Download Anatomy Review: Digestive System

Orientation: Digestive System
Graphics are used with permission of:
Pearson Education Inc., publishing as Benjamin Cummings (http://www.aw-bc.com)
 The gastrointestinal (GI) or digestive system digests food and
transports (absorbs) nutrients (including salts and water) into the
blood.
 Digestion involves breaking down foods both chemically and
mechanically into smaller components that can be transported
(absorbed) through the digestive tract wall (epithelium) and into the
blood (most breakdown products) or lymph (for fat breakdown
products).
 Many secretions of the digestive system together with the muscular
action of the GI tract are necessary to complete digestion.
 Hunger and satiety are controlled via hormones and other chemicals
that influence the hypothalamus control center for ingestion. Social
factors and the availability of food also influence the amount of food
that we eat.
Anatomy Review: Digestive System
Graphics are used with permission of:
Pearson Education Inc., publishing as Benjamin Cummings (http://www.aw-bc.com)
Page 1: Introduction
 The digestive system consists of two components: the alimentary canal
(a.k.a. digestive tract) and accessory organs.
 After food is ingested and then processed in the digestive tract, undigested
food leaves the system as feces.
Page 2: Goals
 To identify the organs and circular muscles (sphincters) of the digestive
tract.
 To list the structures found in a representative section of the wall of the
digestive tract
 To recognize the accessory organs of the digestive system.
 To describe the general function for each organ of the digestive system.
Page 3: The Wall of the Digestive Tract
 A typical section of the digestive tract reveals four main layers. From
inside (the lumen) to outside they are:
o Mucosa
o Submucosa
o Muscularis (externa)
o Serosa (a.k.a. visceral peritoneum)
LABEL THESE LAYERS BELOW
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Different regions of the digestive tract wall have unique structures that are
related to the specialized functions of those regions.
The mucosa is subdivided into three layers. From the lumen outward they
are:
o A simple columnar epithelium densely populated with goblet cells.
o A lamina propria connective tissue layer containing blood and
lymphatic vessels
o A smooth muscle sheet called the muscularis mucosa
The mucosal epithelium functions in both secretion of digestive
substances and in absorption of nutrients.
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Goblet cells secrete mucus (a hydrated mucin protein), while other
mucosal epithelial cells secrete digestive fluids and other substances such
as water and salts.
Enteroendocrine cells of the mucosa produce hormones that are released
into the blood via the capillaries of the lamina propria.
Nutrients are transported (absorbed) through the epithelial cells and into
either the capillaries (most nutrients) or lacteal lymphatic vessels (fats).
The mucosal epithelial cells are mitotically active, thus the epithelium is
replaced approximately every three to six days.
The function of the double-layered muscularis mucosa is to aid in
digestion and absorption by moving the mucosal villi in the small intestine.
Blood and lymph vessels as well as an intrinsic network of neurons (the
submucosal plexus) are located in the submucosa.
The muscularis externa contains two sheets of muscle (circular and
longitudinal layers) throughout most of the alimentary canal wall (the
stomach has three layers). The fibers in the two layers are arranged at
right angles to each other
Peristalsis and segmentation are produced by the contractions of the
circular and longitudinal layers of muscle in the muscularis externa.
The myenteric plexus is a network of neurons in the muscularis externa; it
is in close communication with the submucosal plexus, and together, the
two plexuses comprise the enteric nervous system.
The outermost layer of the digestive tract wall is the serous fluid-producing
serosa, which both lubricates and reduces friction of the digestive tract
within the ventral body cavity.
Page 4: The Upper Part of the GI Tract
 Ingestion occurs in the mouth.
 Chemical digestion (saliva w/amylase for starch digestion) and mechanical
digestion (teeth & tongue) occur in the mouth.
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The lining of the oral cavity and pharynx is a stratified squamous
epithelium mucosa.
The partially digested bolus of food is moved from the mouth to the
esophagus, and then the stomach.
There is a transition in the esophagus wall from striated (skeletal) to
smooth muscle, from the upper to lower portions, respectively,.
The muscular stomach is involved in chemical (mostly protein) and
mechanical digestion, as well as storage of food.
The cardia, fundus, body, and pyloric (w/antrum) regions are specialized
areas of the stomach.
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The muscularis externa layer of the stomach wall is unique in that it has
three sheets of muscle (circular, longitudinal, and oblique).
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The stomach can expand greatly because of internal folds called rugae.
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Once food is mixed with gastric juices in the stomach it is called chyme,
which is then moved from the pylorus to the duodenum of the small
intestine.
Page 5: The Lower Part of the GI Tract
 The majority of chemical digestion and virtually all-nutrient absorption
occur in the small intestine.
 The three regions of the small intestine are the duodenum, jejunum, and
ileum
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The three modifications of the inner wall of the small intestine that function
to increase surface area are (from macroscopic to microscopic) the plicae
circularis (circular folds), villi, and microvilli
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The intestine aids the body in its defense against pathogens by secreting
antibacterial enzymes and antibodies (immunoglobulins) and by providing
specialized sites in the ileum (lymphoid nodules called Peyer’s patches)
where leukocytes can fight pathogens
 The large intestine absorbs water, salt, and vitamin K
 The large intestine includes the cecum, appendix, colon, rectum, and anal
canal
LABEL THESE AREAS BELOW
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Three bands of smooth muscle called taeniae coli cause the outer portion
of the colon to be puckered into pockets called haustra
Epiploic appendages are fat storage areas located on the outside of the
colon
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The final section of the digestive tract, the anus, is lined with stratified
squamous epithelium
Feces are composed of indigestible food, bacteria, inorganic substances,
and sloughed off epithelial cells from the digestive tract wall
Page 6: Sphincters
 Sphincters regulate the passage of food from one region of the digestive
tract to the next, and finally, out of the body as feces
 The sphincters of the digestive tract, from mouth to anus, are the:
o Upper esophageal sphincter or UES (circular skeletal muscle – an
anatomical sphincter)
o Lower esophageal sphincter or LES (a physiological sphincter)
o Pyloric sphincter (circular smooth muscle)
o Ileocecal sphincter or valve (circular smooth muscle)
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o Internal anal sphincter or IAS(circular smooth muscle)
o External anal sphincter or EAS (circular skeletal muscle)
The UES prevents air from entering the esophagus
The LES prevents acid reflux from the stomach into the esophagus
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The pyloric sphincter regulates passage of chyme from the stomach into
the duodenum
The ileocecal valve regulates passage of chyme from the ileum to the
large intestine
The IAS is under involuntary control; when relaxed, it produces the urge to
defecate
The EAS is under voluntary control; when relaxed, it allows for defecation.
Page 7: Accessory Glands
 The accessory glands that produce secretions to aid in digestion are the
salivary glands (3 pair), liver, and pancreas.
 Salivary glands moisten food, cleanse and protect the mouth, and produce
amylase to begin enzymatic digestion of starch
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The liver produces bile, which emulsifies fats to increase their surface
area for subsequent chemical digestion by lipases; bile is stored in and
released from the gall bladder into the duodenum
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The pancreas is the main digestive enzyme-producing exocrine organ in
the body. It releases a host of digestive enzymes into the duodenum via
the pancreatic duct; it also produces bicarbonate to neutralize the chyme
from the stomach
THE DIGESTIVE SYSTEM
Topic 2: Control of the Digestive System
Graphics are used with permission of:
Pearson Education Inc., publishing as Benjamin Cummings (http://www.aw-bc.com)
Page 1: Title Page
 The autonomic nervous system, hormones, and other chemicals control
motility and secretion of the digestive system.
The Autonomic Nervous System
Parasympathetic
NS
Sympathetic
NS
Page 2: Goals
 To list the phases of GI control
 To describe the interaction between the enteric and autonomic nervous
systems
 To discuss short and long reflexes.
 To list the hormones that control digestion and describe the function of
each hormone.
Page 3: Control of the GI tract depends on the location of food
 The sight, smell, taste, and mental images of food trigger the cephalic
phase of digestion via the vagus nerve (N X) which includes:
o salivation
o gastric juice production
o gastric contractions
 Increased volume of food in the stomach and subsequent stimulation of
stomach stretch receptors triggers the gastric phase of digestion which
includes:
o gastric juice production
o increased gastric motility
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As food moves into the small intestine (duodenum), the chemical
composition and volume of that food triggers specific reflexes during the
intestinal phase of digestion which may include:
o pancreatic secretion of bicarbonate into the duodenum
o pancreatic secretion of digestive enzymes into the duodenum
o gall bladder release of bile into the duodenum
o segmentation contractions of the small intestine
The small intestine reflexively slows gastric emptying to allow for
neutralizing, enzymatic digestion, and absorption of its contents
Page 4: Parasympathetic and sympathetic nerves innervate the GI tract
 Both parasympathetic and sympathetic divisions of the autonomic nervous
system control digestion by contacting the enteric nervous system in the
wall of the digestive tract
 The parasympathetic division typically stimulates digestion while the
sympathetic division typically inhibits it.
 The vagus and pelvic splanchnic nerves send preganglionic
parasympathetic fibers to synapse with enteric neurons.
 Sympathetic postganglionic innervation of the digestive tract is both direct
to smooth muscle, glands, and blood vessels and indirect via synapses
with the enteric NS.
 LABEL THE NERVE FIBERS BELOW
The Autonomic Nervous System
Preganglionic fiber
of Vagus nerve
Postganglionic fiber
Preganglionic fibers
of pelvic splanchnic
nerves
Parasympathetic Division
Sympathetic Division
DivisionNS
Page 5: The enteric nervous system serves the GI tract
 The submucosal and myenteric plexuses are the two nerve networks of
the enteric nervous system.
 The enteric nervous system controls many digestive functions
independent of the rest of the nervous system, such as lower esophageal
peristalsis and mobility of the small intestine.
Page 6: Reflexes coordinate and modulate digestive activity
 Reflexes (stimulus, integration, and response) that are totally controlled by
the enteric nervous system are termed short reflexes.
 Reflexes that involve the CNS as an integration center are called long
reflexes
 Short and long reflexes can occur simultaneously
 Larger volumes of food in the stomach produce stronger gastric
contractions than smaller volumes of food.
Small volume → weaker contractions
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Chemical composition of food influences the rate of digestion: lipid rich
meals take longer to digest than carbohydrate rich meals
Lipid rich meal → Longer digestion time
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Large volume → stronger contractions
Carbohydrate rich meal → shorter digestion time
Emotional stressors cause the brain to override the intrinsic controls of
digestion and subsequently cause problems such as constipation,
diarrhea, and stomachaches.
Page 7: There are many neurotransmitters in the GI tract
 All preganglionic fibers of the ANS release acetylcholine (ACh).
 Parasympathetic postganglionic fibers also release ACh
 Sympathetic postganglionic fibers release norepinephrine
 LABEL
THE
FIBERS
BELOW
AND
INCLUDE
NEUROTRANSMITTER RELEASED BY THE FIBER
The Autonomic Nervous
System
Preganglionic fiber
of Vagus nerve
(releases ACh)
Postganglionic fiber
(releases ACh)
Preganglionic
fibers of pelvic
splanchnic nerves
(releases ACh)
Parasympathetic NS
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THE
Postganglionic fiber
(releases
norepinephrine)
Preganlionic fiber
(releases ACh)
Sympathetic NS
Other enteric nervous system neurotransmitters include serotonin,
vasoactive intestinal peptide (VIP), nitric oxide (NO), and somatostatin
(SST)
ACh and substance P stimulate smooth muscle of the digestive tract.
Smooth muscle of the digestive tract is inhibited by norepinephrine, VIP,
and NO
Enkephalins released in the submucosal and myenteric plexuses slow
intestinal motility, inhibit intestinal secretion, and contract the LES, pyloric
and ileocecal sphincters.
Page 8: Hormones modulate digestive activity
 GI hormones are peptides (amino acid based).
 GI hormones include gastrin, cholecystokinin (CCK), secretin, glucosedependent insulinotropic peptide (GIP) and motilin.
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Enteroendocrine cells of the GI mucosa secrete the peptide hormones.
Pyloric antrum G cells secrete gastrin, which stimulates HCl production
and growth of the gastric mucosa
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CCK is secreted by the “I” cells in the duodenum and jejunum.
CCK cause gall bladder contraction and subsequent release of bile into
the duodenum
CCK causes the pancreas to release digestive enzymes into the
duodenum
CCK inhibits gastric emptying
CCK stimulates growth of the pancreas and gall bladder mucosa
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Duodenal “S” cells produce secretin
Secretin causes the pancreas, and to a lesser extent the liver, to release
bicarbonate into the duodenum
Secretin inhibits HCl secretion by the stomach
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Duodenal and jejunum cells secrete GIP
When glucose is present, GIP stimulates the pancreas to secrete insulin,
thus enhancing the secretion of insulin
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Duodenal and jejunum cells secrete motilin during the postabsorptive state
Motilin stimulates GI motility thereby moving intestinal contents toward the
end of the ileum
1. GI hormones, like all hormones, enter the circulatory system, and then
return to the target organ(s); in this case, back to the GI tract.
2. Potentiation of hormones involves the combined effect of two or more
hormones being greater than the sum of their individual actions
THE DIGESTIVE SYSTEM
Topic 3: Motility
Graphics are used with permission of:
Pearson Education Inc., publishing as Benjamin Cummings (http://www.aw-bc.com)
Page 1: Title Page
 The muscles of the digestive tract wall are responsible for propelling and
mixing its contents.
Page 2: Goals
 To discuss the types of motility found in each section of the digestive tract
 To describe the function of each type of motility
 To describe the control of motility throughout the digestive tract.
Page 3: Chewing occurs in the mouth
 Chewing is a mechanical digestive process that tears and grinds food into
pieces small enough to be swallowed as a bolus
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Chewing mixes food with saliva, thereby lubricating the bolus so that it can
be swallowed easily
Chewing has both voluntary and involuntary reflex components
The small intestine reflexively slows gastric (stomach) emptying to allow
for neutralizing, enzymatic digestion, and absorption of its contents
Page 4: Swallowing initiates primary peristalsis in the esophagus
 The only function of the esophagus is to move the bolus from the pharynx
(throat) to the stomach
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The esophagus moves its contents via peristalsis (now is a good time to
play the animation on page 4 of the Motility topic)
Swallowing begins voluntarily but is completed by reflexive (involuntary)
primary peristalsis controlled by the swallowing center in the brain stem
The sequence of events in swallowing is as follows:
1. The soft palate rises to close off nasopharynx and prevent bolus
from rising into the nasal cavity
2. The tongue retracts to force the bolus into the oropharynx
3. The larynx elevates and the glottis closes
4. The epiglottis covers the glottis
5. The pharyngeal muscles contract and the UES relaxes to allow the
bolus to move from the oropharynx into the upper esophagus
6. Primary peristalsis begins and both the LES and stomach relax
7. The bolus moves into stomach and LES closes
The larger the size of the bolus, the more force generated by peristalsis in
the esophagus
It takes approximately 9 seconds for a typical bolus to move from the
esophagus to the stomach; liquids, like water, take about 1 second to
travel down the esophagus
Page 5: Stretch of the esophageal wall initiates secondary peristalsis
 Secondary peristalsis (a second wave of peristalsis) begins if a food bolus
does not make it to the stomach via primary peristalsis
 Distension of the esophagus causes its stretch receptors to send signals
to the CNS, which then responds by triggering secondary peristalsis
Page 6: Relaxation and peristalsis occur in the stomach
 The stomach stores food, mixes it with gastric juice for chemical digestion,
and empties the partially digested food (chyme) into the small intestine
(duodenum)
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Receptive relaxation of the fundus and body allow for approximately 1 liter
of food to enter the stomach
Peristaltic contractions of the stomach (~ 3-5/min) mix the stomach
contents with gastric juice and empty the chyme into the duodenum
The frequency of peristaltic contractions is regulated by the interaction
between pacemaker cells and smooth muscle cells
Larger volumes of food in the stomach produce stronger gastric
contractions than smaller volumes of food
Small volume → weaker contractions
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Large volume → stronger contractions
Chemical composition of food influences the rate of digestion: lipid rich
meals take longer to digest than carbohydrate rich meals
Contractions of the antrum propel chyme into the duodenum in small
squirts (gastric emptying) via the pyloric sphincter (play the animation on
page 6 of the Motility topic)
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Closure of the pyloric sphincter forces chyme back into the stomach
(retropulsion) for further mixing
The rate of gastric emptying is slowed by the presence of fats, acids, and
hypertonic solutions in the duodenum; distention of the duodenum also
slows the rate of gastric emptying
Page 7: Nerves and hormones control gastric motility
 Nerves control the response of the stomach during the cephalic phase of
digestion
 The cephalic phase is regulated by long reflexes
 The vagus nerve carries signals from the brain to the stomach
 Gastric motility increases in preparation for the receipt of food during the
cephalic phase
 Both nerves and hormones control the response of the stomach during the
gastric phase of digestion.
 Gastrin is the hormone that regulates gastric secretion.
 Stretching the intestinal wall stimulates its stretch receptors and causes a
response by the duodenum
 Gastric motility/emptying decrease as the duodenum begins to receive
chyme from the stomach; this allows the duodenum sufficient time to
process the chyme
 Fats in the duodenum cause the release of the hormone CCK, which
causes gastric motility to decrease
 CCK also stimulates the gall bladder to release bile into the duodenum,
which causes fat emulsification
 Both the hormone secretin and nerves elicit a response from the
duodenum when it contains acid
 Hypertonic solutions in the duodenum elicit a response, but the precise
mechanism of the response is unknown
 The automatic communication between the intestine and the stomach is
called the enterogastric reflex
 Sympathetic nervous system activity decreases digestive processes while
parasympathetic activity increases them
Page 8: Segmentation occurs in the small intestine during digestion
 Segmentation and limited peristalsis are the two types of motility in the
small intestine
 Segmentation involves oscillatory, alternating contractions and relaxations
of the small intestine’s smooth muscle. These contractions move the
chyme in a bidirectional fashion
 Segmentation in the intestine mixes chyme with intestinal secretions and
brings it into repeated contact with the intestinal absorptive epithelium
(check out the animation on page 8 of the Motility topic).
 The frequency of segmentation contractions is greatest in the duodenum
(~12/min) and least in the ileum (~ 9/min), and this frequency is regulated
by pacemaker cells
 The slow passage of chyme in the small intestine insures that nutrients will
be absorbed
Page 9: Nerves and hormones control small intestine motility
 Long reflexes act on the ileum to increase its activity when food is in the
stomach
 Increased peristalsis in the ileum moves undigested contents into the
large intestine for ultimate elimination as feces
 Gastrin, produced by the stomach during the gastric phase, stimulates
peristalsis of the ileum and relaxation of the ileocecal sphincter; this is the
gastroileal reflex
 Distention of the small intestine stimulates stretch receptors, which results
in an increase in segmenting contraction strength (a neural reflex)
 Sympathetic nervous system activity decreases intestinal motility;
parasympathetic activity increases it
Page 10: Migrating motility complexes occur during fasting
 After a meal is digested (i.e. during the inter-digestive period),
segmentation is replaced by migrating motility complexes.
 Migrating motility complexes are peristaltic waves from stomach to ileum
that sweep undigested material toward the terminal ileum
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The frequency of migrating motility complexes is approximately one every
90 minutes or 6-8 overnight.
Migrating motility complexes are controlled by the enteric nervous system
Page 11: Segmentation and mass movements occur in the colon
 There are two majors functions of the large intestine:
1. Storing and concentrating fecal matter
2. Absorption of water, salts, and vitamin K
 The ileocecal sphincter opens to allow chyme to enter the cecum and then
closes to prevent backflow
 About 500 ml of chyme enters the cecum daily
 Slow, segmenting contractions (~ 1-5/min) allow for vitamin K, water and
salts to be absorbed through the large intestine’s epithelium
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Pouches called haustra are formed by contractions in the transverse and
descending colon
 Mass movements are sustained, intense peristaltic contractions of the
large intestine (the animation on page 11 of the Motility topic nicely
demonstrates these).
 Haustral contractions and mass movements propel feces toward the
sigmoid colon and finally into the rectum
 Distention of the rectum causes the internal anal sphincter (involuntary,
smooth muscle) to relax, which produces the urge to defecate
 The external anal sphincter (skeletal muscle) is under voluntary control;
relaxation of this sphincter, coupled with contraction of the rectum and
sigmoid colon, results in defecation
 Only about 150 ml of the 500 ml of chyme that enter the cecum is
eliminated as feces; most of the remaining 350 ml is absorbed water
 Feces contain mostly undigested foodstuffs and bacteria (mostly E. coli ~
1/3 dry weight of feces)
Page 12: Reflexes govern the activity of the colon
 The gastroileal reflex promotes mass movements of the colon
 Distention (stretching) of the rectum stimulates the defecation reflex
 Both long and short reflexes are involved in defecation
 The internal anal sphincter is under involuntary control while the external
anal sphincter is under voluntary control
 Emotions influence colonic motility
o Pain, fear, depression – may produce constipation
o Anger, anxiety, and hostility – may cause diarrhea
Page 13: Vomiting moves stomach contents orally
 The vomiting reflex is coordinated in the brainstem
 The vomiting reflex may be stimulated by:
o Excessive stretching of the stomach
o Abnormal vestibular stimulation (e.g. seasickness)
o Urogenital pain (esp. testicular)
o Other painful injuries
o Increased intracranial pressure
o Tickling to the back of the throat
o Noxious and/or toxic chemicals
 Vomiting is preceded by copious saliva production
 The sequential events of vomiting are as follows:
o Reverse peristalsis moves bile-laden contents from the small
intestine into the stomach
o The stomach antrum contracts, forcing stomach/intestinal contents
through the relaxed LES, up the esophagus, through the UES, and
out the mouth
 Vomiting may serve a protective function, i.e. to remove harmful
substances from the GI tract.
THE DIGESTIVE SYSTEM
Topic 4: Secretion
Graphics are used with permission of:
Pearson Education Inc., publishing as Benjamin Cummings (http://www.aw-bc.com)
Page 1: Title Page
 Digestive system secretion involves the production and release of juices
and hormones by the GI tract and its accessory glands.
Page 2: Goals
 To list the secretions of the digestive tract
 To describe the function of each secretion
 To describe the control of secretion throughout the digestive tract.
Page 3: Large volumes of fluid move in and out of the GI tract
 For a typical daily consumption of food (800 g) and fluid (2.0 L):
o About 1.5 L of saliva is secreted into the mouth.
o About 2.0 L of gastric juice are produced
o The pancreas delivers about 1.5 L of pancreatic juice to the
duodenum
o The liver/gallbladder delivers about 0.5 L of bile into the duodenum
o The small intestine produces about 1.5 L of fluid
o The total of all of the above secretions = about 9.0 L
 The small intestine absorbs about 8.5 L of fluids & most of the ingested
food
 The large intestine absorbs about 0.35 L of fluid, some salts and vitamin K
 Although the GI tract contains about 9.0 L of fluid every day, only about
0.15 L is eliminated with the feces
 Of the approximately 800 g of food ingested in a typical daily diet, only
about 50 g (< 10%) of undigested food are eliminated as feces
Page 4: Salivary glands secrete saliva
 The extrinsic salivary glands include the paired parotid, submandibular
and sublingual glands
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Parotid glands produce serous fluid containing enzymes, electrolytes, and
limited mucin
Submandibular and sublingual gland produce a more viscous fluid than
parotid glands
Saliva functions include:
o Protection (esp. antibacterial lysozyme and IgA antibodies)
o Taste (dissolved food chemicals)
o Lubrication (mucus)
o Digestion (esp. starch via amylase)
Page 5: Nerves control salivation
 The control of salivation is almost exclusively via the autonomic nervous
system
 Both parasympathetic and sympathetic innervation stimulate salivation
 Both the facial nerve (CN VII) and glossopharyngeal nerve (CN IX) carry
parasympathetic nerve fibers to the salivary glands
 Parasympathetic stimulation causes mostly watery, enzyme-rich secretion
of the salivary glands
 The though, sight, and/or smell of food stimulate the salivatory nuclei in
the medulla to increase parasympathetic innervation to the salivary glands
 Acidic substances and the pressure of chewing also cause an increase in
parasympathetic innervation to the salivary glands
 Nausea and intestinal irritation also stimulate salivation
 Fear, fatigue, sleep, and dehydration inhibit salivation
 Sympathetic stimulation of the salivary glands causes them to produce
small amounts of viscous (mucus) saliva
 LABEL THE NERVE FIBERS BELOW INDICATING WHICH ARE
SYMPATHETIC AND WHICH ARE PARASYMPATHETIC
Page 6: The esophagus secretes mucus
 The only secretion of the esophagus is mucus
Page 7: Gastric secretions are produced regionally
 The gastric mucosa produces exocrine, endocrine, and paracrine
secretions*
 Exocrine secretions, collectively called gastric juice, include mucus,
pepsinogen, HCl, and intrinsic factor; they are released into the stomach
lumen as follows:
o Mucus – throughout the stomach
o Pepsinogen – throughout the stomach
o HCl – fundus and body
o Intrinsic factor (IF) – fundus and body
*Play the animation on page 7 of the Secretion topic to help reinforce this
regional distribution of chemical secretions in the stomach.
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Enteroendocrine cells in the pylorus release gastrin into the bloodstream;
it returns to the stomach to exert its effects
Gastrin
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Paracrine cells in the fundus and body of the stomach release histamine
into the lamina propria interstitium
Page 8: Specialized cells produce each gastric secretion
 The stomach mucosa is invaginated to form deep wells called gastric pits;
gastric glands are located within the pits
Gastric pit & gland: fundus
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Gastric glands produce mucus and pepsinogen throughout the stomach
Gastric glands in the body and fundus produce HCl and intrinsic factor and
other cells in the gastric pits of these regions produce histamine
Two types of mucus are produced in the stomach
o Thick, alkaline mucus in the luminal mucosa
o Thin, watery mucus from the mucus neck cells of the gastric pits
Parietal cells in the gastric glands produce HCl and IF
Chief cells, a.k.a. zymogenic cells (a zymogen is an inactive proteolytic
enzyme) in the gastric glands produce pepsinogen
Some cells in the gastric glands of the pylorus secrete gastrin while other
secrete mucus and pepsinogen
G-cell (gastrin)
Gastric gland in the pylorus
Page 9: The stomach produces many secretions (The interactive animations
on page 9 are really great here; play them again to help “digest” this material)
 Mucus protects the stomach from self-digestion (a.k.a. auto-digestion) by
neutralizing stomach acid and inhibiting pepsin (a proteolytic or proteindigesting enzyme)
 Mucus + tight junctions between cells in the gastric mucosa are
collectively known as the gastric mucosal barrier
 Only aspirin and alcohol are absorbed across the stomach’s mucosal
epithelium
 When aspirin and/or alcohol pass through the stomach’s mucosal barrier,
they destroy cells, thus leaving the stomach’s wall susceptible to peptic
ulcer development
 HCl, secreted by parietal cells, lowers the luminal pH to between 1.5-2
(remember that because pH is on a logarithmic scale, each point change
on the scale represents a 10-fold change in pH; in the stomach, for
example, a pH of 2 is about 100,000 times more acidic than the pH of near
7 in the mouth)
 The highly acidic gastric environment is lethal to most bacteria and other
microorganisms
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HCl function includes:
o breaking down plant cell walls (mostly cellulose) and connective
tissue
o denaturing proteins
o converting pepsinogen to pepsin (optimal pH near 2.0)
Pepsin, a proteolytic enzyme, begins the chemical digestion of proteins in
the stomach
Parietal cells also secrete intrinsic factor (IF), which is required by the
intestine to absorb vitamin B12
Vitamin B12 is needed for maturation of RBCs – without it, pernicious
anemia may develop
Peptides in the stomach trigger the release of gastrin from G-cells into the
bloodstream
Gastrin stimulates HCl secretion by parietal cells and histamine secretion
by paracrine cells
Histamine acts synergistically with gastrin to stimulate HCl release from
parietal cells
Page 10: Nerves and hormones control gastric secretion*
 The thought, sight, and/or smell of food triggers an increase in gastric
juice secretion from chief and parietal cells via the vagus nerves (a long
neural reflex)
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Indirectly, long neural reflexes cause increased gastric juice secretion by
stimulating an increased production of gastrin from the G-cells
Gastrin, in turn, stimulates the production of histamine from paracrine cells
Histamine acts together with gastrin to stimulate increased release of HCl
The gastric phase of digestion begins when the stomach contains
peptides and is distended
Both neural reflexes and the hormone gastrin mediate increased gastric
juice secretion during the gastric phase
The intestinal phase of digestion begins when the meal enters the
duodenum
Both neural reflexes and hormones (CCK & secretin) mediate the
response of the stomach during the intestinal phase
Lipids in the duodenum cause the release of CCK, which slows gastric
emptying
Acid in the duodenum causes the release of secretin
The sympathetic nerves inhibit digestive activities while the
parasympathetic nerves stimulate them
*Filling in this table on page 10 should help to reinforce these concepts.
Page 11: The pancreas secretes enzymes and bicarbonate into the small
intestine
 Most chemical digestion and absorption occur in the small intestine
 The secretions that initiate chemical digestion in the small intestine come
from the exocrine (acinar) pancreas
Pancreatic acinus (exocrine)
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Bile, produced by the liver and stored in/released from the gall bladder,
emulsifies fats to increase their surface area for subsequent chemical
digestion by pancreatic lipases
The exocrine pancreas produces two types of pancreatic juice:
o enzyme-rich pancreatic juice (stimulated by CCK)
o bicarbonate-rich pancreatic juice (stimulated by secretin)
Exocrine pancreas secretions are delivered through the hepatopancreatic
sphincter (a.k.a. sphincter of Oddi) into the duodenum via the pancreatic
duct
Exocrine pancreatic secretions include the following enzymes:
o Proteases (a.k.a. proteolytic enzymes)
o Amylase
o Lipase
Pancreatic proteases (in zymogenic or inactive form) include trypsinogen,
chymotrypsinogen, procarboxypeptidase
Enterokinase in the intestinal cell membranes, converts (activates)
trypsinogen into trypsin
Once produced, trypsin activates more trypsinogen in a positive feedback
mechanism
Duct cells secrete bicarbonate into the duodenum to neutralize acid from
the stomach; this produces an optimal pH environment for pancreatic
digestive enzymes to function in
The endocrine pancreas secretes two antagonistic hormones:
o Insulin – regulates the absorptive state
o Glucagon – regulates the post-absorptive state
Page 12: The liver secretes bile and bicarbonate into the small intestine
 The main digestive function of the liver is to produce bile
 Bile backs up into the gallbladder for storage/concentration when the
hepatopancreatic sphincter (of Oddi) is closed)
 The two components of bile are:
o Organic compounds (esp. bile salts) to emulsify fats
o Bicarbonate solution
 Bile emulsifies fat to increase surface area for subsequent digestion with
pancreatic lipase
 The organic compounds of bile include
o Bile salts
o Lecithin
o Cholesterol
o Bilirubin
 Cholesterol and bilirubin are eliminated in the feces
 Bile salts are recycled; they stimulate the secretion of bile from the liver
(via the enterohepatic circulation – play the interactive animation here to
visualize this circulation)
 When stimulated by secretin (“nature’s antacid”), bile duct cells secrete a
bicarbonate solution that is identical to pancreatic bicarbonate; this
protective function of the liver neutralizes acidic chyme in the duodenum
Page 13: The small intestine secretes fluid, mucus, and hormones
 The small intestine secretes watery mucus and hormones
 Mucus, secreted by abundant epithelial goblet cells, protects the intestinal
mucosa from auto-digestion by proteases and acid
 Intestinal glands or crypts (of Lieberkuhn) secrete water and electrolytes
to combine with mucus to form intestinal juice
 Intestinal epithelial cells contain brush border enzymes in their microvilli
cell membranes; these enzymes complete the chemical digestion of
foodstuffs
Enzymes
Page 14: Nerves and hormones control secretions entering the small
intestine*
 Fat in the duodenum causes it to release of CCK, which triggers
contraction of the gall bladder and release of bile into the duodenum
 Acid in the duodenum causes it to release of secretin, which causes the
release of bicarbonate into the duodenum from the pancreas and liver
 Distention of the small intestine and/or acidic/hypertonic chyme trigger a
neural reflex that increases intestinal juice secretion
 Sympathetic stimulation decreases intestinal digestive activity while
parasympathetic stimulation increases it
* Complete the interactive table here for reinforcement
Page 15: The large intestine secretes mucus and bicarbonate
 Alkaline mucus containing bicarbonate and potassium ions is secreted by
the large intestine for protection from bacterial acid
 Mucus lubricates feces and protects the large intestine wall from
mechanical damage
 Both long and short reflexes, triggered by mechanical stimulation and
acid, increase secretion of alkaline mucus from the large intestine
THE DIGESTIVE SYSTEM
Topic 5: Digestion and Absorption
Graphics are used with permission of:
Pearson Education Inc., publishing as Benjamin Cummings (http://www.aw-bc.com)
Page 1: Title Page
 Chemical digestion involves breaking down food with enzymes into
molecules (nutrients, salts, water) that can be absorbed
 Absorption involves moving those molecules through the GI epithelium and
into the blood (most molecules) or lymph (lipids)
Page 2: Goals
 To discuss the action of digestive enzymes (amylases, proteases, lipase)
and bile salts
 To describe trans-epithelial transport of simple sugars (monosaccharides)
and amino acids
 To discuss emulsification, chemical digestion, and absorption of lipids.
Page 3: Food is broken down mechanically and chemically
 Ingested food first is broken down mechanically in the mouth (mastication
or chewing) into pieces small enough to be swallowed, and then into even
smaller particles in the stomach that can move into the small intestine
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These small particles contain both major nutrients (a.k.a. macronutrients)
and minor nutrients (e.g. minerals)
The major nutrients must be broken down enzymatically into their
component parts, which then can be absorbed.
The major nutrients are: carbohydrates, proteins, lipids
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The main dietary sources of carbohydrates include: starch (a
polysaccharide), and the disaccharides sucrose (table sugar), lactose
(milk sugar), and maltose (grain or brewer’s sugar)
All carbohydrates must be digested enzymatically into their component
monosaccharides (the monomers of carbohydrates) for absorption. For
example:
 Starch is digested to glucose monomers
 Sucrose is digested to one glucose monomer and one fructose
monomer
 Lactose is digested to one glucose monomer and one galactose
monomer
 Maltose is digested to two glucose monomers
Proteins (both animal and plant) are digested to amino acids and small
peptide chains of two (dipeptides) or three (tripeptides) amino acids
Most dietary fat is in the form of neutral fats or triglycerides (a.k.a.
triacylglycerols)
 Each triglyceride molecule is broken down into one monoglyceride
(= glycerol + one fatty acid) and two free fatty acids
Non-polar products of digestion (e.g. lipid breakdown products) can be
absorbed by simple diffusion (passive) through the phospholipids bi-layer
of the intestinal epithelial cells; most polar substances are absorbed using
either active (i.e. ATP-requiring) or passive carrier-mediated transport
mechanisms
Page 4: Carbohydrate digestion begins in the mouth
 Plant starch and glycogen are long polymers of glucose; they are
abundant in the diet.
 Chemical digestion of starch begins in the mouth with the enzyme,
salivary amylase (optimal pH ~ 7).
 Amylase breaks down starch into the following components*:
o Maltose (a disaccharide)
o Maltotriose (a trisaccharide)
o Limit dextrin (small branched fragments)
*The interactive animation here illustrates these components nicely
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Stomach acid denatures salivary amylase
Page 5: Protein digestion begins in the stomach
 The enzyme pepsin (activated from pepsinogen by HCl) begins the
digestion of proteins in the stomach
 Pepsin (optimal pH ~2) breaks the peptide bond between tyrosine and
phenylalanine amino acids, thereby producing peptide fragments and a
few individual amino acids
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The neutral pH of the duodenum denatures pepsin, rendering it inactive
Page 6: Most digestion and absorption occur in the small intestine
 Most chemical digestion and nearly all the absorption occur in the small
intestine
 Pancreatic digestive enzymes alone are sufficient to digest carbohydrates
and proteins
 Pancreatic lipase is essential for the bulk of fat digestion
 Cellulose and certain other plant complex carbohydrates cannot be
digested by humans; we lack the enzymes to hydrolyze them
 Indigestible plant polysaccharides serve as an important source of dietary
fiber
 Certain fiber types (insoluble) help to speed the movement of stool
through the colon
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Vegetables and fruits contain many valuable vitamins, minerals, and other
nutrients
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Most dietary salt and water are absorbed in the small intestine by
either transcellular (through cells) or paracellular (between cells)
transport
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Transcellular transport of water is linked to the active transport of
sodium via sodium-potassium pumps
o Sodium is actively pumped out of the digestive tract at the
basolateral membrane of the epithelial cells
o Sodium then moves passively from the GI lumen into the
epithelial cells through ion channels (co-transported with
glucose or amino acids) down its concentration gradient
o Chloride follows sodium (electrochemical attraction)
o Water follows passively via osmosis
Page 7: Carbohydrates are digested and absorbed in the small intestine
 Pancreatic amylase (optimal pH ~7) continues the digestion of
carbohydrates in the small intestine (duodenum)
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Intestinal brush border enzymes complete the digestion of carbohydrates
to monosaccharides, which then can be absorbed*
o Glucoamylase breaks down maltose and maltotriose
o Dextrinase breaks down limit dextrin
o Sucrase breaks down sucrose
o Lactase breaks down lactose
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Most nutrients are absorbed by transepithelial transport
Secondary active transport is the process by which glucose and galactose
(co-transported w/sodium using the same transport protein) enter the
luminal side of GI epithelial cells
Fructose enters the epithelial cells on its own transporter via facilitated
diffusion
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*This interactive animation demonstrates enzymatic hydrolysis of these
carbohydrates
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Once inside the epithelial cells, all monosaccharides exit the basolateral
side of the cells on the same type of transport molecule via facilitated
diffusion
Page 8: Protein is digested and absorbed in the small intestine
 A variety of proteins and protein breakdown products (e.g. peptides from
pepsin digestion) enter the small intestine for their final enzymatic
breakdown
 Trypsin (activated from trypsinogen), chymotrypsin (activated from
chymotrypsinogen),
and
carboxypeptidase
(activated
from
procarboxypeptidase) are the major pancreatic proteases (optimal pH ~
7)*
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Trypsin and chymotrypsin split proteins into smaller peptides and some
single amino acids
Carboxypeptidase splits single amino acids from the carboxyl end of
proteins
The brush border enzymes, aminopeptidase and dipeptidase continue the
digestion of peptides.
Single amino acids, dipeptides, and tripeptides are absorbed through the
small intestine
A number of amino acids (but not all) are co-transported into the luminal
side of the epithelial cells with sodium via secondary active transport
There are a number of different amino acid transporters
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Most protein is absorbed as dipeptides and tripeptides, which are further
digested to single amino acids inside the GI epithelial cells
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More hydrophobic amino acids tend to leave the basolateral side of the
epithelial cells via simple diffusion
More hydrophilic amino acids tend to exit GI epithelial cells via facilitated
diffusion or by cotransport with sodium
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* Now is a good time to view the function of these hydrolytic enzymes in the
animation
Page 9: Fat is digested and absorbed in the small intestine
 Most dietary fats are triglycerides, which are made up of three fatty acids
(short, medium or long hydrocarbon chains) each bound to a glycerol
molecule via an ester linkage
 Most lipid digestion occurs in the duodenum
 Two mechanisms act to increase the surface area of fats for subsequent
chemical digestion:
o Segmentation in the small intestine disperses fat into the aqueous
layer (like oil and vinegar in salad dressing)
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o Bile salts attach to smaller fat droplets to prevent them from
coalescing into larger droplets
Because bile salt molecules are amphipathic (polar on one side, non-polar
on the other), they can surround small lipid droplets (with the non-polar
side toward the lipid) and prevent them from coming together (because
the polar regions of the bile salts face away from the attached lipid
molecule), thereby increasing the total surface area of the lipid
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Increasing the surface area of the lipid allows for more efficient hydrolysis
of the lipid by pancreatic lipase (pay close attention to the orientation of
the bile salts on the lipid droplet in the animation; not that the bile salts do
NOT hydrolyze the lipid droplet)
Lipase digests triglycerides into monoglycerides and free fatty acids
Bile salts also surround monoglycerides and free fatty acids to form tiny
micelles droplets (about 1 million times smaller than emulsified fat
droplets)
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When micelles come close to the luminal membrane of the epithelial cells,
they release their monoglycerides and free fatty acids into the cells via
simple diffusion through the lipid bilayer
Micelles
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Monoglycerides and free fatty acids are reassembled into triglycerides
once inside the cell, and then coated with lipoproteins to form
chylomicrons to keep them emulsified
Chylomicrons exit the basolateral surface of the epithelial cell via
exocytosis and enter the lacteal lymphatic capillaries
Page 10: Salt, water, and bacterial products are absorbed in the large
intestine
 Neither the large intestine’s cells nor it’s secretions are digestive in
function
 Symbiotic enteric (colic) bacteria can digest some of the indigestible
carbohydrates enzymatically and then use the released nutrients
 By products of colic bacteria metabolism include small amounts of certain
B complex vitamins and substantial quantities of vitamin K; both are
absorbed in the large intestine
 Vitamin K is essential for producing certain blood clotting proteins
 The colon absorbs small quantities of salt and water as the feces are
concentrated there and eventually eliminated through the rectum and anus
Study Questions on Digestion & Absorption: Digestive System:
1. (Page 3.) Where does mechanical digestion occur?
2. (Page 3.) List the major nutrients (macronutrients) and briefly describe the
primary dietary sources of each.
3. (Page 3.) List three major carbohydrate sources in the diet and their
constituent monomers (monosaccharides).
4. (Page 3.) What are proteins enzymatically digested into?
5. (Page 3.) Describe the breakdown products of neutral fats.
6. (Page 3.) Briefly compare and contrast the different mechanisms required
for absorption of polar versus non-polar nutrients.
7. (Page 4.) What is the name of the salivary enzyme that breaks down plant
starch and glycogen?
8. (Page 4.) List the breakdown products of plant starch and glycogen in the
mouth.
9. (Page 5.) What is the name of the gastric protease and what is its
optimum pH?
10. (Page 5.) What happens to the gastric protease when it reaches the small
intestine?
11. (Page 6.) Where do most of the digestive enzymes that function in the
duodenum originate?
12. (Page 6.) Describe the function of cellulose in the diet.
13. (Page 6.) Why are vegetables and fruits important components of the
diet?
14. (Page 7.) Describe the transcellular transport mechanism of water
absorption in the small intestine.
15. (Page 7.) What enzymes are used to complete the digestion of
carbohydrates in the duodenum?
16. (Page 7.) Describe the function of brush border enzymes in the
duodenum.
17. (Page 7.) Compare and contrast the mechanisms for intestinal absorption
of glucose and fructose. Be sure to describe both how they enter and exit
the luminal epithelial cells.
18. (Page 8.) List the major pancreatic proteases. What is the optimum pH for
these enzymes?
19. (Page 8.) How are pancreatic proteases activated?
20. (Page 8.) What are the breakdown products of each pancreatic protease?
21. (Page 8.) List the protein-digesting (proteolytic) brush border enzymes
and briefly describe the function of each.
22. (Page 8.) How do many amino acids enter the luminal side of the
intestinal epithelium?
23. (Page 8.) Compare and contrast the mechanisms by which hydrophilic
and hydrophobic amino acids exit the basolateral side of the intestinal
epithelial cells.
24. (Page 9.) Describe the two mechanisms that increase lipid surface are for
digestion in the duodenum.
25. (Page 9.) What is the name of the enzyme that breaks down neutral fats
in the duodenum and what are the breakdown products of this digestion?
26. (Page 9.) What are micelles?
27. (Page 9.) How do neutral fat breakdown products enter the luminal side of
the intestinal epithelial cells?
28. (Page 9.) What happens to the breakdown products of neutral fats once
inside the luminal cells?
29. (Page 9). How do neutral fat breakdown products exit the luminal
epithelial cells?
30. (Page 9.) How are fat breakdown products transported away from the
small intestine?
31. (Page10.) Describe the symbiotic relationship between colic bacteria and
humans.
32. (Page 10.) What is the absorptive function of the colon?
Study Questions on Secretion: Digestive System:
1. (Page 3.) List the general secretions of the digestive tract from mouth to
anus.
2. (Page 3.) Where do the majority of ingested materials get absorbed?
3. (Page 3.) Approximately what percentage of ingested solids is eliminated
as feces? Liquids?
4. (Page 4.) List the three pair of salivary glands and briefly describe their
secretions.
5. (Page 5.) Which cranial nerves send parasympathetic innervation to the
salivary glands?
6. (Page 5.) Describe the difference in saliva composition and volume as
stimulated by the parasympathetic versus the sympathetic nervous
systems.
7. (Page 7.) List the exocrine secretions of the stomach and briefly describe
the functions of each.
8. (Page 7.) Which hormone do stomach cells release?
9. (Page 8, 9.) List the cells found in the gastric glands, the secretion(s)
produced by each cell type, and briefly describe the function of each
secretion.
10. (Page 10.) Discuss the relationship between long reflexes, gastrin,
histamine, and HCl production during the cephalic phase of digestion.
11. (Page 10.) Describe the roles of CCK and secretion during the intestinal
phase of secretion.
12. (Page 10.) Why are aspirin and alcohol problematic in the gastric
environment?
13. (Page 11.) What is the source and role of bile in the digestive process?
14. (Page 11.) What are the two types of pancreatic juice? What are the roles
of each? What is the stimulus for the secretion of each type?
15. (Page 11.) Discuss the activation and function of the pancreatic
proteases.
16. (Page 11.) What are the two endocrine secretions of the pancreas and
when do they function?
17. (Page 11, 12.) Discuss the cooperative effort of bile and pancreatic lipase
in the digestion of dietary lipids.
18. (Page 12.) List the chemical constituents of bile.
19. (Page 12.) What is the relationship between the liver and the gall bladder
regarding bile?
20. (Page 13.) List the chemical secretions of the small intestine and briefly
describe the function of each.
21. (Page 13.) What are brush border enzymes?
22. (Page 14.) Compare and contrast the chemical and mechanical stimuli for
secretions that function in the small intestine.
23. (Page 15.) List the secretions of the large intestine and briefly describe
the function of each.
Study Questions on Motility: Digestive System:
1. (Page 3.) In addition to grinding food into smaller pieces to be swallowed,
what other function or functions does the mouth serve?
2. (Page 4.) Briefly list the sequence of events that occur during swallowing.
3. (Page 4, 5.) Discuss the difference between primary and secondary
peristalsis.
4. (Page 6.) What is the function of peristaltic contractions in the stomach?
5. (Page 6.) What is the rate of peristaltic contractions in the stomach?
6. (Page 6.) What nervous system component(s) controls the frequency of
peristaltic contractions in the stomach?
7. (Page 6.) Describe the difference between gastric emptying and
retropulsion.
8. (Page 6.) What would cause the rate of gastric emptying to slow?
9. (Page 7.) Do short or long reflexes control the cephalic phase of
digestion?
10. (Page 7.) Gastric motility decreases during the cephalic phase of
digestion. True or false?
11. (Page 7.) Which hormone regulates gastric secretion during the gastric
phase?
12. (Page 7.) Describe the dual role of CCK during digestion.
13. (Page 7.) Discuss the enterogastric reflex.
14. (Page 8.) Compare and contrast segmentation and peristalsis.
15. (Page 8.) Compare the rate of segmentation in different regions of the
small intestine.
16. (Page 8.) Why is chyme moved so slowly through the small intestine?
17. (Page 9.) Describe the activity of the ileum when food is in the stomach.
18. (Page 9.) What effect does gastrin have on the ileum during the gastric
phase of digestion?
19. (Page 10.) Compare and contrast migrating motility complexes and
segmentation.
20. (Page 10.) How often do migrating motility complexes occur and what
neural mechanism controls this process?
21. (Page 11.) Compare and contrast mass movements and segmentation in
the colon.
22. (Page 11.) What are the major functions of the large intestine?
23. (Page 11.) Discuss the neuromuscular mechanisms that produce
defecation.
24. (Page 11.) What are feces primarily composed of?
25. (Page 12.) Which reflex regulates mass movements?
26. (Page 13.) Where is the control center for the vomiting reflex located?
27. (Page 13.) Describe the sequence of events that occur during vomiting.
28. (Page 13.) What might be an adaptive function of vomiting?
Study Questions on Digestive System Control:
1. (Page 3.) Looking at a picture of strawberry shortcake with whipped cream
would likely trigger the ______ phase of digestion.
2. (Page 3.) As the stomach expands, the _____ phase of digestion is
triggered.
3. (Page 3). Bicarbonate from the pancreas neutralizes acid chyme entering
the duodenum during the ______ phase of digestion.
4. (Page 4.) Increasing digestive processes is typically caused by stimulation
from the _______ division of the autonomic nervous system.
5. (Page 4.) What is the name of the cranial nerve that contains most of the
pre-ganglionic parasympathetic to the enteric nervous system?
6. (Page 5.) What are the two plexuses that comprise the enteric nervous
system?
7. (Page 6.) _____ reflexes are controlled by the central nervous system,
whereas _____ reflexes are controlled by the enteric nervous system.
8. (Page 6.) What does stomach contraction strength depend upon?
9. (Page 6.) Which would take longer to digest: 6 oz of deep-fried chicken or
6 oz of whole wheat bread?
10. (Page 6.) Worrying excessively about the quiz on this material may cause
constipation in some individuals. True or False?
11. (Page 7.) Preganglionic fibers of both the sympathetic and
parasympathetic divisions of the ANS release the neurotransmitter ____.
12. (Page 7.) Which ANS fibers release norepinephrine?
13. (Page 7.) Which ANS neurotransmitter inhibits digestion?
14. (Page 7.) Which neurotransmitter(s) released by the enteric nervous
system inhibits gastric motility and causes several sphincters to contract?
15. (Page 8.) GI hormones are steroids. True or False?
16. (Page 8.) List the hormones that influence digestive activity.
17. (Page 8.) Which hormone stimulates hydrochloric acid production in the
stomach?
18. (Page 8.) Which duodenal hormone would be secreted to stimulate the
emulsification process of lipids?
19. (Page 8.) Which organ secretes most of the hydrolytic digestive
enzymes?
20. (Page 8.) Which hormone would be released to stimulate neutralization of
acidic chyme in the duodenum?
21. (Page 8.) What is the function of GIP?
22. (Page 8.) Which duodenal hormone is released to speed the passage of
material through the lower digestive tract?
Study Questions on Anatomy Review: Digestive System:
1. (Page 3.) Which histological layer of the digestive tract contains goblet
cells for mucous secretion?
2. (Page 3). Which histological layer of the digestive tract is responsible for
producing peristaltic contractions?
3. (Page 3). Which network of neurons would you find in the muscularis
externa?
4. (Page 3). In which histological layer of the digestive tract would you find
lacteals?
5. (Page 4). What is the name of the 3rd muscularis externa layer found only
in the stomach?
6. (Page 5). List the three modifications of the small intestine that increase
surface area for digestion and absorption.
7. (Page 5). List the regions of the large intestine.
8. (Page 6). Which sphincter allows for defecation and is under voluntary
control?
9. (Page 7). Which accessory gland is located in the u-shaped fold of the
duodenum and is connected via a duct to that organ?