Digestive syestum

11/8/2014 2
AUTHOR:-
M HUMAYYUN JAMIL
REFERENCE:-
ESSENTIALS OF MEDICAL
PHYSIOLOGY

 Introduction to digestive system
Mouth and salivary glands
Stomach
Pancreas
Liver
Large intestine
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Process by which food is broken down into
simple chemical subctances that can be
absorbrd and used by the body
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Digestive Syestum is accomplished by
mechanical and enzymatic breakdown of
food particles into smaller food particles
A normal young healthy consumes about
1kg of solid diet and 1-2 L of liquid daily
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 Intake of food
Breaking them into smaller particles
Transport of smaller particles to all parts of
body
Secretion of necessary enzymes
Digestion of food particles
Absorption of digestive products
Removal of unwanted substances from
body
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GIT consist of 4 major layers
1.mucus or mucosa layer
2.submucus layer
GIT consist of 4 major layers
3.muslar layer
1.mucus or mucosa layer
4.serous layer
2.submucus layer
3.muslar layer
4.serous layer
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Tubular structure extending from
oral cavity to anus is called GIT
It is about 30 feet
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 It is innermost layer of GIT
It consist of further 3 layers
 EPITHELIAL LAYER
 It is made up of connective tissues
Epithilial layer of lips,oral cavity,pharyunx
and esophagus has squamous epithelial
cells
Epithelial layer of remaining part of GIT
has collomunar epithelial cells
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 It is also made up of connective tisssues
 It consist of
lymphocytes,macrophages,fibroblasts,esino
phills
MUSCULAR MUCOSA
• IT CONSIST OF SMOOTH MUSCLES
• IT IS ABSENT IN MOUTH AND PHARYNX
• IT IS PRESENT FROM ESOPHAGUS TO ONWARD
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IT IS ALSO ABSENT IN MOUTH AND PHYRYNX
IT IS PRESENT FROM ESOPHAGUS TO
ONWARD
IT CONSIST OF CONNECTIVE TISSUES
IT HAS SMOOTH MUSCLE FIBERS AND OTHER
LOOSE COLLEGEN FIBERS
IT HAS BLOOD VESSELS,L YMPHATIC VESSEL
AND NERVE PLEXUS
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Muscular layer of lips,tounge,mouth and
pharynx has skeltal muscle fibers
Muscular layer of esophagus has both
skeltal and smooth muscle fiers
Muscular layer of small intestine and
stomach has smoth muscle fibers
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Serous layer is outermost layer
Serous layer also consist of connective
tissues
 It is found in small intestine and stomach
While fibrous layer is found in esophagus
and pharynx
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PRIMARY ORGANS SECONDARY ORGANS
Esophagus
Pharynx
Small intestine
Large intestine
stomach
Oral cavity
Tounge
Teeth
Glands
Liver
Gall bladder
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Oral cavity is starting point of GIT
Oral cavity consist of;
Mouth
Toung
Lips
Teeth
Palate
Oral cavity opens both anteriorly and
posteriorly
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Taking in food
Griding of food
Lubrication of food
Mixing of food with saliva to form bolus
Transport of food particles to all parts of
body
Role in speech
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SALIVA IS SECRETED MAINLY
BY FOLLOWING MAJOR
GLANDS
SALIVA IS SECRETED
MINORLY BY
 PAROTID GLANDS
 SUBMANDIBULAR
GLANDS
 SUBLINGUAL GLANDS
 LABIAL GLAND
 LINGUAL SEROUS GLAND
 Lingual mucous gland
 Palatal gland
 Buccal gland
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 It is larges gland
 Its wight is 20-30 gm
 It is located on side of face below and
infront of ear
 Its secretion is poured into mouth against
the upper second molar teeth through
STENSON DUCT which is 35-40 mm long
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 Its wight is 8-10 gm
 It is located in submaxillary triangle medial
to mandible
 Saliva from these glands is emptied into
the oral cavity by Wharton duct, which is
about 40 mm long. The duct opens at the
side of frenulum of tongue, by means of a
small opening on the summit of papilla
called caruncula sublingualis.
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 It is smallest gland
 Its weight is 2-8 gm
 It is located in mucosa on the flour of mouth
 It pours its saliva into mouth through 5-15
smaller ducts called duct of ravinus which open
on small papilla beneath tounge
 One of the larger duct is BARTHOLIN duct
 It drains the anterior part of the gland and
opens on caruncula sublingualis near the
opening of submaxillary duct.
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Volume of saliva; 1000-1500mL/Day
PH of saliva; 6.35-6.85
Gravity of PH; 1.002-1.012
Tonicity; hypotonic to plasma
Reaction; acidic
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Parotid glands; 25%
Submandibular gland; 70%
Sublingual gland; 5%
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Prepration of food for swallowing
Appreciation of taste
Digestive function
Cleaning and protective function
Excretory function
Water ragulation
Maintinance of temperature
Social functions
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STOMACH AND GASTRIC GLANDS
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Stomach is a muscular, hollow organ
 located in the upper left abdominal quadrant,
immediately below the diaphragm.
located between the esophagus and small
intestine
Volume of empty; 5o ml but capable of
extending upto 4 L
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Outer serous layer; Formed by peritoniun
Muscular layer; divided into
oblique,circular and longitudinal layer
Submuscus layer; formed by blood
vessels, lymphatic vessels and messiener
nerve plexus
Inner muscular layer; it has small gastric
pits where gastric glands open. Lined by
mucussecreting columnar epithelial cells.
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 Cardiac; upper part where esophagus ends
and has a sphincter called cardiac sphincter
 Fundic region; a small domeshaped structure.
It is elevated above the level of esophageal
opening.
 Body; Centeral region which encloses 80%
volume
 Pyloric region; lower ending region that opens
to duedenum.It is further divided to
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Antrum; where body ends
Pyloric canal; lower tube like portion
Point where fusion of antrum and pyloric
canal takes place is called incisura
angularis
Pyloric region also has a sphincter called
pyloric sphincter
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Fundic glands; glands found in fundic
region
Cardiac glands; found in cardiac region
Pyloric glands; found in pyloric region
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 It is long tubular gland
 It has following cells
chief cells
parietal cells
mucus cells
EC cells
ECL cells
 It is diff. from other glands due to parietel
cells because they pour their secretion into
lumen through their canaliculus
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 It is short and tortous
mucus cells
goblet cells
EC cells
ECL cells
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 It is also short and tortous
chief cells
mucus cells
EC cells
ECL cells
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99.5 % WATER .5 % SOLID
 Organic substances
 Inorganic subctances;
mucus
intrinsic factor
 Enzymes;
pepsin
renin
urase
gelatinin
gastric lipase
 Inorganic substances
sodium
calcium
potasium
bicorbonates
phosphate
sulphur
HCL
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.5
further
consist
of

Ph; 0.9-1.2
Volume; 1200-1500 ml/day
Specific gravity; 1.002-1.004
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Mechanical function
Digestive function
Hemopoitic function
Protective function
Excretory function
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 i.Storage Function; Food is stored in the
stomach for a long period, i.e. for 3 to 4 hours
and emptied into the intestine slowly. The
maximum capacity of stomach is up to 1.5 L.
Slow emptying of stomach provides enough
time for proper digestion and absorption of
food substances in the small intestine.
 ii.Formation of Chyme; Peristaltic movements
of stomach mix the bolus with gastric juice
and convert it into the semisolid material
known as chyme.
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 EXCRETORY FUNCTION:
Many substances like toxins, alkaloids and
metals are excreted through gastric juice.
 HEMOPOIETIC FUNCTION:
Intrinsic factor of Castle, secreted by parietal
cells of gastric glands plays an important
role in erythropoiesis. It is necessary for the
absorption of vitamin B12 (which is called
extrinsic factor) from GI tract into the blood.
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 Gastric juice acts mainly on proteins. Proteolytic enzymes of
the gastric juice are pepsin and rennin Gastric juice also
contains some other enzymes like gastric lipase, gelatinase,
urase and gastric amylase.
 Pepsin ;Pepsin is secreted as inactive pepsinogen.
Pepsinogen is converted into pepsin by hydrochloric acid.
Optimum pH for activation of pepsinogen is below 6. Pepsin
converts proteins into proteoses, peptones and polypeptides.
Pepsin also causes curdling and digestion of milk (casein).
 Gastric Lipase ;Gastric lipase is a weak lipolytic enzyme It is
active only when the pH is between 4 and 5 and becomes
inactive at a pH below 2.5 and hydrolyses tributyrin into faaaty
acids and glycerol
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 i.Gelatinase: Degrades type I and type V gelat in and
type IV and V collagen (which are proteo glycans in
meat) into peptides
 ii.Urase: Acts on urea and produces ammonia
 iii.Gastric amylase: Degrades starch (but its action is
insignificant)
 iv. Rennin: Curdles milk (present in animals only)
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 FUNCTION OF MUCUS
 Mucus is a mucoprotein, secreted by mucus neck
cells of the gastric glands and surface mucus cells
in fundus, body and other parts of stomach. It
protects the gastric wall by the following ways:
 Mucus:
 i. Protects the stomach wall from irritation or
mechanical injury, by virtue of its high viscosity.
 ii.Prevents the digestive action of pepsin on the
wall of the stomach, particularly gastric mucosa.
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 According to Davenport theory, hydrochloric acid secretion is an
active process that takes place in the canaliculi of parietal cells in
gastric glands. The energy for this process is derived from oxidation
of glucose. Carbon dioxide is derived from metabolic activities of
parietal cell. Some amount of carbon dioxide is obtained from blood
also. It combines with water to form carbonic acid in the presence of
carbonic anhydrase. This enzyme is present in high concentration in
parietal cells. Carbonic acid is the most unstable compound and
immediately splits into hydrogen ion and bicarbonate ion. The
hydrogen ion is actively pumped into the canaliculus of parietal cell.
Simultaneously, the chloride ion is also pumped into canaliculus
actively. The chloride is derived from sodium chloride in the blood.
Now, the hydrogen ion combines with chloride ion to form
hydrochloric acid. To compensate the loss of chloride ion, the
bicarbonate ion from parietal cell enters the blood and combines with
sodium to form sodium bicarbonate. Thus, the entire process is
summarized as (Fig. 38.4): CO2 + H2O + NaCl → HCl + NaHCO3
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 Pepsinogen is synthesized from amino acids in the
ribosomes attached to endoplasmic reticulum in chief
cells. Pepsinogen molecules are packed into zymogen
granules by Golgi apparatus. When zymogen granule is
secreted into stomach from chief cells, the granule is
dissolved and pepsinogen is released into gastric juice.
Pepsinogen is activated into pepsin by hydrochloric acid.
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 It is a dual organ
 It has both endocrine and exocrine
function
Endocrine is to produce harmones
Exocrine is to secrete pancreatic juice
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 Volume; 500-800 ml/day
 Ph; 8-8.3
 Specific gravity; 1.010-1.018
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WATER 99.9% SOLID .5%
 Organic subctances
 Sodium
 Calcium
 Potassium
 Magnisium
 Phosphate
 Bicarbonate
OTHER
INORGANIC
SUBSTANCE
S;
Albumin
Glubulin
ENZYMES;
trypsin
Chympotry
psin
Carboxype
ptidase
Elastases
Nucleases
Collagenas
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Digestion of protein
Digestion of lipids
Digestion of carbohydrates
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Lipid is a dual organ having both secretory
and excretory function
Largest gland
Weighs about 1.5 kg
Located in upper right side of abdominal
cavity beneath diaphgram
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Hepatic lobes
Hepatic lobules
Hepatocytes
Hepatic plates
Portal triads
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Biliary syestum is made of;
Gallblader
Extrahepatic bile
duct
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Right +left hepatic duct=common
hepatic duct
Common hepatic duct+cystic duct
=common bile duct
Common bile duct+pancreatic
duct=ampula of vater

Liver recives blood supply of about
1500ml/min. through 2 sources
HEPATIC ARTERY:
It arises fromm aorta
Supplies oxygenated blood
PORTAL VEIN;
Formed by superior mesenteric vein and
sphlencic vein
Oxygen content is less in portal blood
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WATER---97.6% SOLID---2.4%
 Organic subctances;
Bile salts
fatty acids
Bile pigments
Lecithin
Mucin
cholesterol
 Inorganic subtances
Sodium
Calcium
Potassium
Chloride
Bicarbonte
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VOLUME; 800-1200ml/day
REACTION; alkaline
PH; 8-8.6
SPECIFIC GRAVITY; 1.010-1.011
CLOUR; golden yellow or green
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Starts from pyloric sphincter upto ileoceacl
valve
About 6 m long
Less in diameter
Small intestine consists of three portions:
1. Proximal part known as duodenum
2. Middle part known as jejunum
3. Distal part known as ileum.
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Intestinal valve has small projections
called villi with height 1mm and diameter
less than 1mm covered by cells called
enterocytes
Each enterocyte has further minute hair
like projections called microvilli
Within each villus, there is a central
channel called lacteal, which opens into
lymphatic vessels. It contains blood
vessels also
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 simple tubular glands of intestine
 do not penetrate the muscularis mucosa
 open into the lumen of intestine between the
villi
 lined by columnar cells.
Types of cells interposed between columnar
cells of intestinal glands:
1. Argentaffin cells or enterochromaffin cells,
which secrete intrinsic factor of Castle
2. Goblet cells, which secrete mucus
3. Paneth cells, which secrete the cytokines
called defensins.
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Volume : 1800 mL/day
 Reaction : Alkaline
 pH : 8.3
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 „1. DIGESTIVE FUNCTION
2. PROTECTIVE FUNCTION
3. ACTIVATOR FUNCTION
4. HEMOPOIETIC FUNCTION
5. HYDROLYTIC PROCESS
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1. DIGESTIVE FUNCTION
2. ABSORPTIVE FUNCTION
3. ACTIVATOR FUNCTION
4. HEMOPOIETIC FUNCTION
5. HYDROLYTIC PROCESS
6. HORMONAL FUNCTION
7. SECRETORY FUNCTION
8. MECHANICAL FUNCTION
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It extends from ileocecal valve up to intestine
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Cecum with appendix
Ascending colon
Transverse colon
Descending colon
Sigmoid colod
Rectum
Anal colon
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Serous layer; formed by peritonium
Muscular layer; further devided to outer
longitudinal and inner circular layer
Submucus layer: not well defined
Mucus layer; it has crypts of liberkuhn and
mucussecreating glands
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Solid .5%
Inorganic subctances
Albumin
Mucin
Globulin
urea
Organic subctances
Sodium
Calcium
Potassium
Phosphate
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Water - 95.5%
Digestive enzymes
are absent

 Neutralization of Acids
Strong acids formed by bacterial action in large intestine
are neutralized by the alkaline nature of large intestinal
juice. The alkalinity of this juice is mainly due to the
presence of large quantity of bicarbonate.
 Lubrication
Activity Mucin present in the secretion of large intestine
lub- ricates the mucosa of large intestine and the bowel
contents, so that, the movement of bowel is facilitated.
Mucin also protects the mucus membrane of large
intestine by preventing the damage caused by
mechanical injury or chemical substances.
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 „1. ABSORPTIVE FUNCTION
Large intestine plays an important role in the
absorption of various substances such as: i. Water ii.
Electrolytes iii. Organic substances like glucose iv.
Alcohol v. Drugs like anesthetic agents, sedatives
and steroids.
 „2. FORMATION OF FECES
After the absorption of nutrients, water and other
substances, the unwanted substances in the large
intestine form feces. This is excreted out.
 „3. EXCRETORY FUNCTION
Large intestine excretes heavy metals like mercury,
lead, bismuth and arsenic through feces.
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4. SECRETORY FUNCTION
Large intestine secretes mucin and
inorganic substances like chlorides and
bicarbonates.
5. SYNTHETIC FUNCTION
Bacterial flora of large intestine synthesizes
folic acid, vitamin B12 and vitamin K. By this
function, large intestine contributes in
erythropoietic activity and blood clotting
mechanism.
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Diarrhea
Constipation
Appendicitis
Ulcerative cilitis
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