Download Chapter 24 The Digestive System Lecture Outline

Chapter 24 The Digestive System Lecture Outline
Digestive system
1. Alimentary canal / Gastrointestinal tract /
Digestive tract
oral cavity, pharynx, esophagus,
stomach, small intestine,
large intestine, rectum, anus
2. Accessory organs
teeth, tongue, salivary glands,
liver, gallbladder, pancreas
Functions
1. ingestion
2. propulsion
peristalsis
3. mechanical processing
4. chemical digestion
5. secretion
6. absorption
7. excretion
defecation: feces
Control
1. Neural: Enteric Nervous System
A. Short reflexes: ENS
B. Long reflexes: ENS + ANS
2. Hormonal
enteroendocrine cells
3. Local
prostaglandins
histamine
Location
Peritoneal cavity
Parietal peritoneum
Visceral peritoneum
Peritoneal fluid
Ascites
Peritonitis
Mesenteries
Peritoneal organs
Retroperitoneal organs
Lesser omentum
Falciform ligament
Greater omentum
Blood supply
Hepatic portal circulation
Histology
1. Mucosa
A. Epithelium
goblet cells
stratified squamous epithelium
simple columnar epithelium
B. Lamina propria
areolar connective tissue
MALT
tonsils
C. Muscularis mucosae
Amy Warenda Czura, Ph.D.
2. Submucosa
dense irregular connective tissue
exocrine glands
Submucosal Nerve plexus
3. Muscularis externa
smooth muscle
sphincters
Myenteric Nerve Plexus
4. Serosa or Adventitia
serosa = visceral peritoneum, mesothelium
adventitia = dense irregular C.T.
Movement
peristalsis
segmentation
ENS
ANS
parasympathetic = ↑ activity
sympathetic = ↓ activity
Anatomy and Physiology
1. Oral cavity
Structure
stratified squamous epithelium
cheeks
tongue
hard palate
soft palate
Functions:
1. analyze (taste buds)
2. process (chew)
3. lubricate (saliva)
4. digest (amylase)
Accessory organs
A. Tongue
papillae
taste buds
Functions:
1. speech
2. manipulate
3. compress bolus
4. analyze
5. secretions
a. mucin
b. lingual lipase
B. Salivary glands
Saliva:
-water
-enzymes (amylase)
-buffers
-mucin
-antibodies (IgA)
-antimicrobials (lysozyme, defensins)
Functions:
1. cleanse
2. dissolve
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SCCC BIO132 Chapter 24 Handout
3. moisten
4. digestion
5. buffer
Glands:
1. Parotid
2. Sublingual
3. Submandibular
dry mouth
C. Teeth
mastication
Pulp cavity
Dentin
Odontoblasts
Crown
Enamel
hydroxyapatite
Root
Cementum
Periodontal ligaments
Alveolus
Types:
1. Incisors
2. Cuspids
3. Bicuspids
4. Molars
Wisdom teeth
20 deciduous teeth
32 permanent teeth
Impacted tooth
Dental caries
Periodontal disease
2. Pharynx
Oropharynx
Laryngopharynx
stratified squamous epithelium
tonsils
3. Esophagus
Gastroesophageal sphincter
Gastroesophageal reflux disease (Heart burn)
Features:
1. stratified squamous epithelium
2. lumen folds
3. esophageal glands
4. skeletal muscle
5. adventitia
Deglutition
1. Buccal phase
2. Pharyngeal phase
3. Esophageal phase
4. Stomach
Functions:
1. storage
2. mechanical breakdown
3. chemical breakdown
4. intrinsic factor: Vitamin B12
Chyme
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Regions:
1. Cardia
gastroesophageal sphincter
gastric glands: mucus
2. Fundus
3. Body
gastric glands: acid + enzyme
4. Pyloric region
pyloric sphincter
gastric glands: hormones
Histology
Rugae
Oblique muscle
simple columnar epithelium
Goblet cells
Gastric pits
gastric glands
Gastric glands
Cardia
mucus
Fundus & Body
1. Parietal cells
A. intrinsic factor
B. H+ & Cl-kill microbes
-denature proteins
-digestion
-activate pepsin
2. Chief cells
A. pepsinogen → pepsin
B. rennin
Pyloric
1. G cells
gastrin
2. D cells
somatostatin
Gastritis
Peptic ulcer
Helicobacter pylori
Regulation:
1. ANS
2. ENS
3. Hormones
Phases:
1. Cephalic phase
parasympathetic
secretions
Gastrin
2. Gastric phase
A. Neural response
ANS + ENS
Parietal & Chief cells
G cells
B. Hormonal response
Gastrin
Parietal and Chief cells
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SCCC BIO132 Chapter 24 Handout
motility
C. Local response
Histamine
Parietal cells
3. Intestinal phase
A. Neural response
Enterogastric reflex
B. Hormonal response
1. lipids
Cholecystokinin
Gastric Inhibitory Peptide
2. acid pH
Secretin
3. proteins
Gastrin
5. Small intestine
A. Duodenum
Pyloric sphincter
Duodenal ampula
Hepatopancreatic sphincter
B. Jejunum
C. Ileum
Peyers patches
Ileocecal valve
Histology
1. Plicae
2. Villi
3. Microvilli: brush border
Lacteals
Glands
1. Goblet cells
2. Intestinal glands in crypts
A. Intestinal juice
B. Lysozyme
C. Hormones
Intestinal gastrin
Cholecystokinin
Secretin
Gastric Inhibitory Peptide
Vasoactive Intestinal Peptide
Somatostatin
D. Epithelial cells
Brush border enzymes
3. Duodenal glands
Secretion
Parasympathetic
Enterocrinin
Intestinal movements
Myenteric reflexes: ENS
Gastroenteric reflex: ANS
Gastroileal reflex: ANS
Emesis reflex
Emetic center: medulla oblongata
6. Pancreas
A. Pancreatic islets
Insulin
Amy Warenda Czura, Ph.D.
Glucagon
B. Pancreatic acini
Pancreatic juice
enzymes + buffers
1. Secretin
2. Cholecytokinin
Enzymes: proenzymes
1. Pancreatic alpha amylase
2. Pancreatic lipase
3. Nucleases
4. Proteolytic enzymes
a. Proteases
b. Peptidases
Enterokinase
Trypsinogen
Trypsin
Pancreatitis
Diabetes mellitus
7. Liver
Lobes
Left
Right
Caudate
Quadrate
Falciform ligament
Ligamentum teres
Lobules
Interlobular septa
Central vein
Portal triad
Hepatic artery
Hepatic portal vein
Bile duct
Hepatocytes
Sinusoids
Kupffer cells
1. pathogens & debris
2. iron
3. lipids
4. heavy metals
Bile pathway:
Bile canaliculi
Bile duct
Common hepatic duct
Cystic duct
Common bile duct
Ampula
Hepatopancreatic sphincter
Liver functions:
1. Metabolic regulation
2. Hematological regulation
A. blood reservoir
B. phagocytosis & antigen presentation
C. hormones
D. antibodies
E. toxins
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F. plasma proteins
3. Bile synthesis
Components
water, electrolytes
bilirubin
cholesterol
phospholipids
bile salts
Emulsification
Enterohepatic circulation
Secretin
Hepatitis
Cirrhosis
8. Gallbladder
Bile
Cholecystokinin
Gall stones
Cholecystitis
Secretion and Absorption in Small Intestine
1. Neural
A. ANS
sympathetic
parasympathetic
2. Hormones of duodenum
A. Enterocrinin
B. Intestinal gastrin
C. Gastric inhibitory peptide
D. Secretin
E. Cholecystokinin
F. Vasoactive Intestinal Peptide
G. Somatostatin
9. Large intestine
Functions:
1. absorb water
2. absorb vitamins & electrolytes
3. store, compact feces & defecation
Bacteria
Vitamin K
Biotin
Vitamin B5
Stercobilins & urobilins
Fermentation products
Flatus
Histology
Teniae coli
Haustra
Intestinal glands
Lymphoid nodules: MALT
Simple columnar epithelium
Goblet cells
Subdivisions
A. Cecum
Ileocecal valve
Appendix
Appendicitis
B. Colon
Amy Warenda Czura, Ph.D.
1. Ascending
2. Transverse
3. Descending
4. Sigmoid
Diverticulitis
C. Rectum
Anal canal
Internal anal sphincter
External anal sphincter
Movements
1. Haustral contractions
2. Mass movements
3. Defecation reflex
Diarrhea
Constipation
Chemical digestion
Hydrolysis
Carbohydrate
Amylases: tri-, disaccharides
Brush border enzymes: monosaccharides
Facilitated diffusion & Cotransport
Lactose intolerant
Lipids
Lipases: monoglycerides & fatty acids
Micelles with bile salts
Chylomicrons
Lacteals
Protein
Pepsin + acid: polypeptides
Proteases & peptidases: amino acids
Facilitated diffusion & Cotransport
Nucleic acids
Nucleases: nucleotides
Brush border enzymes: nitrogenous bases,
pentose sugar, phosphate ions
Active transport
Water
Osmosis
Ions
Na+, Ca++, K+, Mg++, Fe++, Cl-, I-, HCO3Diffusion, Cotransport, Active transport
Vitamins
Fat soluble (A,D, E, K): chylomicrons
Water soluble (B, C): diffusion
Vitamin B 12: intrinsic factor
Age
↓ cell division ↑ ulcer
↓ smooth muscle function
↑ constipation
↑ diverticulitis
↑ hemorrhoids
↑ gastroesophageal reflux disease
↑ damage, ↑ cancer
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SCCC BIO132 Chapter 24 Handout
Digestive System
Alimentary canal / Gastrointestinal tract (G.I.):
Accessory digestive organs:
Oral cavity
Teeth
Pharynx
Tongue
Esophagus
Salivary glands
Stomach
Liver
Small intestine
Gallbladder
Large intestine
Pancreas
Rectum
Anus
Amy Warenda Czura, Ph.D.
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SCCC BIO132 Chapter 24 Handout
Histology of G.I.
1. Mucosa (Mucous membrane)
Functions to secrete mucus, digestive enzymes, and hormones, to absorb end products of digestion, and
provide protection from pathogens
A. Epithelium (continuously renewed, surface cells last only 2-6 days)
Stratified squamous: oral cavity, pharynx, esophagus, anus
Simple columnar: stomach, intestine: has goblet cells (mucus) and enteroendocrine cells (hormones)
B. Lamina propria
Loose areolar connective tissue with blood vessels, lymphatic vessels, nerves, mucous glands and
lymphoid tissue (extending from submucosa): MALT (mucosa associated lymphatic tissue e.g.
Peyer’s patches) or tonsils
C. Muscularis mucosae
Bands of smooth muscle and elastic fibers: one layer circumferential one longitudinal
Functions to change shape of plicae and villi
Villi: finger-like projections of the mucosa layer; increase surface area
Plicae (small intestine): folds of mucosa and submucosa; increase surface area
Rugae (stomach): pleats of mucosa and submucosa; expand to accommodate volume
2. Submucosa
Dense irregular connective tissue, contains large vessels, glands to secrete digestive enzymes and mucus,
houses the Submucosal Nerve Plexus (autonomic nervous system control of glands and smooth
muscle of mucosa)
3. Muscularis Externa
Consists of inner circular layer and outer longitudinal layer of smooth muscle for mixing and moving
lumenal contents, circular layer thickened to create sphincters at junctions to prevent backflow
Contains the Myenteric Nerve Plexus to control G.I. mobility via local reflex arcs and ANS stimulation
4. Serosa or Adventitia
Serosa = visceral peritoneum: areolar connective tissue plus mesothelium, covers all abdominal /
peritoneal G.I. tract organs
Adventitia = dense irregular connective tissue, anchors organs to surrounding tissues, covers oral cavity,
pharynx, esophagus, and rectum
Amy Warenda Czura, Ph.D.
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SCCC BIO132 Chapter 24 Handout
Regulation of gastric activity
Prepares stomach for food
Triggered by seeing, smelling, or thinking of food
Lasts a few minutes
Neural response: parasympathetic ANS triggers increase in all
gastric secretions (mucus, enzymes, acid) and triggers G cells
to release Gastrin (causes secretion and motility)
Initiates stomach digestive activities
Triggered by food entering stomach (stimuli = distension,
peptides, low acidity)
Lasts 3-4 hours (Three responses:)
Neural response: stretch receptors activate ENS reflexes and
parasympathetic ANS innervation, both stimulate secretions
from parietal cells (acid), Chief cells (pepsin) and G cells
(Gastrin)
*(Sympathetic stimulation
shuts down gastric secretion
via somatostatin from D
cells)
Hormonal response: triggered by neural response, peptides and
increased pH, G cells release Gastrin which trigger secretion by
parietal and chief cells and also gastric mobility
Local response: triggered by distortion, Mast cells release
histamine which stimulates parietal cells
Controls chyme entry into duodenum
Triggered by chyme entering duodenum
Lasts many hours
*Greatest acid production
via 3-fold stimulation of
parietal cells:
1. Ach from ENS &
parasympathetic ANS
2. Gastrin from G cells
3. Histamine from Mast
cells
Involves excititory and inhibitory control of
gastric activity depending on chyme
composition
Neural response: stretch receptors trigger
Enterogastric Reflex which turns off ENS and
parasympathetic stimulation of G cells and
stimulates sympathetic stimulation of pyloric
sphincter (contracts)
Hormonal responses: (different hormones
depending on chyme composition):
Lipids, carbohydrates, peptides →
Cholecystokinin and Gastric Inhibitory Peptide:
inhibit gastric secretion and motility (also
stimulates pancreas + gallbladder secretion)
Low pH → Secretin: inhibits gastric secretion
(also stimulates pancreas and liver secretion)
Proteins → Intestinal Gastrin: stimulates parietal
and chief cells, stimulates gastric mobility
Amy Warenda Czura, Ph.D.
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SCCC BIO132 Chapter 24 Handout
Coordination of Secretion and Absorption in the Small Intestine:
1. Neural Mechanisms
A. ANS:
parasympathetic = increase digestive activity
sympathetic = decrease digestive activity
B. ENS reflexes:
coordinate movement of materials from one region to next
2. Hormonal Mechanisms
Hormones from intestinal glands of duodenum control small intestine, stomach, and accessory
organs to coordinate digestive activities
A. Enterocrinin:
released when chyme enters duodenum, stimulates mucus production in duodenum
B. Intestinal Gastrin:
released when chyme contains protein, stimulates gastric activity
(“activity” = secretion and motility)
C. Gastric Inhibitory Peptide:
released when chyme contains lipids and carbohydrates, inhibits gastric activity
D. Secretin:
released when chyme is acidic, stimulates release of bile from liver and buffers from
pancreas, and reduces gastric activity
E. Cholecystokinin:
released when chyme contains lipids and peptides, stimulates:
-secretion of enzymes from pancreas,
-contraction of gallbladder for bile release
-relaxes hepatopancreatic sphincter to allow entry of bile and enzymes into
duodenum
-inhibits gastric activity
-reduces hunger sensation (20min post food consumption)
F. Vasoactive Intestinal Peptide:
released when chyme enters duodenum, inhibits gastric secretion, stimulates intestinal
secretion, dilates local capillaries for absorption
G. Somatostatin:
released in response to sympathetic stimulation,
-inhibits gastric activity
-inhibits secretion from pancreas and gallbladder
-inhibits blood flow to intestine thus inhibiting absorption
Amy Warenda Czura, Ph.D.
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SCCC BIO132 Chapter 24 Handout
Amy Warenda Czura, Ph.D.
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SCCC BIO132 Chapter 24 Handout
Substance
Digestion Method
Absorption Method
Carbohydrates Amylases (saliva, pancreas):
polysaccharides → di- and trisaccharides
Brush Border Enzymes (small intestine):
di- and trisaccharides → monosaccharides………………... Facilitated diffusion or Cotransport of monosaccharides
Lipids
Bile salts (liver):
emulsification
Lipases (tongue, pancreas)
triglycerides → monoglycerides and fatty acids…………... Micelles form: monoglycerides, fatty acids and bile salts
Micelles absorbed by intestinal epithelium,
proteins added = chylomicron (water soluble)
Chylomicrons exocytosed into lumen
Chylomicrons absorbed by lacteal
Proteins
Mastication (mouth)
Churning (stomach)
Pepsin + Acid (stomach)
protein → polypeptide
Proteases + Peptidases (pancreas, brush border)
polypeptide → amino acids……………………………….. Facilitated diffusion or Cotransport of amino acids
Nucleic Acids Nucleases (pancreas)
nucleic acid → nucleotides
Brush Border Enzymes (small intestine)
nucleotides → nitrogenous bases + sugar + phosphate ions Active transport of nitrogenous bases + sugar + phosphate ions
Water
No digestion required
Osmosis (95% in small intestine)
2L from food, 7L from secretions
(~150ml lost in feces)
Ions
No digestion required
Na+, Ca++, K+, Mg++, Fe++, Cl-, I-, HCO3Diffusion, Cotransport, Active Transport
Vitamins
No digestion required
Fat soluble: A, D, E, K…………………………………….. Mixed with fats in micelle → chylomicrons (fat soluble)
Water soluble: most B vitamins, C………………………... Diffusion (water soluble)
Vitamin B12………………………………. Bound to intrinsic factor, binds receptors, endocytosed (B12)
Digestion And Absorption
Summary of all the hormones involved in digestion:
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SCCC BIO132 Chapter 24 Handout