DIGESTIVE PROCESSES
&
REGULATION
KEY CONCEPTS




As a multi-cellular organism, the human body
requires a system to acquire and dismantle nutrients
so that they become available to cells around the
body.
Contraction and secretion along the alimentary canal
is triggered by mechanical and chemical stimuli and
mediated through complex neural and hormonal
pathways that may be intrinsic or extrinsic.
The triggers, controls, and pacing of contraction and
secretion vary at different locations along the
alimentary canal, and may even include influence
from higher brain centers.
Gastrointestinal disturbances of contraction and
secretion are highly prevalent.
LEARNING OUTCOMES
1.
Explain the common principles for regulating
contraction and secretion along the alimentary
canal.
2.
Explain the receptors/stimuli, control pathways,
and pacing of contraction and secretion at each
location of the alimentary canal.
3.
Discuss causes, consequences, and potential
interventions for gastrointestinal disturbances
of contraction and secretion.
To what necessary life functions does the digestive system
contribute?...
What is the relationship between the digestive system and
the survival needs?...
What are the anatomical and physiological relationships
between the digestive system and other body systems?...
Why is a digestive system needed?...
What is unique about the location of digestive functions
compared to other body processes?...
What are the major activities of the alimentary canal?
COMPREHENSION CHECK
Mechanical digestion occurs in the following organs except
______________.
A.
Stomach
B.
Small intestine
C.
Mouth
D.
Large intestine
RECEPTORS & STIMULI
What types of receptors/stimuli are involved in regulating digestive
functions?

Mechanoreception


Respond to stretch of organ by food in lumen
Chemoreception

Respond to osmolality, pH, products of digestion
CONTROL PATHWAYS
What control pathways are involved in regulating digestive functions?



Extrinsic

Long reflexes of CNS and autonomic (parasympathetic)
neural pathways

Higher brain centers
Intrinsic

Short reflexes mediated by “enteric plexuses”

Hormones
Control dis-assembly line pace

Slow down stomach

Speed up bowel emptying
COMPREHENSION CHECK
Extrinsic control of digestive processes involve the following
components except __________________.
A.
CNS
B.
enteric neurons
C.
ANS
D.
hormones

Which digestive functions can be regulated?
COMPREHENSION CHECK
How does the parasympathetic division control the salivary
glands and gallbladder?
A.
Increases secretion
B.
Decreases secretion
C.
Variable influence
D.
No effect
COMPREHENSION CHECK
What is the enteric nervous system?
A.
Consists of the parasympathetic division
B.
Made up of sympathetic nerves
C.
Contains interconnected enteric neurons
D.
Found in the wall of the digestive tract
COMPREHENSION CHECK
Modified true or false:
Statement 1: Long reflex is an extrinsic reflex.
Statement 2: Short reflex uses afferent and efferent nerve
signals to and from the brain.
A.
Both statements are true.
B.
Both statements are false.
C.
Only statement A is true.
D.
Only statement B is true.
COMPREHENSION CHECK
If the parietal cells are damaged, which macromolecule is not
digested in the stomach?
A.
Protein
B.
Fat
C.
Nucleic acid
D.
Carbohydrates
COMPREHENSION CHECK
The following substances are released by enteroendocrine
cells except ________________.
A.
Serotonin
B.
Somatostatin
C.
Lipase
D.
Histamine
SALIVA SECRETION
What receptor/stimuli and control pathways are involved in saliva
secretion?

Mechano & chemoreception (strong acids)

Extrinsic: facial (VII) & glossopharyngeal (IX)
How much saliva is produced per day?

1 L/day
COMPREHENSION CHECK
Which gland releases sticky saliva?
A.
Parotid
B.
Submandibular
C.
Buccal
D.
Sublingual
What receptors/stimuli and control pathways are involved in
mastication and deglutition?
MASTICATION & DEGLUTITION



Voluntary reflex & involuntary
mechanoreception
Extrinsic: trigeminal (V), hypoglossal (XII),
glossopharyngeal (IX), & vagus (X)
Deglutition involves complex coordination of
voluntary and involuntary contractions of over 22
different muscles
Voluntary
Involuntary
ESOPHAGEAL PERISTALSIS
What receptors/stimuli and control pathways are involved in
esophageal peristalsis?

Mechanoreception

Extrinsic: vagus (X)
How long does esophageal peristalsis take?
~ 1-2 sec. fluid
 ~ 4-8 sec. solid

STOMACH CONTRACTION
What receptors/stimuli and control pathways are involved in stomach
motility and emptying?





Mechanoreception
Extrinsic:
Intrinsic:
Intrinsic:
Intrinsic:
vagus (X)
pacemaker cells in smooth muscle (3/min.)
gastrin hormone from stomach stimulates
small intestine plexus/hormones inhibit
How long does it take to completely empty the stomach?

~ 4 hrs. for complete emptying
COMPREHENSION CHECK
The following components are involved in stomach motility
and emptying except _______________.
A.
Gastrin
B.
Pacemaker cells
C.
Vagus nerve
D.
Lipase
What are the three phases of stomach secretion?...
CEPHALIC PHASE OF STOMACH SECRETION
What receptors/stimuli and control pathways are involved in the
cephalic phase of stomach secretion?

Perception of food & chemoreception (smell, taste)

Extrinsic: vagus (X)
Occurs:

Minutes or less to elicit response
COMPREHENSION CHECK
What induces the cephalic phase of stomach secretion?
A.
Stretch of oral cavity
B.
Short reflex
C.
Long reflex
D.
Smell of food
What receptors/stimuli and control pathways are involved in
the gastric phase of stomach secretion?
GASTRIC PHASE



Mechano and chemoreception (peptides, caffeine)
Extrinsic: vagus (X)
Intrinsic: gastrin (triggered by chemoreception) from
stomach stimulates
Occurs:


3-4 hrs.
Produces 2/3 of gastric juice

~ 3 L/day of enzymes and HCl
What receptors/stimuli and control pathways are involved in
the intestinal (enterogastric reflex) phase of stomach
secretion?
COMPREHENSION CHECK
What is an enterogastric reflex?
A.
Stimulation of contraction of stomach wall
B.
Inhibition of acid secretion
C.
Use of short reflex
D.
Use of long reflex
INTESTINAL PHASE
(ENTEROGASTRIC REFLEX)

Mechano & chemoreception (low pH) in
duodenum
Intrinsic: plexus signals from small intestine
inhibit
 Intrinsic: secretin, cholecystokinin (CCK), &
vasoactive intestinal peptide (VIP) from
duodenum inhibit


Timeframe parallels gastric phase
COMPREHENSION CHECK
What is the importance of the vasoactive intestinal peptide?
A.
Constrict the blood vessels in intestine
B.
Increase release of gastrin
C.
Relaxes smooth muscles of intestine
D.
Inhibits intestinal absorption
COMPREHENSION CHECK
The following events inhibit the phases of stomach secretion
except ______________.
A.
Very low pH
B.
Presence of irritants in duodenum
C.
Secretin and CCK
D.
Peptides
COMPREHENSION CHECK
Which of the following events does not occur in the formation
of HCl in the stomach?
A.
Bicarbonate ion is exported into the blood.
B.
Chloride ion enters the interstitial space from the
enterocytes.
C.
H+ exits the parietal cell through the H+-K+ ATPase.
D.
Carbonic acid splits into H+ and bicarbonate in the
parietal cell.
SMALL INTESTINE SEGMENTATION
THEN PERISTALSIS
What receptors/stimuli and control pathways are involved in small
intestine segmentation and peristalsis?




Mechanoreception
Extrinsic: vagus (X)
Intrinsic: pacemaker cells in smooth muscle (up to 14/min.
depending on segment)
Intrinsic: plexus signals (gastroileal reflex) and gastrin from
stomach stimulate movement of chyme out of ileum
How long does segmentation and peristalsis
take?

~ 2 hrs. x 2 (3-6 hrs.)
COMPREHENSION CHECK
What is the importance of the gastroileal reflex?
A.
Causes peristalsis
B.
Leads to segmentation
C.
Constricts the ileocecal valve
D.
Maintains the pH in the stomach
BILE RELEASE
What receptors/stimuli and control pathways are involved in bile
release?

Chemoreception (acidic/fatty chyme) in
duodenum
Extrinsic: vagus (X)
 Intrinsic: CCK from duodenum stimulates

PANCREATIC JUICE RELEASE
What receptors/stimuli and control pathways are involved in pancreatic
juice release?

Chemoreception (acidity, protein, & fat) in
duodenum
Extrinsic: vagus (X)
 Intrinsic: secretin & CCK from duodenum
stimulate release of bicarbonate & enzymes,
respectively

COMPREHENSION CHECK
What are the target organs of CCK?
A.
Small intestine and stomach
B.
Gallbladder and hepatopancreatic sphincter
C.
Liver and pyloric sphincter
D.
Ileocecal valve and cardiac sphincter
COLON MOTILITY & EMPTYING
What receptors/stimuli and control pathways are involved in colon
motility and emptying?




Mechanoreception
Extrinsic: vagus (X)
Intrinsic: haustral contractions (every 30 min.)
Intrinsic: mass movements (gastrocolic reflex) ( 3-4 times
daily)
How long does it take to completely empty the
colon?

12-24 hrs. for complete emptying
DEFECATION
What receptors/stimuli and control pathways are involved in defection?


Involuntary mechanoreception & voluntary reflex
(Valsalva’s maneuver)
Extrinsic: sacral nerves
COMPREHENSION CHECK
What type of reflex is involved in defecation?
A.
Enterogastric
B.
Gastroileal
C.
Gastrocolic
D.
Spinal
COMPREHENSION CHECK
What is happening to the external anal sphincter during the
passage of feces through the anus?
A.
Stimulated
B.
Inhibited
C.
Constricted
D.
Relaxed
What are the causes and consequences of gastrointestinal
disturbances of contraction and secretion? Interventions?
https://www.niddk.nih.gov/health-information/digestive-diseases
https://medlineplus.gov/ency/article/007447.htm
https://my.clevelandclinic.org/health/articles/7040gastrointestinal-diseases
Conclusion
IN-CLASS LECTURE QUIZ
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Mechanoreceptors detect distention of the gut wall due to the presence of
food molecules. (True, False)
Long reflexes involve nerve signals outside the digestive system. (True,
False)
Enteroendocrine cells of the stomach are more important than other cells
of the gastric gland. (True, False)
Swallowing or deglutition is a voluntary process until food reaches the
stomach. (True, False)
Pacemakers cells are found in the esophagus and stomach. (True, False)
The four phases of stomach secretion occur at the same time. (True,
False)
The gastroileal reflex helps move chyme. (True, False)
The enterogastric reflex occurs in low pH. (True, False)
Gastrocolic reflex occurs only in the large intestine. (True, False)
The spinal reflex is a function of the parasympathetic division. (True,
False)