Disha Parikh
M.Pharm (Pharmacology)
 The digestive system comprises of alimentary canal
gastrointestinal tract (GIT) and some accessory organs.
 The tract starts from mouth and ends at anus
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GIT mainly involves:
Mouth
Pharynx
Oesophagus
Stomach
Small intestine
Large intestine
Rectum
Anus
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The Accessory organs are:
Pancreas
Liver
Gall bladder
or
 The activity of digestive system involves the following:
 Ingestion: Taking the food into the alimentary canal (eating or
drinnking)
 Propulsion: Mixing and moving the contents along the tract.
 Digestion: it consist of:
• Mechanical breakdown of food: Mastication (the processes of
grinding & tearing of food and mixing with saliva involve movement
of jaws, cheeks, lips and tongue)
• Chemical digestion: large food molecules are converted to small
molecules by the enzymes present in digestive juices produced by
digestive glands and accessory organs.
 Absorption: the process by which the digested food substances
pass through the walls of GIT into the blood circulation and is used
by the body cells.
 Elimination: the undigested and unabsorbed food is excreted out
of GIT in form of faeces by the process of defecation.
 The first enlarged part of tract is the oral cavity.
 The oral cavity is lined throughout with mucous membrane,
containing startified squamous epithelium conataing small mucus
secreting glands.
 The part of mouth between the gums and the cheeks is called
vestibule.
 The dome shaped roof of the oral cavity is called palate.
 The front part is hard palate and behind is the soft palate.
 The muscular fold hanging from the middle of the soft palate is
called uvula.
 At the arch of the soft palate the pharyngeal tonsils are present
which act as gate keepers and protect against the infection.
TONGUE:
 The voluntary muscular structure present at the floor of the mouth.
 It is attached to the base by the thin membranous covering called
frenulum.
 The surface of the tongue consist of stratified squamous epithelim
with numerous papillae (little projections acting as sensory
receptors) and taste buds (sense of taste).
 The papillae are of following types:
• Filiform papillae: narrow and conical in shape distributed all over
the tongue. Taste buds are absent in filiform papillae.
• Fungiform papillae: present at the tip and edges of the tongue
consist of few taste buds. More in no. as compared to filiform
papillae.
• Circumvallate papillae: these are the largest papillae present at
the base of the tongue. They are arranged as inverted ‘V’ shape at
the base of the tongue.
 The taste buds are present on the sides of the papillae.
The tongue plays an important role in mastication (chewing),
deglutition (swallowing), speech and taste.
TEETH
 There are 16+ 16=32 teeth in mouth that are fixed in the
socket in the upper jaw (maxilla) and the lower jaw
(mandible).
 The order of the teeth from front to back is incisors, canines,
pre-molars and molars.
Right :
M P C I
I C P M
:Left
Upper jaw:
3 2
1 2
2 1 2 3
:Upper jaw
Lower jaw:
3 2
1 2
2 1 2 3
:Lower jaw
M:Molars, P: Pre-molars, C: Canines, I: Incisors
 Function of the teeth:
• The incisor and canine are the cutting teeth and are used for the
bitting off the pieces of the food.
• The premolar and molar are broad and flat surface teeth used for
the grinding and chewing of the food.
 Structure of tooth:
• Enamel The hard outer layer of
the crown. Enamel is the hardest
substance in the body.
• Dentine Not as hard as enamel,
forms the bulk of the tooth and can
be sensitive if the protection of the
enamel is lost.
• Pulp Soft tissue containing the
blood and nerve supply to the
tooth. The pulp extends from the
crown to the tip of the root.
• Cementum The layer of bone-like
tissue covering the root. It is not
as hard as enamel.
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SALIVARY GLANDS
pairs of salivary glands are present:
Parotid gland
Submaxiliary or Submandibular gland
Sublingual gland
Parotid gland: situated besides the
second upper molar and below the ear.
The gland is present on either sides. It
secretes ptyaline (digestion of starch).
The duct opens on either side of
cheeks
Submaxiliary gland:
they are
situated on each side at bottom of the
mouth. The duct opens on the tongue.
About 70% of saliva is produced by it.
Sublingual gland: they are situated
bellow the tongue. The duct opens on
both the sides of the fernulum.
SALIVA:
• It is the secretion form the salivary glands which contains water,
inorganic salts, NaCl, KCl, enzymes such as ptyalin (salivary
amylase), phosphatase, lipase ; lysozymes and mucin.
• The pH of saliva is slightly acidic (6-7).
Functions of saliva:
• Chemical Digestion: saliva contains amylase
converts compound sugars to simple sugars.
Starch
Amylase
Maltose
Maltase
Glucose
enzyme
which
• Lubrication of food: dry food is lubricated by saliva which can be
easily swallowed. Also prevent damage due to rough food.
• Cleaning: adequate flow of saliva cleans the mouth, keep it soft
and moist.
• Non- specific defense: lysosomes present in saliva may combat
with the invading microbs.
• Taste: the taste of the food can be only sensed if the food gets
mixed with the saliva.
• Protection: it dilute hot and pungent substances and prevent
injury to the mouth.
• Other functions:
 It helps in mastication and formation of bolus.
 It facilitates in speech .
 It helps in sensation of thirst thus maintain water balance.
 It acts as buffer by maintaining the level of bicarbonate and
phosphate in blood. It maintains the consistency of blood pH.
It is the tubular space between mouth and oesophagus.
Subdivided into 3 parts:
• Nasopharynx
• Oropharynx
• Laryngopharynx
The oropharynx and laryngopharynx are the passages common
between both respiratory and digestive system.
 The base of the skull forms the
roof of the pharynx.
 The adenoid or the tonsil is the
lymph node present at the back
of nasopharynx.
 When it gets inflamed, it
obstructs the breathing.
 Such a breathing through mouth
is called paranoid facies.
 Tonsils help in trapping the
bacteria and destroy them.
 It is the long hollow tube of 25 cm length and 2 cm in diameter.
 It lies in the thorax region behind the trachea and heart.
 It continues with the pharynx and just below the diaphragm it joins
the stomach.
 The upper and the lower ends of the oesophagus are closed by the
sphincters.
 The upper sphincter prevents the
entry of the air during inspiration
and aspiration of oesophageal
contents.
 The lower oesophageal sphincter
prevents the reflux of the acid and
gastric contents back into the
oesophagus.
Histologically oesophagus have 3 layers
• Muscular
• Sub mucosal
• Mucosal
The muscular layer consist of striated muscle in upper one third
region and smooth muscle in lower one third region.
The middle region consist of both muscles.
Mucosa
Sub-mucosa
Muscularis
It is the J shape organ lying in the abdomen under the diaphragm.
The major part is to the left of the midline.
It has the capacity of 1-2 liters.
It mechanically digest the food by gastric contractions and
biochemically by the gastric juice it secretes.
 The gastric glands are of 3 types:
• Peptic glands: it secretes pepsin (digestion of protein)
• Oxyntic glands: it secretes HCl.
• Mucus gland: secretes alkaline mucus
 The oxyntic glands are situated in the fundus of the stomach.
 The peptic and mucus glands are situated in pylorus of the
stomach.
 The stomach has the rich supply of blood vessels and nerves.
 It is supplied with the autonomic
parasympathetic.
nerves both sympathetic and
 Sympathetic nerve inhibits the secretory activity of stomach
whereas parasympathetic stimulates the same.
Gastric juice:
 The mucosal layer of the stomach secretes the gastric juice.
 It is clear and colorless fluid containing 0.4% HCl and enzymes such
as pepsin, gastric renin and gastric lipase.
 The pH of gastric juice is 0.9-1.5-highly acidic.
Mechanism of gastric secretion:
 The fundus part secretes the acidic juice while the pyloric part
secretes alkaline juice.
 In fasting condition the stomach secretes 10-60ml of juice per hour
whereas 500ml juice per hour during meals.
 The mechanism of juice secretion was studied using animals (dogs).
• Sham feeding experiment
• Pavlov’s pouch
Sham feeding experiment
Pavlov’s pouch experiment
Secretion of gastric juice has following phases:
Cephalic/Nervous phase:
 The flow of juice occurs before the food enters the stomach.
 It is due to the stimulation of the vagus (parasympathetic) nerves
which is initiated by sight, smell or taste of the food.
 When the vagus nerve is cut (vagotomy) these phase stops.
Sympathetic stimulation occurs during emotional stress which
inhibits gastric activity.
Gastric phase:
 When the food enters the stomach the pyloric antrum and
duodenum secretes gastrin (hormone) which passes into the blood
circulation
 This gastrin comes to the blood vessels that supplies to the
stomach.
 The gastrin will stimulate gastric glands to secrete more gastric
juice thus gastric secretion is a continuous process.
 Gastrin secretion is suppressed when the pH of the pyloric antrum
falls to 1.5.
Intestinal Phase:
 When the partially digested food (chyme) enters the intestine 2
hormones secretin and cholecystokonine and gastric inhibiting
peptide are secreted.
 They all inhibit the gastric acid secretion and reduce gastric
motility.
 As a result the chyme gets more time to mix with the bile and
pancreatic juice.
 This phase is most marked following a meal with a high fat
content.
Functions of gastric juice:
 The enzyme pepsin along with HCl digests proteins to is peptones
and proteoses.
 Renin acts on milk protein caseinogen to form casein which is then
digested by pepsin
 HCl carry out hydrolysis of food and also act as antiseptic
 Gastric juice excrete out toxins, heavy metals and certain drugs
such as opium.
 It contains blood extrinsic (Castel’s) factor responsible for
absorption of vit B12 (cynocobalamine)
Functions of stomach:
 Mechanical functions: act as reservoir of the food. Movement of the
stomach helps in mixing of the food with the digestive juices. It
propels the food further in the duodenum.
 Secretion: it secretes the digestive juice which converts the food
into the chyme which can be further digested
 Antiseptic: HCl destroys the microbs and prevents infection
 Digestion: the gastric juice helps in digestion of proteins and fats.
 Absorption: water, alcohol, glucose and certain drugs are absorbed
from the walls of the stomach. Vit B12 is also absorbed through
extrinsic factor.
 Excretion: helps in excretion of toxins and drugs.
 Reflux action:
Gastro-salivary reflux
It is the coiled up tubular structure consisting 3 parts:
• Duodenum
• Jejunum
• Ileum
It is 5-7 m long
Duodenum:
• c- shaped first part of intestine
• The descending part consist of opening for bile and pancreatic
duct.
• They open jointly as common bile duct
• Bile is secreted from liver and stored in gall bladder
• Pancreatic juice is secreted from pancreas
• The main function of duodenum is partial digestion of food
Jejunum:
It is the continuation of duodenum forms the 2/5th part of small
intestine
It is coiled structure and performs the movement of peristalsis
because of its muscular coat
It is bound behind the mesentery which carries blood vessels,
autonomic nerves.
It consist of innumerable glands for the digestion of food also
performs the function of absorption.
Ileum: it follows jejunum ,its is 3/5th fold of small intestine. It ends
at caecum.
It is coiled up portion and contains many villi
It consist of payer’s patches which are minute lymphoid structures
which serves as defense against microbial invasion
It also consist of digestive glands but less than jeunum
Histology of small intestine:
It consist of serosa layer and muscularis externa and submucosal
layer
The muscularis externa consist of smooth muscle layer arranged in
two layers:
1.Outer layer: consist of longitudinal muscles
2. Inner layer: consist of circular muscle
The submucosal layer consist of brunner gland which secrets
alkaline mucus
The muscularis interna is not well defined
The ileum consist of villi which performs the function of absorption
These are the minute finger like projections which increase the
surface area for the absorption
The villi consist of folds columnar cells containing lymphatics in the
center called lacteals surrounded by blood vessels
The blood vessels absorb carbohydrates and proteins and lymphatics
absorb fats.
In addition ileum consist of goblet cells that secret mucus
Movements of small intestine:
Peristalsis:
It the wave of contraction proceeded by relaxation. Helps in
propelling the food further in ileum and jejunum the speed is 2-25
cm/sec
Segmental: circular muscles contracts at regular intervals thus
divides the intestine into segments. Helps in mixing the food with
digestive juices and absorption of digested food
Pendular: movement in pendular fashion a rate 5cm/sec. it is like
segmental helps in mixing the food with digestive juices and also
absorption.
Functions:
Pancreatic secretions: secretion from pancreas into duodenum. The
pH is 7.1-8.2 (alkaline). Contains various digestive enzyme for
digestion of following:
• Carbohydrate digestion: amylase and maltase enzymes digest
carbohydrate.
• Fat digestion: lipase (steapsin) cause breakdown of fat. Bile helps
in emulsification of fat reducing the big fat globules into small fat
globules.
• Protein digestion: enterokinase enzyme converts trypsiongen to
tripsin, these trypsin converts chymotrypsinogen to chymotripsin.
The tripsin and chymotrypsin then act on proteins for its
breakdown to peptones and proteoses
Then carboxypeptidase enzyme will act at carbonyl end of protein to
convert it to peptides and amino acids
Succus entericus: it is the intestinal juice that contains enzymes
erepsin, lipase, amylase, sucrase and lactase
Erepsin converts dipeptides and polypeptides to amino acids.
It 1.5 cm in length and wider then small intestine. It does not contain
villi.
Functions of large intestine:
• Absorption of water and formation of solid stool
• Absorption of saline, glucose, amino acids and some drugs
• Secretion of mucus for lubrication
• Excretion: Some heavy metals gets directly excreted from blood to
colon
• Synthesis of vitamins: the microflora of large intestine helps in
synthesis of folic acid, vit B12 and vit K.
• Microbial digestion: Microbs digest other pathogenic products and
fight against infection
Microflora:
They
include
E.coli,
Eenterobacter
aerogenes,
Streptococcus faecalis and Clostridium perfringens. These microbs are
commensals. However become pathogenic if transferred to other part
of body e.g. E.coli may cause urinary bladder infection if it gains
access in urinary bladder.
Movements: Peristalsis and Mass peristalsis (pushes the stool into
rectum)
Straight tube present at center of the pelvis behind the urinary
bladder. It has mucosal coat. When intra-rectal pressure goes to 4050mmHg the feces passes out of anus (defecation).
It is the lower end of rectum dilates during defecation and the
contracts
• It is a pale grey gland situated transversely on the posterior
upper abdominal wall.
• It has a head, body and a tail. The tail touches the spleen.
• It is a mixed type of gland consisting of Exocrine and Endocrine
part.
• The exocrine part consist of lobules full of secretory glands
secreting pancreatic juice.
• The pancreatic juice is carried to the duodenum via pancreatic
duct. Just before entering to the duodenum the pancreatic duct
joins to common bile duct to form hepatopancreatic ampulla. The
opening of the ampulla at the duodenum is controlled by a
sphincter called as sphincter of oddi.
• The pancreatic juice contains various enzymes for the digestion of
carbohydrate, proteins and lipids.
• The endocrine part consist of islets of Langerhans which consist of
α and β cells. These cells secrete glucagon and insulin hormones
to maintain blood sugar levels.
• The liver is the wedge shaped organ present beneath the
diaphragm and to the side of the stomach.
• It has the superior convex and inferior concave surfaces with
anterior sharp and posterior blunt boarders.
• It has major two parts right lobe and left lobe with the apex in the
left. The right lobe is larger then the left lobe.
• The two lobe are joined by a ligamentous band called as falciform
ligament.
• On the inferior of the organ the two bands subdivides the organs
into 4 compartments
1. Right lobe 2. left lobe 3. Quadrate lobe 4. caudate lobe
Blood vessels of liver:
• The liver is made up of lobules and the lobules consist of liver
cells.
• Between the lobules there is connective tissue containing blood
vessels, nerves, bile ducts and lymphatics etc.
Circulation:
Portal vein: it enters the liver carrying blood from the stomach,
spleen, pancreas, and small & large intestine.
Hepatic artery: it is the branch of abdominal aorta which carries
arterial blood.
The hepatic artery and portal vein takes the blood to the liver and
drains into the central veins of liver lobules. These veins combine to
form hepatic veins which drains into inferior vena cava.
There are bile cannaliculi in between the hepatic cells which secretes
bile , these bile is drained to hepatic ducts that passes through the
liver and terminate into gall bladder.
Functions of Liver:
Carbohydrate metabolism:
• Imp role in maintaining the plasma glucose levels
• It is the site for glycogenesis (formation of glycogen from
glucose), glycogenolysis (destruction og glycogen to glucose),
neoglycogenesis (formation of glucose from sources other then
carbohydrates such as proteins and fats)
Protein metabolism:
 Deamination: the removal of nitrogen from amino acid not
required for new protein; urea is formed from these nitrogen
which is excreted in urine.
 Transamination: removal of nitrogen from aminoacid and
attaching it to other carbohydrate molecule forming new nonessential aminoacid.
 Synthesis of plasma proteins: albumin, globulins, clotting factors
such as plasminogen etc are also synthesized.
Fat metabolism:
The fats are synthesized and stored in the liver. The oxidation of fats
occurs through beta oxidation and the liberated energy is utilized by
the tissues.
Defense against the microbs:
Reticulo-endothelial cells (Kuffer Cells) manufacture antibodies in
form of agglutinins, precipitins and bacteriolysins against the invades
microb.
Detoxification:
Various drugs, ethanol and heavy metals are detoxified and are
finally excreted through bile via gall bladder.
Production of heat: due to its high metabolic rate it produces a great
deal of heat
Secretion of bile: the hepatocytes synthesize the bile which include
bile salts ( sodium taurocolate & glycolate and bile pigments such as
bilirubin & biliverdin)
Storage:
The substance include:
• Glycogen
• Fat soluble vitamins-A,D,E,K
• Iron, copper
• Some water soluble vitamins e.g. Vit B12
It is the sac like structure which is serves as the reservoir of the
bile. It is anteriorly under the liver and on the right to the abdominal
surface.
It opens through the cystic duct which joins the common hepatic
duct to form the common bile duct. The common bile duct carries
the bile juice and opens jointly into the pancreatic duct in the
duodenum.
It contacts under the influence of cholecystokinin and autonomic
nerves. The bile and pancreatic juices are poured simultaneously in
to duodenum.
Functions:
• It acts as a reservoir of bile
• It concentrates bile and helps in absorption of water and inorganic
salts
• It secretes mucus and excretes cholesterol
• It maintains pressure in the billiary tract
Bile juice:
• Bile is the secretory and excretory product of the liver.
• The common bile duct takes the bile juice to the duodenum.
• The bile juice is continuously synthesized in liver but the entry in
the duodenum starts only after the ingestion of the food.
Composition of bile juice:
It is a yellowish fluid containing many substances but no enzyme.
The substances include:
• Water
• Mineral salts such as chloride, carbonates, phosphates of sodium,
potassium and calcium
• Bile salts such as sod. Taurocolate and sod. Glycolate derieved from
bile acids such as colic acid and chenodeoxycholic acid
• Bile pigments such as bilirubin, biliverdin
• cholesterol
Functions:
 Fat digestion: It reduces surface tension an helps in fat digestion.
It activates the enzyme lipase which helps in breakdown of the fat.
Helps in digestion of fat, protein and carbohydrates.
 Absorption: helps in digestion of various substance such as iron,
calcium and fat soluble vitamins-A,D,E & K.
 Laxative action: it stimulates peristalsis and produce laxative
action (rapid defecation)
 Buffer action: contains mucin which act as buffer to maintain the
pH
 Excretion: heavy metals, bacteria, cholesterol and lecithin are
excreted in bile
 Optimum pH: it maintains the pH which helps in action of the
digestive enzymes.
 Cholagogue: bile itself stimulates the biliary secretion. This is
known as cholagogue action
 Secretogogue: it stimulates secretin, a local hormone which
stimulates the pancreatic, biliary and intestinal secretion
Constipation:
Delay in defecation and formation of hard stool. It might be due to:
• Continuously ignoring/ preventing
• Decreased colonic motility
• Ageing
• Emotions
• Low bulk diet
• Atonic or spastic colon
• Chronic amoebiasis
Diarrhea:
Frequent defecation, usually with high fluid fecal matter (watery stool)
It may be due to:
• Increase intestinal motility
• Fluid overload in colon
• Salt overload in colon
• Infection
• Allergy
• toxemia
Nausea: felling of vomiting prior to vomit
Vomiting: sudden spasmodic expulsion of the contents of stomach.
It may be due to central effect, reflex, toxic , obstruction
Anorexia: loss of appetite might be due to anxiety or dipression
Gastritis: acute or chronic inflammation of gastric mucosa arising
due to irritant substance, infection, emotions or obstruction
Heart Burn: sour burning sensation in upper oesophagus due to
evacuation of acidic contents in mouth leading to burning sensation
behind the sternum
Cholecystitis: inflammation of gall bladder
Gastroenteritis: inflammation in upper GIT manifested with the
symptoms such as nausea, anorexia, vomiting abdominal discomfort,
diarrhea. It may be due to bacterial and fungal infection or
poisoning.
Dysphagia: difficulty in swallowing
Aerophagy: swallowing of air in the stomach unknowingly
Peptic ulcer disease: it is ulceration of mucus membrane , these
ulcers may penetrate in muscularis mucosa. It occurs in the areas
that are bath by the acid and pepsin in stomach and/or duodenum
(duodenal ulcers). May occur due to excessive vagal nerve
stimulation resulting in excessive acid secretion, disturbed mind or
consumption of irritating food.
Appendicitis: inflammation in appendix.
Peritonitis: Inflammation of peritoneum of the abdomen
Flatulence: accumulation of gas in the stomach or intestine due to
aerophagy, intestinal fermentation, deficient absorption or
constipation
Hemorrhoids (piles): swelling or dilation or varicose veins present
in the mucus membrane of the rectum or skin of the annus
Fatty liver: accumulation of fats, triglycerides or cholesterol in the
liver
Hepatitis: inflammation of liver. Histologically there is necrosis of
hepatic cells. Occurs due to vital or amoebic infection
Cirrhosis of liver: hardening of the liver. Liver functions are
adversely affected. Often produce ascities (free fluid accumulation in
abdomen)
Endoscopy: it is the diagnostic technique to view the hollow organs
from inside using light and magnification.