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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 muscleInner circular muscle
Myenteric plexus
Epithelial lining
Lamina propria
Muscularis mucosaLumen
Serosa or adventitia
(outermost layer)
Submucosa
(second layer)
Duct from external exocrine gland
Submucosal plexus
Muscularis externa
(third layer)
Mucosa(innermost
layer)
Fig. 2-2, p. 26
esophagus
stomach
Small intestine
Mouth
Esophagus
Stomach
Upper GI Tract
Chronic reflux disease
GERD – gastro esophageal reflux diseaseSymptoms:
Treatments:
Antacids
Histamine H2 receptor blockers
Promotility agents
Proton pump inhibitors
Licorice
Aloe Vera
Gamma Oryzanol
Fig. 2-1, p. 25
Cystic duct
Right hepatic bile duct
Left lobe of liver
Left hepatic bile duct
Common hepatic bile duct
Common bile duct
Pancreatic duct
Pancreas
Main pancreatic duct
Duodenum
Sphincter of Oddi
Gallbladder
Right lobe of liver
Fig. 2-4a, p. 28
Hepatic plates
Lymphatic vesselPortal
vein
Bile duct
Bile canaliculi
Hepatic artery
Portal vein
Hepatic cells (hepatocytes)
Sinusoids
Central vein
Fig. 2-3, p. 27
Stomach
Bile duct from liver
Duodenum
Duct cells secrete aqueous NaHCO3 solution
Acinar cells secrete digestive 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.
Blood
Hormones (insulin, glucogen)
Fig. 2-4b, p. 28
Lumen
Villi
Intestinal wall
Nerve plexusesSubmucosal
Myenteric
LumenVilli
Central lacteal
Blood vessels
Intestinal glands
Crypts of Lieberkühn
Mucosa
Submucosa
Muscularis
Serosa
Fig. 2-5, p. 29
Blood capillaries
Lacteal
Microvilli brush border
Tight junction
Desmosome
Cell membrane
MitochondrionRough endoplasmic reticulum
Ribosome
Golgi’s sacculeNucleus
Enterocyte Brush border
Glycocalyx
Glycocalyx
Actin filaments
Cell membrane
Myosin filaments
Terminal web
Fig. 2-6, p. 30
02CO, p. 24
Transverse colon
Cecum
Appendix
Ascending colon
Ileum
Descending colon
Tenia coli
Haustra
Sigmoid colon
Rectum
Anal sphincter
Fig. 2-7, p. 31
Table 2-1, p. 32S=stimulates I=inhibits O=no effect or information not available
Pharynx
Esophagus
Mouth
Salivary glands
Parotid
Sublingual
Submandibular/submaxillary
Saliva containingWater Electrolytes Mucus Enzymes* Antibacterial and antiviral compounds
*Main enzyme in saliva is salivary amylase, which hydrolyzes 1-4 bonds in starch Fig. 2-8, p. 34
-amylase
Lingual lipase
Mucins
Water and electrolytes
IgA
EsophagusFundus
Lower esophageal sphincter
Cardia
Rugae
PylorusPyloric sphincter
Duodenum
Pyloric portion (or antrum)
Body
Pacemaker location
Greatercurvature
Fig. 2-9, p. 35
Lumen of gland or gastric pit
Gastric epithelial mucosa
Neck or mucus cells
Bicarbonate and mucus
Peptic or chief cells
Pepsinogens
Oxyntic or parietal cells
Hydrochloric acid and intrinsic factor
Enteroendocrine (G)cell Gastrin
Stomach
Fig. 2-10, p. 36
Fig. 2-11, p. 37
Duodenum
Esophagus
No enzymatic activity
Stomach
Protein Polypeptides
Starch Dextrins
Pepsin
Salivary amylase
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 glandsPepsinogen (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
Triacylglycerol
Phospholipid
Cholesterol
Glycerol
3 fatty acids
2-monoacylglycerol or
2 fatty acids
Bile from liver
Micelle
Fatty acids
2-monoacylglycerol
Enterocyte
Lymphatic system lacteal
Blood capillary
Chylomicron
PhospholipidsCholesterol
Protein
Triacylglycerol synthesis
+
+
Pancreaticlipase
Fig. 2-15, p. 43
Liver
Hepatic portal vein
Gallbladder
Ileum
Jejunum
Duodenum
Bile
Bile
Bile
Bile
Bile
Bile
Bile
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
Stomach
Duodenum
Jejunum
Ileum
Large intestine
CalciumPhosphorusMagnesiumIronCopperSeleniumThiaminRiboflavinNiacinBiotinFolateVitamins A, D, E, and K
LipidsMonosaccharidesAmino AcidsSmall peptides
Vitamin CFolateVitamin B12
Vitamin DVitamin KMagnesiumOthers*
WaterEthyl alcoholCopperIodideFlourideMolybdenum
ThiaminRiboflavinNiacinPantothenateBiotinFolateVitamin B6
VitaminCVitamins A, D, E, and KCalciumPhosphorusMagnesiumIronZincChromiumManganeseMolybdenum
LipidsMonosaccharidesAmino AcidsSmall peptides
Bile salts and acidsSodiumChloridePotassium
Short-chain fatty acids
Water
Vitamin KBiotin
Fig. 2-20, p. 47
Diffusion
Facilitated diffusion
Active transport
Pinocytosis
Energy(ATP)
Cell membrane
Water
Small lipids
Cell membrane
Cell membrane
Cell membrane
Fig. 2-21, p. 48
DiffusionCell membrane
Water
Small lipids
Fig. 2-21a, p. 48
Facilitated diffusion Cell membrane
Fig. 2-21b, p. 48
Active transport
Energy(ATP)
Cell membrane
Fig. 2-21c, p. 48
PinocytosisCell membrane
Fig. 2-21d, p. 48