Download 21a +b + c

THIRD EDITION
HUMAN PHYSIOLOGY
AN INTEGRATED APPROACH
Dee Unglaub Silverthorn, Ph.D.
Chapter 21
Digestion
PowerPoint® Lecture Slide Presentation by
Dr. Howard D. Booth, Professor of Biology, Eastern Michigan University
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
About this Chapter
• Overview of the digestive system & how it is
organized
• How products are moved and the role of digestive
secretions
• How and where food is broken down and
absorbed
• How digestive wastes are concentrated and
eliminated
• How digestion is regulated in the gastrointestinal
(GI) tract
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Processes of the Digestive System: Overview
• Ingestion
• Digestion:
enzymatic
• Motility
• Secretion
• Absorption
• Elimination
• (Self protection)
Figure 21-1: Processes of the digestive system
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Digestive Anatomy: Overview
• Oral cavity
• Salivary glands
• Esophagus
• Stomach
• Fundus
• Body
• (rugae)
• Antrum
• pyloris
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Chemical and mechanical digestion in the mouth
• Saliva
• Lubricates and softens food
• Salivary amylase
• Breaks down starches into smaller carbs
• Mechanical digestion; mastication
• Protection
• Lysosomes and immunoglobulins kill viruses
and bacteria.
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 21-17: Integration of secretion in the stomach
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Intestinal Phase: ENDOCRINE RESPONSE
• The pyloric sphincter
sends chyme into the
duodenum in spurts.
• Acidic chyme in the
duodenum stimulates
hormone release into the
blood of:
• Secretin,
cholecystokinin, GIP
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Digestive Anatomy: Overview
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 21-2a: ANATOMY SUMMARY: The Digestive System
More Digestive Anatomy
• Small intestine
• Duodenum
• Jejunum
• Ileum
• Pancreas
• Liver
• Large intestine
• Colon
• Rectum
• Anus
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Digestive Anatomy: Histological Overview
• Stomach wall
• Mucosa
• Gastric glands
• Muscularis mucosa
• Submucosa
• Muscularis Externa
• Serosa
• Small intestine wall
• Vili & microvilli
• Peyer's patches
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Digestive Anatomy: Histological Overview
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 21-2c: ANATOMY SUMMARY: The Digestive System
Digestive Anatomy: Histological Overview
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 21-2e: ANATOMY SUMMARY: The Digestive System
Motility: Smooth Muscle Contractions
• Tonic – support
• Phasic – move
products
• Parastalsis –
moves 
• Segmentation –
mixes
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 21-4: Contractions in the GI tract
Digestive Secretions:
(7 L / Day From Tissues into Lumen)
• Salivary glands
• Pancreas
• Water
• Enzymes
• Mucus
• Ions: H+, K+, Na+
•
HCO3-, Cl-
• Mass Balance (H2O)
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 21-5: Daily mass balance in the digestive system
Chemistry of Digestion: Carbohydrates
• Complex carbohydrate foods
• Long polymers
• Enzyme hydrolysis
• Amylase
• Maltase
• Sucrase
• Lactase
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Chemistry of Digestion: Carbohydrates
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 21-6: Carbohydrate digestion
Chemistry of Digestion: Carbohydrates
• Disccharides
• Monosccharides
• (Absorption)
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Chemistry of Digestion: Proteins
• Proteins  enzyme
hydrolysis  amino acids
• Enzymes: endopeptidases
& exopeptidases
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 21-7: Endopeptidases and exopeptidases
Chemistry of Digestion: Fats
• Bile emulsification to small fat droplets
• Enzymes: lipases, colipases & phospholipases
• Triglycerides  monoglycerides & free fatty acids
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Chemistry of Digestion: Fats
Figure 21-8: Fat digestion
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Regulating Digestion: CNS and Enteric Nervous
System (ENS)
• Long (cephalic) reflexes: CNS, feed forward &
emotional reflexes
• Short reflexes – ENS ("little brain") 
integration, motility & secretion: enzymes &
hormone/paracrine GI peptides
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Regulating Digestion: CNS and Enteric Nervous
System (ENS)
Figure 21-9: The enteric nervous system
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Phases of Digestion: Overview
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 21-11: Overview of functions in different regions of the digestive system
Cephalic and Oral Phases of Digestion
• Cephalic: anticipation of food
• CNS  ANS long reflex
• Enteric  cells short reflex
• GI motility
• GI secretions
• Mouth: starts digestion
• Grind, mix & liquefy
• Saliva: water, enzymes, mucus & lysozyme
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Cephalic and Oral Phases of Digestion
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 21-12: Long and short reflexes in the stomach
Swallowing reflex: Soft Palate & Esophagus
• Deglutition
• Epiglottis
• Upper esophageal sphincter
• Lower esophageal sphincter
• (heartburn)
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Swallowing reflex: Soft Palate & Esophagus
Figure 21-13: The swallowing reflex
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Gastric Phase: The Stomach
• Storage
• Digestion
• HCl – parietal C.
• Lipase – chief C.
• Pepsin – chief C.
• Protect walls
• HCO3• Mucus
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Secretion in the Stomach
• Parietal cells – pH-1
• Chief cells – inactive pepsinogen  active pepsin
• D cells – somatostatin
• Enterochromaffin-like (ECL) cells – histamine
• G cells – the hormone gastrin.
• Mucuos cells – mucus and bicarbonate
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Gastric Phase: The Stomach
Figure 21-17: Integration of secretion in the stomach
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Gastric Phase: The Stomach
Figure 21-15: The mucus-bicarbonate barrier of the gastric mucosa
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Regulation of the Stomach Digestive Activities
• CNS – cephalic input
• ENS – ANS integration w/hormones &
paracrines
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Regulation of the Stomach Digestive Activities
Figure 21-17: Integration of secretion in the stomach
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Intestinal Phase: Reflexes Direct Digestive Action
• Limit chyme entrance rate & motility
• Neutralize HCl, add bile & enzymes
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Intestinal Phase: EXOCRINE RESPONSE
• Pancreatic bicarbonate secretions
• Secretin stimulates bicarbonate release.
• Neutralize HCl, add bile & enzymes
• Pancreatic exocrine enzyme secretions
• CCK stimulates pancreatic release of inactive enzymes
• Figure 21-20
• Liver adds bile via gall bladder
• CCK stimulates gall bladder contraction
• Bile; a non-enzyme
• Bile salts
• Act as detergents
• Bilirubin
• cholesterol
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Intestinal Phase: Pancreatic Secretions
• Enzymes
• HCO3• Insulin
• Glucagon
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 21-18: The intestinal phase of gastric function
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Intestinal Phase: Pancreatic Secretions
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 21-19: The hepatic portal system
Intestinal Phase:
Liver-Nutrient Storage & Conversions
• Bile secretion
• Hepatic portal system directs absorbed nutrients
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Intestinal Phase:
Liver-Nutrient Storage & Conversions
Figure 21-24: Carbohydrate absorption
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Intestinal Phase:
Carbohydrate Digestion & Absorption
• Hydrolysis to simple sugars
• Absorption: transport
• Na+/ glucose symport
• Fructose GLUT
• To ECF  capillary
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 21-23: Bile salts
Let’s remember what “fat” is. . .
• Phospholipids
• Triglycerides
• cholesterol
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Intestinal Phase: Fat Digestion & Absorption
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 21-26: Fat digestion and absorption
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Intestinal Phase:
Large Intestine, H2O Absorption & Defecation
• (Small intestine reabsorbs  7.5 L/day of water)
• Large Intestine reabsorbs 1.4 L/day
• Defecation Reflex: mass movement  rectal
distension
•  internal sphincter (invol) 
external sphincter (vol)
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Intestinal Phase:
Large Intestine, H2O Absorption & Defecation
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 21-27: Anatomy of the large intestine
Intestinal Phase:
Large Intestine Digestion & Absorption
• Bacterial digest significant amounts of complex
carbs and proteins through fermentation.
• Most remaining water is reabsorbed
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 21-28: NaCl reabsorption by colonocytes
Intestinal Phase:
Large Intestine Digestion & Absorption
• Bacterial
fermentation:
Vit. K , lactate &
buterate
• Water and
electrolyte
secretion &/or
absorption
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 21-28: NaCl reabsorption by colonocytes
Digestive Health: Protection & Problems
• Immune defense: M-cells, Peyer's patches,
lymphocytes
• Irritable bowel disease – chronic inflammation
• Diarrhea: leads to dehydration (4 million
deaths/yr)
• Osmotic-solutes prevent H2O reabsorption
• Secretory- bacterial toxins ("flush out'
pathogens)
• Vomiting (emesis) can lead to alkalosis
• Ulcers- H. pylori
• "heart-burn"  acid reflux disease
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Summary
• Processes of digestion: ingestion, digestion,
absorption, secretion, motility, reabsorption &
defecation
• Anatomy of digestion: mouth, esophagus, stomach,
small & large intestines, rectum, anus (pancreas &
liver)
• Enzyme hydrolysis of carbohydrates, proteins, lipids
and nucleic acids provide the nutrients, absorbed &
conducted to liver for storage
• Regulation from CNS (long reflex) and ENS (short
reflex) integrate hormones & paracrines to
coordinate digestion
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings