Download Digestive Ch23-part 1

Ch. 23 The Digestive System
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I. Basic Concepts & Processes Shared By
Most Digestive Organs
A. Two Groups of Organs:
1.
Alimentary canal =
•
1.
Organs: Students Do
Accessory digestive organs =
B. Digestive Processes (Text p. 1040)
1.
Ingestion
Ingestion
2.
Propulsion
• Peristalsis
Propulsion
3.
Mechanical digestion
• Mastication
Mechanical
Digestion
• Segmentation
4.
Chemical digestion
5.
Absorption
6.
Defecation
Absorption
Defacation
Propulsion& Segmentation
From
mouth
(a) Peristalsis: successive
waves of contraction move food
distally (1-way).
(b) Segmentation: Food
mixing/slow food propulsion
occurs.
Figure 23.3
C. Control of Digestive Processes
1. Mechanical and Chemical#3
stimuli STUDENTS DO
2. Nervous System Control:
a) Extrinsic: via CNS & autonomic nerves
• Use long reflexes (brain to gut)
b) Intrinsic = Enteric Nerves
• In digestive organs-- Use short reflexes
• Submucosal nerve plexus: within submucosa
• Myenteric nerve plexus within muscularis externa
• Myenteric nerve plexus
• Submucosal nerve plexus
4. Hormonal Controls
• Stomach
• Gastrin:
• Small Intestine
• Secretin:
• Cholecystokinin (CCK)
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D. Blood Supply: Splanchnic Circulation
Celiac trunk
Branches of Abdominal Aorta
• Students Do
• Celiac Trunk
• Superior mesenteric
• Inferior mesenteric
• Hepatic
Superior
mesentericPortal
artery Vein
Inferior mesenteric artery
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E. Peritoneum Students Do
• Peritoneum, Greater Omentum, Mesentery
Dorsal
mesentery
Parietal
peritoneum
Visceral
peritoneum
Ventral
mesentery
Alimentary
canal organ
Liver
Peritoneal
cavity
Figure 23.5a
F. Histology of Alimentary Canal
1. Mucosa
• Epithelium
• Lamina Propria
• Areolar
• Lympoid Follicles:
= collection of small
lymphoid nodules
• Part of MALT =
Mucus-Associated
• Muscularis Mucosae
2. Submucosa
• Areolar
• Many vessels
• Glands (Duodenal in s.i.)
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Mucosa
Muscularis
Muscosae
Lympoid
Follicles
2. Submucosa …
• Lympathic tissue (Lymph
Nodules in s.i.)
• Submucosal nerves
plexus
3. Muscularis externa
•
Circular (inner)
•
Sphincters
•
Longitudinal
•
Myenteric nerve
plexus
4. Serosa = Visceral Peritoneum
• Areolar
• Mesothelium (simple squ.)
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Submucosa
Histology of Alimentary Canal …
Nerve
Artery
Vein
Mesentery
Gland in mucosa
Lymphatic
vessel
#6
Glands in submucosa
Mucosa
• Epithelium
• Lamina propria
• Muscularis
mucosae
Submucosa
Muscularis
externa
• Longitudinal
muscle
• Circular muscle
Serosa
• Epithelium
• Connective
tissue
Lumen
Mucosa-associated
lymphoid tissue (MALT)
II. Digestive System Organs of the Head and
Thorax: Anatomy & Function
A. The Mouth & Associated Organs
Students Do Following
1. Mouth Anatomy
•
•
•
2.
Tissue Lining:
Palate: Hard &Soft
Uvula:
Overall Functions:
• Ingestion, Mechanical
Digestions
• Chemical digestion:
amylase
• Swallowing (Deglutition)
2. The Tongue STUDENTS DO
• Composition:
• Functions: 3
• Bolus
Lingual
Lipase
Lingual
Tonsil
3. The Salivary Glands
Students Do
• 3 pairs of Glands
• Functions
• Composition of Tongue
Saliva
of
1. Lubrication Ducts
sublingual
gland
2. hydration of food
3. chemical digestion
Sublingual
gland
4. protection from
microbes
(clinical medium)
Parotid
gland
Parotid duct
Masseter muscle
Body of
mandible (cut)
Submandibular
gland
Submandibular
duct
B. Pharynx
• Regions: Students Do
• Stratified squamous e.t.
• skeletal muscle
• Propulsion
Oropharynx
Laryngopharynx
C. Esophagus = propulsion only
• Muscular tube
• Esophageal hiatus
• Upper & Lower Esophageal
Sphincters (Lower =
Gastroesophageal Sphincter)
• Histology:
stratified
squamous
D. Digestive Processes: Mouth to Esophagus-SWALLOWING (Text p. )
STUDENTS DO FOLLOWING
1) MOUTH: Voluntary
(Buccal) Phase - tongue
presses against hard palate;
bolus oropharynx.Bolus of food
Tongue
Pharynx
Epiglottis
Glottis
Trachea
Uvula
Bolus
Epiglottis
Esophagus
2) Pharyngeal (-Esophageal) Phase: uvula and larynx block
airways. Upper esophageal sphincter relaxes and pharynx
muscles force bolus into esophagus. Upper esophageal
sphincter closes
Figure 23.13, step 2
Bolus
Gastroesophageal
sphincter opens
3) Esophageal Phase:. And Bolus moved to stomach by
peristalsis; Gastroesophageal (a.k.a. cardiac) sphincter
opens, food  stomach.
Figure 23.13, step 3
III. Digestive Organs of the Abdomen-Pelvis
Cardia
A. The Stomach:
1. Overall Functions
a) Store Food
b) Mechanical D.
c) Chemical D. Proteins
d) Intrinsic Factor
Lesser
2. Gross
curvature
Anatomy
a) Regions
• Body
• Cardia
• Pyloric
Duodenum
Pyloric Region
• Fundus
b) Rugae
Fundus
Serosa
Body
Rugae of
mucosa
Greater
curvature
Pyloric sphincter
Figure 23.14a
A. The Stomach …
Cardia
2. Gross Anatomy …
c) Curvatures
• Greater
• Lesser
d) Sphincters
• Cardiac
• Pyloric
Fundus
Serosa
Body
Lesser
curvature
Rugae of
mucosa
Greater
curvature
Duodenum
(a)
Pyloric Region
Pyloric sphincter
Figure 23.14a
2. Gross Anatomy …
e) Mesentaries
• Lesser omentum
• From liver to lesser
curvature
• Greater omentum
• Drapes from greater
curvature
• Anterior to small intestine
Lesser
omentum
Greater
omentum
The Stomach: …
Gross Anatomy …
f) Muscular tunic has
extra 3rd layer –
inner most oblique
layer = churning
action
Cardia
• Slide: difficult Lesser
to
see; is thin curvature
Fundus
Serosa
Body
Rugae of
mucosa
Greater
curvature
Duodenum
(a)
Pyloric
Pyloric
antrum
canal
Pyloric sphincter
(valve) at pylorus
Figure 23.14a
3. Microscopic Anatomy of the
Stomach
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3. Microscopic Anatomy of Stomach …
a) Mucosa
i) Simple Columnar E.T. in loops
Goblet cells
ii) Gastric Pits lead to the 
• Gastric Glands which produce
• Gastric Juice– mostly from
Fundus and Body
iii) Cells of Gastric Glands
• Muscus Neck Cells
o Alkaline mucus– bicarbonate
rich
o Function: protect cells from
pH1.5 – 3.5 gastric juice
o In all stomach regions
w/
Esophagus
Stomach
Gastric Pits
Mucous neck
cells
Gastric Glands
Figure 23.12b
STOMACH
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a) Mucosa
iii) Gastric Gland Cells …
Gastric pits
• Parietal Cells
o Function: Hydrochloric
Acid (HCl) for activation
of enzyme pepsinogen Gastric
and intrinsic factor for pit
B12 absorption in small
intestine)
Pepsinogen
HCl
Pepsin
o HCl also kills bacteria
Gastric
gland
Surface
epithelium
(mucous cells)
Mucous neck
cells
Parietal cell
Chief cell
o Slide: Round, large,
pinkish cells
Enteroendocrine cell
(b) Enlarged view of gastric pits
and gastric glands
a) Mucosa
iii) Gastric Gland Cells …
• Chief Cells
o Function: produce
enzyme Pepsinogen
o HCl Activates it to
Pepsin
o Most numerous cells
o Slide: Small, purplish
cells
• Enteroendocrine cells
o G cells:
o Function: produce
hormones Gastrin,
Histamine which
promote secretion of
gastric juices w/ HCl
and Pepsinogen
Gastric pits
Gastric
pit
Surface
epithelium
(mucous cells)
Mucous neck
cells
Gastric
gland
Parietal cell
Chief cell
Enteroendocrine cell
(b) Enlarged view of gastric pits
and gastric glands
Stomach
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4. Digestive Processes Occurring in the Stomach
a) Introduction
i) Secretions: Up to 3L gastric juices
per day secreted
ii) Nervous Control:
• Parasympathetic NS via Vagus
Nerve: stimulates glands
• Sympathetic NS: depress
secretary action
• Enteric Plexuses
iii) Hormonal Control
• Gastrin, most important hormone
Stimulates secretion of enzymes,
HCl, & intestinal enzymes
iv) Stimulus: Head, Stomach, and
Small Intestine
4. Digestive Processes occurring in the Stomach …
b. Regulation of Gastric
Cephalic
Secretion
phase
• 3 Phases
i) Cephalic (reflex) phase: a
few min.
Stimulatory events
1 Sight and thought
of food
Cerebral cortex
Conditioned reflex
2 Stimulation of
taste and smell
receptors
Hypothalamus
and medulla
oblongata
Vagus
nerve
• Gets stomach ready for
digestive processes
• Long Reflexes from CNS to
Enteric Ganglia
Stomach
secretory
activity
Figure 23.17
• Conditioned Reflex
(1) Sight and Thoughts  Hypothalamus  Medulla nuclei
 Vagus Nerve  Ach/Stomach  increased secretions
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a. Cephalic Phase …
(2) Taste and Smell  Cephalic
phase
Hypothalamus 
Medulla vagal nuclei 
vagus nerve  Ach/
stomach  ↑ secretion of
gastric juices
•
Inhibitory Events: From
Cerebrum-- Depressed
or not hungry then 
Parasympathetic NS. Not
stimulated  Cephalic
Phase inhibited
Stimulatory events
1 Sight and thought
of food
Cerebral cortex
Conditioned reflex
2 Stimulation of
taste and smell
receptors
Hypothalamus
and medulla
oblongata
Vagus
nerve
Stomach
secretory
activity
Figure 23.17
Figure 23.17
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2. Regulation of …
b. Gastric Phase– 3-4 hours, after food first enters stomach
• Produces 2/3 gastric juice produced
(1) Stomach distention  Myenteric Reflex (local)  AND
Vagovagal Reflex =  Vagus  Medulla  Vagus 
 at Stomach AcH released  increased gastric juices

(2) Food Chemicals (proteins) & Rising pH 
Chemoreceptors  activate G cells (enteroendocrine
cells)  Gastrin (hormone)  increased HCl secretion by
Parietal Cells Stimulatory events
Inhibitory events
Gastric
phase
1 Stomach
Vagovagal
1 Stomach reflexes
distension
Vagovagal
activates
distension
reflexes
stretch
activates
receptors
stretch
Local
receptors
reflexes
Local
reflexes
Medulla
Medulla
Vagus
nerve
Vagus
nerve
2 Food chemicals
G cells
Gastrin
(especially
peptides and
2
release
G
cells
Gastrin
Food chemicals
caffeine) and rising pH
to blood
release
(especially
peptides
activate
chemoreceptors
to blood
Stimulate
Inhibit
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and caffeine) and
rising pH activate
chemoreceptors
Presence
Ach
Gastrin
secretion
Gastrin
declines
secretion
declines
Overrides
parasymOverrides
pathetic
parasymcontrols
pathetic
controls
Stomach
secretory
Stomach
activity
secretory
activity
Enterogastric
reflex
G cells
G cells
Excessive
1. 1Excessive
acidity
acidity
(pH <2)
(pH
<2)
in stomach
in stomach
2 Emotional
Sympathetic
upset
nervous
Sympathetic
system
nervous
2. Emotional
activation
system
upset
activation
Local
reflexes
1
Figure 23.17
(2) Food Chemicals …
• The increase in acidity activates pepsinogen to pepsin so that
proteins can be digested
Inhibitory Events
• Negatie Feedback Loop:
• Acidity: Low H+ (High pH) stimulates release of Gastrin
• High H+ (low pH) inhibits release of Gastrin
• Emotional distress– activates sympathetic N.S.
Stimulatory events
Gastric
phase
Stimulate
Inhibit
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1 Stomach
Vagovagal
1 Stomach reflexes
distension
Vagovagal
activates
distension
reflexes
stretch
activates
receptors
stretch
Local
receptors
reflexes
Local
reflexes
Medulla
Medulla
Inhibitory events
Vagus
nerve
Vagus
nerve
2 Food chemicals
G cells
Gastrin
(especially
and
2 Foodpeptides
chemicals
G cells release
Gastrin
caffeine)
and rising
pH and
(especially
peptides
to blood
release
activate
chemoreceptors
caffeine)
and rising pH
to blood
activate chemoreceptors
Ach
Gastrin
secretion
Gastrin
declines
secretion
declines
Overrides
parasymOverrides
pathetic
parasymcontrols
pathetic
controls
Stomach
secretory
Stomach
activity
secretory
activity
Entero-
G cells
G cells
Sympathetic
nervous
Sympathetic
system
nervous
activation
system
activation
Local
1 Excessive
1 Excessive
acidity
(pHacidity
<2)
in stomach
(pH <2)
2 in
Emotional
stomach
2 Emotional
upset
upset
1
c. Intestinal Phase
• In Duodenum
• Begins when stomach begins
to empty chyme to duodenum
• Two parts: Excitatory and
Inhibitory
Intestinal
phase
EXCITATORY PART
• Brief effect
(1) Partially digested food
(including fats), low pH, &
hypertonic solution 
release Intestinal Gastrin 
Stomach glands continue to
secrete gastric fluids briefly
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Stimulatory events
1 Presence of low
pH, partially digested
foods, fats, or
hypertonic solution
in duodenum when
stomach begins to
empty
Stimulate
Inhibit
Intestinal
(enteric)
gastrin
release
to blood
Stomach
secretory
activity
Brief
effect
Figure 23.17
c. Intestinal Phase …
INHIBITORY PART
(1) Distension of Duodenum, very low pH, fats, part dig.
proteins, & irritants  Enterogastric Reflex inhibits
gastric secretion and closes the Pyloric Sphincter
Function: to move a small bit of chyme into duodenum
and to protect it from over-distension
(2) Distension of Duodenum, …  Release of intestinal
Figure 23.17
Hormones
Intestinal Phase …
• Cholecystokinin (CCK)
Inhibitory events
• Secretin
• TO BE CONTINUED
UNDER SM. INTESTINE
Stomach
secretory
activity
Enterogastric
reflex
Local
reflexes
Vagal
nuclei
in medulla
Pyloric
sphincter
Stimulate
Inhibit
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1 Distension
of duodenum;
presence of
fatty, acidic,
hypertonic
chyme, and/or
irritants in
the duodenum
2 Distension;
Release of intestinal
presence of
hormones (secretin,
cholecystokinin, vasoactive fatty, acidic,
partially
intestinal peptide)
digested food
in the
duodenum
B. Small Intestine
1. Gross Anatomy
• 2–4 m long;
• Subdivisions
1. Duodenum– 10
inches
2. Jejunum– 8 feet
3. Ileum– 12 feet
a) Duodenum
• Most chemical dig.
& absorption
occurs here
• Receives bile from
liver & enzymes
and bicarbonate
from pancreas
Small
intestine
Duodenum
Jejunum
Ileum
a. Duodenum …
i) Hepatopancreatic Ampulla: Bulb-like point where Bile duct & main
pancreatic duct join
• Major Duodenal Papilla: Volcano-shaped opening into
Duodenum H. Ampulla attached and releases contents to
Papilla  Duodenum
• Hepatopancreatic Sphincter: at Ampulla/Papilla junction
ii) Plicae Circulares—deep folds of mucosa and submucosa
Bile duct and sphincter
Major duodenal
papilla
Plicae
Circulares
Hepatopancreatic
Main pancreatic duct
and sphincter
b. Jejunum
• Attached to Duodenum
• Location In central and lower part of
Abdominal Cavity
• Coiled
c. Ileum
• Attached to Jejunum
• Location– same
• Coiled
•
Both framed by Large Intestine
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2. Microscopic Anatomy
Small Intestine
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2. Microscopic Anatomy …
a. Mucosa w/ folds & loops
i) Villi—loops of mucosa (epithelia = scattered goblets
among absorptive cells)
• Blood vessels, nerves, and lacteal
• Cells with Microvilli: small loops at apical side of
cells; form brush border
• Digestive Enzymes embedded in microvilli
• Function of folds and loops:
Small Intestine
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2. Microscopic Anatomy …
ii) Intestinal Glands (Crypts) in
Mucosa = tubular glands b/n
villi
• Secretory cells epithelium
produce intestinal juice: water,
some mucus, slightly alkaline
(pH =7.4-7.8) and low in
enzymes
Lacteal
• Enteroendocrine cells
(secrete CCK, secretin among
others)
Absorptive cells
Goblet cell
Vilus
Intestinal crypt
iii) Lamnia Propria
- agregations of intestinal
nodules (MALT)
Duodenal gland
Enteroendocrine
cells
Venule
Lymphatic vessel
Submucosa
b) Submucosa of small intestine
Areolar Tissue
• Peyer’s patches =
aggregated lymphoid
follicles; increase towards
end sm. int. They protect
distal areas against bacteria
• Have lymphocytes
• Duodenal (Brunner’s)
glands: of duodenum
secrete alkaline
(bicarbonate)mucus to
neutralize the acidic chime
coming in from stomach
c. Muscularis Externa
d. Serosa
Duodenal gland
Submucosa
Peyer’s Patches
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Small Intestine
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END PPT
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Review Questions
The mucosa of the lower pharanx and esophagus has
_________
__________ epithelia.
stratified squamous
___________,
Deglutition i.e. swallowing, involves over 22 muscle
groups and moves a _________
bolus from the oral cavity to
the stomach.
Review Questions
amylase which is responsible
Enzymes in saliva include _________,
for starch breakdown.
2I, 1C, 2PM, 3M
Review Questions
Short reflexes of the GI tract are housed and
completed within _____
enteric ____
nerve ______
plexuses while
long
_______
reflexes involve the CNS.
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Review Questions
In the small intestine, ___________
plicae circulares
__________,
__________,
and ___________
villi
microvilli all contribute to
expanding the surface area for adequate
__________.
absorption
Review Questions
From the esophagus to the anus, the GI tract contains how
many layers?
4: mucosa, submucosa, muscularis externa, serosa
Which 2 layers contain smooth muscle?
Mucosa & muscularis externa
Participating…
gastric phase is responsible for the production of
The _________
most gastric secretions by releasing the hormone
gastrin
_________.
What other 2 hormones promote gastric secretions?
ACh and Histamine
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Review Questions
Parietal cells of _______
gastric glands produce HCl and
________
___________
__________. __________
cells produce
intrinsic factor
Chief
pepsinogen.
What is intrinsic factor for?
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B12 absorption
Stimulatory events
Cephalic
phase
Gastric
phase
1 Sight and thought
of food
Cerebral cortex
Conditioned reflex
2 Stimulation of
taste and smell
receptors
Hypothalamus
and medulla
oblongata
1 Stomach
distension
activates
stretch
receptors
Vagovagal
reflexes
1 Presence of low
pH, partially digested
foods, fats, or
hypertonic solution
in duodenum when
stomach begins to
empty
Stimulate
Inhibit
Medulla
Vagus
nerve
Vagus
nerve
Local
reflexes
2 Food chemicals
G cells
(especially peptides and
caffeine) and rising pH
activate chemoreceptors
Intestinal
phase
Inhibitory events
Gastrin
release
to blood
Intestinal
(enteric)
gastrin
release
to blood
Lack of
stimulatory
impulses to
parasympathetic
center
Cerebral
cortex
Gastrin
secretion
declines
G cells
Overrides
parasympathetic
controls
Sympathetic
nervous
system
activation
1 Excessive
acidity
(pH <2)
in stomach
2 Emotional
upset
Stomach
secretory
activity
Enterogastric
reflex
Brief
effect
1 Loss of
appetite,
depression
Local
reflexes
Vagal
nuclei
in medulla
Pyloric
sphincter
1 Distension
of duodenum;
presence of
fatty, acidic,
hypertonic
chyme, and/or
irritants in
the duodenum
2 Distension;
Release of intestinal
presence of
hormones (secretin,
cholecystokinin, vasoactive fatty, acidic,
partially
intestinal peptide)
digested food
in the
duodenum
Figure 23.17
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Stimulatory events
Cephalic
phase
Gastric
phase
1 Sight and thought
of food
Cerebral cortex
Conditioned reflex
2 Stimulation of
taste and smell
receptors
Hypothalamus
and medulla
oblongata
1 Stomach
distension
activates
stretch
receptors
Vagovagal
reflexes
1 Presence of low
pH, partially digested
foods, fats, or
hypertonic solution
in duodenum when
stomach begins to
empty
Stimulate
Inhibit
Medulla
Vagus
nerve
Vagus
nerve
Local
reflexes
2 Food chemicals
G cells
(especially peptides and
caffeine) and rising pH
activate chemoreceptors
Intestinal
phase
Inhibitory events
Gastrin
release
to blood
Intestinal
(enteric)
gastrin
release
to blood
Lack of
stimulatory
impulses to
parasympathetic
center
Cerebral
cortex
Gastrin
secretion
declines
G cells
Overrides
parasympathetic
controls
Sympathetic
nervous
system
activation
1 Excessive
acidity
(pH <2)
in stomach
2 Emotional
upset
Stomach
secretory
activity
Enterogastric
reflex
Brief
effect
1 Loss of
appetite,
depression
Local
reflexes
Vagal
nuclei
in medulla
Pyloric
sphincter
1 Distension
of duodenum;
presence of
fatty, acidic,
hypertonic
chyme, and/or
irritants in
the duodenum
2 Distension;
Release of intestinal
presence of
hormones (secretin,
cholecystokinin, vasoactive fatty, acidic,
partially
intestinal peptide)
digested food
in the
duodenum
Figure 23.17
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b) Intrinsic = Enteric Nervous System (Gut Brain)
• CNS is linked via extrinsic long ANS fibers
Intrinsic nerve plexuses
• Myenteric nerve plexus
• Submucosal nerve plexus
Gingivae (gums)
Hard palate
Soft palate
Uvula
Palatine tonsil
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Posterior wall
of oropharynx
•
•
•
•
Serous & Mucous Cells
Water content
Enzyme =
Mucin
Control of Salivation:
Parasym. Sys. via chemo& mechano-receptors
100 million
bacteria/mL of saliva!
Hiatal hernia
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Homeostatic Imbalance
• Peptic or gastric ulcers: erosion of stomach wall
• Helicobacter pylori bacteria
Bacteria
Mucosa
layer of
stomach
(a) A gastric ulcer lesion
(b) H. pylori bacteria
Regulation of Gastric Secretion
Stimulatory events
Cephalic
phase
Gastric
phase
Cerebral cortex
Conditioned reflex
2 Stimulation of
taste and smell
receptors
Hypothalamus
and medulla
oblongata
Vagovagal
reflexes
1 Presence of low
pH, partially digested
foods, fats, or
hypertonic solution
in duodenum when
stomach begins to
empty
Stimulate
Inhibit
Copyright © 2010 Pearson Education, Inc.
Medulla
Vagus
nerve
Vagus
nerve
Local
reflexes
2 Food chemicals
G cells
(especially peptides and
caffeine) and rising pH
activate chemoreceptors
Intestinal
phase
Inhibitory events
1 Sight and thought
of food
1 Stomach
distension
activates
stretch
receptors
Figure 23.17
Gastrin
release
to blood
Intestinal
(enteric)
gastrin
release
to blood
Lack of
stimulatory
impulses to
parasympathetic
center
Cerebral
cortex
Gastrin
secretion
declines
G cells
Overrides
parasympathetic
controls
Sympathetic
nervous
system
activation
1 Excessive
acidity
(pH <2)
in stomach
2 Emotional
upset
Stomach
secretory
activity
Enterogastric
reflex
Brief
effect
1 Loss of
appetite,
depression
Local
reflexes
Vagal
nuclei
in medulla
Pyloric
sphincter
1 Distension
of duodenum;
presence of
fatty, acidic,
hypertonic
chyme, and/or
irritants in
the duodenum
2 Distension;
Release of intestinal
presence of
hormones (secretin,
cholecystokinin, vasoactive fatty, acidic,
partially
intestinal peptide)
digested food
in the
duodenum
Regulation of Gastric Secretion
Stimulatory events
Cephalic
phase
Gastric
phase
1 Sight and thought
of food
Cerebral cortex
Conditioned reflex
2 Stimulation of
taste and smell
receptors
Hypothalamus
and medulla
oblongata
1 Stomach
distension
activates
stretch
receptors
Vagovagal
reflexes
Medulla
Vagus
nerve
Vagus
nerve
Local
reflexes
2 Food chemicals
G cells
(especially peptides and
caffeine) and rising pH
activate chemoreceptors
Intestinal
phase
Inhibitory events
1 Presence of low
pH, partially digested
foods, fats, or
hypertonic solution
in duodenum when
stomach begins to
empty
Gastrin
release
to blood
Intestinal
(enteric)
gastrin
release
to blood
Inhibit
Cerebral
cortex
Gastrin
secretion
declines
G cells
Overrides
parasympathetic
controls
Sympathetic
nervous
system
activation
1 Loss of
appetite,
depression
1 Excessive
acidity
(pH <2)
in stomach
2 Emotional
upset
Stomach
secretory
activity
Enterogastric
reflex
Local
reflexes
Vagal
nuclei
in medulla
Pyloric
sphincter
Brief
effect
Stimulate
Copyright © 2010 Pearson Education, Inc.
Lack of
stimulatory
impulses to
parasympathetic
center
Figure 23.17
1 Distension
of duodenum;
presence of
fatty, acidic,
hypertonic
chyme, and/or
irritants in
the duodenum
2 Distension;
Release of intestinal
presence of
hormones (secretin,
cholecystokinin, vasoactive fatty, acidic,
partially
intestinal peptide)
digested food
in the
duodenum
3. Gastric Motility & Emptying
• Stretch-Relaxation Response: Relaxes to recieve food, then
contracts
• Contractile Activity: Pacemaker cells (in smooth muscle) initiate
bi-directional peristalsis 3X a min = BER (basic electrical rhythm)
• Stimulated by neural and hormonal factors
each
• Stomach & Duodenum coordinated: 3 mL chyme  duodenum/time
• Emptying time: 4 hours normally, if much fat up to 6 hours
Pyloric
valve
closed
2. Grinding: Most
Propulsion:
Peristaltic waves vigorous peristalsis/
move from fundus mixing action occur
near pylorus.
toward pylorus.
1
Pyloric
valve
slightly
opened
Retropulsion: Small
amounts of chyme enter
duodenum, most moves
backward = more mixing
3.
Figure 23.19