The digestive system breaks down food through a multi-step process. The alimentary canal begins at the mouth and runs through the throat, chest, abdomen and pelvis, ending at the anus. Accessory organs like the liver, pancreas and salivary glands help break down food through mechanical and chemical digestion. Food is broken into smaller molecules that can be absorbed and used by the body before waste is eliminated. The digestive system is made up of organs like the mouth, esophagus, stomach and intestines that work together through processes like ingestion, digestion, absorption and elimination.

1. DIGESTIVE
SYSTEM
Presented By:
Mr. Nandish . S
Associate Professor
Mandya Institute of Nursing Sciences

2. Introduction :
 The Digestive system describes alimentary canal, its
accessory organs & variety of digestive process that prepare
food eaten in the diet for absorption.
 The Alimentary canal begins at the mouth, passes through
thorax, abdomen, pelvis and ends at Anus.
 It has all basic structures that is modified at different levels.
 The digestive process gradually break down the foods eaten
until they are in a form suitable for absorption.

3. Functions / Activities of Digestive system:
- Ingestion : this is taking of food into alimentary canal (Eating
& Drinking).
- Propulsion : this mixes the contents & moves them along
alimentary tract.
- Digestion :
o Mechanical breakdown of food by mastication
(Chewing)
o Chemical digestion of food into small molecules by the
action of enzymes produced by glands & accessory
organs.

4. - Absorption : it is the process by which products of digestion
pass through the walls of some organs of alimentary canal ,
into the blood and lymph capillaries for circulation & use by
body cells.
- Elimination : food that has been eaten, but cannot be
digested & absorbed is excreted in the form of Faeces by the
process of Defaecation.

5. Alimentary canal / GI Tract
 It is a long tube through which food passes.
 It commences at mouth and terminates at Anus.
 In Adults, it is around 5 meters in Length.
 The Parts are :
- Mouth
- Pharynx
- Oesophagus
- Stomach
- Small intestine
- Large intestine
- Rectum &
- Anal canal

7. Accessory Organs:
 Various secretions are released into the GI Tract, some by
glands in the membrane lining
 (Gastric Juice by glands in the stomach lining) and some by
glands situated outside the tract.
 They consists of
- Three pairs of Salivary glands
- The pancreas
- The liver & Biliary tract.
 These organs & glands are linked physiologically as well as
anatomically in the digestion & absorption.

8. Structure of Alimentary / GI Tract:
The layers of the walls of alimentary canal follow consistent
pattern from the Oesophagus onwards.
The walls of GI tract are formed by four layers of tissue.
- Serosa or Adventitia : outer covering.
- Muscle Layer (Muscularis Mucosa)
- Submucosa
- Mucosa : Mucosal Lining.

9. Serosa / Adventitia :
o This is the outermost layer.
o In thorax, it consists of loose fibrous tissue & in abdomen,
the organs are covered by serous membrane called
“Peritoneum”.
Peritoneum:
 It is the largest serous membrane of the body.
 It is a single membrane, forming a close sac & containing a
small amount of serous fluid.
 It provides a physical barrier to local spread of infection &
prevent involving of other abdominal structures.

10. Peritoneum :
It has two layers.
- The Parietal peritoneum lines abdominal wall.
- The visceral peritoneum covers the organs within the
abdominal & pelvic cavities.
The Two layers are in close contact, friction between them is
prevented by the presence of peritoneal fluid (a serous fluid
secreted by peritoneal cells).

12. o The abdominal organs are covered to varying degrees by the
loops and folds of the visceral peritoneum, which attaches
firmly to the abdominal wall.
o If the organs are completely covered by the visceral layer,
then it is said to be intraperitoneal (stomach, intestine,
liver) and they are double fold.
o If the organs are covered on the anterior / superior side only,
then it is said to be retroperitoneal (Pelvic organs,
Pancreas, spleen, kidneys adrenal glands).

13. Muscle Layer / Muscularis Mucosa
 This consists of Two layers of smooth muscle.
 The outer layer consists of muscle fibres arranged in
Longitudinally, where as inner layer consists of circular
fibres.
 Between these Two layers there are blood vessels, lymph
vessels and plexus of sympathetic & parasympathetic
nerves.

14. Submucosa :
 This layer consists of loose areolar connective tissue
containing collagen and elastic fibres which binds the
muscle layer to the mucosa.
 It includes blood vessels, nerves, lymph vessels & varying
amount of lymphoid tissue.

15. Mucosa :
It is the lining of GI Tract. Its most superficial layer is mucous
membrane.
It has mainly three functions.
- Protection
- Secretion
- Absorption.

16. o Inner most layer consists of stratified squamous epithelium
with mucous secreting glands below the surface.
o Mucous lubricates the walls of the tract & provides a
physical barrier that protects from damaging effects of
digestive enzymes.
o Under the epithelial lining there are varying amount of
lymphoid tissue that protect against ingested microbes.

17. Nerve Supply :
- The alimentary canal & accessory organs are supplied by
nerves from both Sympathetic & Parasympathetic divisions.
- Their actions are generally antagonistic to each other & one
has a greater influence than the other according to the body
needs.
- Increased parasympathetic activity to digestive organs
promotes digestive processes & increased sympathetic activity
inhibits them.

18. Mouth :
Mouth or Oral Cavity is formed by:
- Anteriorly by Lips
- Posteriorly it is continuous with Oropharynx.
- Laterally by the muscles of Cheek.
- Superiorly by bony hard palate & muscular soft palate.
- Inferiorly by the muscular tongue.

19.  Oral cavity is lined with mucous membrane consisting of
stratified squamous epithelium containing small mucus –
secreting glands.
 The palate forms the roof of mouth & is divided into the
Anterior hard palate and Posterior soft palate.
 The Hard palate is formed by the Maxilla & Palatine bones.
 The Soft palate is muscular in nature and blends with walls
of Pharynx at the sides.
 Uvula is a curved fold of muscle covered with mucous
membrane, hanging from the middle of free border of soft
palate.

21. Tongue :
 The tongue is composed of voluntary muscle.
 It is attached by its base to the hyoid bone and by a fold of
its mucous membrane covering called Frenulum to the floor
of mouth.
 The superior surface consists of stratified squamous
epithelium with numerous papillae (little Projections).
 Many of these contain sensory receptors for the sense of
taste in taste buds.

22. Blood Supply:
Arterial supply : Lingual Branch of external carotid artery
Venous drainage : Lingual vein which joins the internal jugular
vein.
Nerve Supply:
The Hypoglossal Nerve – voluntary muscle of tongue.
Lingual branch of Mandibular Nerve – somatic sensation (Pain,
Temperature, Touch)
Facial & Glossopharyngeal Nerves – for taste.
Functions :
It plays an important role in :
Chewing (Mastication), swallowing (Deglutition), speech and
Taste.

23. Teeth:
o They are embedded in the sockets of alveolar ridges of the
Mandible and Maxilla.
o There are two sets of teeth :
- Temporary or Deciduous teeth
- Permanent teeth
o There are 20 Temporary Teeth, 10 in each Jaw. They begin to
erupt at about 6 months and should be present by 24
months.
o The permanent teeth begin to replace Temporary Teeth
between 6 and 13 years.
o The dentition consists of 32 teeth and usually complete by
the age of 20 years.

24. Structure :
Shape of teeth may vary, but structure is same. It consists of
The Crown : part that protrudes from Gum.
The Root : part embedded in the bone.
The Neck : narrowed region where the crown merges with root.
In the centre of tooth, there is a pulp cavity containing blood
vessels, lymph vessels & Nerves.
It is surrounded by hard Ivory like substance called Dentine.
Dentine of the crown is covered by a thin layer of very hard
substance called Enamel.
Root of the tooth are covered with substance resembling bone
called Cementum, which secures tooth in its socket.

27. Blood Supply :
Arterial Supply : Maxillary arteries.
Venous Drainage : small branches of internal Jugular veins.
Nerve Supply:
Upper Teeth : Branches of Maxillary Nerves.
Lower Teeth : branches of Mandibular Nerves.
Functions:
Teeth have different shape depending on their functions.
Incisors & Canines are cutting teeth where as premolar & molar
teeth with broad, flat surfaces used for grinding / chewing of
Food.

28. Salivary Glands:
There are three main pairs of salivary glands.
- Parotid glands
- Submandibular glands
- Sublingual glands.
There are numerous smaller salivary glands scattered around
the mouth.
Parotid Glands:
 These are situated one on each side of the face, just below
the external acoustic meatus.
 Each gland has parotid duct opening into mouth at the level
of second upper molar teeth.

29. Submandibular Glands:
These lie one on each side of the face under the angle of Jaw.
The submandibular ducts open on the floor of mouth, one on
each side of Frenulum of Tongue.
Sublingual Glands:
These lie under the mucous membrane of the floor of mouth in
front of submandibular glands.
They have numerous small ducts that open into floor of mouth.

30. Composition of Saliva:
Saliva is the combined secretion from salivary glands & the
small mucous secreting glands of the oral mucosa.
About 1.5 litres of saliva is produced daily & it consists of :
- Water
- Mineral salts
- Salivary Amylase : a digestive enzyme.
- Mucus
- Antimicrobial substances : Antibodies & enzyme Lysozyme.

31. Secretion of Saliva:
 It is controlled by Autonomic nervous system.
 Parasympathetic stimulation causes profuse secretion of
watery saliva with low content of enzymes & organic
substances.
 Sympathetic stimulation results in secretion of small amount
rich in organic material.
 Reflex secretion occurs when there is food in mouth.
 Secretion also occurs during sight, smell & even thought of
smell.

32. Functions of Saliva:
- Chemical digestion of polysaccharides (enzyme amylase
begins breakdown of complex sugars into disaccharide
maltose).
- Lubrication of Food.
- Cleaning & Lubrication of Mouth.
- Non specific defence.
- Taste (dry food stimulate sense of taste only after mixing with
Saliva)

33. Pharynx:
 It is divided into three parts, namely Nasopharynx,
Oropharynx & Laryngopharynx.
 Oro and Laryngopharynx are passages common to both
Respiratory & Digestive system.
 Food passes into the pharynx & then to the oesophagus
below, with which it is continuous.
 It consists of three layers; inner, middle & outer layer.

34. Inner mucosa is made up of stratified squamous epithelium. This
provides thick sturdy, lining.
Middle layer consists of connective tissue which becomes thinner
towards lower end, contains blood & lymph vessels with nerves.
Outer layer consists of involuntary muscles that are involved in
swallowing.
Blood supply:
Artery : branches of Facial arteries.
Venous drainage : Facial veins & Jugular veins.
Nerve Supply:
Parasympathetic : Glossopharyngeal & Vagus Nerves
Sympathetic : Cervical Ganglia

35. Oesophagus :
 It is a narrow muscular tube extending from pharynx to
stomach, descends in front of vertebral column goes through
superior and posterior mediastinum.
 It begins with lower part of the neck at the inferior border of
cricoid cartilage (C-6), extending to the Cardiac orifice of
stomach (T-11).
 It lies in the median plane in thorax behind Trachea and
Heart.

37. Dimensions :
Length : 25 cm or 10 Inches.
Width : 2 cm
Lumen : Its flattened Antero-posteriorly.
- Normally its kept closed (collapsed) and opens (dilates)
only during the passage of Food.

38. - It is continuous with Pharynx & just below the diaphragm it
joins stomach.
- The upper and lower ends of Oesophagus are closed by
sphincters.
A) the upper oesophageal sphincter prevents passage of
air into the oesophagus during inspiration &
aspiration of oesophageal contents.
B) the lower oesophageal sphincter (cardiac) prevents the
reflux of gastric contents into the oesophagus.
- There is no thickening of muscle in this area.
- When intra abdominal pressure raised (inspiration &
defaecation), the tone of lower oesophageal sphincter
increases.

39. Structure:
There are Four layers of tissue.
 the outer covering (The Adventitia) consists of elastic fibrous
tissue that attaches oesophagus to surrounding structures.
The proximal third is lined by stratified squamous epithelium
for protection during swallowing.
The Distal third is covered by columnar epithelium.
The middle third is covered by mixture of two.

40. Blood Supply :
Artery :
Thoracic region : paired oesophageal arteries.
Abdominal region : branches from inferior phrenic arteries &
left gastric branch of coeliac artery.
Venous Drainage :
Thoracic region : Azygos & hemiazygos veins.
Abdominal region : Left gastric vein.

41. Functions of Mouth, Pharynx & Oesophagus:
1) Formation of Bolus.
 When food is taken into mouth, it is chewed (masticated) by
teeth and moved around the mouth by tongue and muscles
of cheeks.
 It is mixed with saliva & formed into soft mass or Bolus
ready for swallowing.
 The length of time that food remains in the mouth largely
depends on the consistency of food.

42. 2) Swallowing :
It occurs in three stages after chewing is complete & the bolus
has been formed.
 oral stage :
With the mouth closed, voluntary muscles of tongue & cheeks
push the bolus backwards into the pharynx.
Pharyngeal stage :
The muscles of pharynx are stimulated by reflex action
initiated in the walls oropharynx & coordinated by the
swallowing centre in the Medulla.
Involuntary contraction of these muscles propels the Bolus
down into the oesophagus.

43. Oesophageal Stage :
o The presence of Bolus in pharynx stimulates a wave of
peristalsis that propels the bolus through the oesophagus to
stomach.
o Peristaltic waves pass only after the swallowing begins, until
that the walls are relaxed.
o After the initiation of peristalsis, the lower oesophageal
sphincter guarding the entrance to the stomach relaxes to
allow descending bolus to pass into stomach.

45. STOMACH :
The stomach is a J – Shaped, muscular, hollow organ & dilated
portion of the alimentary tract situated in the epigastric, umbilical &
left hypochondriac regions of the abdominal cavity.
Organs associated with Stomach:
Anterior : left lobe of Liver.
Posterior : Abdominal Aorta, Pancreas, Spleen, Left kidney & adrenal
gland.
Superior : Diaphragm, oesophagus & left lobe of Liver.
Inferior : Transverse colon & small Intestine.
To the Left : diaphragm & spleen
To the right : Liver & Duodenum.

47. Structure :
It is continuous with oesophagus at lower oesophageal
sphincter & with duodenum at pyloric sphincter.
It has two curvatures.
- Lesser curvature is short & is continuation of the posterior
wall of Oesophagus.
- Just before the pyloric sphincter, it curves upwards to
complete J shape and forms greater curvature.
Stomach is divided into Three regions:
o The Fundus
o The body
o The pylorus

48.  Cardia is not an anatomically distinct region of stomach.
 The fundus is formed in the upper curved part.
 Body is the main, central region of stomach.
 Pylorus is the lower section of stomach that empties
contents into duodenum.
 At the distal end of pylorus, is the pyloric sphincter guarding
opening between stomach & duodenum. When stomach is
inactive / empty the pyloric sphincter is relaxed and open,
when stomach contains food sphincter is closed.

50. Walls of stomach:
It has Four layers of tissue that comprise basic structure of
Alimentary canal with some modifications.
Muscularis :
it consists of three layers of smooth muscle fibres.
- An outer layer of Longitudinal fibres
- A Middle layer of circular fibres
- An Inner layer of Oblique fibres.
This arrangement allows churning action characteristic of
gastric activity.

51. Mucosa :
 When stomach is empty, the numerous membrane lining
thrown into longitudinal folds or Rugae.
 When stomach is full, rugae are ironed out giving surface a
smooth, velvety appearance.
 Numerous gastric glands are situated below surface in
mucous membrane. They contain specialised cells including
chief cells & parietal cells which secrete gastric juice
constituents.

53. Gastric Juice:
About 2 litres of gastric juice are secreted daily by specialised
secretory glands in mucosa.
It consists of :
 Water – liquifies food.
 Mineral salts
 Mucous – prevents mechanical injury to stomach.
 Hydrochloric acid – acidifies food, kills ingested microbes,
provide acid environment for pepsin.
 Intrinsic Factor – absorption of Vit B12
 Inactive enzyme precursors – Pepsinogen.

54. Functions of Stomach :
 Temporary storage : stomach size varies with volume of food it
contains (1.5 litres in adults). After food consumption, it
accumulates in stomach in layers.
 Chemical digestion : pepsin breaks proteins into polypeptides.
 Mechanical breakdown: three muscle layers enable the
stomach to act as a churn, gastric juice is added and
contents are liquefied into Chyme.
 Limited absorption: water, alcohol, lipid soluble drugs.
 Non specific defense against microbes.
 Preparation of Iron for absorption.
(to be continued….)

55.  Production & Secretion of Intrinsic Factor.
 Regulation of passage of gastric contents into the duodenum.
 Secretion of hormone Gastrin – it circulates in the blood and
stimulates gastric glands to produce more gastric Juice.
Blood Supply :
Arterial Supply: it is by Left Gastric artery a branch of Coeliac
artery, Right Gastric artery and Gastroepiploic artery.
Venous drainage : branches of Portal vein.

56. Pancreas:
 It is a creamy pink gland weighing about 60 gm.
 It is about 12 – 15 cm long & situated in the Epigastric and
left hypogastric regions of the abdominal cavity.
 It consists of broad Head, a Body & a Narrow Tail.
 Head lies in the curve of Duodenum, body behind the
stomach & tail in front of the left Kidney.
 Abdominal Aorta & Inferior vena cava lie behind the gland.
 It is both an exocrine and an endocrine gland.

58. Exocrine Pancreas :
• This consists of large number of Lobules, made up of small
Acini (it composed of secretory cells).
• Each Lobules is drained by tiny ducts, which unite to form
pancreatic duct and they open into Duodenum.
• Just before they enter Duodenum, pancreatic duct joins
common bile duct to form Hepato-pancreatic Ampulla.
• The duodenal opening of ampulla is controlled by Sphincter
of Oddi.
• Function of exocrine pancreas is to produce pancreatic juice
containing enzymes which digest Carbohydrates, Proteins &
Fat.

59. Endocrine Pancreas :
o They consists of a group of specialised cells called
Pancreatic Islets (Islets of Langerhans).
o These cells have no ducts, hence Hormones directly
diffuse into the blood circulation.
o They secrete hormones like Insulin, glucagon which are
concerned with regulation of blood sugar level.

60. Blood Supply :
Artery : splenic & mesenteric arteries
Venous drainage : pancreatic vein that join other veins to
form Portal vein.
Nerve Supply :
Parasympatheic N.S.: its stimulation increase pancreatic
secretion.
Sympathetic N.S.: Its stimulation depress pancreatic
secretion.

62. Liver :
 It is the Largest gland in the body.
 It is reddish brown in colour and weighs between 1 to 2.3 kg.
 It is situated in the upper part of the abdominal cavity, it
occupies greater part of Right hypochondriac region, part of
epigastric region & extends into left hypochondriac region.
 Its upper & anterior surfaces are smooth and curved to fit
under the diaphragm.

65. Organs Associated with Liver :
 Superiorly & Anteriorly: Diaphragm & anterior abdominal
wall
 Inferiorly :stomach, bile duct, duodenum, right kidney &
adrenal gland
 Posteriorly : Oesophagus, Inferior Vena Cava, Aorta, Gall
bladder, Vertebral column & diaphragm.
 Laterally : lower ribs & Diaphragm.

66.  The liver is enclosed by thin inelastic Capsule and a layer of
peritoneum.
 Liver is held in position partly by ligaments and partly by
pressure of the organs in Abdominal cavity.
 Liver has Four lobes.
 The Two most obvious are – large right lobe and smaller,
wedge shaped left lobe.
 The other Two : the Caudate & the Quadrate lobes are found
on posterior surface.

67. Portal Fissure :
It is located on posterior surface of the liver where various
structures enter & leave the gland.
- Portal veins enters carrying blood from stomach, spleen,
pancreas, small and large intestines.
- Hepatic artery enters carrying oxygenated blood.
- Nerve fibres.
- Right & left hepatic ducts carrying bile from liver to gall
bladder.
- Lymph vessels.

68. Blood Supply :
Artery : Hepatic artery and portal veins carry pure blood
Venous Drainage: it is by variable number of hepatic veins
which join Inferior vena cava.

69. Structure :
 The lobes of the Liver are made up of tiny functional units
called Lobules, which are visible to the naked eye.
 Lobules are Hexagonal in outline & are formed by cuboidal
cells called “Hepatocytes”.
 Hepatocytes are arranged in pairs of columns of cells.
 Between two pairs of columns of cells, we have sinusoids,
blood vessels with incomplete walls.
 Among the lining cells, there are Hepatic Macrophages
(Kupffer cells), whose function is to ingest & destroy worn out
blood vessels & any foreign particles present in the blood
flowing through the Liver.

70.  Blood drains from sinusoids into central or centrilobular
veins.
 These then merge with veins from other lobules forming
progressively large veins until they become Hepatic veins.
 Each column of hepatocytes has blood sinusoid on one side
& bile canaliculus on the other.
 The canaliculi joins up to form large bile canals until they
form right & left hepatic ducts, which drain bile from the
Liver.

71. Functions :
The Liver is extremely active metabolically with multiple inter
related functions.
- Carbohydrate metabolism.
- Fat metabolism.
- Protein metabolism.
- Breakdown of erythrocytes
- Detoxification of drugs & toxic substances.
- Inactivation of hormones
- Production of heat.
- Secretion of Bile.

72. Storage : it stores substances like
o Glycogen
o Fat soluble vitamins (A,D,E,K)
o Iron , Copper
o Water soluble vitamins like B12.

73. Bile Juice :
Bile is secreted by liver everyday. Around 500 to 1000 ml of
juice is secreted daily.
It consists of :
 Water
 Mineral salts
 Mucus
 Bile pigments (Bilirubin)
 Bile salts
 Cholesterol.
Functions : - Digestion of Fat.
- Excretion of Bilirubin.

74. Gall Bladder :
 It is a pear shaped sac attached to the posterior surface of
Liver by connective tissue.
 It has Fundus, Body or main part and Neck, which is
continuous with cystic duct.
 Wall of gall bladder has same layers as that of Alimentary
tract.
 Blood supply : artery – cystic artery, A branch of Hepatic
artery.
Vein : cystic vein which joins Portal vein.

76. Functions :
- Storage of Bile.
- Concentration of the bile by upto 10 or 15 fold by the
absorption of water through walls of gall bladder.
- Release of stored bile.

78. Bile Ducts:
 The right and Left hepatic ducts join to form the common
Hepatic duct outside the portal Fissure.
 The hepatic duct passes downwards for about 3cm & then it
is joined by the Cystic duct from Gall bladder.
 The cystic & hepatic ducts merge to form common bile duct,
which passes downwards behind pancreas.
 Common bile duct is joined by main pancreatic duct at
Hepatopancreatic ampulla & opens into duodenum.
 The common bile duct is about 7.5cm long & has a diameter
of about 6mm.

79. Small Intestine :
 It is continuous with the stomach at the pyloric sphincter.
 It is about 2.5 cm in diameter and around 05 metres long.
 It leads into the large intestine at the Ileocaecal valve.
 It lies in the abdominal cavity surrounded by large intestine.
 Small intestine comprised of Three continuous parts.
- Duodenum
- Jejunum
- Ileum

81. Duodenum :
 It is about 25cm long and curves around the head of the
pancreas.
 Secretions from gall bladder & Pancreas merge in common
structure – hepatopancreatic ampulla that enter duodenum.
Jejunum :
This is the middle section of small intestine & its about 2
metres long.
Ileum :
This terminal section is about 3 metres long & ends at the
ileocaecal valve.

82. Structure of Small Intestine :
The walls of intestine are composed of the four layers with some
modifications.
Peritoneum: The Mesentry, a double layer of peritoneum
attaches Jejunum and Ileum to the posterior abdominal wall. It
is fan shaped. The large blood vessels & Nerves lie on posterior
abdominal wall.
Mucosa: the surface area of mucosa is greatly increased by
permanent circular folds, Villi & Microvilli. They promote mixing
of Chyme as they pass along.
(..continued)

83.  The Villi are tiny Finger like projections of the mucosal layer
into the intestinal lumen, about 0.5 – 1mm long.
 Their covering consists of columnar epithelial cells or
enterocytes, with tiny Microvilli (I micro meter long) on their
free border.
 Goblet cells which secrete mucus are interspersed between
the enterocytes.
 The villi contain network of blood capillaries & central lymph
capillaries.
 These lymph capillaries are called lacteals, because
absorbed fat gives the lymph a milky appearance.

84.  The intestinal glands are simple tubular glands situated
below the surface between the villi which are made up of
epithelial cells.
 These epithelial cells produce digestive enzymes that lodge in
the microvilli & together with intestinal juice complete
digestion of Carbohydrates, Fats & proteins.
Blood Supply :
Artery : Superior Mesenteric artery
Venous drainage : superior mesenteric vein which joins
portal vein.

86. Intestinal Juice :
o About 1500 ml of intestinal juice is secreted daily by glands
of small intestine.
o It is slightly basic and consists of water, lubricating mucus &
bicarbonate to neutralise gastric acid.
o Mechanical stimulation of intestinal glands is the main
stimulus to the secretion of intestinal juice.

87. Functions :
- Onward movement of its contents by peristalsis.
- Secretion of intestinal juice.
- Completion of chemical digestion of CHO, Fats & Proteins.
- Protection against infection by microbes.
- Secretion of Hormones CCK & secretin.
- Absorption of nutrients.

88. Pancreatic Juice:
 It is secreted by exocrine pancreas. It enters the duodenum
at duodenal papilla.
 It consists of :
- Water
- Mineral salts
- Enzymes : Amylase, Lipase, Nuclease
- Inactive enzyme precursors : Trypsinogen,
Chymotrypsinogen.
 Pancreatic juice is alkaline in nature, because it contains
significant amount of bicarbonate ions which are basic.

89. Functions :
Digestion of proteins (Trypsin & Chymotrypsin)
Digestion of Carbohydrates (Pancreatic Amylase)
Digestion of Fats (Lipase)
Control of Secretion:
The secretion of Pancreatic juice is stimulated by Secretin &
cholecystokinin, which are produced by endocrine cells in the
walls of Duodenum.

90. Large Intestine :
• It is about 1.5 metres long. It begins at caecum in the right
iliac fossa & terminating at the rectum and anal canal.
• Its lumen is about 6.5 cm in diameter, larger than that of
small intestine.
• It forms an arch around round the coiled – up small
intestine.
• It is divided into The caecum, colon, Rectum & anal canal.

91. Caecum :
 It is the first part of large intestine.
 It is a dilated region that has blind end inferiorly & is
continuous with ascending colon superiorly.
 The vermiform appendix (meaning worm like) is a fine tube,
closed at one end, which leads from caecum.
 It is about 8 – 9 cm long and has the same structure of large
intestine, but contains more lymphoid tissue.
 The appendix has no digestive functions.
 It can cause significant problems when it becomes inflamed.

92. Colon :
The colon has 4 parts, which have same structure & functions.
The Ascending colon passes upwards from the caecum to the
level of liver, where it curves acutely to left at hepatic flexure.
The transverse colon extends across abdominal cavity in
front of the duodenum & stomach to the area of spleen,
where it forms splenic flexure and curves acutely downwards.
The descending colon passes down the left side of abdominal
cavity, then curves towards midline.
The sigmoid colon is ‘S’ shaped curve in the pelvic cavity that
continues downwards to become Rectum.

93. Rectum :
• It is slightly dilated section of large intestine.
• It is about 13 cm long.
• It starts from sigmoid colon & terminates at Anal canal.
Anal Canal :
• This is a short passage about 3.8 cm long in adults.
• It leads from rectum to the exterior.
• Two muscular sphincters control the Anus :
• Internal sphincter consisting of smooth muscle, is under the
control of Autonomic Nervous system.
• External sphincter formed by skeletal muscle, is under
voluntary control.

94. Structure :
- All the four layers which are described in the basic structure
of GI Tract are present in caecum, colon, rectum & anus.
- The arrangement of longitudinal fibres are modified in
caecum & colon.
- In rectum, the anal sphincters are formed by thickening of
circular muscle layer.
- In submucosal layer, there is more lymphoid tissue(for more
protection against organisms).
- In mucosal lining of colon & rectum, there are large number
of mucus secreting goblet cells within tubular glands. They
produce mucus, which lubricates passage of solid faeces.

95. Blood supply :
Arterial :
Superior Mesenteric artery – caecum, Ascending colon,
transverse colon.
Inferior Mesenteric artery – descending colon, sigmoid colon
Middle & inferior Rectal arteries – distal part of Rectum &
Anus.
Venous drainage :
Superior & Inferior mesenteric veins
Veins draining the distal part of Rectum & Anus join internal
Iliac veins.

96. Functions :
 Absorption : absorption of water (by osmosis), mineral salts,
vitamins and some drugs.
 Microbial activity : large intestine normally contain certain
types of bacteria like, E.Coli, Enterobacter aerogens,
streptococcus faecalis & clostridium perfringens. They
synthesize vitamin K & Folic acid. Few gases are produced by
bacterial fermentation of unabsorbed nutrients (Hydrogen,
carbon dioxide, Methane).
 Mass movement : large intestine does not exhibit peristaltic
movement. Only at long interval (4 – 6 times a day) a wave of
strong peristalsis sweeps along with transverse colon forcing
its content to descending & sigmoid colon.

97.  Defaecation :
o Rectum is usually empty. But when mass movement forces
the contents of sigmoid colon into rectum, the nerve endings
in the walls are stimulated.
o The external anal sphincter is under conscious control
through Pudendal nerve.
o Defaecation involves involuntary contraction of muscles of
rectum & relaxation of internal anal sphincter.

98. Constituents of Faeces :
It is a semisolid brown mass. The brown colour is due to
presence of Stercobilin.
 60 – 70 % of the weight is due to presence of water.
 Fibre (indigestible cellular plant & animal material)
 Dead & live microbes
 Epithelial cells shed from the walls of the tract.
 Fatty acids
 Mucus secreted by epithelial lining of Large intestine.

99. Metabolism :
It constitutes all the chemical reactions that occur in the body
to provide chemical energy essential for all cellular activities.
Metabolism involves two types of processes.
- Catabolism
- Anabolism
Catabolism : it breaks down large molecules into smaller ones,
releasing chemical energy, which is stored as Adenosine
Triphosphate (ATP) & heat. The heat generated maintains core
body temperature at the optimum level for chemical activity.

100. Anabolism : this is building up or synthesis of large molecules
from smaller ones require source of energy (ATP).
Energy :
 All body cells require energy to carry out their metabolic
process.
 It includes multiplication for replacement of worn – out cells,
muscle contraction & synthesis of glandular secretions.
 The energy produced in the body measured & expressed in
either joules or kilocalories.
 1 gm of Carbohydrate provides 4 kcal
1 gm of Protein provides 4 kcal
1 gm of Fat provides 9 kcal of energy.

101. Metabolic rate :
 It is the rate at which energy is released from the fuel
molecules inside the cells.
 It can be estimated by measuring oxygen uptake or carbon
dioxide excretion.
 Basal Metabolic Rate (BMR) is the rate of the metabolism
when the individual is at rest in a warm environment & is in
the post absorptive state (i.e. has not had a meal for at least
12 hours).
 In this state, energy released is sufficient to meet only
essential needs of vital organs (Heart, Lungs, Brain, Kidneys).

102. Carbohydrate Metabolism:
o Digested carbohydrate (Glucose) is absorbed into blood
capillaries of the villi of small intestine. It is transported by
portal circulation to Liver.
o Glucose is oxidised to provide chemical energy in the form of
ATP that is necessary for metabolic activity.
o If the glucose is in excess of requirements, then will be
converted to insoluble polysaccharide Glycogen by hormone
insulin in Liver & Skeletal Muscles.
o Glucagon, Adrenaline & Thyroxine are associated with
breakdown of glycogen into glucose.
o One molecule of Glucose can generate 38 ATP after complete
break down in the presence of Oxygen.

103. Protein Metabolism :
 Dietary protein consists of number of Amino acids. About 20
of them are identified, out of which 9 are Essential amino
acids i.e. they cannot be synthesized in the body & need to
be supplemented through food.
 Others are Non – Essential amino acids, because they can be
synthesized by many tissues.
 Digestion breaks down protein into amino acids, then
absorbed into blood by villi in small intestine.
 Amino acids are transported in the portal circulation to the
Liver & then into general circulation.

104.  It makes them available to all body cells & tissues. Different
cells choose particular amino acids required for building or
repairing their specific type of tissues and for synthesizing
their secretions.
Ex : Antibodies, Enzymes, hormones.
 In adults, 80 – 100 gm of protein are broken down & replaced
every day. The entire intestinal mucosa is replaced about
every 5 days.

105. Fat Metabolism :
 Fats are digested & absorbed as fatty acids and glycerol into
Lacteals are transported via cisterna chyli to the blood
stream and then to Liver.
 Fatty acids and glycerol circulating in the blood are used by
cells to provide energy & synthesize some secretions.
 In Liver, some fatty acids & glycerol are used to provide
energy & heat. Some are recombined to form Triglycerides,
the form, in which Fat is stored.


106. Signs / symptoms of GI Disorders :
1. Anorexia – loss of appetite that reduces eating.
2. Constipation – passage of faeces less frequently than
normal.
3. Diarrhoea – unusual frequent passage of loose watery
faeces / stools.
4. Dysphagia – difficulty in swallowing.
5. Haematemesis – vomiting of blood either fresh or partly
digested.
6. Melaena – passing blood in the faeces which are black &
tarry.
7. Vomiting – an involuntary reflex in which there is a forceful
ejection of stomach contents through mouth.

107. GI System Diseases:
Gingivitis :
It is an inflammation of Gums, which may be acute or chronic.
It occurs in response to accumulation of bacterial plaque
around the teeth. It cause bleeding gums.
Dental Caries:
Tooth decays with discoloration & then formation of cavities. It
occurs when bacteria present on the plaque on teeth act on
sugar, forming acid which destroy the hard parts of teeth.

108. Mumps :
It is an acute inflammatory condition of the parotid salivary
glands. It is caused by mumps virus, which is one of the
parainfluenza group.
GERD (Gastro – Esophageal Reflux Disease):
It is the most common cause for Heartburn or indigestion. It is
caused by persistent regurgitation of acidic gastric contents
acidic gastric juice into the oesophagus causing irritation,
inflammation & painful ulceration.

109. Gastritis :
It is an inflammation of stomach, which can be acute or
chronic.
It is due to consumption of irritant drugs (aspirin) or alcohol,
Helicobacter Pylori infection, physiological stress, and others.
Peptic ulcer :
A sore that develops on the lining of the Oesophagus, stomach
or small intestine.
Ulcer occurs when stomach acid damages the lining of the
digestive tract. Helicobacter Pylori infection is very common
affecting 50 – 60 % of the victims.

110. Appendicitis :
A condition in which the appendix becomes inflammed, filled
with pus and causes pain. Appendix is a finger shapes pouch
that projects from your colon on the lower right side of
abdomen. Microbial infection, hard fecal matter imposition,
kinking, inflammatory exudate with fibrin and phagocytes are
few common causes.
Hernia:
Protrusion of the organ or part of organ through a weak point
or aperture in the surrounding structures. Here, a piece of
bowel protrudes through a weak point on anterior abdominal
wall or an existing opening.

111. Pancreatitis :
It is an inflammation of pancreas cuased due to acting of
activated enzymes, when they are still in pancreas. Common
causes are pacreatic cancer, viral infections, hypercalcemia,
severe hypothermia, drugs…
Hepatitis :
It is a serious liver infection and inflammation of liver due to
death of hepatocytes. It is caused due to viral infections, toxic
substances, circulatory disturbances,…

112. Cholecystitis :
It is an inflammation of gall bladder associated with presence of
gall stones.
Cholangitis :
It is an inflammation of bile ducts caused by bacterial infection
and is accompanied by abdominal pain, fever & jaundice.
Jaundice :
It is not a disease, but yellowing of the skin & mucous
membrane is a sign of abnormal bilirubin metabolism and
excretion.

113. Digestion of food
In mouth:
Starch Salivary Amylase Maltose
In Stomach:
Pepsinogen HCl Pepsin
Proteins Pepsin Polypeptides

114. In small intestine : Pancreatic Juice
Trypsinogen Enterokinase Trypsin
Chymotrypsinogen Enterokinase Chymotrypsin
Polypeptides Trypsin Dipeptides, Aminoacids
Chymotrypsin
Starch Pancreatic Amylase Disaccharides

115. In small intestine : Bile Juice
Polypeptides Peptidase Amino Acids
Emulsified Fat Lipase Fatty acids & Glycerol
Sucrose Sucrase Glucose & fructose
Maltose Maltase 2 Glucose Molecules
Lactose Lactase Glucose & Galactose

116. Thank
You