1. Digestive System 1B

2. 17.6: Stomach
The stomach is a J-shaped, pouch-like organ, about centimeters long
It hangs inferior to the diaphragm in the upper-left portion of the abdominal cavity
The stomach has two layers of smooth muscle
An inner circular layer
An outer longitudinal layer
(There may be a third inner layer of oblique fibers.)

3. Parts of the Stomach Greater curvature Esophagus Lower esophageal
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Esophagus
Lower esophageal
sphincter
Fundus
Circular
fibers
Esophagus
Body
Cardia
Longitudinal
fibers
Pyloric
sphincter
Lesser
curvature
Greater
curvature
Duodenum
Pyloric opening
Esophagus
Pyloric
canal
Pylorus
Oblique
fibers
Pyloric
antrum
Gastric folds
(rugae)
(b)
Longitudinal
fibers
(a)

4. Parts of the Stomach Fundus Pyloric sphincter Gastric folds Duodenum
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Fundus
Pyloric sphincter
Gastric folds
Duodenum
Body
Pylorus
© Dr. Kent M. Van De Graaff

5. Gastric Secretions
The mucous membrane of the stomach has tubular gastric glands that secrete:
Pepsinogen
From the chief cells
Inactive form of pepsin
Pepsin
From pepsinogen in the presence of hydrochloric acid
Is a protein splitting enzyme
Hydrochloric acid
From the parietal cells
Needed to convert pepsinogen to pepsin
Mucus
From the goblet cells and the mucous glands
Protective to stomach wall
Intrinsic factor
Is required for vitamin B12 absorption

6. b: © The McGraw-Hill Companies, Inc./Al Telser, photographer
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Portion of
a gastric gland
Gastric pits
Gastric pit
Mucous cell
Mucous cell
Mucosa
Parietal cell
Gastric gland
Portion of a
gastric gland
Parietal cell
Submucosa
Muscle
layers
Chief cell
Serosa
Chief cell
(a)
(b)
b: © The McGraw-Hill Companies, Inc./Al Telser, photographer

9. Gastric Absorption
Gastric enzymes begin breaking down proteins, but the stomach is not well-adapted to absorb digestive products
Why not ???
The stomach does absorb:
Some water
Certain salts
Certain lipid-soluble drugs
Alcohol

10. Mixing and Emptying Actions
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Stomach
Food
entering
Duodenum
Pyloric sphincter
contracted
Chyme
Pyloric sphincter
relaxed
(a)
(b)
(c)

11. Nerve impulses inhibit peristalsis in stomach wall From CNS Vagus
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Nerve impulses
inhibit peristalsis
in stomach wall
From CNS
Vagus
nerve
To CNS 1
Duodenum
fills with chyme 3
Sensory nerve
impulses travel
to central
nervous system 2
Sensory stretch
receptors are
stimulated

12. 17.7: Pancreas
The pancreas has a dual function as both an endocrine gland and exocrine gland
The exocrine function is to secrete digestive juice called pancreatic juice

13. Structure of the Pancreas
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Right hepatic duct
Left hepatic duct
Cystic duct
Common hepatic duct
Bile duct
Gallbladder
Pancreatic duct
Pyloric sphincter
Minor duodenal
papilla
Duodenum
Tail of pancreas
Major duodenal
papilla
Bile duct
Pancreatic duct
Sphincter muscles
Head of pancreas
Major duodenal papilla
Intestinal lumen
Hepatopancreatic
ampulla
Hepatopancreatic
sphincter

14. Pancreatic Juice
Pancreatic juice contains enzymes that digest carbohydrates, fats, proteins, and nucleic acids, and include:
Pancreatic amylase – splits glycogen into disaccharides
Pancreatic lipase – breaks down triglycerides
Trypsinogen, chymotrypsinogen, and carboxypeptidase
Digest proteins
Nucleases – digest nucleic acids
Bicarbonate ions – make pancreatic juice alkaline

15. Regulation of Pancreatic Secretion
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Acidic chyme
enters
duodenum 1 4
Pancreatic juice rich in bicarbonate ions passes down
pancreatic ducts to the duodenum
Bicarbonate ions
neutralize acidic
chyme 5
Secretin stimulates
pancreas to secrete
bicarbonate ions 3 2
Intestinal mucosa
releases secretin
into bloodstream
Bloodstream
Hormonal signals
released into bloodstream
Stimulation of effector organ

16. 17.8: Liver The liver is the largest internal organ
It is located in the upper-right abdominal quadrant just beneath the diaphragm

17. Liver Structure Inferior vena cava Gallbladder Quadrate lobe
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Inferior vena cava
Gallbladder
Quadrate lobe
Coronary ligament
Right lobe
Left lobe
Cystic duct
Falciform ligament
Hepatic duct
Hepatic artery
Hepatic portal
vein
Right lobe
Left lobe
Round
ligament
Bile duct
Gallbladder
Inferior vena cava
Caudate lobe
(a)
(b)

18. c: © The McGraw-Hill Companies, Inc./Al Telser, photographer
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Bile duct
Branch of hepatic portal vein
Branch of hepatic artery
Plates of liver cells
Central vein
Branch of
hepatic portal vein
Bile canaliculi
Bile ductule
Hepatic
sinusoids
Bile duct
(a)
Branches of
hepatic artery
Sinusoids
(b)
(c)
c: © The McGraw-Hill Companies, Inc./Al Telser, photographer

19. Liver Functions
The liver carries on many important metabolic activities, including:
Produces glycogen from glucose
Breaks down glycogen into glucose
Converts non-carbohydrates to glucose
Oxidizes fatty acids
Synthesizes lipoproteins, phospholipids, and cholesterol
Converts carbohydrates and proteins into fats
Deaminating amino acids
Forms urea
Synthesizes plasma proteins
Converts some amino acids to other amino acids
Stores glycogen, iron, and vitamins A, D, and B12
Phagocytosis of worn out RBCs and foreign substances
Removes toxins such as alcohol and certain drugs from the blood

20. Composition of Bile Emulsify fats
Bile is a yellowish-green liquid that hepatic cells continuously secrete
Bile contains:
Water
Bile salts:
Emulsify fats
Help absorb fatty acids, cholesterol, and fat-soluble vitamins
Bile pigments
Cholesterol
Electrolytes

21. Gallbladder
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22. © Carroll Weiss/Camera M.D. Studios
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
© Carroll Weiss/Camera M.D. Studios

23. Regulation of Bile Release
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Cystic duct
Common
hepatic duct
Gallbladder 3
CCK stimulates muscular layer of gallbladder wall to contract
Bile duct 1
Chyme with
fat enters
duodenum 4
Bile passes down the cystic duct and bile duct to duodenum 5
Hepatopancreatic sphincter relaxes and bile enters duodenum
Pancreatic
duct
Cells from the
intestinal mucosa
secrete the hormone
cholecystokinin (CCK)
into the bloodstream 2
Duodenum
Hormonal
signals released
into bloodstream
Bloodstream
Stimulation of
effector organ

25. Functions of Bile Salts
Bile salts aid digestive enzymes
They reduce surface tension and break fat globules into droplets (like soap or detergent) and this is called emulsification
They enhance absorption of fatty acids and cholesterol
They help absorb fat-soluble vitamins A, D, E and K
Bile salts are recycled as they return to the liver