chapter 21c
DESCRIPTION
Chapter 21c. The Digestive System. The Cephalic Phase. Chemical and mechanical digestion begins in the mouth Salivary secretion is under autonomic control Softens and lubricates food Chemical digestion: S alivary amylase and some lipase Saliva also has a protective function - PowerPoint PPT PresentationTRANSCRIPT
Chapter 21c
The Digestive System
The Cephalic Phase
• Chemical and mechanical digestion begins in the mouth
• Salivary secretion is under autonomic control• Softens and lubricates food
• Chemical digestion: Salivary amylase and some lipase
• Saliva also has a protective function• Chewing: mastication
Swallowing Reflex
Figure 21-24, step 1
Tongue pushes bolus against softpalate and back of mouth, triggeringswallowing reflex.
Hard palate
Tongue
Bolus
Epiglottis
Tonically contracted upperesophageal sphincter
Larynx
Soft palate
Glottis
1
Swallowing Reflex
Figure 21-24, step 2
Upper esophageal sphincter relaxeswhile epiglottis closes to keepswallowed material out of the airways.
Epiglottis
2
Swallowing Reflex
Figure 21-24, step 3
Food moves downward into theesophagus, propelled by peristalticwaves and aided by gravity.
3
The Gastric Phase
• Storage • Stomach
• Digestion • Stomach• Acid, enzymes, and signal molecules
• Protection
The Gastric Phase
• Activity of secretory cells of the gastric mucosa
Figure 21-25
Gastric mucosa
Openingof gastric
gland
Cell Types Substance Secreted Stimulus for Release Function of Secretion
Mucousneck cell
Mucus
Bicarbonate
Tonic secretion;with irritation ofmucosaSecreted withmucus
Physical barrier betweenlumen and epithelium
Buffers gastric acid toprevent damage toepithelium
Parietalcells
Gastric acid (HCl)
Intrinsic factorAcetylcholine,gastrin, histamine
Activates pepsin;kills bacteriaComplexes with vitaminB12 to permit absorption
Enterochromaffin-like cell Histamine Acetylcholine,
gastrinStimulates gastricacid secretion
Chief cellsPepsin(ogen)Gastric lipase
Acetylcholine; acid,secretin
Digests proteins
Digests fats
D cells Somatostatin Acid in the stomach Inhibits gastric acidsecretion
G cells GastrinAcetylcholine,peptidesand amino acids
Stimulates gastricacid secretion
The Gastric Phase
• Integration of cephalic and gastric phase secretion in the stomach
Figure 21-26
Lumen ofstomach
Gastric mucosa
Entericplexus
Chiefcell
Gastrin
Somatostatin
Amino acidsor peptides
Input viavagus nerve
Entericsensoryneuron
Entericsensoryneuron
ECLcell
G cell
D cell
H+
Food
Histamine
Pepsin Pepsinogen
Parietalcell
Negative feedbackpathway
Food or cephalic reflexesinitiate gastric secretion.
Gastrin stimulates acidsecretion by direct actionon parietal cells or indirectlythrough histamine.
Acid stimulates short reflexsecretion of pepsinogen.
Somatostatin release by H+
is the negative feedbacksignal that modulates acidand pepsin release.
1
2
3
4
1
2
3
4
1
+
The Gastric Phase
Figure 21-26, step 1
Lumen ofstomach
Gastric mucosa
Entericplexus
Gastrin
Amino acidsor peptides
Input viavagus nerve
Entericsensoryneuron
G cell
Food
Food or cephalic reflexesinitiate gastric secretion.
1
11
The Gastric Phase
Figure 21-26, steps 1–2
Lumen ofstomach
Gastric mucosa
Entericplexus
Gastrin
Amino acidsor peptides
Input viavagus nerve
Entericsensoryneuron
ECLcell
G cell
H+
Food
HistamineParietal
cell
Food or cephalic reflexesinitiate gastric secretion.
Gastrin stimulates acidsecretion by direct actionon parietal cells or indirectlythrough histamine.
1
2
1
2
1
The Gastric Phase
Figure 21-26, steps 1–3
Lumen ofstomach
Gastric mucosa
Entericplexus
Chiefcell
Gastrin
Amino acidsor peptides
Input viavagus nerve
Entericsensoryneuron
Entericsensoryneuron
ECLcell
G cell
H+
Food
Histamine
Pepsin Pepsinogen
Parietalcell
Food or cephalic reflexesinitiate gastric secretion.
Gastrin stimulates acidsecretion by direct actionon parietal cells or indirectlythrough histamine.
Acid stimulates short reflexsecretion of pepsinogen.
1
2
3
1
2
3
1
The Gastric Phase
Figure 21-26, steps 1–4
Lumen ofstomach
Gastric mucosa
Entericplexus
Chiefcell
Gastrin
Somatostatin
Amino acidsor peptides
Input viavagus nerve
Entericsensoryneuron
Entericsensoryneuron
ECLcell
G cell
D cell
H+
Food
Histamine
Pepsin Pepsinogen
Parietalcell
Negative feedbackpathway
Food or cephalic reflexesinitiate gastric secretion.
Gastrin stimulates acidsecretion by direct actionon parietal cells or indirectlythrough histamine.
Acid stimulates short reflexsecretion of pepsinogen.
Somatostatin release by H+
is the negative feedbacksignal that modulates acidand pepsin release.
1
2
3
4
1
2
3
4
1
+
The Gastric Phase
• The mucus-bicarbonate barrier of the gastric mucosa
Figure 21-27Capillary
Stomachlumen
Gastric juice pH ~ 2
Mucuslayer
Mucusdroplets
Gastricmucouscell
pH ~ 7 at cell surface
HCO3– HCO3
–
The mucus layer is a physical barrier.
Bicarbonate is a chemicalbarrier that neutralizes acid.
Reflexes of Cephalic and Gastric Phases
• Long and short reflexes of the cephalic and gastric phases of digestion
Figure 12-23
The Intestinal Phase
• Chyme in the small intestine inhibits gastric motility and secretion
Figure 21-28
Acid secretion
Gastric motility
Pepsin and lipase secretion
Entericnervoussystem
AcidHyper-
osmoticsolution
CarbohydratesFats,
proteins
? Endocrine cell
GIP GLP-1 CCK Secretin
Pancreaticbicarbonate
secretion
Pancreaticenzyme
secretion
Insulinsecretion
Foodinto
stomach
Chymeinto smallintestine
STOMACH
SMALLINTESTINE
PANCREAS
The Intestinal Phase
• Bicarbonate neutralizes gastric acid• Goblet cells secrete mucus for protection and
lubrication• Bile • Fat digestion
• Digestive enzymes• Enteropeptidase
The Intestinal Phase
• Activation of pancreatic zymogens
Figure 21-29
Lumen of small intestine
Intestinalmucosa
Pancreatic duct
• Chymotrypsinogen• Procarboxypeptidase• Procolipase• Prophospholipase
• Chymotrypsin• Carboxypeptidase• Colipase• Phospholipase
Pancreatic secretions(include inactive
zymogens)
Trypsinogen
Trypsin
Enteropeptidasein brush border
activates trypsin.
ZYMOGENS
ACTIVATED ENZYMES
activates
Hepatic Portal System
• Most fluid is absorbed in the small intestine
Figure 21-30
Aorta
Hepaticvein
Inferiorvena cava
Digestivetract arteries
Hepaticportal vein
Hepatic artery
Capillariesof liver
Capillaries of digestivetract: stomach, intestines,
pancreas, and spleen
Liver
The Intestinal Phase
• Most digestion occurs in small intestine• Large intestine concentrates waste for
excretion• Motility in large intestine• Mass movement triggers defecation• Defecation reflex
• Digestion and absorption in large intestine• Diarrhea can cause dehydration
The Intestinal Phase: Anatomy of the Large Intestine
Figure 21-31
RectumRectum
Internal anal sphincter
AnusExternal anal sphincter
Cecum
Appendix
IleumIleocecal valve
Ascendingcolon
Transverse colon
AortaHepatic portal vein
Inferior vena cava
Descendingcolon
Sigmoid colon
Haustra
Tenia coli
Circular muscle
Longitudinal layer(tenia coli)
Intestinalglands
Lymphoidnodule
Submucosa
Muscularisexterna
Muscularis mucosae
The Intestinal Phase: Anatomy of the Large Intestine
Figure 21-31 (1 of 3)
The Intestinal Phase: Anatomy of the Large Intestine
Figure 21-31 (2 of 3)
The Intestinal Phase: Anatomy of the Large Intestine
Figure 21-31 (3 of 3)
Immune Function
• M cells sample the contents of the gut• Immune cells secrete cytokines• Cytokines trigger inflammatory response• Increase in Cl–, fluid, and mucus secretion
• Vomiting is a protective reflex
Summary
• Function and processes• Digestion, absorption, motility, secretion, and
GALT• Anatomy• Motility• Tonic and phasic contractions• Slow wave potentials, interstitial cells of Cajal,
migrating motor complex, peristaltic contractions, and segmental contractions
Summary
• Secretion• Parietal cells, CFTR chloride channel, mucous
cells, goblet cells, saliva, and bile salts• Regulation• Short reflexes, ENS, long reflexes, intrinsic
neurons, gastrin family, secretin family, and other hormones
Summary
• Digestion and absorption• Amylase, disaccharidases, endopeptidases,
exopeptidases, lipase, colipase, micelles, chylomicrons, and intrinsic factor
• The cephalic phase• The gastric phase• Mucous cells, chief cells, D cells, ECL cells, and
G cells
Summary
• The intestinal phase• Brush border, mass movement, and defecation
reflex• Immune functions• M cells and vomiting