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The Digestive System
Objectives
• Understand the major parts and functions of the
digestive tract
• Learn how the digestive process is regulated
• Analyze how nutrients are broken down by
secretions and enzymes of the digestive system
• Appreciate how diseases of the digestive system
can affect overall nutrition
• Learn some common dietary propensities for GI
problems and some remedies for digestive
system pathologies
Mouth
Esophagus
Duodenum
Stomach
Fig. 2-1, p. 25
Outer longitudinal muscle
Inner circular muscle
Myenteric plexus
Muscularis
externa
(third layer)
Serosa or
adventitia
(outermost layer)
Submucosa
(second layer)
Duct from
external exocrine
gland
Epithelial lining
Submucosal plexus
Lamina propria
Lumen
Muscularis mucosa
Mucosa
(innermost
layer)
Fig. 2-2, p. 26
esophagus
Small intestine
stomach
Upper GI Tract
Mouth
Esophagus
Chronic reflux disease
Stomach
GERD – gastro esophageal reflux disease
Symptoms:
Treatments:
Antacids
Histamine H2 receptor blockers
Promotility agents
Proton pump inhibitors
Licorice
Aloe Vera
Gamma Oryzanol
Fig. 2-1, p. 25
Cystic
duct
Right lobe
of liver
Right hepatic
bile duct
Left lobe
of liver
Left hepatic bile duct
Common hepatic bile duct
Common bile duct
Pancreatic duct
Gallbladder
Sphincter of Oddi
Pancreas
Main
pancreatic duct
Duodenum
Fig. 2-4a, p. 28
Hepatic plates
Lymphatic
Portal vessel
vein
Bile duct
Central
vein
Bile
canaliculi
Hepatic
artery
Portal
vein
Hepatic cells
(hepatocytes)
Sinusoids
Fig. 2-3, p. 27
Bile duct
from liver
Stomach
Duodenum
Hormones
(insulin,
glucogen)
Blood
Acinar cells
Duct cells
secrete aqueous secrete digestive
NaHCO3 solution enzymes
Exocrine portion of pancreas
acinar and duct cells
Endocrine portion
of pancreas
(Islets of Langerhans)
The glandular portions of
the pancreas are grossly
eggagerated.
Fig. 2-4b, p. 28
Lumen
Lumen
Villi
Villi
Central lacteal
Mucosa
Blood
vessels
Intestinal wall
Nerve plexuses
Submucosal
Myenteric
Intestinal glands
Submucosa
Muscularis
Serosa
Crypts of
Lieberkühn
Fig. 2-5, p. 29
Glycocalyx
Microvilli
brush border
Glycocalyx
Tight junction
Desmosome
Cell membrane
Blood
capillaries
Lacteal
Actin
filaments
Mitochondrion
Rough
endoplasmic
reticulum
Ribosome
Cell
membrane
Myosin
filaments
Golgi’s
saccule
Nucleus
Terminal web
Enterocyte
Brush border
Fig. 2-6, p. 30
02CO, p. 24
Transverse colon
Descending
colon
Ascending
colon
Tenia coli
Haustra
Ileum
Sigmoid colon
Cecum
Appendix
Rectum
Anal sphincter
Fig. 2-7, p. 31
S=stimulates
I=inhibits
O=no effect or information not available
Table 2-1, p. 32
Mouth
Pharynx
Salivary glands
Parotid
Sublingual
Submandibular/
submaxillary
Esophagus
*Main enzyme in saliva is salivary amylase,
which hydrolyzes  1-4 bonds in starch
Saliva containing
Water
Electrolytes
Mucus
Enzymes*
Antibacterial and
antiviral compounds
Fig. 2-8, p. 34
-amylase
Lingual lipase
Mucins
Water and
electrolytes
IgA
Fundus
Esophagus
Greater
curvature
Lower
esophageal
sphincter
Pacemaker
location
Cardia
Rugae
Pylorus
Pyloric
sphincter
Body
Duodenum
Pyloric portion
(or antrum)
Fig. 2-9, p. 35
Lumen of gland or gastric pit
Gastric epithelial mucosa
Neck or
mucus cells
Peptic or
chief cells
Bicarbonate and
mucus
Stomach
Pepsinogens
Hydrochloric acid
Oxyntic or
and intrinsic
parietal cells
factor
Enteroendocrine
(G)cell
Gastrin
Fig. 2-10, p. 36
Fig. 2-11, p. 37
Esophagus
No enzymatic
activity
Duodenum
Stomach
Protein
Starch
Pepsin
Salivary  amylase
Polypeptides
Dextrins
Fig. 2-12, p. 37
Regulation of Gastric Secretion
Both neurotransmitters and hormones: acetylcholine, gastrin, histamine –all
receptor mediated to activate secretion
Histamine and Gastrin –predominantly activate acid
secretion by
parietal glands
Acetylcholine –activates all types of secretion in gastric glands
Pepsinogen (peptic cells)
Hydrochloric acid (parietal cells)
Mucus (mucus cells)
PHASES OF SECRETION
Cephalic
Gastric
Intestinal
INHIBITION OF SECRETION
Fig. 2-13, p. 41
Fig. 2-13a, p. 41
Fig. 2-13b, p. 41
Fig. 2-14, p. 43
Lumen of small intestine
Bile from liver
Pancreatic
lipase
Triacylglycerol
Enterocyte
Fatty acids
2 fatty acids
+
2-monoacylglycerol
Phospholipid
2-monoacylglycerol
or
Cholesterol
3 fatty acids
+
Glycerol
Micelle
Triacylglycerol
Lymphatic
synthesis
system lacteal
Protein
Cholesterol
Phospholipids
Chylomicron
Blood
capillary
Fig. 2-15, p. 43
Liver
Duodenum
Bile
Bile
Bile
Hepatic
portal
vein
Gallbladder
Jejunum
Bile
Ileum
Fig. 2-16, p. 44
Fig. 2-17, p. 44
Fig. 2-17a, p. 44
Fig. 2-17b, p. 44
Fig. 2-18, p. 45
Fig. 2-19, p. 46
Table 2-2, p. 33
Esophagus
Calcium
Phosphorus
Magnesium
Iron
Copper
Selenium
Thiamin
Riboflavin
Niacin
Biotin
Folate
Vitamins A, D, E, and K
Stomach
Duodenum
Jejunum
Lipids
Monosaccharides
Amino Acids
Small peptides
Vitamin C
Folate
Vitamin B12
Vitamin D
Vitamin K
Magnesium
Others*
Water
Vitamin K
Biotin
Ileum
Large
intestine
Water
Ethyl alcohol
Copper
Iodide
Flouride
Molybdenum
Thiamin
Riboflavin
Niacin
Pantothenate
Biotin
Folate
Vitamin B6
VitaminC
Vitamins A, D, E,
and K
Calcium
Phosphorus
Magnesium
Iron
Zinc
Chromium
Manganese
Molybdenum
Lipids
Monosaccharides
Amino Acids
Small peptides
Bile salts and acids
Sodium
Chloride
Potassium
Short-chain fatty acids Fig. 2-20, p. 47
Cell membrane
Diffusion
Water
Small lipids
Facilitated diffusion
Active transport
Cell membrane
Cell membrane
Energy
(ATP)
Pinocytosis
Cell membrane
Fig. 2-21, p. 48
Diffusion
Cell membrane
Water
Small lipids
Fig. 2-21a, p. 48
Facilitated diffusion
Cell membrane
Fig. 2-21b, p. 48
Active transport
Cell membrane
Energy
(ATP)
Fig. 2-21c, p. 48
Cell membrane
Pinocytosis
Fig. 2-21d, p. 48
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