4/23/2012
About this Chapter
• • • • • •
About this Chapter
• • • •
Digestion function and processes Anatomy of the digestive system Motility Secretion Regulation of GI function Digestion and absorption
The cephalic phase The gastric phase The intestinal phase Immune functions of the GI tract
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Copyright © 2009 Pearson Education, Inc.
Digestive Function and Processes
Four Basic Processes of the Digestive System
• The volume of fluid entering the GI tract must equal the volume leaving
Food SECRETION
DIGESTION Fluid input into digestive system Ingestion 2.0 L food and drink
ABSORPTION
Secretion 1.5 L saliva (salivary glands)
0.5 L bile (liver)
Fluid removed from digestive system
MOTILITY 2.0 L gastric secretions
Absorption 7.5 L from small intestine
1.5 L pancreatic secretions 1.5 L intestinal secretions
1.4 L from large intestine Excretion 0.1 L in feces
9.0 L Total input into lumen
Lumen of digestive tract
9.0 L removed from lumen
Figure 21-1
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Digestion and Absorption
KEY
Salivary gland Upper esophageal sphincter Esophagus Lower esophageal sphincter Liver Gallbladder
Pylorus Pancreas
Ileocecal valve Rectum Anal sphincters Copyright © 2009 Pearson Education, Inc.
Interstitial fluid
Blood Figure 21-2
Digestive System Anatomy
• Summary of motility, secretion, digestion, and absorption in different regions of the digestive system
M: motility S:secretion D:digestion A:absorption
Wall
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ORAL CAVITY AND ESOPHAGUS
• Oral cavity esophagus stomach small intestine large intestine rectum
M: swallowing, chewing S: saliva (salivary glands), lipase D: carbohydrates, fats (minimal) A: none
ANATOMY SUMMARY
THE DIGESTIVE SYSTEM
Oral cavity Salivary glands Esophagus
STOMACH
M: peristaltic mixing and propulsion S :HCl (parietal cells); pepsinogen and gastric lipase (chief cells); mucus and HCO3– (surface mucous cells); gastrin (G cells); histamine (EC cells) D: proteins, fats A: lipid-soluble substances such as alcohol and aspirin SMALL INTESTINE
M: mixing and propulsion primarily by segmentation S: enzymes; HCO3– and enzymes (pancreas); bile (liver); mucus (goblet cells); hormones: CCK, secretin, GIP, and other hormones D: carbohydrates, fats, polypeptides, nucleic acids A: peptides by active transport; amino acids, glucose, and fructose by secondary active transport; fats by simple diffusion; water by osmosis ions, minerals, and vitamins by active transport
Gallbladder Pancreas Small intestine Rectum
LARGE INTESTINE
M :segmental mixing; mass movement for propulsion S: mucus (goblet cells) D: none (except by bacteria) A: ions, water, minerals, vitamins, and small organic molecles produced by bacteria
Liver Stomach Large intestine
(a) Figure 21-22
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Figure 21-3a
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Digestive System Anatomy
Digestive System Anatomy • A closer look at the structure of the stomach and small intestine
• Stomach • Fundus body antrum
• Pyloric valve • Small intestine
STRUCTURE OF THE STOMACH AND INTESTINE Esophagus Fundus
ANATOMY SUMMARY
Diaphragm
THE DIGESTIVE SYSTEM
Body Antrum
• Duodenum jejunum ileum
Oral cavity Salivary glands Esophagus
• Accessory organs: pancreas and liver • Large intestine: colon and rectum • Anus
Pylorus
Mesentery Mucosa Submucosa
Rugae: Surface folding increases area (b) The stomach
Gallbladder Pancreas Small intestine Rectum (a)
Liver Stomach Large intestine
Plica Circular muscle Longitudinal muscle
Submucosal Serosa Villi glands (d) Structure of the small intestine
Figure 21-3a–b, d
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Copyright © 2009 Pearson Education, Inc.
Digestive System Anatomy
Digestive System Anatomy SECTIONAL VIEWS OF THE STOMACH
• Mucosa • Created from
Opening to gastric gland
• Epithelial cells • Lamina propria • Muscularis mucosae
Mucosa
Epithelium
Lymph vessel
• Modifications increase surface area
Lamina propria
• Submucosa • Muscularis externa • Serosa
Artery and vein
Muscularis mucosae Submucosa Oblique muscle Muscularis externa
Circular muscle Myenteric plexux
Longitudinal muscle Serosa (c)
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Figure 21-3c
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Digestive System Anatomy
Motility
SECTIONAL VIEWS OF THE INTESTINE
Villi
Crypt Mucosa
KEY
Lymph vessel Submucosal plexus
Muscularis mucosae Submucosa
Muscularis externa
Circular muscle
Myenteric plexus
M: motility S:secretion D:digestion A:absorption Salivary gland Upper esophageal sphincter Esophagus Lower esophageal sphincter
Longitudinal muscle Serosa
Liver Gallbladder
Pylorus Pancreas
Submucosal artery and vein
Peyer’s patch Ileocecal valve
(e)
Rectum Anal sphincters
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Figure 21-3e
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ORAL CAVITY AND ESOPHAGUS
M: swallowing, chewing S: saliva (salivary glands), lipase D: carbohydrates, fats (minimal) A: none STOMACH
M: peristaltic mixing and propulsion S :HCl (parietal cells); pepsinogen and gastric lipase (chief cells); mucus and HCO3– (surface mucous cells); gastrin (G cells); histamine (EC cells) D: proteins, fats A: lipid-soluble substances such as alcohol and aspirin SMALL INTESTINE
M: mixing and propulsion primarily by segmentation S: enzymes; HCO3– and enzymes (pancreas); bile (liver); mucus (goblet cells); hormones: CCK, secretin, GIP, and other hormones D: carbohydrates, fats, polypeptides, nucleic acids A: peptides by active transport; amino acids, glucose, and fructose by secondary active transport; fats by simple diffusion; water by osmosis ions, minerals, and vitamins by active transport LARGE INTESTINE
M :segmental mixing; mass movement for propulsion S: mucus (goblet cells) D: none (except by bacteria) A: ions, water, minerals, vitamins, and small organic molecles produced by bacteria
Figure 21-22
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Motility
Contractions in the GI Tract • Peristalsis promotes forward movement • Contraction of circular muscles (relaxation of longitudinal muscles)
Different regions display different types of contraction • Tonic contractions • Sustained (minutes to hours) • Occur in sphincters and anterior stomach • Keep bolus from moving backwards • Phasic contractions • Last a few seconds • Peristalsis moves bolus forward • Segmentation mixes • Posterior stomach and small intestine Copyright © 2009 Pearson Education, Inc.
Figure 21-5a
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Intestinal Contractions and Motility
Motility • Segemental contractions promote mixing
• Slow wave potentials • Occur automatically via endogenous pacemaker activity • Contractions are driven by graded depolarizations (slow waves • Produced by nonneuronal/non-muscular cells called Interstitial cells of Cajal (ICC)
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Figure 21-5b
Intestinal Contractions and Motility
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Secretion: Ions, water, hormones, mucus, others • • • • •
Frequency of slow waves influence duration of contraction
7 liters of secretions/ day! Digestive enzymes secreted into mouth, stomach and intestine Mucous cells in stomach and goblet cells in intestine Saliva is an exocrine secretion Liver secretes bile KEY
M: motility S:secretion D:digestion A:absorption Salivary gland Upper esophageal sphincter Esophagus Lower esophageal sphincter Liver Gallbladder
Pylorus Pancreas
Ileocecal valve Rectum Anal sphincters Copyright © 2009 Pearson Education, Inc.
18-46
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ORAL CAVITY AND ESOPHAGUS
M: swallowing, chewing S: saliva (salivary glands), lipase, amylase D: carbohydrates, fats (minimal) A: none STOMACH
M: peristaltic mixing and propulsion S: HCl (parietal cells); pepsinogen and gastric lipase (chief cells); mucus and HCO3– (surface mucous cells); gastrin (G cells); histamine (EC cells) D: proteins, fats A: lipid-soluble substances such as alcohol and aspirin SMALL INTESTINE
M: mixing and propulsion primarily by segmentation S: enzymes (SI); HCO3– and enzymes (pancreas); bile (liver); mucus (goblet cells); hormones: CCK, secretin, GIP, and other hormones D: carbohydrates, fats, polypeptides, nucleic acids A: peptides by active transport; amino acids, glucose, and fructose by secondary active transport; fats by simple diffusion; water by osmosis ions, minerals, and vitamins by active transport LARGE INTESTINE
M :segmental mixing; mass movement for propulsion S: mucus (goblet cells) D: none (except by bacteria) A: ions, water, minerals, vitamins, and small organic molecles produced by bacteria
Figure 21-22
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Secretion: Stomach
Acid Secretion (Stomach) • • •
Cell Types
Substance Secreted Stimulus for Release
Mucus Opening of gastric gland
Mucous neck cell
Bicarbonate
Tonic secretion; with irritation of mucosa Secreted with mucus
Gastric acid (HCl) Parietal cells
Intrinsic factor
Enterochromaffinlike cell
Histamine Pepsin(ogen)
Acetylcholine, gastrin, histamine
Interstitial fluid H2O
Physical barrier between lumen and epithelium
H+
Buffers gastric acid to prevent damage to epithelium Activates pepsin; kills bacteria Complexes with vitamin B12 to permit absorption
Acetylcholine, gastrin
Stimulates gastric acid secretion
Acetylcholine; acid, secretin
Digests proteins
Gastric lipase
D cells
Somatostatin
Acid in the stomach
Inhibits gastric acid secretion
G cells
Gastrin
Acetylcholine, peptides and amino acids
Stimulates gastric acid secretion
Chief cells
Lumen of stomach
Function of Secretion
Capillary
Gastric mucosa
Parietal cells secrete hydrochloric acid (HCl) into the lumen of the stomach HCL breaks apart proteins, kills some bacteria Lumen can reach a pH of 1!!!!
H+ + OH–
ATP
CA
K+ K+
HCO3–
HCO3– CO2
Cl–
Cl –
Cl –
Cl –
Digests fats
Parietal cell
CA = Carbonic anhydrase
Figure 21-25
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Bicarbonate Secretion Pancrease)
Figure 21-6
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Secretion
• Anatomy of the exocrine and endocrine pancreas
• Bicarbonate secretion in pancreas
• Endocrine gland: Pancreatic Islets (Insulin, Glucogon) • Exocrine gland: Pancreatic ancini (Enzymes & Sodium Bicarbonate NaHCO3) • Into pancreatic duct and duodenum
(Similar in some small intestine and colonic cells)
• Bicarbonate neutralizes acidic chyme
Duct cells secrete NaHCO3
CL- HCO3 exchanger HCO3–
Pancreatic duct cell or duodenal cell
Interstitial fluid
H2O + CO2
CO2
CA HCO3– + H+
Na+
Cl–
Pancreatic islet cells
Capillary
Lumen of pancreas or intestine
Na+
Cl– CFTR channel
ATP
K+ Na+ 2 Cl– NKCC channel K+
Acinar cells
K+ Pancreatic acini
H2O, Na+
Figure 21-7
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Digestion and Absorption
H2O, Na+
Figure 21-8
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Digestion and Absorption
• Mechanical and chemical digestion occurs along entire system • GI secretions facilitate digestion • Most absorption occurs in small intestine • Villi and microvilli enhance surface area • Nutrients absorbed entire capillaries within villi • Except lipids which enter Lacteals
Brush border Microvilli
• A villus and a crypt in the small intestine • Increase surface area Enterocyte
KEY
M: motility S:secretion D:digestion A:absorption Salivary gland Upper esophageal sphincter Esophagus
(absorption & secrete enzymes)
ORAL CAVITY AND ESOPHAGUS
D: carbohydrates, fats (minimal) A: none
Enterocytes Capillaries
STOMACH
D: proteins, fats A: lipid-soluble substances such as alcohol and aspirin
Goblet cells
Lower esophageal sphincter Liver Gallbladder
Pylorus Pancreas
Ileocecal valve Rectum Anal sphincters Copyright © 2009 Pearson Education, Inc.
Crypt lumen
SMALL INTESTINE
D: carbohydrates, fats, polypeptides, nucleic acids A: peptides by active transport; amino acids, glucose, and fructose by secondary active transport; fats by simple diffusion; water by osmosis ions, minerals, and vitamins by active transport
Lacteals Crypt cells (secrete ions and water) stem cells Lamina propria
LARGE INTESTINE
D: none (except by bacteria) A: ions, water, minerals, vitamins, and small organic molecles produced by bacteria
Endocrine cells (hormones) Muscularis mucosae
Figure 21-22
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Figure 21-13
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Digestion and Absorption
Digestion and Absorption •
• ½ of what we eat is Carbs (starch and surgar) • break down into monosaccharides for transport
Glucose polymers
Carbohydrate absorption in the small intestine
digest to
Lumen of intestine
Starch, glycogen
Na+
Glucose or galactose
Fructose (not Na+ dependent)
Disaccharides
Amylase Maltose
Maltase
Sucrose
Lactose
Sucrase
Lactase
Na+
Intestinal mucosa
K+
Disaccharidases (brush border enzyme) Glucose enters the cell with Na+ on the SGLT symporter and exits on GLUT2. Fructose enters on GLUT5 and exits on GLUT2.
1 glucose + 1 glucose + 1 fructose 1 galactose
2 glucose
Monosaccharides
GLUT5
Figure 21-14
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Digestion and Absorption (Proteins) •
Not all proteins equally digestable • 2 groups of protein enzymes 1) Endopeptidase (protease) 2) Exopepatidase •
Figure 21-15
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Digestion and Absorption (Proteins)
Amino acids
Aminoterminal end
KEY SGLT GLUT2
Peptide bonds
Carboxyterminal end
H2N
COOH
• Note: Na/K+ pump helps maintain Na+ gradient for apical diffusion of Na+
(a) Peptide structure
Protease: digests internal peptide bonds. +H2O
Proteins
Peptides
Di- and tripeptides
COOH
H2N
H+
Digestion produces AAs, dipeptides, and tripeptides • Some larger proteins can be absorbed
H2N
H2N
COOH
(b)
H+
Small peptides are carried intact across the cell by
transcytosis.
Na+
COOH
2 smaller peptides Na+
Exopeptidase digests terminal peptide bonds to release amino acids. Aminopeptidase
Peptidases
Carboxypeptidase
+H2O
+H2O
K+ ATP
COOH
H2N
H+ H2N
Amino acids
cotransport with H+. cotransport with Na+.
COOH
H2N
Amino acid (c)
H2N
Na+
Na+
COOH
Amino acid
Blood
To the liver
COOH Peptide
Figure 21-16
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Digestion and Absorption (Fats)
Figure 21-17
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Digestion and Absorption (Fats)
• Triglycerides digest into monoglycerides and free fatty acids
Bile salts facilitate fat digestion - From liver -Coat lipid
Bile Salt
Bile salt-coated lipid droplet
Lipases also used to digest fat
Hydrophobic side associates with lipids.
Water
Triglyceride
Polar side chains (hydrophilic side associates with water)
Lipase, Colipase Bile salt Micelle
Free fatty acids
Cholesterol Bile salt
+ Monoglyceride Copyright © 2009 Pearson Education, Inc.
Monoglyceride
Phospholipids
Diglyceride
Free fatty acids Copyright © 2009 Pearson Education, Inc.
Figure 21-19
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Digestion and Absorption of Fats Bile salts from liver
1
1 Bile salts from liver coat fat droplets.
Large fat droplets from stomach
Bile salts recycle
Lipase 22 and colipase Micelles
3a Monoglycerides and fatty acids move out of micelles and enter cells by diffusion.
•
3b Cholesterol is transported into cells by a membrane transporter.
3b
3a
•
2 Pancreatic lipase and colipase break down fats into monoglycerides and fatty acids stored in micelles.
Emulsion Lumen of small intestine
Digestion and Absorption
4 Absorbed fats combine with cholesterol and proteins in the intestinal cells to form chylomicrons.
Smooth ER 4 Triglycerides + cholesterol + protein Cells of small intestine
5 Chylomicrons are released into the lymphatic system.
Chylomicron Golgi apparatus
• Iron: Heme by apical transporter Fe+ then removed and absorbed via transporter
5 Interstitial fluid Capillary
Nucleic acids are digested into nitrogenous bases and monosaccharides • Bases active transport • Monosaccharides Intestine absorbs vitamins and minerals • Fat-soluble vitamins (A,D,E,K) absorbed with fats • Water-soluble vitamins (C & Most B) by mediated transport • Except: Vitamin B12 attaches to intrinsic factor and absorbed in ileum (Needed for RBC production) • Minerals by active transport
• Or Free Fe+ Co-trapnsport with H+
Lacteal Lymph to vena cava
Figure 21-20
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Digestion and Absorption
Digestion and Absorption
• NaCl reabsorption in the small intestine and colon Lumen of small intestine or colon
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Intestinal cell
• Summary of motility, secretion, digestion, and absorption in different regions of the digestive system
Interstitial fluid KEY
K+ 1
Na+ 2
Na+
M: motility S:secretion D:digestion A:absorption
Na+ reabsorbed.
Salivary gland Upper esophageal sphincter
Na+
Cl–
ATP
Na+
K+ Esophagus
H+
Lower esophageal sphincter
HCO3– Cl–
Liver Gallbladder
Cl–
Pylorus Pancreas
Ileocecal valve
1 Na+ enters cells by multiple pathways. Copyright © 2009 Pearson Education, Inc.
2 The Na+-K+-ATPase pumps Na+ into the ECF.
Rectum Anal sphincters
Figure 21-21
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ORAL CAVITY AND ESOPHAGUS
M: swallowing, chewing S: saliva (salivary glands), lipase D: carbohydrates, fats (minimal) A: none STOMACH
M: peristaltic mixing and propulsion S :HCl (parietal cells); pepsinogen and gastric lipase (chief cells); mucus and HCO3– (surface mucous cells); gastrin (G cells); histamine (EC cells) D: proteins, fats A: lipid-soluble substances such as alcohol and aspirin SMALL INTESTINE
M: mixing and propulsion primarily by segmentation S: enzymes; HCO3– and enzymes (pancreas); bile (liver); mucus (goblet cells); hormones: CCK, secretin, GIP, and other hormones D: carbohydrates, fats, polypeptides, nucleic acids A: peptides by active transport; amino acids, glucose, and fructose by secondary active transport; fats by simple diffusion; water by osmosis ions, minerals, and vitamins by active transport LARGE INTESTINE
M :segmental mixing; mass movement for propulsion S: mucus (goblet cells) D: none (except by bacteria) A: ions, water, minerals, vitamins, and small organic molecles produced by bacteria
Figure 21-22
6
