Anatomy and Physiology of the Upper GI Tract

Anatomy and
Physiology of upper
GI Tract
Edited by: Std.Dr.Orlando Joseph
Course:Sytemic Pathology
Insituition:Georgetown American University

Introduction
ofUpperGI
tract
 The GI, or digestive, tract extends from mouth to anus.
The division of the GI tract into upper and lower is a
matter of some confusion and debate.
 On embryologic grounds, the GI tract should be divided
into upper (mouth to major papilla in the duodenum),
middle (duodenal papilla to mid-transverse colon), and
lower (mid-transverse colon to anus), according to the
derivation of these 3 areas from the foregut, midgut,
and hindgut, respectively.
 Nevertheless, the GI tract is conventionally divided into
upper (mouth to duodenojejunal (DJ) junction).

UpperGI
structures
 Mouth
 Oral cavity
 Teeth
 Tongue
 Palates
 SalivaryGlands
 Tonsils
Stomach
 Greater and Lesser omentum
 Ligaments of stomach
 Muscles of stomach
 Cardia
 Fundus
 Body
 Pylorus
 Greater curvatures
 Lesser curvatures
 Blood and Nerve supply
 Esophagus
 EsophagealTube
 Muscular layer
 Esophageal constriction
 Esophageal sphincters
 Ligament, blood and
nerve supply
Small intestine(Duodenum)
 Parts of the duodenum
 Ligaments ,Blood and nerve
supply

Oral cavity
 The oral cavity is an internal area of the head that is
created by the bony space between the base of the skull
and its connection to the mandible via the
temporomandibular joint
 The oral cavity spans between the oral fissure (anteriorly
– the opening between the lips), and the oropharyngeal
isthmus (posteriorly – the opening of the oropharynx).

Divisions of the
oral cavity
 It is divided into two parts by
the upper and lower dental
arches(formed by the teeth
and their bony scaffolding).
 The two divisions of the oral
cavity are the vestibule, and
the mouth cavity proper.

Vestibule
 The horseshoe-shaped vestibule is situated anteriorly. It is the
space between the lips/cheeks, and the gums/teeth.
 The vestibule communicates with the mouth proper via the space
behind the third molar tooth, and with the exterior through the
oral fissure.The diameter of the oral fissure is controlled by the
muscles of facial expression – principally the orbicularis oris.
 Opposite the upper second molar tooth, the duct of the parotid
gland opens out into the vestibule, secreting salivatory juices

Mouth Proper
 The mouth proper lies posteriorly to the vestibule. It is
bordered by a roof, a floor, and the cheeks.The tongue fills a
large proportion of the cavity of the mouth proper.
The Roof
 The roof of the mouth proper consists of the hard and soft
palates.
 The hard palate is found anteriorly. It is a bony plate that
separates the nasal cavity from the oral cavity. It is covered
superiorly by respiratory mucosa and inferiorly by oral mucosa
 The soft palate is a posterior continuation of the hard palate. It
is a muscular structure. It acts as a valve that can lower to close
the oropharyngeal isthmus, and elevate to separate the
nasopharynx from the oropharynx.

Superficial
features of
palate
 The mucosa of the hard palate is tightly bound to the
underlying bone
 Deep to the mucosa are mucus-secreting palatine
glands with a pitted (orange-peel) appearance.
 Incisive papillaThis elevation of the mucosa lies directly
anterior to the underlying incisive fossa
 Transverse palatine folds or rugae folds assist with
manipulation of food during mastication.(laterally from
the incisive papilla)
 Palatine raphe is a narrow whitish streak(Passing
posteriorly in the midline of the palate from the incisive
papilla)

Hard and soft palates. A: transverse rugae
of hard palate; B: median raphe of hard
palate; C: median raphe of soft palate.

Mouth Proper
The Floor
 The floor of the oral cavity consists of several structures:
 Muscular diaphragm – comprised of the bilateral mylohyoid
muscles. It provides structural support to the floor of the mouth,
and pulls the larynx forward during swallowing.
 Geniohyoid muscles – pull the larynx forward during swallowing.
 Tongue – connected to the floor by the frenulum of the tongue, a
fold of oral mucosa.
 Salivary glands and ducts.

TheCheeks
 The cheeks are formed by the
buccinator muscle, which is lined
internally by the oral mucous
membrane.
 The buccinator muscle contracts to keep
food between the teeth when chewing,
and is innervated by the buccal branch
of the facial nerve (CNVII).

Innervation
 Sensory innervation of the oral cavity is supplied by the branches
of the trigeminal nerve (CNV).
 The hard palate is innervated by the greater palatine and
nasopalatine nerves, both of which are branches of the maxillary
nerve (CNV2).The soft palate is innervated by lesser palatine
nerve, another branch of the maxillary nerve.
 The floor of the oral cavity receives sensory innervation from the
lingual nerve – a branch of the mandibular (V3) division of the
trigeminal nerve.The tongue is also innervated by special sensory
fibers for taste from the chorda tympani, a branch of the facial
nerve (CNVII).
 The cheeks are innervated by the buccal nerve. It is also a branch
of the mandibular division of the trigeminal nerve.

TheTeeth
 The teeth are set in the tooth sockets and are used in mastication
and in assisting in articulation.
 A tooth is identified and described on the basis of whether it is
deciduous (primary) starting as teeth buds or permanent
(secondary), the type of tooth, and its proximity to the midline or
front of the mouth.
 Children have 20 deciduous teeth; adults normally have 32
permanent teeth

Classifications
ofTeeth
 The types of teeth are identified by their
characteristics:
 incisors, thin cutting edges
 canines, single prominent cones
 premolars (bicuspids),or two cusps
 molars, three or more cusps

Teeth
Structure
 The crown projects from the gingiva and is covered by enamel
 The neck is between the crown and root.
 The root is fixed in the tooth socket by the periodontium.They are
connected to the bone by fibrous joint called a dento-alveol syndesmosis or
gomphosis and is covered by cementum
 Pulp cavity a soft connective tissue-filled space covered by dentin. It has an
opening (apical foramen) permits the entrance and exit of blood vessels,
lymphatics, and nerves of the pulp cavity.

Teeth
Structure
 Dentine(L. dentinium), which is covered by enamel over the crown
with variable amount of trabeculated bone
 The periodontium (periodontal membrane) is composed of
collagenous fibers that extend between the cement of the root
and the periosteum of the alveolus.
 It is abundantly supplied with tactile, pressoreceptive nerve
endings, lymph capillaries and glomerular blood vessels that act as
hydraulic cushioning to curb axial masticatory pressure.
 The periodontal ligaments are bundles fibers inserted into both
the cementum and alveolar bone, fixing the tooth firmly in its
bony socket (alveolus)

Gingivae
 The gingivae (gums) are composed of fibrous tissue covered with
mucous membrane.
 The gingiva proper is normally pink, stippled, and keratinizing
 The gingiva proper (attached gingiva) is firmly attached to the
alveolar processes of the mandible and maxilla and the necks of
the teeth.
 The alveolar mucosa(un attached gingiva) is normally shiny red
and non-keratinizing.

Innervation
and
vasculature
 The superior and inferior alveolar arteries, branches of the
maxillary artery, supply the maxillary and mandibular teeth.
 The alveolar veins have the same names and distribution
accompany the arteries. Lymphatic vessels from the teeth and
gingivae pass mainly to the submandibular lymph nodes.
 The nerves supplying the teeth are (other slide)The named
branches of the superior (CNV2) and inferior (CNV3) alveolar
nerves give rise to dental plexuses that supply the maxillary and
mandibular teeth.

Tongue
 The tongue (L. lingua;G. glossa) is a mobile muscular organ
covered with mucous membrane.
Parts and surfaces of tongue
The root-of the tongue is the attached posterior portion,
extending between the mandible, hyoid, and the nearly vertical
posterior surface of the tongue
The body of the tongue is the anterior, approximately two thirds
of the tongue between root and apex.
The apex (tip) of the tongue is the anterior end of the body, which
rests against the incisor teeth.
The body and apex of the tongue are extremely mobile.

Surfaces of
theTongue
The tongue features two surfaces.
 Dorsum of the tongue commonly
(TopTongue) is the more extensive,
superior and posterior surface is the
foramen cecum.
 It is characterized by aV-shaped
groove, the terminal sulcus of the
tongue
 The terminal sulcus divides the
dorsum of the tongue transversely
into a presulcal anterior part in the
oral cavity proper and a postsulcal
posterior part in the oropharynx.
 The inferior surface of the tongue
(commonly referred to as its
“underside”) usually rests against
the floor of the mouth.

Lingual
Papillae
 A midline groove divides the anterior part of the tongue into right
and left parts.
 The mucosa of the anterior part of the tongue is relatively thin and
closely attached to the underlying muscle. It has a rough texture
because of numerous small lingual papillae:
Vallate papillae
Foliate papillae
Filiform papillae
Fungiform papillae
• The vallate, foliate, and most of the fungiform papillae contain
taste receptors in the taste buds.

 Vallate papillae(or circumvallate): large and flat topped, lie directly
anterior to the terminal sulcus and are arranged in aV-shaped row.They are
surrounded by deep circular trenches, the walls of which are studded with
taste buds.The ducts of the serous glands of the tongue open into the
trenches.
 Foliate papillae: small lateral folds of the lingual mucosa.They are poorly
developed in humans.
 Filiform papillae: long and numerous, contain afferent nerve endings that
are sensitive to touch.These scaly, conical projections are pinkish gray and
are arranged inV-shaped rows that are parallel to the terminal sulcus, and
transverse at apex.
 Fungiform papillae: mushroom shaped pink or red spots scattered among
the filiform papillae but most numerous at the apex and margins of the
tongue.

Inferior
surface of the
tongue
 The inferior surface of the tongue is covered with a
 thin, transparent mucous membrane .
 This surface is connected to the floor of the mouth by a midline fold called
the frenulum of the tongue.The frenulum allows the anterior part of the
tongue to move freely.
 On each side of the frenulum, a deep lingual vein is visible through the thin
mucous membrane.
 A sublingual caruncle (papilla) is present on each side of the base of the
lingual frenulum that includes the opening of the submandibular duct from
the sub mandibular salivary gland.

Salivary
Glands
 The salivary glands are exocrine glands that are positioned in and
around the oral cavity and secrete their salivary contents into the
mouth .
 They are divided into the major and minor salivary glands and the
difference between them is that firstly the major ones are much
larger in size and are a collection of exocrine tissue that secretes
as a whole into a salivary duct.
 The main role of the minor glands is to lubricate the oral cavity,
while digestive and protective saliva is produced by the major
glands.

Types of
Salivary
Glands
The Major &
Minor
Glands
 The parotid gland is the largest of the major salivary glands and it
sits bilaterally in between the ramus of the mandible and the
sternocleidomastoid muscle. It produces between twenty five and
thirty percent of the total daily salivary output which is released
through Stensen’s duct whose orifice can be seen on the buccal
wall at the level of the maxillary second molar.
 The submandibular gland is the second largest of the major
salivary glands and like all three of them it is a paired gland which
lie along the body of the mandible, partly superior and partly
inferior to the posterior half of the mandible, and partly superficial
and partly deep to the mylohyoid muscle. It produces by far the
largest amount of saliva of all .
 Wharton’s duct opens at the sublingual papilla under the tongue.

 The sublingual gland is the smallest with each almond-shaped
gland lying in the floor of the mouth between the mandible and
the genioglossus muscle. Its has several ductal openings that run
along the sublingual folds.The glands from each side unite to form
a horseshoe-shaped mass around the connective tissue core of the
lingual frenulum.
 The minor salivary glands account for less of the total daily
salivary output.They can be found in patches around the oral
cavity such as the bucca, the labia, the lingual mucosa, the soft
palate, the lateral parts of the hard palate, the floor of the mouth
and between the muscle fibers of the tongue.

Tonsils
 The tonsils are masses of lymphoid tissue arranged inWaldeyer’s ring
and acts act as the first line of defense against ingested or inhaled
pathogens.
Palatine tonsils-These are located between the palatoglossal arch
anteriorly and the palatopharyngeal arch posteriorly.They are located in
the isthmus of the fauces (a cavity bound laterally by the palatoglossal
arches, superiorly by the soft palate and by the tongue underneath).
Lingual tonsils-These are small round elevations that sit on the most
posterior part of the tongue base.
Tubal tonsils -These tonsils are located just posterior to the opening of
the Eustachian tube (the torus tubaris) in the nasopharynx.
Pharyngeal tonsils/Adenoids-These are the most superior tonsils that lie
in the superior part of the nasopharynx. It is attached to the periosteum
of the sphenoid bone by connective tissue.

The
Esophagus
 The esophagus is a muscular tube
(approximately 25 cm[10 in] long) with an
average diameter of 2 cm that conveys food
from the pharynx to the stomach.
 It originates at the inferior border of the cricoid
cartilage, C6, extending to the cardiac orifice of
the stomach,T11.
 It descends downward into the superior
mediastinum of the thorax. Here, it is situated
between the trachea and the vertebral bodiesT1
toT4.
 It then enters the abdomen by piercing the
muscular right crus of the diaphragm, through
the esophageal hiatus (simply, a hole in the
diaphragm) at theT10 level.

Esophageal
Constrictions
 Cervical constriction (upper esophageal sphincter): at its
beginning at the pharyngo esophageal junction, approximately 15
cm from the incisor teeth; caused by the cricopharyngeus muscle
 Thoracic (broncho-aortic) constriction: a compound constriction
where it is first crossed by the arch of the aorta, 22.5 cm from the
incisor teeth, and then where it is crossed by the left main
bronchus, 27.5 cm from the incisor teeth; the former is seen in
anteroposterior views, the latter in lateral views.
 Diaphragmatic constriction: where it passes through the
esophageal hiatus of the diaphragm, approximately 40cm from
the incisor teeth

Features of the
Esophagus
 Follows the curve of the vertebral column as it descends through the
neck and mediastinum—the median partition of the thoracic cavity
 Has internal circular and external longitudinal layers of muscle.
 In its superior third, the external layer consists of voluntary striated
muscle; the inferior third is composed of smooth muscle, and the middle
third is made up of both types of muscle.
 Passes through the elliptical esophageal hiatus in the muscular right crus
of the diaphragm, just to the left of the median plane at the level of the
T10 vertebra.
 Terminates by entering the stomach at the cardial orifice of the stomach
to the left of the midline at the level of the 7th left costal cartilage and
T11 vertebra
 Is encircled by the esophageal (nerve) plexus distally

 The phrenoesophageal ligament connects the esophagus to the border of the
esophageal hiatus.This permits independent movement of the esophagus and
diaphragm during respiration and swallowing.
 The trumpet-shaped abdominal part of the esophagus, only 1.25 cm long,
passes from the esophageal hiatus in the right crus of the diaphragm to the
cardial orifice of the stomach, widening as it approaches, passing anteriorly and
to the left as it descends inferiorly.
 Its anterior surface is covered with peritoneum of the greater sac and it fits into
a groove on the posterior (visceral) surface of the liver.

 The posterior surface of the abdominal part of the
esophagus is covered with peritoneum of the omental
bursa, continuous with that covering the posterior
surface of the stomach.
 The right border of the abdominal esophagus is
continuous with the lesser curvature of the stomach;
however, its left border is separated from the fundus of
the stomach by the cardial notch between the
esophagus and fundus .
 The esophagogastric junction lies to the left of theT11
vertebra on the horizontal plane that passes through
the tip of the xiphoid process called Z-line. Its a change
from esophageal mucosa to gastric mucosa.

Esophageal
Sphincters
Upper Esophageal Sphincter
 The upper sphincter is an anatomical, striated muscle sphincter at
the junction between the pharynx and esophagus. It is produced
by the cricopharyngeus muscle. Normally, it is constricted to
prevent the entrance of air into the esophagus.
Lower Esophageal Sphincter
 The lower esophageal sphincter is a physiological sphincter
located in the gastro-esophageal junction (junction between the
stomach and esophagus).The gastro-esophageal junction is
situated to the left of theT11 vertebra, and is marked by the
change from esophageal to gastric mucosa.

Lower
Esophageal
Sphincter
The sphincter is classified as a physiological (or functional)
sphincter, as it does not have any specific sphincteric muscle.
Instead, the sphincter is formed from four phenomena:
The esophagus enters the stomach at an acute angle.
The walls of the intra-abdominal section of the esophagus are
compressed when there is a positive intra-abdominal pressure.
The folds of mucosa present aid in occluding the lumen at the
gastro-esophageal junction.
The right crus of the diaphragm has a “pinch-cock” effect.

Vasculatures
Thoracic
 The thoracic part of the esophagus receives its arterial supply from the
branches of the thoracic aorta and the inferior thyroid artery (a branch of the
thyrocervical trunk).Venous drainage into the systemic circulation occurs via
branches of the azygous veins and the inferior thyroid vein.
 Abdominal
 The abdominal esophagus is supplied by the left gastric artery (a branch of
the coeliac trunk) and left inferior phrenic artery.This part of the esophagus
has a mixed venous drainage via two routes:
To the portal circulation via left gastric vein
To the systemic circulation via the azygous vein.
 These two routes form a porto-systemic anastomosis, a connection between
the portal and systemic venous systems.

Lymphatics
and
Innervation
 The lymphatic drainage of the esophagus is divided into thirds:
 Superior third – deep cervical lymph nodes.
 Middle third – superior and posterior mediastinal nodes.
 Lower third – left gastric and celiac nodes.
 The esophagus is innervated by the esophageal plexus, formed by the
vagal trunks (becoming anterior and posterior gastric branches), and
the thoracic sympathetic trunks via the greater (abdominopelvic)
splanchnic nerves and periarterial plexuses around the left gastric and
inferior phrenicarteries.

TheStomach
 The stomach is a
digestive organ located
between the esophagus
and the duodenum.
 It has a ‘J’ shape
 An empty stomach is only
of slightly larger caliber
than the large intestine;
however, it is capable of
considerable expansion
and can hold 2–3 L of
food.

Anatomical
Position
 The stomach is located in the superior aspect of the abdomen. It lies
in the epigastric and umbilical regions, mostly protected by the lower
portion of the rib cage.
 The exact size, shape and position of the stomach can vary from
person to person.
 Its change is a result of diaphragmatic movements during respiration,
the stomach’s contents (empty vs. after a heavy meal), and the
position of the person.
 In the supine position, the stomach commonly lies in the right and
left upper quadrants, or epigastric, umbilical, and left hypochondrium
and flank regions.
 In the erect position, the stomach moves inferiorly. In asthenic (thin,
weak) individuals, the body of the stomach may extend into the
pelvis

Stomach
coverings
Greater and
Lesser
Omenta
 The greater and lesser omenta are two structures that consist of
peritoneum folded over itself (two layers of peritoneum – four
membrane layers). Both omenta attach to the stomach, and are
useful anatomical landmarks:
 Greater omentum – hangs down from the greater curvature of the
stomach. It drapes over the transverse colon and folds back upon
itself before reaching the posterior abdominal wall. It features
many lymph nodes, which contain macrophages to help combat
infections of the GI tract.
 Lesser omentum – continuous with peritoneal layers of the
stomach and duodenum.These two layers combine at the lesser
curvature, and ascend to attach to the liver.The main function of
the lesser omentum is to attach the stomach and duodenum to
the liver.
 The bed of the stomach, on which the stomach rests in the supine
position, is formed by the structures forming the posterior wall of
the omental bursa

Ligaments of
stomach
Lesser omentum Ligaments
The hepatogastric ligament extends from the fissure of the ligamentum
venosum and porta hepatis to the lesser curvature of the stomach.
Hepatoduodenal ligament is the peritoneal ligament of lesser omentum,
which attaches the duodenum to the liver.
Greater omentum ligament
The gastrosplenic ligament extends from the greater curvature of the
stomach to the hilum of the spleen. It contains the short gastric arteries.
Splenorenal ligament is a peritoneal ligament. It represents the dorsal
most part of dorsal mesentery.

Parts of
stomach
 Cardia: the part surrounding the cardial orifice
(opening),the superior opening or inlet of the stomach.
In the supine position, the cardial orifice usually lies
posterior to the 6th left costal cartilage, 2–4 cm from
the median plane at the level of theT11 vertebra.
 Fundus: the dilated superior part that is related to the
left dome of the diaphragm, limited inferiorly by the
horizontal plane of the cardial orifice.The cardial notch
is between the esophagus and the fundus.The fundus
may be dilated by gas, fluid, food, or any combination
of these. In the supine position, the fundus usually lies
posterior to the left 6th rib in the plane of the MCL

Parts of
stomach
 Body: the major part of the stomach between the
fundus and pyloric antrum.
 Pyloric part: the funnel-shaped outflow region of the
stomach; its wider part, the pyloric antrum, leads into
the pyloric canal, its narrower part .The pylorus (G.,
gatekeeper) is the distal, sphincter region of the pyloric
part.
 It is a marked thickening of the circular layer of smooth
muscle that controls discharge of the stomach
contents through the pyloric orifice (inferior opening or
outlet of the stomach) into the duodenum.

Normal Pyloric area of the stomach

Curvatures
of the
Stomach
 Lesser curvature: forms the shorter
concave right border of the stomach.
The angular incisure (notch), the most
inferior part of the curvature, indicates
the junction of the body and pyloric
part of the stomach.The angular
incisure lies just to the left of the
midline.The lesser curvature gives
attachment to the hepatogastric
ligament
 Greater curvature: forms the longer
convex left border of the stomach. It
passes inferiorly to the left from the
junction of the 5th intercostal space
and MCL, then curves to the right,
passing deep to the 9th or 10th left
cartilage as it continues medially to
reach the pyloric antrum.

Sphincters
of the
Stomach
 Inferior Esophageal Sphincter
 The inferior esophageal sphincter is located
between the esophagus and the stomach. It
is located to the left of theT11 vertebra.
Situated immediately superior is the
esophageal hiatus, an opening in the
diaphragm through which the esophagus
travels.
 Pyloric Sphincter
 Its an anatomical sphincter.The pyloric
sphincter lies between the pylorus and the
duodenum. It controls of the exit of chyme
(food and gastric acid mixture) from the
stomach is smooth muscle through pyloric
orifice.
 Emptying of the stomach occurs
intermittently when intragastric pressure
overcomes the resistance of the pylorus.

Interior of
theStomach
 The smooth surface of the gastric mucosa is reddish brown during life,
except in the pyloric part, where it is pink. In life, it is covered by a
continuous mucous layer that protects its surface from the gastric acid the
stomach’s glands secrete.
 When contracted, the gastric mucosa is thrown into longitudinal ridges or
wrinkles called gastric folds (gastric rugae) .The gastric folds diminish and
obliterate as the stomach is distended (fills)
 Gastric canal forms between the longitudinal gastric folds along the lesser
curvature during swallowing. Saliva and small quantities of masticated food
and other fluids drain along the gastric canal to the pyloric canal when the
stomach is mostly empty.

Anatomical
Relations of
Stomach

Neurovascular
Supply
 The arterial supply to the stomach comes from the coeliac trunk and its
branches. Anastomoses form along the lesser curvature by the right and left
gastric arteries and along the greater curvature by the right and left gastro-
omental arteries:
 Right gastric – branch of the common hepatic artery, which arises from the
coeliac trunk.
 Left gastric – arises directly from the coeliac trunk.
 Right gastro-omental – terminal branch of the gastroduodenal artery, which
arises from the common hepatic artery.
 Left gastro-omental – branch of the splenic artery, which arises from the
coeliac trunk.
 The veins of the stomach run parallel to the arteries.The right and left
gastric veins drain into the hepatic portal vein.The short gastric vein, left and
right gastro-omental veins ultimately drain into the superior mesenteric
vein.

Lymphatic
drainage and
Innervation
 The stomach receives innervation from the autonomic
nervous system:
 Parasympathetic nerve supply comes from the
posterior vagal trunks, derived from the vagus nerve.
 Sympathetic nerve supply from theT6-T9 spinal cord
segments pass to the coeliac plexus. It also carries
some pain transmitting fibres.
 The gastric lymphatic vessels travel with the arteries
along the greater and lesser curvatures of the stomach.
Lymph fluid drains into the gastric and gastro-omental
lymph nodes found at the curvatures.
 Efferent lymphatic vessels from these nodes connect
to the coeliac lymph nodes, located on the posterior
abdominal wall.

Small
Intestine
 The small intestine is an organ
located within the
gastrointestinal tract. It assists
in the digestion and absorption
of ingested food.
 The small intestine, consisting
of 3 parts
 duodenum
 jejunum
 ileum

The
Duodenum
 The duodenum (L. breadth of 12 fingers), the first and
shortest (25 cm) part of the small intestine, is also the
widest and most fixed part.
 The duodenum pursues a C-shaped course around the
head of the pancreas.
 It begins at the pylorus on the right side and ends at the
duodenojejunal flexure (junction) on the left side.This
junction occurs approximately at the level of the L2
vertebra, 2–3 cm to the left of the midline.

 The junction usually takes the form of an acute angle,
the duodeno jejunal flexure.
 Most of the duodenum is fixed by peritoneum to
structures on the posterior abdominal wall and is
considered partially retroperitoneal.

Parts of the
Duodenum
 Superior duodenum
 Descending duodenum
 Inferior duodenum
 Ascending duodenum

Parts of the
duodenum
The Superior Parts(L1)
 The first section of the duodenum (‘the cap’) is 5cm in length. It
ascends upwards from the pylorus of the stomach and lies
anterolateral to the body of the L1 vertebra.
 It is connected to the liver by the hepatoduodenal ligament.
 The initial 3cm of the superior duodenum is covered anteriorly and
posteriorly by visceral peritoneum, with the remainder
retroperitoneal (only covered anteriorly).

Descending Part (L1-L3)
 The descending portion curves inferiorly around the head of the
pancreas. It lies posteriorly to the transverse colon, and anterior to
the right kidney.
 Internally, the descending duodenum is marked by the major
duodenal papilla – an opening for bile and pancreatic secretions to
enter.The duct responsible carrying these secretions is known as
the ampulla ofVater (hepatopancreatic ampulla).

Inferior Part (L3)
 The inferior duodenum travels laterally to the left, crossing over
the inferior vena cava and aorta. It is located inferiorly to the
pancreas, and posteriorly to the superior mesenteric artery and
vein.
Ascending (L3-L2)
 After the duodenum crosses the aorta, it ascends and curves
anteriorly to join the jejunum at a sharp turn known as the
duodenojejunal flexure.
 Located at the duodenojejunal junction is a slip of muscle called
the suspensory muscle of the duodenum. Contraction of this
muscle widens the angle of the flexure, and aids movement of the
intestinal contents into the jejunum.

Vasculature
The arterial supply of the duodenum is derived from two sources:
 Proximal to the major duodenal papilla – supplied by the
gastroduodenal artery (branch of the coeliac trunk).
 Distal to the major duodenal papilla – supplied by the inferior
pancreaticoduodenal artery (branch of superior mesenteric
artery).
 This transition is important – it marks the change from the
embryological foregut to midgut.The veins of the duodenum
follow the major arteries and drain into the hepatic portal vein.

Lymphatics
and
Innervation
 The nerves of the duodenum derive from the vagus and greater
and lesser (abdominopelvic) splanchnic nerves by way of the celiac
and superior mesenteric plexuses.The nerves are next conveyed
to the duodenum via peri-arterial plexuses extending to the
pancreaticoduodenal arteries

UpperGI
Functions
Basic GI Regulations
 Enteric Nervous System
 Autonomic GI Neural Control
 Cholecystokinin
 Gastrin
 Secretin
 Gastrin Inhibitory Peptide
GI Secretion
 Salivary Secretion
 Gastric Secretion
 StomachAcid Secretion
 Small Intestine Secretion
GI Motility
 Basic GI Motility
Mechanisms
 Electrical Basis of GI
Rhythmic Contractions
 GI Motility Patterns
 Mastication
 Swallowing
 Gastric Motility
 Small Intestinal MotilityGI Digestion and
Absorption
 Carbohydrate Digestion
and Absorption
 Protein Digestion and
Absorption
 GI Lipid Digestion
 GI LipidAbsorption
 GIVitaminAbsorption

OralCavity
Function
 The oral cavity, better known as the mouth, is the start of the
alimentary canal. It has three major functions:
 Digestion – receives food, preparing it for digestion in the
stomach and small intestine.
 Communication – modifies the sound produced in the larynx to
create a range of sounds.
 Breathing – acts as an air inlet in addition to the nasal cavity.

Teeth
Function
 The chief functions of teeth are to:
 Incise (cut), reduce, and mix food material with salivary during
mastication (chewing).
 Help sustain themselves in the tooth sockets by assisting the
development and protection of the tissues that support them.
 Participate in articulation (distinct connected speech).

TheTongue
 The tongue’s main functions are articulation (forming words
during speaking) and squeezing food into the oropharynx as part
of deglutition (swallowing).
 The tongue is also involved with mastication, taste, and oral
cleansing.

Salivary
Glands
Function
The clear, tasteless, odorless, viscid, fluid, saliva, secreted by these
glands and the mucous glands of the oral cavity:
 Keeps the mucous membrane of the mouth moist.
 Lubricates the food during mastication.
 Begins the digestion of starches.
 Antimicrobial
 Plays significant roles in the prevention of tooth decay and in the
ability to taste

Esophagus
Function
 The Esophagus aid the passage of food from the pharynx to the
stomach.
 This is done by the esophagus ability to create a contracting wave
known as peristalsis which contracts the smooth and longitudinal
muscles of the tube to allow movement of food in a forward
motion.
 The lower and upper esophageal sphincter helps to prevents the
reflux of food back up the tract

Stomach
Function
 The stomach is specialized for the accumulation of ingested food,
which it chemically and mechanically prepares for digestion and
passage into the duodenum.
 It acts as a food blender and reservoir; its chief function is
enzymatic digestion.
 The gastric juice gradually converts a mass of food into a
semiliquid mixture, chyme (G. juice), which passes fairly quickly
into the duodenum.

Enteric
Nervous
system
 This network of neurons exerts substantial, independent control
on GI functions and is termed the "Enteric Nervous System".
Location and Functionality
 Most of the neurons of the enteric nervous system are located in
the submucosa and the muscular is propria of the GITract.
 The submucosal plexus(Messiner)is located within the GI
submucosa and mostly regulates GI Secretion.
 The myenteric plexus(Auerbach) is located between the circular
and longitudinal muscle layers of the GI and mostly regulates GI
motility.

Circuitry
Internal Connections:
 The submucosal and myenteric plexuses possess significant
connections between one another.There is also significant neural
input from the GI epithelium, especially to the submucosal plexus,
which helps regulate secretion and absorption.
External Connections
 The enteric nervous system also possesses significant afferent and
efferent connections with the autonomic nervous system.This
allows the CNS to modulate the alimentary tract and conversely
allows the alimentary tract to modulate central behavior.The
connections between the enteric nervous system and the
autonomic nervous system are described in Autonomic GI Neural
Control.

Autonomic
Nervous
System
Parasympathetic Nervous System Innervation
Generally speaking, parasympathetic stimulation tends to enhance nearly all
functions of the alimentary tract including motility and secretion.
Circuitry
 Preganglionic parasympathetic fibers innervating the alimentary tract
travel via the vagus nerve and the pelvic nerve and are located in the GI
walls
 Neurotransmitters:
 Most parasympathetic post-ganglionic neurons release acetylcholine.
However, some parasympathetic post-ganglionic neurons release non-
traditional peptide neurotransmitters, termed "Neurocrines", the major
examples of which includeVIP, GRP, NeuropeptideY.

Sympathetic Nervous System Innervation
 Generally speaking, sympathetic activity tends to inhibit nearly all
functions of the alimentary tract including motility and secretion.
Circuitry
 SNS pre-ganglionic fibers exit throughout the levels of the spinal
cord and synapse onto ganglia located outside the alimentary
tract such as the celiac ganglia and other mesenteric ganglia. Post-
synaptic neurons run from these ganglia to innervate the length of
the GI tract.
Neurotransmitters
 SNS post-ganglionic neurons generally release norepinephrine.

Gastrointestinal
Regulatory
Substances

Gastrointestinal
Neurosubstance
Regulation

Gastrointestinal
Hormone
Regulation

Satiety
 The centers that control appetite and feeding behavior are located
in the hypothalamus.A satiety center, which inhibits appetite even
in the presence of food, is located in the ventromedial nucleus
(VPN) of the hypothalamus and a feeding center is located in the
lateral hypothalamic area (LHA). Information feeds into these
centers from the arcuate nucleus of the hypothalamus.
 The arcuate nucleus has various neurons that project onto the
satiety feeding centers.
 Anorexigenic neurons release pro-opiomelanocortin (POMC) and
cause decreased appetite; orexigenic neurons release
neuropeptideY and cause increased appetite.

Motility
 Motility is a general term that refers to contraction and relaxation
of the walls and sphincters of the gastrointestinal tract.
 Motility grinds, mixes, and fragments ingested food to prepare it
for digestion and absorption, and then it propels the food along
the gastrointestinal tract.
 All of the GI muscles are smooth except the pharynx ,upper 1/3 GI
and external anal sphincter(striated)
 The GI tract motility occurs by unitary smooth muscles vis gap
junction using its two muscles , circular muscle(shortening of a
ring of smooth muscle, which decreases the diameter of that
segment) and longitudinal muscle (contracts, it results in
shortening in the longitudinal direction, which decreases the
length of that segment)

Contractions
of
Gastrointestinal
smooth muscle
 Phasic contractions are periodic contractions followed by
relaxation. Phasic contractions are found in the esophagus, gastric
antrum, and small intestine, all tissues involved in mixing and
propulsion.
 Tonic contractions maintain a constant level of contraction or tone
without regular periods of relaxation.They are found in the orad
(upper) region of the stomach and in the lower esophageal,
ileocecal, and internal anal sphincters.

Slow waves
 Slow waves are a unique feature of the electrical activity of gastrointestinal
smooth muscle.They are oscillating depolarization and repolarization of the
membrane potential of the smooth muscle cells.
 Frequency of slow waves.The intrinsic rate, or frequency, of slow waves varies
along the gastrointestinal tract, from 3 to 12 slow waves per minute.(Its no
influence by neural or hormonal inputs)
 Origin of slow waves. It is believed that slow waves originate in the interstitial
cells of Cajal, which are abundant in the myenteric plexus.They act as the
pacemaker of the GI tract.
 Mechanism: occurs vis opening of Ca2+ channels to depolarized the
membrane causing an action potential and contraction while K+ causes
repolarization of the membrane.
 The SNS when acts on the GI system allows hyperpolarizing of the GI slow
ways while PNS depolarizes it to allow GI activation and motility of slow ways

Pattern of
Slow wave
Contraction
Peristalsis
 Peristalsis is a pattern of GI motility which propels GI
contents unidirectionally, generally toward the Anus.
 Physical Basis
 Peristalsis is generally initiated by distension of a
particular segment of the GI tract. Distention initiates
contraction of a ring of muscle several centimeters
behind the bolus, thus pushing the bolus anally.
Additionally, distention induces alimentary segments
several centimeters in front of the bolus to relax,
facilitating its forward movement.
 Regulatory Basis
 Coordination of peristalsis is achieved by the
myenteric plexus. However, the autonomic nervous
system can modulate the amount of peristalsis that
occurs, with the parasympathetic nervous system
generally enhancing peristalsis and the sympathetic
nervous system generally displaying an inhibitory
effect.

Mixing Movements
 Mixing movements are a pattern of GI motility that helps to mix and
churn GI contents.
 Physical Basis
 Some mixing is achieved by performing peristalsis against a closed
sphincter and this is the primary basis of mixing in the stomach (See:
Gastric Motility). In other cases, a contractile rings occur intermittently at
random segments throughout a section of the GI tract.This pattern,
referred to as "Segmentation", effectively chops the GI contents, thus
mixing it without moving it in any particular direction.
 Regulatory Basis
 Coordination of mixing movements is achieved by the myenteric plexus.
However, the autonomic nervous system can modulate the amount of
mixing movements, with the parasympathetic nervous system generally
enhancing mixing and the sympathetic system generally displaying an
inhibitory effect.

Mastication
 Mastication is the physical act of chewing food and is performed in the oral
cavity with the aid of teeth.This is the first step of digestion .Mastication has
3 function:
(1) It mixes food with saliva, lubricating it to facilitate swallowing
(2) it reduces the size of food particles, which facilitates swallowing (although
the size of the swallowed particles has no effect on the digestive process)
(3) it mixes ingested carbohydrates with salivary amylase to begin
carbohydrate digestion.
 Mastication has both voluntary and involuntary components.The
involuntary component involves reflexes initiated by food in the mouth.
 Sensory information is relayed from mechanoreceptors in the mouth to the
brain stem, which orchestrates a reflex oscillatory pattern of activity to the
muscles involved in chewing.Voluntary chewing can override involuntary or
reflex chewing at any time.

Swallowing
 Swallowing is initiated voluntarily in the mouth, but thereafter it is
under involuntary or reflex control.The reflex portion is controlled
by the swallowing center, which is located in the medulla.
 Somatosensory receptors near pharynx detects sensory
information and transmits it to medulla via CNX and CN IX.
 The medulla coordinates the sensory information and directs the
motor, or efferent, output to the striated muscle of the pharynx
and upper esophagus
 Three phases are involved in swallowing: oral, pharyngeal, and
esophageal.The oral phase is voluntary, and the pharyngeal and
esophageal phases are controlled by reflexes.

Phases of
Swallowing
Oral phase
 The oral phase is initiated when the tongue forces a bolus of food back toward
the pharynx, which contains a high density of somatosensory receptors which
activates and initiates swallowing
Pharyngeal phase
 The purpose of the pharyngeal phase is to propel the food bolus from the
mouth through the pharynx to the esophagus in the following steps:
 (1)The soft palate is pulled upward, creating a narrow passage for food to move
into the pharynx so that food cannot reflux into the nasopharynx.
 (2)The epiglottis moves to cover the opening to the larynx, and the larynx
moves upward against the epiglottis to prevent food from entering the
trachea.
 (3)The upper esophageal sphincter relaxes, allowing food to pass from the
pharynx to the esophagus.
 (4) A peristaltic wave of contraction is initiated in the pharynx and propels food
through the open sphincter. Breathing is inhibited during the pharyngeal phase
of swallowing.

Esophageal phase.
 The esophageal phase is controlled in part
by the swallowing reflex and the enteric
nervous system where food from esophagus
to stomach.
 Once the bolus has passed through the UES
in the pharyngeal phase, the swallowing
reflex closes the sphincter so that food
cannot reflux into the pharynx.
 A primary peristaltic wave, also coordinated
by the swallowing reflex, travels down the
esophagus, propelling the food along.
 A secondary peristatic wave is initiated to
clear the esophagus if the bolus gets stuff .

Esophageal
Motility
 The UES opens and allows the bolus to move from the pharynx to
the esophagus.Once the bolus enters the esophagus and the UES
closes
 A primary peristaltic contraction, allowing peristalsis.This occurs
by a high pressure just behind the bolus, pushing it down the
esophagus which can be accelerated by gravity. If the bolus is not
clear a second peristalsis wave is initiated.
 As the peristaltic wave and the food bolus approach the lower
esophageal sphincter, LES opens.The vagus nerves releasesVIP
LES relaxation and the orad region of the stomach also relaxes
called receptive relaxation.
 Food enters the stomach and the LES returns back to normal to
prevent gastric reflux

Gastric
Motility
 There are three components of gastric motility:
(1)Receptive Phase
Relaxation of the orad region of the stomach to receive the food bolus from the
esophagus. Receptive relaxation is a vagovagal reflex. Mechanoreceptors
present in the stomach detects the distention of the region and releaseVIP to aid
in relaxation of orad region.
(2) Segmentation and Digestion
Gastric segementation is mediated by peristaltic waves that begin in the mid-
stomach and progress through the caudad stomach. During mixing the pylorus
muscle is contracted, thus preventing any stomach contents from emptying into
the small intestine.The waves become stronger as they approach the closed
pylorus, thus helping mix and break up the food into a semi-liquid slurry known
as 'Chyme'.This is down by the longitudinal,circular and circular muscles of the
stomach
Retropulsion occurs in the stomach to allow food to be mix properly by allowing
increase in pressure that closes the pylorus as stomach muscles spins the food
like a cake mixer.

 (3)Gastric Emptying
 Gastric emptying occurs when the pressures
created by the gastric peristaltic waves exceed the
closing pressure of the pylorus muscle, causing
'Chyme' to be forced through the pyloric sphincter.
This occurs either by increasing the peristaltic
pressures or relaxing the pylorus muscle. In general,
gastric emptying is delayed if there is excessive acid
or undigested fats within the small intestine.
 Two major factors slow or inhibit gastric emptying
(i.e. Increase gastric emptying time): the presence
of fat that allowsCCK release causing inhibition to
allow proper fat digestion and the presence of H+
ions (low pH) that cause pylorus muscle via
ENS(myenteric plexus) to contract when they enter
the duodenum.

 Parasympathetic stimulation and the hormones gastrin and
motilin increase the frequency of action potentials and the force of
gastric contractions.
 Sympathetic stimulation and the hormones secretin and GIP
decrease the frequency of action potentials and the force of
contractions.
 During fasting, there are periodic gastric contractions, called the
migrating myoelectric complexes, which are mediated by motilin.
These contractions occur at 90-minute intervals and function to
clear the stomach of any residue remaining from the previous
meal.

Small Intestine
Motility
 Motility of the small intestine allows ingested foods to be mixed
with digestive fluids, exposes foods to the small intestine mucosa
for absorption, and moves the foods along the length of the
intestine.This motility occurs vis segmentation and peristalsis.
Segmentation Contractions
 Segmentation contractions serve to mix the chyme and expose it
to pancreatic enzymes and secretions .
 When a bolus enters into the intestine a wave of contraction
breaks the bolus in the middle and then relaxes.This process
occurs along the orad and caudad regions of the tube.

Peristaltic Contractions
 Peristaltic contractions are designed to propel the chyme along
the small intestine toward the large.
 This occurs by contraction initiating at the back of the bolus at
orad section and relaxation at the caudad section.The chyme is
thereby propelled in the caudad direction.This motion is repeated
until the bolus reaches small intestine caudad region.
 Small intestine motility occurs via inverse contraction of the
longitudinal and circular muscles of the intestine.
 The peristaltic reflex of small intestine occurs enterochromaffin
cells of the intestinal mucosa that senses the bolus and release
serotonin (5-hydroxytyptamine, 5-HT).The 5-HT binds to
receptors on intrinsic primary afferent neurons (IPANs) and the
reflex start.

Peristalsis of
Small
intestine

Salivary
Secretion
 Saliva, which is produced by the salivary glands at the rate of 1 L
per day, is secreted into the mouth and compose of water,
electrolytes, α-amylase, lingual lipase, kallikrein, and mucus.
 Saliva is a aqwous hyptonic solution filled with high concertation
of K+ and HCO3− and low Na+ and chloride (Cl−) concentrations
 The functions of saliva include initial digestion of starches and
lipids by salivary enzymes; dilution and buffering of ingested
foods, which may otherwise be harmful; and lubrication of
ingested food with mucus to aid its movement through the
esophagus.
 It produce in acinar cells of salivary acini that drains into
intercalated ducts onto striated ducts lined by ductal cells that
modifies its composition.Mypepiteheal cells present in the salivary
glands aids in its ejection into the mouth

Formation of
Saliva
HCO3- + H+
H2CO3
H2O +CO2

GastricJuice.
 The cells of the gastric mucosa secrete a fluid called gastric juice.
 The four major components of gastric juice are hydrochloric acid
(HCl), pepsinogen, intrinsic factor, and mucus.
 Together, HCl and pepsinogen initiate the process of protein
digestion. Intrinsic factor is required for the absorption of vitamin
B12 in the ileum, and it is the only essential component of gastric
juice.
 Mucus protects the gastric mucosa from the corrosive action of
HCl and also lubricates the gastric contents.

 The body of the stomach contains
oxyntic glands that empty their
secretory products, via ducts, into the
lumen of the stomach.The openings of
the ducts on the gastric mucosa are
called pits, which are lined with
epithelial cells. Deeper in the gland are
mucous neck cells, parietal (oxyntic)
cells, and chief (peptic) cells.
 The antrum of the stomach contains the
pyloric glands, which are configured
similar to the oxyntic glands but with
deeper pits.The pyloric glands contain
two cell types: the G cells and the
mucous cells.The G cells secrete gastrin,
not into the pyloric ducts but into the
circulation.The mucous neck cells
secrete mucus, HCO3−, and pepsinogen.
Mucus and HCO3− have a protective,
neutralizing effect on the gastric
mucosa.

HCL secretion
 A major function of the parietal cells is secretion of HCl, which
acidifies the gastric contents to between pH 1 and 2.
Physiologically, the function of this low gastric pH is to convert
inactive pepsinogen, which is secreted by the nearby chief cells, to
its active form, pepsin, a protease that begins the process of
protein digestion.
 The cellular mechanism of HCl secretion by parietal cells will be
described first, followed by discussion of the mechanisms that
regulate HCl secretion and the pathophysiology of H+ secretion.

Pepsinogen
Secretion
 Pepsinogen, the inactive precursor to pepsin, is
secreted by chief cells and by mucous cells in
the oxyntic glands.
 When the pH of gastric contents is lowered by
H+ secretion from parietal cells, pepsinogen is
converted to pepsin, beginning the process of
protein digestion.
 In the cephalic and gastric phases of H+
secretion, vagal stimulation is the most
important stimulus for pepsinogen secretion.
 H+ also triggers local reflexes, which stimulate
the chief cells to secrete pepsinogen.These
complementary reflexes ensure that
pepsinogen is secreted only when the gastric
pH is low enough to convert it to pepsin.

Intrinsic Factor
Secretion
 Intrinsic factor, a mucoprotein, is the
“other” secretory product of the parietal
cells. Intrinsic factor is required for
absorption of vitamin B12 in the ileum, and
its absence causes pernicious anemia.
Intrinsic factor is the only essential
secretion of the stomach by parietal cells.
 Thus, following gastrectomy (removal of
the stomach), patients must receive
injections of vitamin B12 to bypass the
absorption defect caused by the loss of
gastric intrinsic factor.

Pancreatic
secretion
 The exocrine pancreas secretes approximately 1 L of fluid per day
into the lumen of the duodenum. It has HCO3- ions for
neutralizing acid and enzymes for break down of macronutrients
in the duodenum by its exocrine glands.
 Pancreatic secretion is produces from acini cells in the acinus of
the pancreas that drains into a branching duct inhabited by ductal
cells flowing into a centro-acinar region that produces the HCO-
ions of the secretion.
 Innervation of secretion is done by PNS via vagus nerves
(activation)and SNS(inhibition) via celiac and superior mesenteric
plexuses.

Phases of
Pancreatic
secretion
Cephalic Phase
 This phase is initiated by the sensory experience of seeing and eating food
and primarily involves vagus nerve stimulation of acinar cells to produce
digestive enzymes. Because little aqueous sodium bicarbonate solution by
ductal cells these enzymes lie inactive within the pancreatic acini and ducts.
Gastric Phase
 This phase is initiated by the presence of food within the stomach and is once
again primarily involves vagus nerve stimulation of acinar cells to produce
digestive enzymes. By the end of the cephalic and gastric phases, the
pancreatic ducts are filled with inactive digestive zymogens ready for
washing out into the intestinal lumen by aquous sodium bicarbonate
solution.
Intestinal Phase
 This phase is initiated by emptying of stomach contents into the small
Intestine and involves release of both secretin and cholecystokinin which
stimulate pancreatic ductal cells to synthesize aqueous sodium bicarbonate
solution.The generation of aqueous sodium bicarbonate solution washes out
all of the inactive pancreatic enzymes waiting within the pancreatic ducts
into the duodenum where they activated as discussed previously.

Formation of
Pancreatic
Secretion
 The enzymes are produce in ER, they are transported by Golgi to
zymogens that stores them in zymogens granules until a stimuli
comes and trigger their secretion.
 The enzyme when secreted are inactive and are activated via
enterokinase of intestinal mucosa.
 Bicarbonate ion is secreted via centroacinar and ductal cells in an
isotonic solution of four ions.Na moves pararcelluarly with H2O
into the blood,H+ exchanged vi aNA+K+ pump for Na+,Co2 reacts
wit H2O to form bicarbonate to be secreted into the lumen and H+
produce is uptaken by venous blood.
 As the pancreatic isotonic fluid flow down the duct more HCO- is
added,Na+ and K+ is balance and Cl- decrease.This is down by a
process called flow rate.

Pancreatic
Secretion
Regulation

BileSecretion
Enterohepatic
circulation

Small
Intestine
Secretion
 Secretions of the small intestine occur from two types of
histological structures: Brunners Glands and Crypts of
Lieberkuhn.
 Brunners Glands mostly secrete mucus which is designed to
protect the small intestine mucosa from damage by stomach acid.
 Secretion from Lieberkuhn's Crypts takes place from two different
cellular subtypes.
Cryptic goblet cells secrete mucus which helps lubricate food and
protects the intestinal mucosa
Cryptic enterocytes secrete large volumes of fluid (nearly 2L/day)
that is added to the intestinal chyme and aids in digestion and
absorption.
• Electrolytes such as Na+,Cl-,K+ and HCO3- are secreted by crypts.

Gastrointestinal
Digestion and
Absorption

Digestion
and
Absorption
 Digestion is the chemical breakdown of ingested foods into
absorbable molecules.The digestive enzymes are secreted in
salivary, gastric, and pancreatic juices and also are present on the
apical membrane of intestinal epithelial cells.
 Absorption is the movement of nutrients, water, and electrolytes
from the lumen of the intestine into the blood.There are two
paths for absorption: a cellular path and a paracellular path
 The small intestine is arranged in longitudinal folds, called folds of
Kerckrin with fingerlike villi projecting from these folds.They
cover epithelial cells with goblet mucus cells.The apical cells of
these cell have microvilli called a brush border for absorption to
take place.Inadditon lacteal are also present for fat absorption.
 Note epithelial cells of the GI are replace every 3-6days.

Digestion of
Lipids
 Most lipids are digested in small intestine via bile salts which cause
the emulsification of fats.
 The pancreatic enzymes (pancreatic lipase, cholesterol ester
hydrolase, and phospholipaseA2) and one special protein (colipase)
are secreted into the small intestine to accomplish the digestive work.
 The rate of gastric emptying, which is so critical for subsequent
intestinal digestive and absorptive steps, is slowed by CCK. CCK is
secreted when dietary lipids first appear in the small intestine.

Small
Intestine
Phase of Fat
Digestion

Fat
Transportation
 Free fatty acids and cholesterol can be toxic if simply released into the blood at high
concentrations.Therefore, within the enterocyte cytosol they are used to
resynthesize triglycerides and cholesterol esters.These lipids are then packaged
within large macro-molecular structures known as chylomicrons which are
subsequently released from the basolateral membrane and into a specialized
lymphatic vessel known as a lacteal from where they eventually enter the blood.

Vitamins
Absorption
 Vitamins are required in small amounts to act as coenzymes or
cofactors for various metabolic reactions. Because vitamins are
not synthesized in the body and acquired by diet.
 Fat-SolubleVitamins
 The fat-soluble vitamins are vitaminsA, D, E, and K.The
mechanism of absorption of fat-soluble vitamins is easily
understood:They are processed in the same manner as dietary
lipids.
 Water-SolubleVitamins
 The water-soluble vitamins include vitamins B1, B2, B6, B12, C,
biotin, folic acid, nicotinic acid, and pantothenic acid. In most
cases, absorption of the water-soluble vitamins occurs via an Na+-
dependent cotransport mechanism in the small intestine.

Vitamin B12
Absorption
 Absorption of vitamin B12 requires intrinsic factor and occurs in the following
steps:
 (1) Dietary vitamin B12 is released from foods by the digestive action of pepsin
in the stomach.
 (2) Free vitamin B12 binds to R proteins, which are secreted in salivary juices.
 (3) In the duodenum, pancreatic proteases degrade the R proteins, causing
vitamin B12 to be transferred to intrinsic factor, a glycoprotein secreted by the
gastric parietal cells.
 (4)The vitamin B12-intrinsic factor complex is resistant to the degradative
actions of pancreatic proteases and travels to the ileum, where there is a
specific transport mechanism for its absorption.

Iron
Absorption
 Iron is absorbed across the apical membrane of intestinal epithelial cells
as free iron (Fe2+) or as heme iron (i.e., iron bound to hemoglobin or
myoglobin).
 Inside the intestinal cells, heme iron is digested by lysosomal enzymes,
releasing free iron.
 Free iron then binds to apoferritin and is transported across the
basolateral membrane into the blood.
 In the circulation, iron is bound to a β-globulin called transferrin, which
transports it from the small intestine to storage sites in the liver.
 From the liver, iron is transported to the bone marrow, where it is
released and utilized in the synthesis of hemoglobin.

Gastrointestinal
Immunity
 The salivary glands secret saliva containing IGA for immunity as
while as secretion found along the GI tract that helps to protects
GI mucosae
 Gastric acids-produced by the stomach destroy pathogens who
have except the mouth with its acidic conditions
• Peyer's Patches:These are lymphoid follicles(MALT) similar in
many ways to lymph nodes, located in the mucosa and
extending into the submucosa of the small intestine, especially
the ileum. In adults, B lymphocytes predominate in Peyer's
patches and are secreted via M-cells.
• Tonsils-masses of lymphoid tissue (MALT) and form an
important part of our immune system and They act as the first
line of defense against ingested or inhaled pathogens

Reference
 Keith.L.Moore etal.The developing Human clinical oriented embryology.9th
Edition.Chapter 9.Pharyngeal apparatus,face and neck.Development of the
tongue.pg 176-179
salivary glands.pg 179
palate.pg 188-196
 Moore.L.Keith PHD.Dally.F.Aurther.Agur.M.R.Anne.Clinical oriented Anatomy,
7th Edition.LippincottsWilliams andWilkins,Walter Kluwer. Chapter
2.abdomen,abdominal viscera.Anatomy Esophagus, Stomach and
Duodenum.229-241
 Linda.S.Costanzo.Canstanzo Physiology.5th Edition. Elsevier Inc .
Gastrointestinal system.Chapter 8.page 329-374
 Khan Khurrum. Baylor College of Medicine.Pathway Medicne. Gastrointestinal
medicine.Gastrointestinal physiology. Retrived from
http://www.pathwaymedicine.org/gi-physiology

Anatomy and Physiology of the Upper GI Tract

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