Complete Notes of Digestive system,

2. Digestive system
• Organs of digestive system: Mouth, tongue,
oesaphageo-pharynx, oesaphagus, stomach,
duodenum, Jejunum, Ileum, Ascending colon,
Transverse colon, Descending colon, Rectum,
Anus.
• Accessory organs of digestive system: Salivary
glands, Tongue, Liver, Gall bladder, Gastric
glands, Intestinal glands, Goblet cells.
• Sphincters of GIT: Cardiac sphincter, Pyloric
sphincter, Ileocecal sphincter, Sphincter of Odii,
Anal sphincter.

3. Functions of Digestive system
• Ingestion, Movement of food, Digestion
(Mechanical digestion eg, maceration with
the help of teeth, mixing of food in the
stomach, and chemical digestion-with the
help of enzymes)Absorption
(Assimilation),Defecation.

4. Histology of GIT: From within outside
• 1. Mucosa: Epithelial cells absorption, secretion,; Goblet cells-
mucus, enteroendocrine cells- hormones. (Lamina propria-blood,
lymphatic vessels, scattered lymph nodules)
• 2. sub-mucosa: Areolar connective tissue that binds to muscularis,
blood vessels, Meissner plexus-ANS, for regulating secretions from
glands)
• 3. Muscularis (inner circular and outer longitudinal smooth
muscles), : Mouth, pharynx, upper esophagus- made of skeletal
muscles use full for swallowing, and external anal sphincter that
helps in controlling defecation.
• Rest of GIT muscularis is made of inner circular and outer longitudinal
muscle cells that helps in the GIT movements namely peristaltic and
pendular / segmental movements to cause movement of food and
mixing food in GI canal. This regulated by Myenteric or Auerbach
plexus present between circular and longitudinal muscles.
• 4. Serosa: Made up of epithelial cells and connective tissue cells.

5. Eating, Masticating, Drinking,
Sucking, Tasting, Breathing,
Vomiting, Digesting, deglutition,
Speaking, Expression ( Smiling -
The upper jaw, that is part of the skull .
The lower jaw, connected with the upper jaw
Laughing - Crying - Kissing –
and with ability to move up-down and from side Whistling, Smiling - Laughing -
to side. Crying - Kissing – Whistling)

6. Mouth: Non-keratinized stratified squamous
epithelium (esophagus and anal canal)
• The mouth or oral cavity is surrounded by the cheeks and
lips.
• The cheeks (buccal) contain buccinator muscle
• The parotid duct opens adjacent to the 2nd molar tooth.
• The lips (labia) contain numerous muscles that control the
mouth.
• Vestibule is part of the cavity between the teeth and the
cheeks or lips.
• Hard palate-anterior part of roof of the mouth (formed by
part of maxilla and palatine bone)
• Soft palate: posterior part of roof of the mouth, it is arch
shaped muscular partition of between oropharynx and
nasopharynx and lined by mucus membrane

7. EATING AND SWALLOWING
• the front teeth cut the food
• - the side teeth tear and shred it
• - the back teeth crush and grind it
• - the saliva moistens the food
• - the action of the tongue and the cheeks mix
it all up so that it is easy to swallow
• - tiny pimples on the surface of the tongue,
the 'taste buds' tell you what you are tasting.

9. Tongue
• The tongue is a muscular organ in the mouth. The tongue is covered with moist,
pink tissue called mucosa. Tiny bumps called papillae give the tongue its rough
texture. Thousands of taste buds cover the surfaces of the papillae. Taste buds are
collections of nerve-like cells that connect to nerves running into the brain.
• In the back of the mouth, the tongue is anchored into the hyoid bone. The tongue
is vital for chewing and swallowing food, as well as for speech.
• The four common tastes are sweet, sour, bitter, and salty.
• The tongue has many nerves that help detect and transmit taste signals to the
brain.
• The extrinsic muscles of tongue, hypoglosssus, styloglossus help to move the
tongue side to side and in and out. These movements maneuver food for
chewing, shape the food into a round mass, force the food to the back of the
mouth for swallowing (deglutition).
• The intrinsic muscles originate and insert within the tongue and alter the size and
shape of the tongue for speech and swallowing.
• The frenulum , a fold of the mucus membrane in the mid line of under surface of
the tongue attached to the floor of the mouth helps in limiting the movements
of the tongue posteriorly.
• Taste buds sends impulses to cortex for expression of specific taste and to
salivatory nuclei in the brain stem and then to salivary glands.

13. Taste buds
• The majority of taste buds on the tongue sit on raised protrusions of the tongue
surface called papillae. There are four types of papillae present in the human
tongue:
• Fungiform papillae - as the name suggests, these are slightly mushroom-shaped if
looked at in longitudinal section. These are present mostly at the apex (tip) of the
tongue, as well as at the sides. Innervated by facial nerve. They appear as red spots
on the tongue - red because they are richly supplied with blood vessels. The total
number of fungiform papillae per human tongue is around 200. Papillae at the
front of the tongue have more taste buds (1-18) compared to the mid-region (1-9).
It has been calculated that there are 1120 fungiform taste buds per tongue.
• Filiform papillae - these are thin, long papillae "V"-shaped cones that don't contain
taste buds but are the most numerous. These papillae are mechanical and not
involved in gustation. They are characterized by increased keratinization.
• Foliate papillae - these are ridges and grooves towards the posterior part of the
roof of the mouth found on lateral margins. Innervated by facial nerve (anterior
papillae) and glossopharyngeal nerve (posterior papillae).
• Circumvallate papillae - there are only about 10 to 14 of these papillae on most
people, and they are present at the back of the oral part of the tongue. They are
arranged in a circular-shaped row just in front of the sulcus terminalis of the
tongue. They are associated with ducts of Von Ebner's glands, and are innervated
by the glossopharyngeal nerve.

14. • Foliate papillae - these are ridges and grooves towards the posterior
part of the roof of the mouth found on lateral margins. Innervated by
facial nerve (anterior papillae) and glossopharyngeal nerve (posterior
papillae). On average 5.4 foliate papillae per side of the tongue, 117
taste buds per foliate papillae, total = 1280 foliate taste buds per
tongue.
• Circumvallate papillae - there are only about 10 to 14 of these
papillae on most people, and they are present at the back of the oral
part of the tongue. They are arranged in a circular-shaped row just in
front of the sulcus terminalis of the tongue. They are associated with
ducts of Von Ebner's glands, and are innervated by the
glossopharyngeal nerve. 3-13 circumvallate papillae per tongue with
252 taste buds per papillae, total = 2200 circumvallate taste buds per
tongue

15. Tongue
• Taste buds contain the receptors for taste. They are located around
the small structures on the upper surface of the tongue, soft palate,
upper esophagus and epiglottis, which are called papillae. These
structures are involved in detecting the five (known) elements of
taste perception: salty, sour, bitter, sweet, and umami.
• Taste buds contain the receptors for taste. They are located around
the small structures on the upper surface of the tongue, soft palate,
upper esophagus and epiglottis, which are called papillae. These
structures are involved in detecting the five (known) elements of
taste perception: salty, sour, bitter, sweet, and savory (or umami). Via
small openings in the tongue epithelium, called taste pores, parts of
the food dissolved in saliva come into contact with taste receptors.
• The gustatory (taste) cells, a chemoreceptor, occupy the central
portion of the bud; they are spindle-shaped, and each possesses a
large spherical nucleus near the middle of the cell. Those tiny hairs
send messages to the brain, which interprets the signals and
identifies the taste for you.

17. Salt taste
• Salt is sodium chloride (Na+ Cl-). Na+ ions
enter the receptor cells via Na-channels.
These are amiloride-sensitive Na+ channel (as
distinguished from TTX-sensitive Na+ channels
of nerve and muscle). The entry of Na+ causes
a depolarization, Ca2+ enters through voltage-
sensitive Ca2+ channels, transmitter release
occurs and results in increased firing in the
primary afferent nerve.

18. Sour taste
• Sour taste is acid and acid is protons (H+). There
is exciting new evidence that there is an acid-
sensing channel - the PKD2L1 channel1.This
channel is a member of the transient receptor
potential channel (TRP) family and is a non-
selective cation channel. The activity of PKD2L1 is
gated by pH (H+ ion concentration). This new
discovery displaces the previous ideas that H+
ions block K+ channels causing a
depolarization, or that H+ ions enter the cell
through ENaC channels. These mechanisms may
exist but do not lead directly to sour perception.

19. Sweet taste
• There are receptors T1R2 + T1R3) in the apical
membrane that bind glucose (sucrose - a
combination of glucose and fructose - and other
carbohydrates). Binding to the receptor activates
a G-protein which in turn activates phospholipase
C (PLC-ß2). PLC generates IP3 and diacyl glycerol
(DAG). These intracellular messengers, directly or
indirectly, activate the TRPM5 channel and
depolarization occurs. Ca2+ enters the cell
through depolarization-activated Ca2+
channels, transmitter is released increasing firing
in the primary afferent nerve.

20. Bitter taste
• Bitter substances bind to the T2R receptors
activating the G-protein and causing activation
of PLC. The second messengers DAG and IP3
are produced (by hydrolysis of
phosphatidylinositol-4,5-bisphosphate)
activating TRPM5 and mediating release of
Ca2+ from internal stores. The elevated Ca2+
causes transmitter release and this increases
the firing of the primary afferent nerve.

21. Umami taste
• Umami is the taste of certain amino acids (e.g. glutamate, aspartate and related
compounds). It was first identified by Kikunae Ikeda at the Imperial University of
Tokyo in 1909. It was originally shown that the metabotropic glutamate receptor
(mGluR4) mediated umami taste. Binding to the receptor activates a G-protein and
this elevates intracellular Ca2+. More recently it has been found that the T1R1 +
T1R3 receptors mediate umami taste. Binding to the receptors activates the non-
selective cation channel TRPM5 as for sweet and bitter receptors (i.e. via G-protein,
PLC, IP3 and DAG - see above). Guanosine 5'-monophosphate (GMP) and inosine 5'-
monophosphate (IMP) potentiate the effect of umami tastes by binding to another
site of the T1R1 receptor.
• Monosodium glutamate, added to many foods to enhance their taste (and the
main ingredient of Soy sauce), stimulates the umami receptors. But, in addition,
there are ionotropic glutamate receptors (linked to ion channels), i.e. the NMDA-
receptor, on the tongue. When activated by these umami compounds or soy sauce,
non-selective cation channels open, thereby depolarizing the cell. Calcium enters,
causing transmitter release and increased firing in the primary afferent nerve

22. Strange taste facts
• Taste is mainly smell. Hold your nose, close your eyes, and try to tell
the difference between coffee or tea, red or white wine, brandy or
whisky. In fact, with blocked nose (clothes peg or similar) you can't
tell the difference between grated apple and grated onion - try it! Of
course, this is because what we often call taste is in fact flavor.
Flavour is a combination of taste, smell, texture (touch sensation) and
other physical features (eg. temperature).
• The durian fruit smells horrible. Some people cannot bear to eat it
because it smells so foul. But it is called the "King of Fruits" and tastes
delicious. It is very large (can be the size of a football) and comes
from South East Asia.

23. Salivary Gland
• Type of Secretory Cells
• Parotid: Serous: Inferior and anterior and anterior to the ears
between the skin and masseter muscle (Stensen’s duct- opens at the upper
second Maxillary Molar tooth).[ANS: parasympathetic through
glossopharyngeal nerve (CN IX) via the otic ganglion]
• Submandibular: Mixed: Beneath the base of the tongue in the posterior
part of the floor of the mouth (Wharton’s ducts run superficially under the
mucosa on either side of midline of the floor of mouth, opening on either
side of the frenulum.[facial nerve (CN VII) via the submandibular ganglion]
• Sublingual: Mucus: Superior to the submandibular glands ,
Lesser sublingual (Rivinus’ ) ducts open to the floor of the mouth
cavity.[facial nerve (CN VII) via the submandibular ganglion]
• Saliva: 99.5% water, 0.5% solids (Na& K -- Cl,HCO3, PO4,urea, uric acid,
serum albumin and globulin,, mucin, lysozyme, & salivary amylase. Direct
Sympathetic innervation of the salivary glands takes place via preganglionic
nerves in the thoracic segments T1-T3 which synapse in the superior
cervical ganglion with postganglionic neurons that release norepinephrine,
cause increase in secretion.

24. Salivary glands
• Minor salivary glands:
They are 1-2mm in diameter and unlike the
other glands, they are not encapsulated by
connective tissue only surrounded by it. The
gland is usually a number of acini connected in
Starch is converted into a tiny lobule. A minor salivary gland may have a
maltotriose and maltose from common excretory duct with another gland, or
amylose, or maltose, glucose may have its own excretory duct. Their
and "limit dextrin" from
amylopectin. Because it can secretion is mainly mucous in nature (except
act anywhere on the for Von Ebner's glands) and have many
substrate, α-amylase tends to functions such as coating the oral cavity with
be faster-acting than β-
amylase( in animals). During saliva. Von Ebner's glands are glands found in
the ripening of fruit, β- circumvallate papillae of the tongue.
amylase breaks starch into They secrete a serous fluid that begin lipid
maltose, resulting in the sweet
flavor of ripe fruit. hydrolysis.
They facilitate the perception of taste.

25. TOOTH ENAMEL (1), is the hardest of the parts of the tooth and also
the hardest of all the tissues of human body. Tooth enamel is a
protective tooth structure that covers the exposed part of a tooth, the
• crown.
DENTIN (2) or IVORY, is the tissue below the tooth enamel that forms
the main mass of a tooth. It supports the tooth enamel and absorbs
the pressure of eating. The dentine consists of a number of micro-
fibers imbedded in a dense homogeneous matrix of collagenous
proteins.
DENTAL PULP (3) , a soft connective tissue containing nerves and
blood vessels, that nourish the tooth. It is the most internal structure
of a tooth, surrounded by the dentine. Dental pulp is found in the soft
center of the tooth, inside the pulp chamber and the root canal.
CEMENTUM (4) , is the part of tooth anatomy that covers the dentine
outside of the root (under the gum line) and it is attached to the bone
of the jaw with little elastic fibers. Cementum is hard as bone but not
as hard as the tooth enamel.
GUMS (5) , the tough pink-colored tissue that covers the bone of the
jaw and supports the tooth structure inside the alveolar bone.
PERIODONTAL LIGAMENT (6) , the tissue between the cementum and
the alveolar bone. It consists of tough little elastic fibers that keep the
tooth attached to the jaw.
ALVEOLAR BONE (7) , the bone of the jaw that keeps the tooth in its
place, it feeds and protects it.

27. Incisors– one root
Canine– one root
First and Second molars have
four cusps
Upper molars have three roots
Lower molars have two roots

28. Teeth
• Incisors. Incisors are the eight teeth in the front and center of your
mouth (four on top and four on bottom). These are the teeth that
you use to take bites of your food. Incisors are usually the first teeth
to erupt, at around 6 months of age for your first set of teeth, and
between 6 and 8 years of age for your adult set.

29. Canines.
• Your four canines are the next type of teeth to develop. These
are your sharpest teeth and are used for ripping and tearing
food apart. Primary canines generally appear between 16 and
20 months of age with the upper canines coming in just ahead
of the lower canines. In permanent teeth, the order is
reversed. Lower canines erupt around age 9 with the uppers
arriving between 11 and 12 years of age.

30. Premolars.
• Premolars, or bicuspids, are used for chewing and grinding
food. You have four premolars on each side of your mouth,
two on the upper and two on the lower jaw. The first
premolars appear around age 10 and the second premolars
arrive about a year later.

31. Molars.
• Primary molars are also used for chewing and grinding food.
These appear between 12 and 15 months of age. These
molars are replaced by the first and second permanent molars
(four upper and four lower). The first molars erupt around 6
years of age while the second molars come in between 11 and
13 years of age.

32. Third molars.
• Third molars are commonly known as wisdom teeth. These
are the last teeth to develop and do not typically erupt until
age 18 to 20, and some people never develop third molars at
all. For those who do, these molars may cause crowding and
need to be removed.

33. Deglutition
• Machanism of moving food into stomach
• Facilitated by : saliva, mucus, mouth, pharynx, and
esophagus
• 1.Voluntary stage: Food moves to oropharynx
• 2.Pharyngeal stage: Involuntary passage of the
bolus from oropharynx to esophagus.
• 3. Esophageal stage: Transit of food from esophagus
to stomach

34. Deglutination
• Oral phase
Prior to the following stages of the oral phase, the mandible depresses and the
lips abduct to allow food or liquid to enter the oral cavity. Upon entering the
oral cavity, the mandible elevates and the lips adduct to assist in oral
containment of the food and liquid. The following stages describe the normal
and necessary actions to form the bolus, which is defined as the state of the
food in which it is ready to be swallowed.
1) Moistening:
Food is moistened by saliva from the salivary glands (parasympathetic).
2) Mastication:
Food is mechanically broken down by the action of the teeth controlled by the
muscles of mastication. Buccinator (VII) helps to contain the food against the
occlusal surfaces of the teeth. The bolus is ready for swallowing when it is held
together by (largely mucus) saliva (VII—chorda tympani and IX—lesser
ppetrosal), sensed by the lingual nerve of the tongue . Any food that is too dry
to form a bolus will not be swallowed.

35. Deglutination
• 3)Trough formation: A trough is then formed at the back of the
tongue by the intrinsic muscles (XII). he trough obliterates against the
hard palate from front to back, forcing the bolus to the back of the
tongue. The intrinsic muscles of the tongue (XII) contract to make a
trough (a longitudinal concave fold) at the back of the tongue. The
tongue is then elevated to the roof of the mouth (by the mylohyoid
(mylohyoid nerve—Vc), genioglossus, styloglossus and hyoglossus
(the rest XII)) such that the tongue slopes downwards posteriorly. The
contraction of the genioglossus and styloglossus (both XII) also
contributes to the formation of the central trough.
• 4) Movement of the bolus posteriorly: propelled posteriorly into the
pharynx. In order for anterior to posterior transit of the bolus to
occur, orbicularis oris contracts and adducts the lips to form a tight
seal of the oral cavity. Next, the superior longitudinal muscle elevates
the apex of the tongue to make contact with the hard palate and the
bolus is propelled to the posterior portion of the oral cavity.

36. Deglutination
• Once the bolus reaches the palatoglossal arch of the oropharynx, the
pharyngeal phase, which is reflex and involuntary, then begins.
Receptors initiating this reflex are proprioceptive (afferent limb of
reflex is IX and efferent limb is the pharyngeal plexus- IX and X).
They are scattered over the base of the tongue, the palatoglossal and
palatopharyngeal arches, the tonsillar fossa, uvula and posterior
pharyngeal wall. Stimuli from the receptors of this phase then provoke
the pharyngeal phase. In fact, it has been shown that the swallowing
reflex can be initiated entirely by peripheral stimulation of the internal
branch of the superior laryngeal nerve. This phase is voluntary and
involves important cranial nerves: V (trigeminal), VII (facial) and XII
(hypoglossal).

37. Deglutination
• Pharyngeal phase: For the pharyngeal phase to work properly
all other egress from the pharynx must be occluded—this includes the
nasopharynx and the larynx. When the pharyngeal phase begins, other
activities such as chewing, breathing, coughing and vomiting are
concomitantly inhibited.
• 5) Closure of the nasopharynx:
• The soft palate is tensed by tensor palati (Vc), and then elevated
by levator palati (pharyngeal plexus—IX, X) to close the
nasopharynx. There is also the simultaneous approximation of
the walls of the pharynx to the posterior free border of the soft
palate, which is carried out by the palatopharyngeus (pharyngeal
plexus—IX, X) and the upper part of the superior constrictor
(pharyngeal plexus—IX, X).

38. Deglutination
• 6) The pharynx prepares to receive the bolus:
The pharynx is pulled upwards and forwards by the suprahyoid and
longitudinal pharyngeal muscles – stylopharyngeus (IX),
salpingopharyngeus (pharyngeal plexus—IX, X) and palatopharyngeus
(pharyngeal plexus—IX, X) to receive the bolus. The palatopharyngeal
folds on each side of the pharynx are brought close together through the
superior constrictor muscles, so that only a small bolus can pass.
7) Opening of the auditory tube
The actions of the levator palati (pharyngeal plexus—IX, X), tensor
palati (Vc) and salpingopharyngeus (pharyngeal plexus—IX, X) in the
closure of the nasopharynx and elevation of the pharynx opens the
auditory tube, which equalises the pressure between the nasopharynx
and the middle ear. This does not contribute to swallowing, but happens
as a consequence of it.

39. Deglutination
• 8) Closure of the oropharynx: The oropharynx is kept closed by
palatoglossus (pharyngeal plexus—IX, X), the intrinsic muscles of tongue
(XII) and styloglossus (XII).
9) Laryngeal closure: A finite period of apnea must necessarily take place with
each swallow. The aryepiglotticus (recurrent laryngeal nerve of vagus)
contracts, causing the arytenoids to appose each other (closes the laryngeal
aditus by bringing the aryepiglottic folds together), and draws the epiglottis
down to bring its lower half into contact with arytenoids, thus closing the
aditus. Additionally, the larynx is pulled up with the pharynx under the tongue
by stylopharyngeus (IX), salpingopharyngeus (pharyngeal plexus—IX, X),
palatopharyngeus (pharyngeal plexus—IX, X) and inferior constrictor
(pharyngeal plexus—IX, X).This phase is passively controlled reflexively and
involves cranial nerves V, X (vagus), XI (accessory) and XII (hypoglossal). The
respiratory center of the medulla is directly inhibited by the swallowing center
for the very brief time that it takes to swallow. This means that it is briefly
impossible to breathe during this phase of swallowing and the moment where
breathing is prevented is known as deglutition apnea.

40. Deglutination
• 10) Hyoid elevation: The hyoid is elevated by digastric (V & VII) and
stylohyoid (VII), lifting the pharynx and larynx up even further.
• 1) Bolus transits pharynx
• The bolus moves down towards the esophagus by pharyngeal
peristalsis which takes place by sequential contraction of the superior,
middle and inferior pharyngeal constrictor muscles (pharyngeal
plexus—IX, X). The lower part of the inferior constrictor
(cricopharyngeus) is normally closed and only opens for the
advancing bolus. Gravity plays only a small part in the upright
position—in fact, it is possible to swallow solid food even when
standing on one’s head. The velocity through the pharynx depends on
a number of factors such as viscosity and volume of the bolus. In one
study, bolus velocity in healthy adults was measured to be
approximately 30–40 cm/s.

41. Deglutination
• Esophageal phase
12) Esophageal peristalsis
Like the pharyngeal phase of swallowing, the esophageal phase of swallowing
is under involuntary neuromuscular control. However, propagation of the food
bolus is significantly slower than in the pharynx. The bolus enters the
esophagus and is propelled downwards first by striated muscle (recurrent
laryngeal, X) then by the smooth muscle (X) at a rate of 3 – 5 cm/sec. The
upper esophageal sphincter relaxes to let food pass, after which various
striated constrictor muscles of the pharynx as well as peristalsis and relaxation
of the lower esophageal sphincter sequentially push the bolus of food through
the esophagus into the stomach.
13) Relaxation phase
Finally the larynx and pharynx move down with the hyoid mostly by elastic
recoil. Then the larynx and pharynx move down from the hyoid to their relaxed
positions by elastic recoil. Swallowing therefore depends on coordinated
interplay between many various muscles, and although the initial part of
swallowing is under voluntary control, once the deglutition process is started,
it is quite hard to stop it.

42. Esophagus
Consists of a muscular tube through which food
passes from the pharynx to the stomach. During
swallowing, food passes from the mouth through
the pharynx into the esophagus and travels via
peristalsis to the stomach. is continuous with the
laryngeal part of the pharynx at the level of the
C6 vertebra. The esophagus passes through posterior
mediastinum in thorax and enters abdomen through a
hole in the diaphragm at the level of the tenth thoracic
vertebrae (T10). It is usually about 10–50 cm long
depending on individual height (20-25 cm) . It is divided into cervical,
thoracic and abdominal parts. Due to the inferior pharyngeal constrictor
muscle, the entry to the esophagus opens only when swallowing or
vomiting.

43. In human anatomy, the greater
sac, also known as the general cavity
(of the abdomen) or peritoneum of
the peritoneal cavity proper, is the
cavity in the abdomen that is inside
the peritoneum but outside of the
lesser sac.
It is connected with the lesser sac via
the omental foramen, also known as
the Foramen of Winslow or Epiploic
Foramen.

44. The peritoneum
• The peritoneum, like the pericardium and pleura, is a serous
membrane that invests viscera. It is comprised of parietal and
visceral peritoneum. There are many specializations of the
peritoneum. All of the special structures that will be covered here
are composed of two layers of peritoneum (much like the
pulmonary ligament). They differ in location and what they
connect. (Greek, peritonaion = stretch around)
• Mesenteries: result from the invagination of "intraperitoneal"
organs into the sac. The mesenteries connect viscera to the
posterior abdominal wall and are VERY important in that they
conduct blood vessels and nerves. (There are no vessels within the
peritoneal cavity, of course.) The mesentery of the colon is usually
called the "mesocolon". For example, we speak of the "transverse
mesocolon" and the "sigmoid mesocolon". (The other parts of the
colon are not completely invested by peritoneum, and are
therefore "retroperitoneal".) Also, often "the mesentery" refers
specifically to the mesentery of the small intestine.

45. Mesenteries & Omenta
• Mesenteries: result from the invagination of "intraperitoneal"
organs into the sac. The mesenteries connect viscera to the
posterior abdominal wall and are VERY important in that they
conduct blood vessels and nerves. (There are no vessels within the
peritoneal cavity, of course.) The mesentery of the colon is usually
called the "mesocolon". For example, we speak of the "transverse
mesocolon" and the "sigmoid mesocolon". (The other parts of the
colon are not completely invested by peritoneum, and are
therefore "retroperitoneal".) Also, often "the mesentery" refers
specifically to the mesentery of the small intestine. (Greek, mes =
in the midst of, enteron = intestine)
• Omenta: generally refers to a free fold of peritoneum. This is
exemplified by the greater omentum, which attaches to the
stomach, droops far down into the abdominal cavity, and comes
back up to attach to the transverse colon. The lesser omentum, on
the other hand, is not really "free". It connects the stomach to the
liver, and its membranous portion is called the hepatogastric
ligament.

46. Retroperitoneal structures
• Primarily retroperitoneal:
• Urinary: adrenal glands, kidneys, ureter, bladder
• Circulatory: aorta, inferior vena cava
• Digestive: esophagus (part), rectum (part, lower third is
extraperitoneal).
• Secondarily retroperitoneal: the head, neck, and body of the pancreas
(but not the tail, which is located in the splenorenal ligament), the
duodenum, except for the proximal first segment, which is
intraperitoneal, ascending and descending portions of the colon (but
not the transverse colon or the cecum).

47. Stomach
1. Body of stomach
* 2. Fundus
* 3. Anterior wall
* 4. Greater curvature
* 5. Lesser curvature
* 6. Cardia
* 9. Pyloric sphincter
* 10. Pyloric antrum
* 11. Pyloric canal
Rugae folds of mucus
* 12. Angular notch
membrane
* 13. Gastric canal
* 14. Rugal folds

49. Fundus
Cardiac Pylorus

50. Stomach- Anatomy
• The stomach is a J shaped muscular, hollow, dilated part of the
digestion system which functions as an important organ of the
digestive tract. It lies in the epigastric, umbilical, and left
hypochondriac regions of the abdomen. It is involved in the second
phase of digestion, following mastication (chewing). The stomach lies
between the esophagus and the duodenum. It is on the left upper part
of the abdominal cavity. The top of the stomach lies against the
diaphragm. Lying behind the stomach is the pancreas. The greater
omentum hangs down from the greater curvature. It has cardiac
orifice, and pyloric orifice. It has greater and lesser curvatures.

51. Stomach
• The stomach is surrounded by parasympathetic (stimulant) and
orthosympathetic (inhibitor) plexuses (networks of blood vessels and
nerves in the anterior gastric, posterior, superior and inferior, celiac and
myenteric), which regulate both the secretions activity and the motor
(motion) activity of its muscles.
• In adult humans, the stomach has a relaxed, near empty volume of about
45 ml and mucus membranes are folded to form rugae. Because it is a
distensible organ, it normally expands to hold about one litre of food, but
can hold as much as two to three litres. The stomach of a newborn human
baby will only be able to retain about 30 ml.
• The lesser curvature of the stomach is supplied by the right gastric artery
inferiorly, and the left gastric artery superiorly, which also supplies the
cardiac region. The greater curvature is supplied by the right gastroepiploic
artery inferiorly and the left gastroepiploic artery superiorly. The fundus of
the stomach, and also the upper portion of the greater curvature, is
supplied by the short gastric artery which arises from splenic artery.

52. At the bottom of gastric pits are
openings of the gastric glands.
Gastric glands:
Chief (Zymogenic) glands:
Pepsinogen, gastric lipase
Parietal (oxyntic) cells:
Hydrochloric acid, Intrensic factor
Mucus cells: Mucus
Above three – gastric juice: 2-3
L/day
G cells: [Pyloric antrum] ---Gastrin
Achylesia
Limited to body of the
stomach
What is endoscopy ?
What is gastroscopy ?

54. Stomach-Secretion of gastric juice
• Gastric acid facilitates digestion of proteins and the absorption of
calcium, iron, and vitamin B12. It also suppresses growth of bacteria,
which can help prevent enteric infections and small intestinal
bacterial overgrowth.
• Cephalic, Gastric, and Intestinal phases:
• The cephalic phase is activated by the thought, taste, smell and site
of food, and swallowing. It is mediated mostly by cholinergic/vagal
mechanisms.
• The gastric phase is due to the chemical effects of food and
distension of the stomach. Gastrin appears to be the major mediator
since the response to food is largely inhibited by immunoneutralizing
or blocking gastrin.
• The intestinal phase accounts for only a small proportion of the acid
secretory response to a meal; its mediators remain controversial.

55. Physiology of stomach
• Gastric juice:
• The pH of gastric acid is 1.35 to 3.5. Causes denaturation of proteins
This exposes the protein's peptide bonds.
• Acidity being maintained by the proton pump H+/K+ ATPase.
• The parietal cell releases bicarbonate into the blood stream in the process,
which causes a temporary rise of pH in the blood, known as alkaline tide.
• HCl activates pepsinogen into the enzyme pepsin [ proteolysis]
• Gastric acid production is regulated by both the autonomic nervous system
and several hormones.
• The parasympathetic nervous system, via the vagus nerve, and the
hormone gastrin stimulate the parietal cell to produce gastric acid, both
directly acting on parietal cells and indirectly, through the stimulation of the
secretion of the hormone histamine from enterochromaffine-like cells (ECL).
• Vasoactive intestinal peptide, cholecystokinin, and secretin all inhibit
production

56. Stimulation of Gastric Acid Secretion
• Endocrine : Gastrin is the digestive hormone that is secreted by the
gastrin (G) cells which are located in the pyloric glands towards the
distal end of the stomach. This hormone is released into the
stomach cavity when the presence of protein is detected in the
stomach contents. Due to the vigorous churning in the stomach, the
gastrin is able to make contact and act upon the ECL [Entero
chromaphin] cells, stimulating it to secrete histamine.
• Nervous : Acetylcholine released by the vagus nerve and enteric
system acts on the ECL cells to secrete histamine, which in turn
stimulates HCl production and secretion. The antral D-cells produce
somatostatin. It is inhibitory of gastric and
• The antral D-cells produce somatostatin. It is inhibitory of gastric
and pancreatic secretions.

57. HCl production
• Parietal cells contain an extensive secretory network (called
canaliculi) from which the HCl is secreted by active transport into the
stomach. The enzyme hydrogen potassium ATPase (H+/K+ ATPase) is
unique to the parietal cells and transports the H+ against a
concentration gradient of about 3 million to 1, which is the steepest
ion gradient formed in the human body.
• Hydrogen ions are formed from the dissociation of water molecules.
The enzyme carbonic anhydrase converts one molecule of carbon
dioxide and one molecule of water indirectly into a bicarbonate ion
(HCO3-) and a hydrogen ion (H+).
• The bicarbonate ion (HCO3-) is exchanged for a chloride ion (Cl-) on
the basal side of the cell and the bicarbonate diffuses into the venous
blood, leading to an alkaline tide.
• Potassium (K+) and chloride (Cl-) ions diffuse into the canaliculi.
• Hydrogen ions are pumped out of the cell into the canaliculi in
exchange for potassium ions, via the H+/K+ ATPase.

59. Gastric juice
• The production of gastric acid in the stomach is tightly regulated by
positive regulators and negative feedback mechanisms. Four types of
cells are involved in this process: parietal cells, G cells, D cells and
enterochromaffine-like cells. Besides this, the endings of the vagus
nerve (CN X) and the intramural nervous plexus in the digestive tract
influence the secretion significantly.
• Nerve endings in the stomach secrete two stimulatory
neurotransmitters: acetylcholine and gastrin-releasing peptide. Their
action is both direct on parietal cells and mediated through the
secretion of gastrin from G cells and histamine from
enterochromaffine-like cells. Gastrin acts on parietal cells directly and
indirectly too, by stimulating the release of histamine.
• The release of histamine is the most important positive regulation
mechanism of the secretion of gastric acid in the stomach. Its release
is stimulated by gastrin and acetylcholine and inhibited by
somatostatin.

60. Absorption from stomach

61. Neutralization
• In the duodenum, gastric acid is neutralized by sodium bicarbonate.
This also blocks gastric enzymes that have their optima in the acid
range of pH. The secretion of sodium bicarbonate from the
pancreas is stimulated by secretin. This polypeptide hormone gets
activated and secreted from so-called S cells in the mucosa of the
duodenum and jejunum when the pH in duodenum falls below 4.5
to 5.0. The neutralization is described by the equation:
• HCl + NaHCO3 → NaCl + H2CO3
• The carbonic acid rapidly equilibrates with carbon dioxide and
water through catalysis by carbonic anhydrase enzymes bound to
the gut epithelial lining[4], leading to a net release of carbon
dioxide gas within the lumen associated with neutralisation. In the
absorptive upper intestine, such as the duodenum, both the
dissolved carbon dioxide and carbonic acid will tend to equilibrate
with the blood, leading to most of the gas produced on
neutralisation being exhaled through the lungs.

62. Control of secretion and motility of stomach
• Gastrin: The hormone gastrin causes an increase in the secretion of HCl
from the parietal cells, and pepsinogen from chief cells in the stomach. It
also causes increased motility in the stomach. Gastrin is released by G-cells
in the stomach in response to distenstion of the antrum, and digestive
products(especially large quantities of incompletely digested proteins). It is
inhibited by a pH normally less than 4 (high acid), as well as the hormone
somatostatin.
• Cholecystokinin: Cholecystokinin (CCK) has most effect on the gall bladder,
causing gall bladder contractions, but it also decreases gastric emptying and
increases release of pancreatic juice which is alkaline and neutralizes the
chyme.
• Secretin: n a different and rare manner, secretin, produced in the small
intestine, has most effects on the pancreas, but will also diminish acid
secretion in the stomach.
• Gastric Inhibitory peptide: Gastric inhibitory peptide (GIP) decreases both
gastric acid release and motility.
• Enteroglucon: enteroglucagon decreases both gastric acid and motility

63. Digestions in stomach
• :
• Pepsinogen is the main gastric enzyme. It is produced by the
stomach cells called "chief cells" in its inactive form
pepsinogen, which is a zymogen. Pepsinogen is then activated
by the stomach acid into its active form, pepsin. Pepsin breaks
down the protein in the food into smaller particles, such as
peptide fragments and amino acids. Protein digestion,
therefore, first starts in the stomach, unlike carbohydrate and
lipids, which start their digestion in the mouth.
• Hydrochloric acid (HCl): This is in essence positively charged
hydrogen atoms (H), or in lay-terms stomach acid, and is
produced by the cells of the stomach called parietal cells. HCl
mainly functions to denature the proteins ingested, to destroy
any bacteria or virus that remains in the food, and also to
activate pepsinogen into pepsin.

64. Digestions in stomach
• .
• Intrinsic factor (IF): Intrinsic factor is produced by the
parietal cells of the stomach. Vitamin B12 (Vit. B12) is
an important vitamin that requires assistance for
absorption in terminal ileum. Initially in the saliva,
haptocorrin secreted by salivary glands binds Vit. B,
creating a Vit B12-Haptocorrin complex. The purpose of
this complex is to protect Vitamin B12 from
hydrochloric acid produced in the stomach. Once the
stomach content exits the stomach into the duodenum,
haptocorrin is cleaved with pancreatic enzymes,
releasing the intact vitamin B12. Intrinsic factor (IF)
produced by the parietal cells then binds Vitamin B12,
creating a Vit. B12-IF complex. This complex is then
absorbed at the terminal portion of the ileum.

65. Digestions in stomach
• Mucin: The stomach has a priority to destroy the
bacteria and viruses using its highly acidic environment
but also has a duty to protect its own lining from its
acid. The way that the stomach achieves this is by
secreting mucin and bicarbonate via its mucous cells,
and also by having a rapid cell turn-over.
• Gastrin: This is an important hormone produced by the
"G cells" of the stomach. G cells produce gastrin in
response to stomach stretching occurring after food
enters it, and also after stomach exposure to protein.
Gastrin is an endocrine hormone and therefore enters
the bloodstream and eventually returns to the stomach
where it stimulates parietal cells to produce
hydrochloric acid (HCl) and Intrinsic factor (IF).

66. Pancreas

67. 1. Bile ducts: 2. Intrahepatic bile ducts, 3. Left and right
hepatic ducts, 4. Common hepatic duct, 5. Cystic
duct,6.Common bile duct, 7. Ampulla of Vater,
8. Major duodenal papilla 9. Gallbladder, 10-11. Right
and left lobes of liver. 12. Spleen. 13. Esophagus. 14.
Stomach. Small intestine: 15. Duodenum, 16. Jejunum
17. Pancreas: 18: Accessory pancreatic duct,
19: Pancreatic duct. 20-21: Right and left kidneys
(silhouette).

68. Pancreas

69. Pancreas

70. • Pancreas

71. Pancreas anatomy
• The pancreas lies in the epigastrium and left hypochondrium areas of
the abdomen at 2nd lumbar vertebral level. Pancreas is a 12-15 – cm
long J-shaped (like a hockey stick), soft, lobulated, retroperitoneal
organ. I00-160 gram in weight. It lies transversely, although a bit
obliquely, on the posterior abdominal wall behind the stomach, across
the lumbar (L1-2) spine. The head fits into the loop of duodenum. The
neck is the constricted part between the head and the body. The body
lies behind the stomach. The tail is the left end of the pancreas. It lies
in contact with the spleen.
Main duct (Wirsung) runs the entire length of pancreas. Joins Common
Bile duct at the ampulla of Vater. It is 2 – 4 mm in diameter, has 20
secondary branches.
Lesser duct (Santorini) drains superior portion of head and empties
separately into 2nd portion of duodenum.

72. Pancreas anatomy
• Blood supply: Variety of major arterial sources (celiac, Superior
mesenteric , and splenic arteries)
• Celiac  Common Hepatic Artery  Gastroduodenal Artery 
Superior pancreaticoduodenal artery which divides into anterior and
posterior branches
• SMA(Superior mesenteric artery)  Inferior pancreaticoduodenal
artery which divides into anterior and posterior branches
• Splenic artery run on the superior border of pancreas going to spleen
and supplies upper portions of pancreas.
• Venous drainage: Follows arterial supply;
Anterior and posterior arcades drain head and the body. Splenic vein
drains the body and tail. Major drainage areas are Suprapancreatic Portal
Vein, Retropancreatic Portal Vein, Splenic vein, Infrapancreatic superior
mesenteric vein and ultimately, into portal vein.

74. Arterial supply to pancreas

75. Venous drainage from pancreas

76. Anatomy of pancreas
• . The body and neck of the pancreas drain into splenic vein; the head
drains into the superior mesenteric and portal veins.
Lymph is drained via the splenic, celiac and superior mesenteric
lymph node.
Innervation of Pancreas: Sympathetic fibers from the splanchnic
nerves. Parasympathetic fibers from the vagus. Both give rise to
intrapancreatic periacinar plexuses. Parasympathetic fibers stimulate
both exocrine and endocrine secretion. Sympathetic fibers have a
predominantly inhibitory effect.
• Exocrine pancreas 85% of the volume of the gland
• Extracellular matrix – 10%
• Blood vessels and ducts - 4%
• Endocrine pancreas – 1%

77. Pancreas
– Acinus →small intercalated ducts → interlobular duct →
pancreatic duct→duodenum.
– Acinar cells which secrete primarily digestive enzymes
– Centroacinar or ductal cells which secrete fluids and electrolytes
• Hormones produced by 5 classes of islet cells include:
– α-cells → Glucagon- a 29 amino acid molecule which targets the
liver to breakdown glycogen and release glucose.
– β cells → Insulin- a 51 amino acid molecule which targets the liver
and most body cells except the brain to take up glucose.
– Delta cells → Somatostatin ↓ release of insulin & glucagon.
– “F” cells → Pancreatic polypeptide
↓ gall bladder contraction.
– “G” cells → Gastrin
↑ acid secretion, gastric motility
and stomach emptying.

78. Insulin
• Insulin is synthesized by the beta cells of the
pancreas
• Insulin and C peptide are packaged into
secretory granules and released together into
the cytoplasm
• 95% belong to reserve pool and 5% stored in
readily releasable pool
• Thus small amount of insulin is released under
maximally stimulatory conditions

79. Physiology – Exocrine Pancreas
• Secretion of water and electrolytes originates in the centroacinar and
intercalated duct cells. Pancreatic enzymes originate in the acinar
cells. Final product is a colorless, odorless, and isosmotic alkaline fluid
that contains digestive enzymes (amylase, lipase, and trypsinogen).
• 500 to 800 ml pancreatic fluid secreted per day. Alkaline pH results
from secreted bicarbonate which serves to neutralize gastric acid and
regulate the pH of the intestine. High pH neutralizes acidic gastric
chyme and provides optimum pH for the enzymatic digestion
• Enzymes digest carbohydrates, proteins, and fats.
• Fluid (pH from 7.6 to 9.0) acts as a vehicle to carry inactive proteolytic
enzymes to the duodenal lumen. Bicarbonate is formed from
carbonic acid by the enzyme carbonic anhydrase.
• Major stimulants: are Secretin, Cholecystokinin, Gastrin,
Acetylcholine.
• Major inhibitors: Atropine, Somatostatin, Pancreatic polypeptide and
Glucagon

80. Exocrine--Enzyme secretion
• Four classes of enzymes are secreted
• Proteolytic--Peptidases
• Lipolytic--lipases
• Carohydrate-hydrolyzing--amylases
• Nucleolytic--nucleases
• Proteolytic enzymes activated when they enter duodenum
• Trypsin secreted as trypsinogen(Trypsin inhibitor in pancreas)
• Chymotrypsin secreted as chymotrypsinogen
• Both zymogens require enterokinases secreted by mucosa of
proximal intestine for activation
• Nucleolytic enzymes hydrolyze phosphodiseter bonds that
unite nucleotides in nucleic acid
• Ductal cells produce high quantity of bicarbonate into the
pancreatic juice.

81. Exocrine--Enzyme secretion
• Enterokinase secreted by the small intestine activates trypsinogen
into trypsin(active), small amount of trypsin formed in intestine can
itself activates trypsinogen into trypsin.
• Trypsin activates conversion of Chymotrypsinogen into chymotrypsin
and conversion of procarboxypeptidase into carboxy peptidase
• Sodium bicarbonhate in pancreatic juice neutralizes the acid pH of
chyme coming from stomach and entering duodenum because
alkaline pH is necessary for pancreatic enzymes digest food in the
small intestine.
• Pancreatic alpha amylase hydrolyses starch, glycogen and most other
complex carbohydrates into disaccharides
• Pancreatic lipases consists of lipase, cholesterol lipase, and
phospholipase hydrolyzes water soluble esters and lipid soluble
esters are hydrolyzed with the help of bile salts present in bile juice.

82. Pancreatic exocrine function
• Trypsin acts on native proteins and partly digested proteins in the
stomach, like metaproteins, proteases, peptones and polypeptides
and converts them into lower peptides containing tripeptides or
dipeptides.
• Chymotrypsin also converts proteins into tri and dipeptides.
• Carboxy peptidases splits amino acids having free carboxyl groups
from proteins.
• Nucleotidases digest nucleoproteins
• Phases of pancreatic secretion:
1. Cephalic phase: Sight, smell or thought of food induce secretion
Enzyme secretion enhanced due to stimulation of enteric neurones
which release acetylchoiline and Vagal stimulation causes secretion of
enzymes and bicarbonate. Bicarbonate secretion is stimulated through
enteric neurones through noradenaline release.
*** In this phase very little pancreatic secretion enters duodenum.

83. Pancreatic exocrine function
• Gastric phase: When stomach distends due to food content
pancreatic juice secretion increases. Vago-vagal reflex-acetylcholine is
the transmitter. Protein breakdown products in the stomach
stimulates G cells in the stomach release gastrin hormone into the
blood which causes low volume, high enzymes juice secretion from
the pancreas.
• Intestinal phase: It occurs after the Chyme entering the small
intestine. Stimulated by Secretin(by ‘S’ cells produce prosecretin
which is converted into active secretin by acidic chyme, this hormone
enters blood and acts on pancreas to cause pancreatic juice) and ‘I’
cells produce cholycystokinin hormones (due to presence of
proteases and long chain fatty acids in the upper small intestine,
goes into blood then to pancreas to increase pancreatic exocrine
secretion)secreted by duodenum and jejunum mucosal cells.

84. Regulation of Pancreatic Secretion
• Two patterns of secretion
– Basal secretion
• Bursts of increased bicarb and enzyme secretion that
last 10 to 15 minutes
– Post prandial stage
• Divided into cephalic phase, gastric phase, intestinal
phase

85. Post Prandial stage
• Cephalic phase
– Occurs in response to the sight or taste of food
– Mediated by the vagus
– Results in the production of enzymes and
bicarbonate

86. Post Prandial stage
• Gastric phase
– Occurs partially in response to distension of
stomach which stimulates gastrin release by vagal
reflex
– Gastrin and neural reflex stimulate acid secretion
by gastric parietal cells and pancreatic enzyme
secretion

87. Post Prandial stage
• Intestinal phase
– Initiated in response to acid entering the duodenum
– Most important phase
– When pH falls <4.5 secretin is released from the intestine
– Secretin inturn stimulates the pancreatic ducts to secrete
bicarbonate
– Presence of fatty acid, oligopeptides and amino acids
results in release of CCK which increase secretion of
pancreatic enzymes

88. Exocrine secretion of pancreas
• Proteases: essential for protein digestion, secreted as
proenzymes and require activation for proteolytic activity.
• Duodenal enzyme, enterokinase, converts trypsinogen to
trypsin
• Trypsin, in turn, activates
chymotrypsin, elastase, carboxypeptidase, and
phospholipase.

89. • Ultimate result of all these actions is food digestion
and absorption
• Inhibitory hormones
– Pancreatic polypeptide
– Peptide YY
• Vagal nerve stimulation induces bicarbonate
secretion – activity mediated through VIP hormones
which is present in vagal nerve endings and
throughout the entire GIT

90. Exocrine secretion of pancreas
• Secretin - released from the duodenal mucosa in response to a
duodenal luminal pH < 3.
• Enzyme Secretion: amylases, lipases, and proteases
• Major stimulants: Cholecystokinin, Acetylcholine, Secretin, VIP
Synthesized in the endoplasmic reticulum of the acinar cells and are
packaged in the zymogen granules. Released from the acinar cells into
the lumen of the acinus and then transported into the duodenal lumen,
where the enzymes are activated.
• Amylase: only digestive enzyme secreted by the pancreas in an active
form. Functions optimally at a pH of 7, hydrolyzes starch and glycogen
to glucose, maltose, maltotriose, and dextrins
• Lipase: function optimally at a pH of 7 to 9, emulsify and hydrolyze fat
in the presence of bile salts.