The digestive system contains both the alimentary canal (gastrointestinal tract) and accessory organs. The alimentary canal includes the mouth, esophagus, stomach, and small and large intestines. Accessory organs that aid digestion include the teeth, tongue, liver, gallbladder and pancreas. The digestive tract walls are composed of four main layers - mucosa, submucosa, muscularis externa, and serosa. Digestion involves both mechanical and chemical breakdown of food, with enzymes from the mouth, stomach, pancreas and small intestine facilitating the process.

1. Introduction
1
The Digestive System

2. The Digestive System
 The organs of the digestive system can be separated into two main
groups; those of the alimentary canal and the accessory organs
2

3. The Digestive System
 The alimentary canal or gastrointestinal (GI) tract is the
continuous muscular digestive tube that winds through
the body
o Mouth, pharynx, esophagus, stomach, small intestine and large
intestine
o Food in this canal is technically out of the body
 The accessory digestive organs are
Teeth, tongue, salivary glands, gallbladder, salivary glands, liver
and pancreas
The accessory organs produce saliva, bile and digestive
enzymes that contribute to the breakdown of foodstuffs
3

4. Digestive System Organs
4

5. Digestive System Organs
 The visceral peritoneum
covers the external surface of
most digestive organs and is
continuous with the parietal
peritoneum that lines the
walls of the abdomino-pelvic
cavity
 Between the two layers is the
peritoneal cavity, containing
serous fluid secreted by the
serous membranes
5

6. Mesentery
6
 A mesentery is a double layer of peritoneum - a sheet of two
serous membranes that attach to the digestive organ from
the body wall
 Mesenteries provide routes for blood vessels, lymphatics
and nerves to reach the digestive viscera
 Mesenteries also serves as a site for fat storage
 Not all alimentary canal organs are suspended with the
peritoneal cavity by a mesentery

7. Digestive System Organs
7

9.  Organs that adhere to the dorsal abdominal wall lose
their mesentery and lie posterior to the peritoneum
 These organs, which also include most of the pancreas
and parts of the large intestine are called retro-
peritoneal organs
 Digestive organs like the stomach that keep their
mesentery and remain in the peritoneal cavity are called
Intra peritoneal organs
9

10. Abdominal regions
10

11. Abdominal regions
11

12. Histology of the Alimentary
Canal
12
 From the esophagus to the anal canal, the walls of every
organ of the alimentary canal are made up of the same four
basic layers or tunics:
o Mucosa
o Submucosa
o Muscularis externa
o Serosa

13. Histology of the Alimentary Canal
13

14. Histology: Mucosa
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 More complex than most other
mucosae the typical digestive
mucosa consists of three sub
layers
o A surface epithelium
o A lamina propria , loose areolar
connective.
o A deep muscularis mucosae
 The epithelium of the mucosa is
a simple columnar epithelium
that is rich in mucus secreting
goblet cells

15. Histology: Submucosa
 The submucosa is a moderately
dense connective tissue containing
blood and lymphatic vessels,
lymph nodules, and nerve fibers.
 Its rich supply of elastic fibers
enables the stomach to regain its
normal shape after storing a large
meal.
15

16. Histology: Muscularis Externa
 The muscularis externa is
responsible for segmentation and
peristalsis.
 This thick muscular layer has an
inner circular and an outer
longitudinal layer.
 In several places along the GI tract,
the circular layer thickens to form
sphincters
 Sphincters act as valves to prevent
backflow and control food passage
from one organ to the next
16

17. Histology: Serosa
 The serosa is the
protective outermost
layer of Intraperitoneal
organ
 This visceral peritoneum
is formed of areolar
connective tissue
covered with
mesothelium, a single
layer of squamous
epithelial cells
17

18. Histology: Serosa
18
 Retroperitoneal organs have both a serosa (on the
side facing the peritoneal cavity) and an adventitia
(on the side abutting the dorsal body wall)
 The adventitia is an ordinary fibrous connective
tissue that binds the esophagus to surrounding
structures

19. Enteric
Nervous
System
 The alimentary canal has its own in-
house nerve supply.
 two major intrinsic nerve
plexuses
o Submucosal nerve plexus
o Myenteric nerve plexus
The enteric nervous system is also
linked to the CNS by afferent
visceral fibers and sympathetic
(inhibit) and parasympathetic
(stimulate)
19

20. Organs of the digestive System
20

21. Mouth, Pharynx, and
Esophagus
21
 The mouth is the only part of the digestive system
that is involved in the ingestion of food
 Most digestive function of the mouth reflect the
activity of accessory organs, chewing the food and
mixing it with salvia to begin the process of
chemical digestion.
 The mouth also begin the propulsive process by
which food is carried through the pharynx and
esophagus to the stomach.

22. The Mouth
 The oral cavity is lined with
mucosa, lined with stratified
squamous epithelium
 It is bounded by the lips anteriorly,
and the tongue inferiorly, the
cheeks laterally and the palate
superiorly.
 Its anterior opening is the oral
orifice
 Posteriorly the oral cavity is
continuous with the oropharynx
via oropharyngeal isthmus
22

23. The Lips and Cheeks
 The labia and the cheeks have
a core of skeletal muscle
covered by skin.
 The orbicularis oris muscle
forms the bulk of the lips
 The cheeks are formed largely
by the buccinators
 The area between the teeth
and gums is the vestibule
 Cavity with in jaw and teeth is
called oral cavity proper
23

24. The Palate
 The palate which forms the roof
of the mouth has two distinct
parts
Hard palate
Soft palate
hard palate
 is a rigid surface against which
the tongue forces food during
chewing
 There exists a center line ridge
called a raphe
 Made from maxilla anteriorly
and palatine bone posteriorly
24

25. The Palate
Soft palate
 mobile fold formed by
skeletal muscle
 Projecting down from its
free edge is the uvula
 The soft palate rises
reflexively to close off the
nasopharynx when
swallowing
25

26. The Pharynx
 From the mouth, the food
passes Posteriorly into the
oropharynx
 The mucosa consists of
stratified squamous
epithelium
 The epithelium is supplied
with mucus producing
glands for lubrication
26

27. The Pharynx
 The external muscle
layer consists of two
skeletal muscle layers
 The muscles of the inner
longitudinal layer
 The outer circular layer,
constrictor muscles
 Sequential contractions
propel food into
esophagus
27

28. The Esophagus
 The esophagus takes a fairly straight course through the
mediastinum of the thorax, pierces the diaphragm at the
esophageal hiatus to enter the abdomen
28

29. The Esophagus
 The esophagus joins the
stomach at the cardiac orifice
 mucosa lined by non-
keratinized stratified
squamous epithelium
 The muscularis externa
changes from skeletal muscle
to a mix of skeletal and
smooth to finally all smooth as
it approaches the stomach
29

30. The Stomach
30
 J shaped enlargement of GIT.
 The stomach functions as a temporary storage tank where
the chemical breakdown of protein begins and food is
converted to a creamy paste called chyme.
 chemical break down of proteins and fat (triglyceride)
starts in the stomach.
 Some substances are absorbed in the stomach such as
 Water, Electrolyte, Some drugs (asprin), Alcohol
 The stomach lies in the upper left quadrant of the
abdominal cavity

31. The Stomach: Gross Anatomy
 The stomach varies from 6 to 10 inches in length, but its
diameter and volume depend on how much food it contains
 When empty it may contain on 50 ml but can expand to hold
about 2 liters of food.
 When empty, the stomach collapses inward, throwing its
mucosa into large, longitudinal folds called rugae
 The major region of the stomach are the cardia region, the
fundus, body, pyloric region (pyloric antrum and pyloric
canal).
 Has the greater and lesser curvatures
31

32. 32

33. Small intestine
 Is the longest part of GIT and site of most
enzymatic digestion and 90% of nutrients are
absorbed here
 begins at pyloric sphincter and ends at ileocecal
sphincter
 Divided in to three segments; duodenum, jejunum
and ileum

34. Duodenum
 Shortest, widest and most fixed part
 forms C- shaped curve around head of pancreas
 starts at pyloric sphincter, extends about 25 cm and merges
with jejunum
 has no mesentery and covered by peritoneum only anteriorly
 receive digestive enzymes from pancreas and bile from gall
bladder by:
o major duedinal papilla
o Minor duedinal papilla

36. 36

37.  Jejunum
 free part of small intestine, covered by peritoneum, greatly
coiled
 jejunum begins at duodenojejunal flexure
 Ileum
 final and longest part
 together are about 6m long (2/5 jejunum and 3/5 ileum)
 join to large intestine at ileocecal sphincter

38. 38

39.  No sharp junction can be observed grossly between the
jejunum and the ileum.
 Both derived from endoderm of mid gut so supplied
with superior mesenteric artery.
 Then what is good to demarcate ?

40. Feature Jejunum Ileum
1. location Upper & left part ,
proximal 2/5th
Lower & right part
Distal 3/5th
2. walls Thicker & more
vascular
Thinner & less
Vascular
3. Lumen Wider & often empty Narrower & often
loaded
4. Mesentry - fat less abundant
- arterial arcades 1-2
vasa recta longer &
fewer
- fat more abundant
- arterial arcades 3-6
vasa recta shorter
& numerous

41. 5.circular mucosal
folds
larger & more
closely set
smaller & sparse
6.villi Large, thick ( leaf like)
& more abundant
Shorter , thinner
( finger like) & less
abundant
7. Peyer’s patches absent Present
8. solitary
lymphatic follicles
fewer numerous

42. IdentifyJ&I

43. Histology small intestine
43
 wall composed of the same four coats with modifications
o Mucosa
 Epithelium- simple columnar, contains absorptive cells( abundant
mitochondria and ER), goblet cells and paneth cells (destroy certain
types of bacteria)
 Mucosa forms a series of villi, and its apical surface containing
microvilli
o Submucosa
o Muscularis
o Serosa
Function of small intestine
 The completion of digestion is the result of collective action of
pancreatic juice, bile and intestinal juice in small intestine

44. 44

45. LARGE INTESTINE
 the last organ of the GIT that extends from ileum to anal orfice
 the material that reaches to it is a largely digested residue that
contains few nutrients
 even though the large intestine absorbs few remaining
nutrients it’s main function is to absorb water and
electrolytes from the digested mass , resulting in semisolid
faces
 wider but shorter than small intestine

46. Large intestine
46
 over most of it’s length the large intestine exhibits three
special features teniae coli, haustra and epipolic appendages
 Teniae coli- ribbons of colon
 are three longitudinal strips,of smooth muscle muscle
 Epipolic appendages (omental appendages)- membrane
covered fat filled pouches of visceral peritoneum.
 Large intestine has the following sub divisions
 Cecum
 Vermiform appendix
 Colon
 Rectum and
 Anal canal

49.  Colon
has ascending colon, transverse, descending and sigmoid
colon
 Ascending colon-on the right side
o begins at upper end of Cecum and ends at inferior surface of liver
where it forms right colic flexure
o right colic flexure (hepatic flexure)- forms the junction b/n ascending
and transverse colon
 Transverse colon-begins at right flexure and ends at left flexure
 Descending colon –on the left side and begins at left flexure
and ends at left iliac fossa
 Sigmoid colon- S shaped begins near the left iliac crest, projects
in ward to the mid line and joins the rectum

51.  Rectum
o in the pelvis the sigmoid colon joins the rectum which
descends along the inferior half of the sacrum
 Anal canal
o lie entirely external to the abdominopelvic cavity in
perineum
o wall of anal canal contains two sphincter muscles
1. Internal anal sphincter- smooth muscle
2. External anal sphincter- skeletal muscle

53. 53
 Accessory organs of digestion
o Teeth
o Tongue
o Gall bladder
 Accessory digestive glands
o Salivary glands
o Liver
o Pancreas

54. Teeth
 Are accessory digestive organs located in the
alveolar process of mandible and maxillae
 Alveolar process are covered by gingivae (gum)
 Humans have two sets of teeth or dentition
 Deciduous teeth(primary dentition)
 Permanente teeth

55.  Deciduous teeth(primary dentition)- primary (milk teeth)
erupts starting from at about 6 month to 2 years of age
 20 in number,2 incisors, 1 canines and 2 molars
 Lost b/n 6-12 years and replaced by permanent teeth
 Permanent teeth-there are 32 permanent teeth 2 incisors, 1
canines and 2 premolars and 3 molars
 Teeth are classified according to their shape and function as incisors,
canines, premolars and molars
o Typical tooth consists of 3 regions
1. crown- visible portion
2. neck- constricted junction b/n crown and root
3. root- embedded in a socket

57. Periodontal ligament (membrane)
 Sockets are lined by periodontal ligament or membrane
o anchors the teeth in position and act as a shock absorber during
chewing
o attaches to the cementum
Teeths are composed of
 Enamel- the dentin of crown is covered by enamel that consists of
calcium phosphate and calcium carbonate
 Dentin : forms the bulk of the teeth and encloses the pulp cavity
 Pulp cavity: lies with in the crown and filled with pulp and contains
blood vessels, nerves and lymphatic vessels
o narrow extension of the pulp cavity (root canal) runs through the root
of the tooth.
o each root canal has an opening at its base = apical foramen through
which blood vessels , lymphatic vessels and nerves extend

58. TONGUE
 an accessory digestive organ composed of skeletal muscle covered with
mucus membrane
 together with it’s associated muscles it forms the floor of the mouth
(oral cavity)
 divided in to lateral halves by a median septum
 has both intrinsic and extrinsic muscles
 lingual frenulum a fold of mucosa on the under surface of the tongue,
attaches the tongue to the floor of the mouth and limits it’s posterior
mov’t

60.  the upper and lateral surface of the tongue has nipple
shaped projections called papillae ,some of them
contain taste buds
1. Fungiform papillae- found near the tip of the tongue
 have taste buds
 less abundant than filiform
2. Circumvallate papillae-line up in a V shaped row
posteriorly
 lies directly anterior to sulcus terminalis, which marks the
border b/n mouth and pharynx
 have taste buds

61. 3. Filiform papillae- distributed in parallel rows
 the smallest and most numerous
 lack taste buds
4. foliate papillae-located in lateral margins of tongue
most of their taste buds degenerate in early child hood
The posterior one third of the tongue , lies in the oropharynx
and covered with lingual tonsil

63. Salivary glands
Release a secretion called saliva in to oral cavity
functions of saliva
 keep mouth and pharynx moist
 cleans mouth and teeth
 lubricates , dissolves and begins chemical break
down of food
Components of saliva
 99.5% water and 0.5% solutes
 Solutes = ions, mucus and enzymes(lysozyme),
digestive enzymes(salivary amylase)

64. Salivary glands classified in to 2
 Small intrinsic and
 Large extrinsic salivary glands
Intrinsic salivary glands
- scattered with in the mucosa of the tongue, palate, lips and
cheeks
- Saliva from this gland keeps the mouth moist at all times
- includes labial, bucal, palatal and lingual glands
Extrinsic salivary glands
 Secrete saliva only during eating
 Includes parotid, Submandibular and
sublingual glands

65.  Parotid gland
 The largest & located anterior and inferior to ears
 Parotid duct pierces buccinator muscle to open in
to the vestibule
 Submandibular gland
Located beneath the base of the tongue in
posterior part of floor of mouth
Submandibular duct run under mucosa on either
side midline of floor of mouth and enter oral
cavity proper lateral to lingual frenulum
 Sub lingual gland
Located superior to submandibular gland
There are 10-12 Sublingual ducts that open in
to floor of mouth

67. Gall bladder
 pear shaped muscular sac, resting in a shallow depression on the visceral
surface of liver
 it has three parts
 fundus- projected beyond
 body- central
 neck- tapering
 it’s function is to store and concentrate bile
produced by liver
 bile is a yellowish , brownish or olive – green
liquid produced by hepatocytes

68. 68

69. LIVER
 heaviest and largest gland , weighting about 1.4 K.g in
adult
 second largest organ after skin
 lies inferior to diaphragm and occupies most of Rt part
of the abdominal cavity
 soft reddish brown
 protected by thoracic cage
 looks like wedge, wide base faces to right and narrow
apex lies just inferior to the level of left nipple

71. Has two surfaces
 diaphragmatic surface - faces anteriorly and superiorly
 visceral surface- faces posteriorly and inferiorly
 the visceral surface contain gall bladder fossa,
inferior vena cava fossa
 liver has 2 lobes (rt and lt) demarcated by
imaginary line from gall bladder fossa to
inferior vena cava fossa
 two other minor lobes , the quadrate and
caudate lobe are visible on the visceral
surface

72. 72

73. The function of liver
 Synthesis, storage and release of glycogen
 Synthesis of blood proteins (albumin, prothrombin,
fibrinogen and lipoproteins)
 Phagocytosis of old red blood cells and bacteria
 Removal of toxic substances (detoxification)

74. PANCREAS
 Retroperitoneal gland lies posterior to the greater curvature of
stomach
 Lies in the left part of the abdomen, it has head, body and tail
 Both an exocrine and endocrine gland
 The exocrine function is performed by acini cells that secrete
pancreatic enzymes(pancreatic juice)

75.  99% of the cells are acini cells and 1% are pancreatic
cells
 Secretions from pancreas enter in to duodenum through
2 ducts
 Accessory pancreatic duct
 Main pancreatic duct
 The main pancreatic duct join with common
bile duct from the liver and gall bladder and
enters the duodenum as hepatopancreatic
ampulla or ampulla of vater