Download Chapter 21 - El Camino College

POWERPOINT® LECTURE SLIDE PRESENTATION
by LYNN CIALDELLA, MA, MBA, The University of Texas at Austin
Additional Text by J Padilla exclusively for Physiolgy at ECC
UNIT 4
21
PART A
The Digestive System
HUMAN PHYSIOLOGY
AN INTEGRATED APPROACH
DEE UNGLAUB SILVERTHORN
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
FOURTH EDITION
Basic Processes of the Digestive System
Molecular
movement
between GI lumen
& blood stream
happens in similar
fashion to what
happens in the
nephron but
instead of
reabsorption you
have absorption
and feces is
excreted instead
of urine
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 21-1
Digestive System Anatomy
Oral cavity  esophagus  stomach  small intestine
 large intestine  rectum
Accessory
Digestive Organs
include the
salivary glands,
pancreas, liver,
and gall bladder.
They are
structures that
work with the GI
tract to assist in
digestion
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 21-2a
Digestion
 Six processes in
digestion:
 Ingestion
 Mechanical
Digestion
 Chemical
Digestion
 Propulsion
 Absorption
 Defication
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Digestive System Anatomy
 Stomach- performs mechanical & chemical digestion,
absorption, secretion, and motility
 Fundus  body  antrum
 Pyloric valve (sphincter) – opposite side to the cardiac
sphincter- opens to allow chyme to move into the small
intestine
 Small intestine- Main functions include chemical digestion,
secretion, absorption, and motility
 Duodenum (where digestive juices are added)  jejunum
(digestion and absorption take place)  ileum (connects to large
intestine)
 Accessory organs: pancreas and liver - provide digestive
enzymes, buffers, and bile
 Large intestine: colon and rectum- absorbs, holds bacteria,
forms feces
 Anus-has voluntary and involuntary sphincters, uses a reflex
mechanism during defication
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Digestive System Anatomy
 Mucosa
 Epithelial cells- simple columnar epithelium
 Lamina propria- supportive layer of connective tissue
 Muscularis mucosae- smooth muscle
 Modifications increase surface area- villi, microvilli(on
plasma membrane), intestinal crypts and plicae circularis
 Submucosa – connective tissue layer with blood and
lymphatic vessels
 Muscularis externa – two layers of smooth muscle in
perpendicular direction- perform peristalsis
 Serosa – Connective tissue layer made by the visceral serosa.
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Digestive System Anatomy
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Digestive System Anatomy
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 21-2c
Digestive System Anatomy
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Motility
 Tonic contractions
 Sustained
 Smooth muscle sphincters and stomach
(fundic/cardiac region)
 Phasic contractions – have contraction-relaxation
cycles, occur in pyloric region and small intestine
 Last a few seconds
 Peristalsis moves bolus forward
 Segmentation mixes
**Contractions do occur when the GI tract is empty.
They serve to remove food remnants and bacteria from
upper GI areas. Irritable bowel syndrome is caused by
motility disorders.
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Motility: Contractions in the GI Tract
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 21-4a
Secretion
Daily mass fluid balance in digestive system
Input of fluids into
the GI tract comes
from what is
ingested, the
accessory organs,
and the epithelial
cells. Notice that
7L of fluid are
added by
digestive organs
and only 0.1 L is
excreted
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 21-5
Secretion
 Digestive enzymes secreted into mouth, stomach and
intestine - exocrine glands or epithelial cells produce
vesicles that protect the protein structure that is exocytosed.
Some enzymes are inactive or remain attached to the plasma
membrane.
 Mucous cells in stomach and goblet cells in intestine –
release mucins (glycoproteins) commonly called mucus. It
protects the lining and secretions increase with infections.
 Saliva is an exocrine secretion –it’s hyposmotic, contains
ions, mucus, and proteins (enzymes & antibody). Controlled
by autonomic NS, sympathetic reduces secretion.
 Liver secretes bile – produced by hepatocytes, contains
salts, pigments, and cholesterol. The salts assist in fat
digestion.
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Acid Secretion by Parietal Cells
Parietal cells in the
stomach epithelia
produce HCl- (pH 1).
Problems with the
chloride channel
lead to cystic
fibrosis. There are
transport proteins
similar to those in
the kidney tubule
cells that move ions.
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 21-6
Bicarbonate Secretion
The bicarbonate
neutralizes the acid
as it enters the
duodenum. Its
production uses
carbonic
anhydrase as in
kidney and RBCs.
Cl- enters cells to
exchange for
HCO3. H+ moving
into blood balance
out HCO3 input by
stomach cells.
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 21-8
Secretion
Cl– secretion by intestinal colonic crypt cells.
This process creates an isotonic sodium solution that mixes with
mucus and lubrincates gut contect
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 21-9
Regulation of GI Function
 Long reflexes integrated in CNS –classic neural
reflex, receptors are in or outside GI tract, CNS
intergrates reflex. Cephalic (feedforward) are
activated by somatic sensory input or emotions.
Parasympathetic excites and sympathetic inhibits.
 Short reflexes integrated in ENS – originate and
are integrated by enteric nerve plexus, take care of
local reflexes related to motility, secretion and
growth.
 Reflexes involving GI peptides – act as hormone
that travel in blood stream and even stimulate the
brain or paracrine siganls for local signaling at the
lumen or GI ECF. They excite or inhibit motilit,
absorption, and secretion.
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Regulation of GI Function
Shows short reflexes in
red arrows
KEY
Stimulus
Receptor
Integrating
center
Efferent pathway
Tissue response
Short reflexes
Local
stimulus
(pH, stretch,
osmolarity,
products of
digestion)
Sensory
receptors
and
neurons
Interneurons
Neurons
of
myenteric
and
submucosal
plexuses
Enteric nervous system
“The little brain”
Smooth
muscles
or
secretory
cells
Effectors
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Muscle contraction/relaxation
or
Exocrine secretion (enzymes,
mucus, acid, bicarbonate),
Paracrines
or
Endocrine secretions
Digestive system
responses
Figure 21-11 (1 of 3)
Regulation of GI Function
Shows long reflexes in blue arrows
External
stimulus
KEY
Stimulus
(sight, smell,
etc.)
Receptor
Sensory
receptors
Integrating
center
Efferent pathway
The
cephalic
brain
Local
stimulus
(pH, stretch,
osmolarity,
products of
digestion)
Sensory
receptors
and
neurons
Tissue response
Sympathetic and
parasympathetic
neurons
Neurons
of
myenteric
and
submucosal
plexuses
Long reflexes
Smooth
muscles
or
secretory
cells
Effectors
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Muscle contraction/relaxation
or
Exocrine secretion (enzymes,
mucus, acid, bicarbonate),
Paracrines
or
Endocrine secretions
Digestive system
responses
Figure 21-11 (2 of 3)
Regulation of GI Function
Integration of long and short reflexes in the digestive system
External
stimulus
KEY
Stimulus
(sight, smell,
etc.)
Receptor
Sensory
receptors
Integrating
center
Efferent pathway
The
cephalic
brain
Local
stimulus
(pH, stretch,
osmolarity,
products of
digestion)
Sensory
receptors
and
neurons
Interneurons
Tissue response
Short reflexes
Sympathetic and
parasympathetic
neurons
Neurons
of
myenteric
and
submucosal
plexuses
Enteric nervous system
“The little brain”
Long reflexes
Smooth
muscles
or
secretory
cells
Effectors
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Muscle contraction/relaxation
or
Exocrine secretion (enzymes,
mucus, acid, bicarbonate),
Paracrines
or
Endocrine secretions
Digestive system
responses
Figure 21-11 (3 of 3)
Regulation of GI Function
Reflexes involving signaling by GI Peptides
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 21-12
ENS versus CNS
Work independently of the brain and sensory organs,
responds to local stimuli in the same manner as lower level
organisms.
 Intrinsic neurons – neurons that lie completely within the
gut wall
 Neurotransmitters and neuromodulators – 30 different
types that are similar to those in the brain. Examplesserotonin, vasoactive intestinal peptide, nitric oxide.
 Support cells – serve a similar function as astroglia cells
 Diffusion barrier – capillaries around the ganglia have
reduced permeability as in the blood-brain barrier
 Integrating center –signals are processed in the ENS and
do not go out to the CNS for integration
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Digestive Hormones
See table 21-1, make flash cards for the molecule
 Gastrin family –hormone families
 Gastrin and CCK -controls secretion of stomach acid
and pacreatic enzymes and bicarbonate
 Secretin family – molecules that act at a site far from
its release, could be hormones or paracrines
 Secretin, VIP, GIP, and GLP-1 – some inhibit acid
secretion or stimulate insulin release in response to
glucose levels.
 Others -can’t be grouped with the ones above
 Motilin –targets smooth muscle to stimulate
movement in gut
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Digestion and Absorption
Summary of motility, secretion, digestion, and
absorption in different regions of the digestive system
There are three
phases in
digestion:
Cephalic phase
Gastric phase
Intestinal phase
PLAY Animation: Digestive System: Digestion and Absorption
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 21-22
The Cephalic Phase
This is the phase of digestion that begins with a stimulus
processed by the cerebrum and an efferent response from the
medulla oblongata. These are also digestive processes within
the head (cephalic) region.
 Chemical and mechanical digestion begins in the mouth –
chewing and mixing food with saliva
 Salivary secretion under autonomic control – sympathetic
decreases and parasympathetic increases activity.
 Softens and lubricates food – allows for better swallowing and
taste detection
 Chemical digestion: Salivary amylase and some lipase –
begin the breakdown of starches and very little fat
 Saliva is protection as well – lysozyme kills bacteria,
antibodies disable bacteria and viruses, fluid rinses mouth
 Chewing: mastication – creates a bolus appropriate for
swallowing
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Swallowing Reflex
Soft palate
closes off
nasopharynx
and
epiglottis
will close of
the larynx.
Upper
esophageal
sphincter
relaxes
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 21-24, step 1
Swallowing Reflex
At this point
respiration
is inhibited.
The larynx
is pushed
up slightly
to meet up
with the
epiglottis
and close
off the entry
point.
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 21-24, step 2
Swallowing Reflex
Peristalsis
moves food
down the
esophagus
until it
reaches the
esophageal
sphincter
(not a true
sphincter)
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 21-24, step 3
Swallowing Reflex
Swallowing is called deglutition. It
requires presice timing and coordination.
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 21-24
The Gastric Phase
 Storage - holding food in one organ and regulating the
flow into the next organ to optimize absorption
 Stomach – relaxes its walls to hold about 3.5 L daily, upper
half holds food, lower half digest
 Digestion – changing food/drinks by chemical or
mechanical digestion so that it can be absorbed
 Stomach – Parietal cells secrete gastric acid and intrinsic
factor, Chief cells secrete pepsinogens, gastric lipase,
 Acid, enzymes, and signal molecules – the acid activates
enzymes, denatures proteins, and targets pathogens,
stomach releases signal molecules and digestion
progresses
 Protection – acid kills pathogen and protects the body, the
stomach protects its lining from the strong acid
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The Gastric Phase
Activity of secretory cells of the gastric mucosa
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 21-25
The Gastric Phase
Two sources stimulate the secretion by stomach cells. Gcells are activated to release gastrin by stretching walls,
protein presence, and vagus stimulation. Gastrin is
inhibited by low pH and somatostatin
1
1
Food
Gastric mucosa
Enteric
sensory
neuron
Amino acids
or peptides
Lumen of
stomach
Input via
vagus nerve
G cell
1 Food or cephalic reflexes
initiate gastric secretion.
Gastrin
KEY
Stimulus
Enteric
plexus
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Receptor
Integrating
center
Efferent pathway
Figure
21-26, step 1
The Gastric Phase
Enterochrmaffin-like cells (ECL) is stimulated by
gastrin and ENS to secrete histamine that
stimulates parietal cells
1
1
Food
Gastric mucosa
Enteric
sensory
neuron
Amino acids
or peptides
Lumen of
stomach
H+
Input via
vagus nerve
G cell
Histamine
Parietal
cell
1 Food or cephalic reflexes
initiate gastric secretion.
2 Gastrin stimulates acid
secretion by direct action
on parietal cells or indirectly
through histamine.
Gastrin
2
ECL
cell
KEY
Stimulus
Enteric
plexus
Receptor
Integrating
center
Efferent pathway
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 21-26, steps 1–2
The Gastric Phase
Acid secretion by parietal cells stimulates a
chemoreceptor that signals a short reflex to activate
cheif cells to release pepisogen (protease)
1
1
Food
Gastric mucosa
Enteric
sensory
neuron
Amino acids
or peptides
Lumen of
stomach
3
Pepsin
G cell
Pepsinogen
3 Acid stimulates short reflex
secretion of pepsinogen.
ECL
cell
Enteric
sensory
neuron
Chief
cell
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
1 Food or cephalic reflexes
initiate gastric secretion.
2 Gastrin stimulates acid
secretion by direct action
on parietal cells or indirectly
through histamine.
Gastrin
2
Histamine
Parietal
cell
H+
Input via
vagus nerve
KEY
Stimulus
Enteric
plexus
Receptor
Integrating
center
Efferent pathway
Figure 21-26, steps 1–3
The Gastric Phase
D cells stimulated by low pH release somatostatin that
inhibits secretion of gastrin, histamine, and pepsinogen.
This process integrates cephalic and gastric secretion.
1
1
Food
Input via
vagus nerve
Gastric mucosa
Enteric
sensory
neuron
Amino acids
or peptides
G cell
Lumen of
stomach
+
2
Gastrin
2
Negative feedback
pathway
Histamine
4
ECL
cell
3
Enteric
sensory
neuron
Stimulus
Enteric
plexus
Chief
cell publishing as Benjamin Cummings
Copyright © 2007 Pearson Education, Inc.,
Pepsin
Pepsinogen
Somatostatin release by H+
is the negative feedback signal
that modulates acid and
pepsin release.
KEY
Parietal
cell
H+
Gastrin stimulates acid
secretion by direct action
on parietal cells or indirectly
through histamine.
3 Acid stimulates short reflex
secretion of pepsinogen.
Somatostatin
4
D cell
1 Food or cephalic reflexes
initiate gastric secretion.
Receptor
Integrating
center
EfferentFigure
pathway21-26,
steps 1–4
The Gastric Phase
The mucus-bicarbonate
barrier of the gastric
mucosa
Helicobacterpylori
bacteria can lead to
wall errosion =ulcer
Excess acid production
can be caused by a
pancreatic acid or
pain killers like
aspirin
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 21-27
The Intestinal Phase
The effects of intestinal-phase events on gastric
function
When chyme
moves into the
small intestinve
mechanism
reduce stomach
secretions and
activates the
pancreas to
release
digestive
enzymes
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 21-28
The Intestinal Phase
 Bicarbonate neutralizes gastric acid – produced by
the pancreas it is secreted into the doudenum as the
chyme enters to neutralize the acid
 Goblet cells secrete mucus for protection and
lubrication – the thin mucus layer also contains
bicarbonate
 Bile – produced by the liver, concentrated at the gall
bladder, it is released through the pancreas.
 Fat digestion – bile salts are unaltered during fat
digestion and recycled. Other components of bile like
bilirubin and wastes are excreted in feces
 Digestive enzymes – most are secreted as zymogens
 Enteropeptidase – converts inactive trypsinogen to
trypsin that changes others into active forms
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Activation of Pancreatic Zymogens
Enzymes are
secreted by
the pancreas
or enteric
cells, those
that in active
are activated
in teh lumen
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 21-29
Hepatic Portal System
Most fluid is absorbed in the small intestine
Capillaries in the
small intestine
connect to veins that
lead into the liver.
The liver filters the
blood removing
harmful substances
(xenobiotics) before
they enter into
circulation
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 21-30
The Intestinal Phase
 Most digestion occurs in small intestine – takes over 17 enzymes released
by the pancreas to finish protein digestion. Pancreatic amylase completes
carbohydrate secretion. Fats enter as an emulsion and digestion is completed with
bile and pancreatic enzymes.
 Large intestine concentrates waste for excretion – 1.5L of unabsorbed
chyme moves to large intestine, water is absorbed until there is about 0.1L of water
left
 Motility in large intestine– segmentation contractions continue
 Mass movement triggers defecation – colonic contraction that moves chyme
along colon
 Defecation reflex –
Digestion and absorption in large intestine – bacteria perform fermenation
to digest complex carbs to provide energy molecules for colonocytes. They
produce vitamin K and other vitamins and gas.
 Diarrhea can cause dehydration – lose stools contain a large amount of
unabsorbed water. Sometimes it is cause by osmotic diarrhea, or copious diarrhea or
secretory diarrheas
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Anatomy of the Large Intestine
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 21-31
Anatomy of the Large Intestine
Defecation reflex –spinal reflex similar to urination
triggered by fecal movement into rectum. Emotional
state also influences
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 21-31c
Immune Function
 The GI tract is the largest immune organ because of the
high amount of pathogen that enter daily.
 M cells sample the contents of the gut – antigen bind
receptors, they move into the cell, and out to the interstitial
fluid where macrophages are activated. Salmonella and
Shigella enter through this mechanism.
 Immune cells secrete cytokines – in high danger conditions
cytokines call a large number of immune cells
 Cytokines trigger inflammatory response – inappropriate
response to normal gut contents
 Increase in Cl–, fluid, and mucus secretion – non-specific
immune mechanisms
 Vomiting is a protective reflex –(emesis) is by reverse
peristalsis from the small intestine up. It is a long reflex so it
can be trigger by other stimuli processed by the cerebrum
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings