4. Digestive System
• The digestive system, also known as the
gastrointestinal system, is responsible for the
physical and chemical breakdown of food
• Breakdown is necessary so food can be taken into
bloodstream and used by body cells and tissues
• System consists of alimentary canal and accessory
organs
K. Soundararajan, SRIHER 4
5. Food Breakdown
• Ingestion
– Taking of food into the body
• Peristalsis
– Physical movement along the tract
• Digestion
– Mechanical and chemical breakdown of food
• Absorption
– Passage of food from digestive tract into body
• Defecation
– Elimination of indigestible substances from body
K. Soundararajan, SRIHER 5
7. Alimentary Canal
• A long, muscular tube that begins at the
mouth and includes the mouth (oral cavity),
pharynx, Oesophagus, stomach, small
intestine, large intestine, and anus
Accessory Organs
• Accessory organs are the salivary glands,
tongue, teeth, liver, gallbladder, and pancreas
K. Soundararajan, SRIHER 7
8. Basic structure of alimentary
canal
Four layer of tissue
Adventitia or
secosa
(peritoneum)
Muscle layer
Sub mucosa
Mucosa lining
K. Soundararajan, SRIHER 8
17. MOUTH OR ORAL CAVITY
Boundaries
Anterior - lips
Posterior - oropharynx
Laterally - muscle of cheek
Superiorly - bony hard palate,
muscular soft palate.
Inferiorly - muscular tongue ,
soft tissue of floor of
mouth K. Soundararajan, SRIHER 17
18. Parts of the Alimentary Canal
• The mouth, also called the buccal cavity,
receives food as it enters body
• While food is in mouth, it is
– Tasted
– Broken down physically by teeth
– Lubricated and partially digested by saliva
– And swallowed
K. Soundararajan, SRIHER 18
20. VESTIBULE
part between cheek &
gum
PALATE
anterior hard palate
posterior soft palate
UVULA
curved fold of muscle
hanging from middle
border of soft palate
20
OPEN MOUTH
K. Soundararajan, SRIHER
21. ARCHES
anterior fold-
palatoglossal arch
posterior fold-
palatopharyngeal arch
PALATINE TONSIL
each side of arches
collection of lymphoid
tissue
21
OPEN MOUTH
K. Soundararajan, SRIHER
22. Parts of the Alimentary Canal
• The hard palate is the bony structure that forms the
roof of the mouth and separates the mouth from the
nasal cavities
• Behind the hard palate is the soft palate, which
separates the mouth from the nasopharynx
• The uvula, a cone-shaped muscular structure, hangs
from the middle of the soft palate and prevents food
from entering the nasopharynx during swallowing
K. Soundararajan, SRIHER 22
23. Tongue
Mostly muscles
Grip and reposition food
Forms “bolus” of food (lump)
Help in swallowing
Speech – help form some consonants
Taste buds contained by circumvallate and fungiform papillae
Lingual tonsil – back of tongue
23K. Soundararajan, SRIHER
26. Tongue
Nerve supply
hypoglossal nerve
lingual (B) of mandibular nerve
fasical & glossopharyngeal nerve
Lymphatic's
drain in to upper deep cervical
retropharyngeal lymph node
K. Soundararajan, SRIHER 26
27. Teeth
Called “dentition” (like dentist)
Teeth live in sockets (alveoli) in the
gum-covered margins of the mandible
and maxilla
Chewing: raising and lowering the
mandible and moving it from side to
side while tongue positions food
between teeth
27K. Soundararajan, SRIHER
28. Teeth
Two sets
Primary or deciduous
“Baby” teeth
Start at 6 months
20 are out by about 2 years
Fall out between 2-6 years
Permanent: 32 total
these 32 teeth complete by
21st year
28K. Soundararajan, SRIHER
30. Teeth are classified according to
shape and function
Incisors: chisel-shaped for
chopping off pieces
Canines: cone shaped to
tear and pierce
Premolars (bicuspids) and
Molars - broad crowns
with 4-5 rounded cusps for
grinding
30
incisor
canine
premolar
molar
K. Soundararajan, SRIHER
31. Tooth structure
Two main regions
A. Crown (exposed)
B. Root (in socket)
C. Meet at neck
Enamel
99% calcium crystals
Hardest substance in
body
Dentin – bulk of the
tooth (bone-like but
harder than bone, with
collagen and mineral)
Pulp cavity with vessels
and nerves
Root canal: the part of
the pulp in the root 31
A
B
C
K. Soundararajan, SRIHER
32. Tooth structure
Cementum – bone
layer of tooth root
Attaches tooth to
periodontal ligament
Periodontal ligament
Anchors tooth in boney
socket of the jaw
Continuous with gingiva
(gums)
32
A
B
C
K. Soundararajan, SRIHER
35. Parts of the Alimentary Canal
• Three pairs of salivary glands
– Parotid (cheek/jaw)
– Sublingual (beneath tongue)
– Submandibular (chin/neck)
• They produce a liquid called saliva
• Saliva lubricates mouth during speech and chewing and
moistens food so it can be swallowed easily
• Also contains enzyme called salivary amylase
• Salivary amylase begins chemical breakdown of
complex carbohydrates, or starches, into sugars that
can be taken into the body
K. Soundararajan, SRIHER 35
37. The Salivary Glands
Produce saliva
Compound tubuloalveolar glands
Parotid glands
Parotid duct – parallel to zygomatic arch
Contains only serous cells
Submandibular glands
Lies along medial surface of mandible
Sublingual glands
Lies in floor of oral cavity
Contains primarily mucous cells
K. Soundararajan, SRIHER 37
38. Salivary glands
(tuboalveolar glands)
Intrinsic salivary glands
Secrete saliva all the time
to keep mouth moist
Extrinsic salivary glands
Paired (2 each)
Parotid
Submandibular
Sublingual
External to mouth
Ducts to mouth
Secrete saliva only right
before or during eating
38
Saliva: mixture of water, ions, mucus, enzymes
keep mouth moist
dissolves food so can be tasted
moistens food
starts enzymatic digestion
buffers acid
antibacterial and antiviral K. Soundararajan, SRIHER
39. Extrinsic salivary glands
Parotids* - largest (think
mumps)
each side of face just
below external acoustic
meatus ends 2 upper
molar tooth
Submandibular # - medial
surface mandible
Each side of face under
angle of jaw
Sublingual + - under
tongue; floor of mouth
Floor of mouth end infront
of sub mandibular gland 39
*
#
K. Soundararajan, SRIHER
41. Parts of the Alimentary Canal
• The teeth are special structures in mouth that
physically break down food by chewing and
grinding
• Process is called mastication
• The tongue is a muscular organ that contains
special receptors, called taste buds
• Taste buds allow a person to taste sweet, salt,
sour, and bitter sensations
• The tongue also aids in chewing and swallowing
foods
K. Soundararajan, SRIHER 41
46. Pharynx
Length - 12cm
Width - 3.5 cm
It is wide muscular
tube situated behind
nose, mouth, larynx.
3 layer of tissue
Mucosa
(lining membrane )
Middle layer
Outer layer
( involuntary muscle)
K. Soundararajan, SRIHER 46
47. Pharynx
Three parts
• Nasopharynx
air ( nasal part )
• Oropharynx
air & food
( oral part )
• Laryngopharynx
food ( laryngeal
part )
K. Soundararajan, SRIHER 47
48. Pharynx
Boundaries
Anterior - nasal, oral cavity, larynx,
anterior wall incomplete
Posterior - pharynx glides freely on
pre vertebral fascia
Superiorly - base of skull, occipital
bone,
pharyngeal tubercle
Inferiorly - lower border of critoid
cartilage
K. Soundararajan, SRIHER 48
52. Oesophagus
Narrow muscular tube
It is collapsible tube
Length – 25cm
Width – 2 cm
Extend :
Lies median plane in thorax in
front of vertebral column
behind trachea, heart
Below diaphragm join
stomach
Greater part – thorax
Lesser part - abdomen
52K. Soundararajan, SRIHER
53. Oesophagus
Sphincters
1. Pharyngeal (or)
upper
oesophageal
sphincter -
prevent air
passage
2. Cardiac (or) lower
oesophageal
sphincter -
prevent reflux of K. Soundararajan, SRIHER 53
54. Contains all 4
layers (see right)
Epithelium: non keratinized stratified squamous epithelium
Mucus glands in wall
Muscle (muscularis externa) changes as it goes down
Superior 1/3 of esophagus: skeletal muscle (like pharynx)
Middle 1/3 mixture of skeletal and smooth muscle
Inferior 1/3 smooth muscle (as in stomach and intestines)
When empty, mucosa and submucosa lie in longitudinal folds
54
Microscopic anatomy of Oesophagus
K. Soundararajan, SRIHER
62. Stomach
It is a J- shaped dilated portion of
alimentary tract
Location:
epigastric , umbilical,
left hypochondriac
Size – 25 cm long
Capacity
birth – 30 ml
puberty – 1 liter
adult – 1.5 to 2 liter
K. Soundararajan, SRIHER 62
64. Stomach Relations
Anterior - left lobe of liver, anterior
abdominal wall, coastal cartilage
Posterior - abdominal aorta, pancreas,
left kidney, adrenal gland,
spleen
Superior - diaphragm, oesophagus,
left lobe of kidney
Inferior – tranverse colon,
small intestine
Left side - diaphragm, spleen
Right side - liver , duodenum
K. Soundararajan, SRIHER 64
66. Stomach Region
Surface
1. anterior or
anterio-superior
(forward, upward)
2. Posterior or
posterio-inferior
(backward,
downward )
K. Soundararajan, SRIHER 66
67. Stomach Region
Sphincter
Cardiac sphincter
(oesophagus)
Pyloric sphincter
(duodenum)
curvature shape omentum border notch
Lesser Concave Lesser Right
( below)
Angular
Greater Convex Greater Left
(above)
cardiac
K. Soundararajan, SRIHER 67
68. Shape of stomach
Shape – pyriform
Obese person-
horizontal
Radio graphic
examination of
stomach after
barium meal gives
shape clearly
K. Soundararajan, SRIHER 68
69. Interior of stomach
It has longitudinal
folds and
irregular in shape
Gastric canal
near lesser
curvature
swallow liquid
Stomach bed is
separate from
stomach by
lesser sac
K. Soundararajan, SRIHER 69
70. Rugae: longitudinal folds on internal surface
(helps distensibility)
Muscularis: additional innermost oblique layer
(along with circular and longitudinal layers)
70K. Soundararajan, SRIHER
71. Layers of stomach
Muscle coat
1. Longitudinal
(outer layer)
2. Inner circular
(middle layer)
3. Deep oblique
(inner layer)
K. Soundararajan, SRIHER 71
72. Histology of
stomach
72
Simple columnar
epithelium:
secrete
bicarbonate-
buffered mucus
Gastric pits
opening into
gastric glands
K. Soundararajan, SRIHER
73. Blood supply - artery
Lesser curvature
left gastric artery (B) –
coeliac trunk
right gastric artery (B)-
proper hepatic artery
Greater curvature
right gastro epiploic
artery(B)- gastroduodenal
artery
left gastro epiploic artery(B)-
spleenic artery
Fundus
5 to 7 short gastric arteries
K. Soundararajan, SRIHER 73
74. Blood supply - vein
Portal vein
Right & left gastric
vein
Right & left gastro
epiploic vein
Superior & inferior
mescentric vein
Short gastric vein
Splenic vein
K. Soundararajan, SRIHER 74
75. Lymphatic's
Right & left gastric
node
Right & left gastro
epiploic node
Short gastric node
Coeliac node
Hepatic node
Pyloric node
Pancreatic splenic
node
K. Soundararajan, SRIHER 75
80. Small intestine
It continuous with
the stomach at
pyloric sphincter
It is longest of
alimentary canal
Greater part of
digestion &
absorption take
place here.
K. Soundararajan, SRIHER 80
81. Small intestine
It is divided in to
three region
i. Duodenum
ii. Jejunum
iii. Ileum
K. Soundararajan, SRIHER 81
82. Duodenum
It is shortest , widest & most fixed part
Extend
From - pylorus
To – duodenojejunal flexure
Length- 25cm
It is ‘c’ shaped , receives opening of
bile & pancreatic duct
Location
epigastric , umbilical
K. Soundararajan, SRIHER 82
83. Parts of duodenum
It is divided into four
parts
1. First or superior
2. Second or
descending
3. Third or horizontal
4. Fourth or ascending
K. Soundararajan, SRIHER 83
84. First or superior part of
duodenum
Begin – pylorus
End – superior duodenal flexure
Relation
Anterior – quadrate lobe of liver, gall
bladder
Posterior – gastro duodenal artery, bile
duct,
portal vein
Superior – epiploic foramen
Inferior – head and neck of pancrease
K. Soundararajan, SRIHER 84
85. Second or descending part
Begin – superior duodenal flexure
End – inferior duodenal flexure
Relation
Anterior – right lobe of liver, transverse of
colon,
root of mesocolon, small intestine
Posterior – anterior surface of right
kidney(medial
border), right renal vessel, right
edge
of inferior venacava, right psoas
K. Soundararajan, SRIHER 85
86. Third or horizontal part
Begin – inferior duodenal flexure
End – front of abdominal aorta, lower margin
of head of pancreas
Relation
Anterior – superior mesenteric vessel,
root of mesentry
Posterior –right ureter, right psoas major, right
testicular or ovarian vessel, inferior
venacava, abdominal aorta
Superior – head of pancreas
Inferior – coil of jejunum
K. Soundararajan, SRIHER 86
87. Fourth or ascending part
Begin – upper border of 2 lumbar
vertebra
End – duodenojejunal flexure at jejunum
Relation
Anterior – transverse colon, transverse
mesocolon, lesser sac, stomach.
Posterior –left renal artery, left gonadal
artery,
inferior mesentric vein, left
sympathetic vein
Superior – body of pancrease
K. Soundararajan, SRIHER 87
88. Blood supply
Artery
Upper half
Superior pancreaticoduodeal artery (B)
gastroduodenal artery
Lower half
Inferior pancreaticoduodenal artery (B)
superior mesenteric artery
Vein
Superior pancreaticoduodeal vein drains
into
portal vein , inferior vein, joins mesenteric
vein
K. Soundararajan, SRIHER 88
90. Duodenum
Lymphatic's
pancreaticoduodenal nodes to gastro
duodenal nodes
celiac nodes
superior mesenteric nodes
Nerve supply
sympathetic & parasympathetic vagus
nerve from celiac & superior
mesenteric plexus
K. Soundararajan, SRIHER 90
91. Jejunum and Ileum
The coil are freely mobile & attached
to posterior abdominal wall by fan-
shaped peritoneum
Begin – duodenojejunal flexure
End – ileoceral junction
K. Soundararajan, SRIHER 91
93. Jejunum and Ileum
Feature Jejunum Ileum
Location Occupies upper left
Part of intestinal area
Occupies lower right
Part of intestinal area
Wall Thicker more vascular Thinner less vascular
villi Large , thick ( leaf –
like)
More abundant
Large , thick ( leaf –
like)
More abundant
K. Soundararajan, SRIHER 93
94. Difference between
Jejunum
• Larger diameter
• Thickening wall
• Prominent fold
• 1-2 vascular
archade
• Long vasa recta
• Fat free
mesentery
Ileum
• Smaller
diameter
• Thinner wall
• Flat and few
• 4-5 vascular
archades
• Short vasa recta
• Abundant
mesenteric fat
K. Soundararajan, SRIHER 94
95. Blood supply
Arteries
branch of superior
mesenteric artery ,
lower part of ileum
by ileocolic artery
Vein
superior
mesenteric node
jejunum
ileumK. Soundararajan, SRIHER 95
96. Jejunum and ileum
Lymphatic’s
intermediate mesenteric node,
superior mesenteric node
Nerve
vagus nerve from superior mesenteric
plexus
sympathetic – T9 – T11 segment
parasympathetic- vagus
K. Soundararajan, SRIHER 96
99. Large intestine
It is about 1.5 m in
long
Extend
begin – caecum
end – anal canal
K. Soundararajan, SRIHER 99
100. Large intestine
It divides into many
parts
Caecum,
Ascending colon,
Transverse colon,
Descending colon,
Sigmoid colon,
Rectum ,
Anal canal
K. Soundararajan, SRIHER 100
101. Caecum
It is large blind sac
forming large
intestine
Long – 6 cm
Relation
anterior :
coil of intestine,
anterior wall of
abdominal wall
posterior :
right psoas, iliacus
medially:
appendix
caecum
K. Soundararajan, SRIHER 101
102. Caecum
Blood supply
Artery
branch of ileocolic artery
Vein
superior mesenteric vein
Lymphatic’s
several mescentric
nodes
Nerve
vagus nerve - superior
mesenteric plexus
K. Soundararajan, SRIHER 102
104. Vermiform Appendix
It is a vestibular
organ
It is narrow ,
muscular contain
large amount of
lymphoid tissue
It base attached to
posterio medial
surface of caecum
below ileoceal
junction
appendix
K. Soundararajan, SRIHER 104
105. Vermiform Appendix
Blood supply
Artery
appendicular artery (B) posterior cecal artery
Vein
appendicular vein drain in to posterior cecal vein
Lymphatic’s
superior mesenteric node
Nerve
vagus nerve - superior mesenteric plexus
K. Soundararajan, SRIHER 105
106. Large intestine – ascending
colon
Length – 13cm
Location – right lower
quadrant
From
caecum
To
inferior surface of right
lobe of liver , right colic
flexure
Sigmoid
colon
K. Soundararajan, SRIHER 106
107. Relation of ascending colon
Anterior
coil of intestine,
greater omentum,
anterior abdominal wall.
Posterior
iliacus, iliac crest,
quadratus lumbrum,
lower pole of kidney
K. Soundararajan, SRIHER 107
108. Ascending colon
Blood supply
Artery
ileocolic & right colic (B) of superior
mesenteric artery
Vein
superior mesenteric vein
Lymphatic’s
superior mesenteric node
Nerve
superior mesenteric plexus ( vagus )
K. Soundararajan, SRIHER 108
109. Large intestine – transverse
colon
Length – 38cm
Location – right &
left upper quadrant
From
right colic flexure
To
left colic flexure
Sigmoid
colon
K. Soundararajan, SRIHER 109
110. Relation of transverse colon
Anterior
greater omentum,
anterior abdominal wall.
Posterior
second part of duodenum,
head of pancrease,
coil of jejunum ,
coil of ileum.
K. Soundararajan, SRIHER 110
111. Transverse colon
Blood supply
Artery
Proximal two third:
middle colic artery (B) superior mesenteric arter
Distal third:
left colic artery (B) inferior mesenteric artery
Vein
the vein correspond to arteries drains in to
superior & inferior mesenteric vein
K. Soundararajan, SRIHER 111
116. Large intestine – sigmoid
colon
Length – 25 to 38cm
Location – left lower
quadrant
From
in front pelvic brim
To
rectum
Sigmoid
colon
K. Soundararajan, SRIHER 116
117. Relation of sigmoid colon
Anterior
Male – urinary bladder
Female – posterior surface of uterus,
upper part of vagina
Posterior
rectum & sacrum
lower coil of terminal part of ileum
K. Soundararajan, SRIHER 117
120. Rectum
Length – 13 cm
Location
posterior part of lesser
pelvic, in front of
sacrum coccyx (lower
3 pieces)
Extend
From
continuation of
sigmoid colon
To
anal canal at
anorectal junction
K. Soundararajan, SRIHER 120
125. Anal canal
Length – 3.8 cm
Location-
below the level of
pelvic diaphragm
Extend
From
rectal ampulla
To
anus
K. Soundararajan, SRIHER 125
126. Relations
Anterior
Male - membranous urethra, bulb of
penis
Female - lower end of vagina
Both sexes- perineal body
Posterior
anococcygeal ligament, tip of coccyx
Laterally
ischioanal fossae
K. Soundararajan, SRIHER 126
137. Liver
–liver is the largest solid organ in
the body, located in the upper right
abdominal cavity.
–An accessory organ of digestion
that contributes to, but is not
physically involved in, the process
of digestion.
–Liver cells (hepatocytes)
continuously produce bile, aK. Soundararajan, SRIHER 137
139. Liver
–Bile produced by the liver flows
through the hepatic ducts, through
the common hepatic duct, and then
into either the cystic duct to the
gallbladder or the common bile
duct.
–All of the ducts that carry bile are
collectively known as the biliary
tree.
K. Soundararajan, SRIHER 139
144. Gallbladder
– An accessory organ of digestion posterior to
the liver.
– Concentrates and stores bile from the liver.
– The presence of fatty chyme in the duodenum
causes the gallbladder to contract, sending bile
into the common bile duct and duodenum to
digest fats.
– It is pear shaped sac
– It is divided into fundus , body , neck
– It is covered by peritoneum
K. Soundararajan, SRIHER 144
145. Gallbladder
Relations
Anterior
anterior abdominal
wall, inferior
surface of liver
Posterior
transverse colon,
first , second part
of duodenum
K. Soundararajan, SRIHER 145
148. PANCREAS
It is pale green gland
Weight – 60 grams
Length – 12 to 15 cm
Location –
epigastric , left hypo gastric
region.
K. Soundararajan, SRIHER 148
150. Pancreas
–An accessory organ of digestion
posterior to the stomach.
–Presence of food in the duodenum
causes the pancreas to secrete
digestive enzymes into the
pancreatic duct to the duodenum.
–Also functions as an organ of the
endocrine system.
K. Soundararajan, SRIHER 150
152. Relations
Anterior
right to left
transverse of colon , lesser sac, stomach
Posterior
right to left
left kidney, hilum of spleen, left
suprarenal gland, left psoas , superior
mesenteric artery, aorta, inferior
venacava, portal & splenic vein, bile duct
K. Soundararajan, SRIHER 152
153. Blood supply
Artery
splenic artery
superior pancreatico
duodenal artery
inferior pancreatico
duodenal artery
K. Soundararajan, SRIHER 153
157. Spleen
It is reddish &
largest single mass
of lymphoid tissue
It act as filter of
blood
It is wedged in
fundus of stomach,
diaphragm
Location
left hypogastric ,
epigastric
K. Soundararajan, SRIHER 157
158. Relations
Anterior
stomach, tail of pancreas, left colic
flexure
left kidney along medial border
Posterior
diaphragm, left pleura, left lungs , 9th to
11th ribs
K. Soundararajan, SRIHER 158