/size-– Upper left abdominal cavity—
– Volume– 50 mL when empty and 1-2 L after a
typical meal.
2. Functions–
– Primarily as a food ____________ organ
– Liquefies the food and begins the chemical
digestion of proteins and fat
– End result: Chyme–
25-4
§ Gross Anatomy (stomach)
1. Lesser curvature—
2. Greater curvature—
3. Four regions— Fig. 25.12 a-b
A. Cardiac region (cardia)– inside the cardiac
orifice
B. Fundic region (fundus)—
C. Body (corpus)– inferior to the cardiac orifice;
greatest part of the organ
D. Pyroric region– narrower pouch at the inferior;
subdivided into antrum and pyloric canal
25-5
25-6
Figure 25.12b
25-7
I. Stomach—
B. Cell types and their
secretions
25-8
§ The stomach wall
• Structures from the outermost layer:
1. Three muscle layers– muscularis externa
2. Gastric rugae– Wrinkles formed by mucosa
and submucosa
3. Gastric pits– depressions in mucosa
• Lined with ____________ epithelium
• Tubular glands (cardiac, pyloric, and gastric
glands) open into the pits
• Cell types– Addressed shortly . . .
• Fig. 25.13 a-b
25-9
Gastric/pyloric glands of the
gastric pits (next slide)
25-10
Tubular glands
differ depending
on areas.
2
§ Cell types of the tubular glands
1. Mucous cells– secrete mucus, predominate in
the cardiac and pyloric glands
2. Regenerative (stem) cells– in the base of the
pit and neck of the gland; function—
3. Parietal cells– mostly in the upper half of the
gastric gland; secrete hydrochloric acid
and intrinsic factor
4. Chief cells– most numerous and only in
gastric glands; secrete chymosin and lipase in
infancy; _________________ later on
5. Enteroendocrine cells– G cells included 25-12
§ Gastric secretions--HCl
• 2-3 L of gastric juice per day--mainly water,
HCl, and pepsin
1. HCl – by parietal cells: Fig. 25.14
-
– CO2 + water (CAH)  H2CO3  HCO3 + H+
– Chloride shift--HCO3 exchanges for chloride
ions (Cl ) from the blood plasma
– Alkaline tide– during digestion, high-pH blood
2. Functions of HCl:
– Activates enzymes—
– Kills ingested bacteria
– Converts Fe(3+) to Fe(2+)
25-13
Chloride shift
CAH
25-14
§ Gastric secretions—
Intrinsic factor
1. Secreted by-- parietal cells
2. Chemistry--Glycoprotein
3. Function– essential to the absorption of
______________ by the small intestine
4. Disorder– pernicious anemia
5. Treatment– injection of vitamin B12 or take
vitamin B12 and intrinsic factor orally
25-15
§ Gastric secretions--Pepsin
1. Chief cells secrete a zymogens (inactive
proteins) called pepsinogen
2. Pepsinogen  pepsin (by HCl)
3. Functions of the pepsin—
A. Digests proteins:
B. Autocatalytic effect of pepsin:
– Once pepsin is formed, pepsin can converts
pepsinogen into MORE pepsin.
Fig. 25.15
25-16
Pepsin has two functions #1 and #2
below (as shown); HCl has function #3



What are functions 1-3,
respectively?
25-17
§ Gastric digestion and absorption
1. Digestion—
– Partially digest protein, starch, and fat
– Most digestion and absorption occurs in the
________________
2. Absorption—
– Not significant amount
– Absorb aspirin, some lipid-soluble drugs, and
little alcohol
25-18
I. Stomach—
C. Protection of the
stomach
25-19
§ protection of the stomach
• 3 ways to protect against harsh acidic and
enzymatic environment (Fig. x)
1. Mucous coat– thick, and alkaline mucus
2. Epithelial cell replacement– cells live 3-6
days; replaced by new cells in the gastric
pits
3. ____________ — prevents gastric juice from
seeping between them to damage CT of the
lamina propria or beyond
25-20
Mucus 
coating
LUMEN
Passage
prevented
Impermeable
to HCI


Tight
junction
Cells lining gastric mucosa
(including those lining gastric pits and glands)
Submucosa
25-21
§ peptic ulcer
1. Definition– erosion in the wall of digestive tract
caused by pepsin and HCl
2. Locations– duodenum most common, also in
_______________________
3. Causes– mucosal defense is compromised;
hypersecretion of acid/pepsin, Helicobacter
pylori (bacterium), smoking, use of aspirin
4. Treatments-- Cimetidine (H2 blocker on
parietal cells); antibiotics against Helicobacter
(better)
Fig. 25.16 a-b
25-22
Normal
Peptic ulcer
25-23
I. Stomach—
D. Regulation of the gastric
function
25-24
§ Regulation of Gastric function
• Three phases— overlap each other and all
three can occur simultaneously
1. Cephalic phase– being controlled by the
brain
2. Gastric phase– being controlled by the
stomach
3. Intestinal phase– being controlled by the
small intestine
25-25
§ Regulation of Gastric function
• The cephalic phase– the stomach
responds to sight, smell, taste, or thought
of food.
• Details–
A. mental inputs converge on the
hypothalamus, to the medulla oblongata
B. vagus nerve fibers from medulla innervate
the stomach to stimulate gastric activity.
• Fig. 25.17
25-26
25-27
§ Regulation of Gastric function
• The gastric phase– swallowed food
activate gastric activity
Details– Presence of food/proteins
A. Stretching– via a long vagovagal reflex and a short
myenteric reflex
B. Through chemicals—Ach, gastrin, histamin
– On parietal cells (by Ach, gastrin, histamin)- to secrete
HCl
– On chief cells (by Ach and gastrin)– pepsinogen
– Digested protein: stimulates the G cells secrete even
more gastrin
Fig. 25.17 b and 25.18
25-28
&
Ach
25-29
Fig. 25.18– Feedback control of gastric secretion.
(+ feedback)
25-30
§ Regulation of Gastric function
• The intestinal– duodenum responds to
_______ and moderates gastric activity
Details–
• Initially enhances gastric secretion
• Soon, acid and semidigested fats trigger the
enterogastric reflex– to:
– Inhibit vagal nuclei
– Stimulate sympathetic neurons
– Secretin and cholecystokinin inhibit gastric
activity
Fig. 25.17c
25-31
_




25-32
II. 25.4—
A. The liver
25-33
§ Gross anatomy
Location– inferior to the diaphragm …
The body’s largest organ—
Functions– Fig. x
Four lobes— right, left, quadrate, and
caudate lobes
5. Other important terminology– falciform
ligament, round ligament; bare area,
porta hepatis
Fig. 25.19
1.
2.
3.
4.
25-34
PROD. &
25-35
25-36
§ Microscopic anatomy
1. Lots tiny cylinders– hepatic lobules
(each 2mm x 1mm)
– Each hepatic lobule– central vein +
radiating hepatic sinusoids + sheets of
hepatocytes
– Functions of hepatocytes and hepatic
macrophages--
Fig. 25.20 a, c
25-37
Fig. 25.20a--The hepatic lobules
Hepatic
sinusoid
Central
vein
Hepatic
triad:
1-Branch of
hepatic
portal v.
Stroma
2-Branch of
Hepatic a.
3-Bile
ductule
(a)
Bile canaliculi
Hepatocytes
25-38
Hepatic
macrophage
Hepatocyte
Endothelial
cells
Fenestration
Sinusoid
25-39
§ Microscopic anatomy
2. Stroma (C.T.)-- Among hepatic lobules
– Hepatic triad– two blood vessels and a bile
ductule
– Blood circulation in the liver– blood vessels of a
triad to the sinusoids, to the central vein, to right
and left hepatic veins and to the _____________
before going back to the heart
25-40
§ Bile
1. Color– yellow-green fluid
2. Secreted by— the liver; @ 1 liter per day
3. Components— bile acids, cholesterol,
–
–
–
–
phospholipids (lecithin), neutral fats, minerals, bile
pigments (major pigment is bilirubin)
Bile acids (steroids) and lecithin aid in fat
digestion and absorption
_____% of bile acids are reabsorbed in the ileum
and reused (called enterohepatic circulation)
All others are wastes, destined in the feces
Waste products too concentrated-- gallstones
25-41
II. 25.4—
B. The gallbladder
25-42
§ Gallbladder and bile flow
1. Gallbladder– (Fig. 25.21)
– Location– on the underside of the liver
– Dimension– 10 cm long
– Pathway-- Its neck (cervix) leads into the
________ duct, which then joins the bile duct
– Function– store and concentrate bile
25-43
1. Hepatic ducts
Gallbladder:
3. Cystic
duct
Neck
Body
2. Common
hepatic duct
4. Bile duct
Head
Accessory
pancreatic duct
Pancreatic duct
Duodenum
Minor duodenal
papilla
6. Hepatopancreatic
sphincter
7. Major duodenal
papilla
5. Hepatopancreatic
ampulla
Pancreas
Duodenojejunal
flexure
Jejunum
25-44
§ Gallbladder and bile flow
3. Bile’s pathway– (see also Fig. 25.21)
– Bile canaliculi (between layers of hepatocytes)
– Small bile ductules of the triads
–
–
–
–
–
Right and left hepatic ducts, converge to form
The common hepatic duct
Joins the cystic duct (of the gallbladder)
Forms the bile duct
Joins the pancreatic duct to become the
hepatopancreatic ampulla
– Terminates at the major duodenal papilla
25-45
II. 25.4—
C. The pancreas
25-46
§ The pancreas
1. Location– anterior/posterior (circle one) to the
greater curvature of the stomach
2. Dimension– 12-15 cm long & 2.5 cm thick
3. Functions– both endocrine (1%; insulin +
glucagon) and exocrine gland (99%; secretes
pancreatic juice)
– Pancreatic juice: alkaline mixture of water,
enzymes, zymogens, sodium bicarbonate, ions
– Path of pancreatic juice: through either main or
accessory pancreatic ducts
25-47
§ The exocrine secretions of the pancreas
1. Zymogens– trypsinogen, chymotrypsinogen,
and procarboxypeptidase (all digest proteins)
– Trypsinogen becomes ________ by enterokinase
(from small intestine); an autocatalytic reac.
– Trypsin also convert the other two zymogens into
active forms
2. Other enzymes-- become fully active upon
exposure to bile or ions in the intestines
– What are they?
Fig. 25.23
25-48
25-49
§ Regulation of pancreatic secretion
1. Acetylcholine– (from vagus and enteric
nerves in response to gastric phases);
stimulates enzymes secretion and release
2. Cholecystokinin– (from duodenum and
jejunum in response to fats); stimulates—
– Discharge of bile into the duodenum
– the secretion of pancreatic enzymes
3. Secretin– (same as #2; in response to acidity
of chyme); stimulates the secretion of sodium
bicarbonate from _____
25-50