Digestive System

1. Digestive SystemDigestive System
Dr. Mrs. Deepa K. Ingawale
(Mandlik)
Dept. of Pharmacology
Poona College of Pharmacy, Pune
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2. SyllabusSyllabus
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3. Digestive SystemDigestive System
 Digestion:
 The breaking down of complex food material into simple food
material with the help of chemicals.
 Gastroenterology:
 The branch of science that deals with structure, function,
diagnosis & treatment of diseases of stomach & intestine.
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4. Digestive systemDigestive system
 Two groups of organs:
 Gastrointestinal (GI) tract
 Accessory digestive organs
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5. Organs of digestive systemOrgans of digestive system
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6. Digestive systemDigestive system
 GI tract includes;
 Mouth
 Pharynx
 Esophagus
 Stomach
 Small intestine
 Large intestine
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7. Digestive systemDigestive system
 Accessory digestive organs includes:
 Teeth
 Tongue
 Salivary glands
 Liver
 Gallbladder
 Pancreas
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8.  Ingestion
• Taking food through the mouth
 Movement
• Movement of food along the GIT
 Digestion (Mechanical & Chemical)
• Breakdown of food by chemical &
mechanical processes
 Absorption
• Transport of digested material into
cardiovascular and lymphatic system for
distribution to cells
 Defecation
• Elimination of indigestible substances
from body in the form of feces 8
The Digestive ProcessThe Digestive Process

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Histology of alimentary tractHistology of alimentary tract
Four layers from esophagus to anus
1. Mucosa
2. Submucosa
3. Muscularis
4. Serosa

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Histology of alimentary tractHistology of alimentary tract
 Inner layer (Mucosa):
 It is inner lining of GI tract.
 Three sub-layers
1. Epithelium
2. Lamina propria
3. Muscularis mucosae

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Histology of alimentary tractHistology of alimentary tract
 Sub-mucosa:
 Present above the mucosa
 Consist of areolar connective tissue.
 Muscularis:
 It is present above the sub-mucosa layer.
 Serosa:
 Outer layer of GI tract.
 Made up of Simple squamous epithelium

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 Oral cavity or buccal
cavity
• Lining: thick stratified
squamous epithelium
 It is formed by the
 Cheeks
 Hard palate
 Soft palates
 Tongue
Mouth

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 Cheeks: Forms the lateral walls of oral cavity.
 The anterior portions of cheeks end at the lips.
 Lips or labia: Fleshy folds surrounding the opening of mouth.
 Palate: It is a septum that separates the oral cavity from the
nasal cavity, forming the roof of mouth.
 Hard palate: The anterior portion of roof of mouth
 Soft palate: The posterior portion of roof of mouth

14. TongueTongue
 Tongue together with other
muscles forms the floor of oral
cavity.
 It is made up of skeletal muscles
covered with mucous
membrane.
 The upper surface and sides of
tongue are covered with
papillae, contains taste buds.
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15. TongueTongue
 There are 3 varieties of papillae;
 Circumvallate papillae:
 These 8 to 12 papillae are arranged in inverted V shape towards the base
of tongue.
 All of them contains taste buds.
 Largest papillae
 Filiform papillae:
 Whitish in color & do not contain taste buds.
 Fungiform papillae:
 Smallest of the three types.
 Present near the tip of tongue.
 Reddish dot & contains taste buds.
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TeethTeeth
 Called as dentes
 Present in sockets of
mandible (lower jaw bone) &
maxilla (upper jaw bone)
 Parts of teeth:
 The crown
 The neck
 The root

17. TeethTeeth
 Crown: Visible portion of tooth above the gums
 Root: Embedded in the gums
 Dentin: Calcified connective tissue covered by enamel
 Enamel is very hard made up of calcium phosphate &
carbonate.
 At the center of tooth is the pulp cavity containing blood
vessels, lymph vessels & nerves
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TeethTeeth
 Two sets of teeth
• Falling out:
 “Baby” teeth
 Start at 6 months
 Fall out between 2-6 years
• Permanent:
• It consist of 32 teeth

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Classification of teeth according toClassification of teeth according to
shape & functionshape & function
 Incisors: Cutting teeth used for
cutting off food
 Canines: Cone shaped used for
cutting off food
 Premolars & molar: Broad, flat
surface used for grinding or
chewing of food
Incisor
Canine
Premolar
Molar

20. Salivary glandsSalivary glands
 It releases saliva into oral cavity.
 3 pairs of salivary glands,
 Parotid gland
 Submandibular gland
 Sublingual gland
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21. Salivary glandsSalivary glands
 Parotid gland:
 Present near to the ears.
 They secrete their secretions into oral cavity by parotid duct.
 Largest salivary gland
 Submandibular gland:
 It is present in the floor of mouth & beneath the tongue.
 Sublingual gland:
 Smallest salivary gland
 Present beneath the tongue
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22. SalivaSaliva
 It is a mixture of water, ions, mucus & enzymes
 About 1 to 1.5 L is secreted every day
 Acidic in nature (6.35 to 6.85)
 Viscous & colorless in nature
 Functions:
 Keep mouth moist
 Dissolves food
 Moistens food
 Starts enzymatic digestion (Amylase=sugars to starch)
 Excretion (Urea, mercury, lead, many drugs)
 Antibacterial & antiviral
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23. PharynxPharynx
 It is a funnel-shaped tube, 13 cm long
 Extends from nose to esophagus
 Composed of skeletal muscle & lined by mucous
membrane
 It is divided into 3 parts:
 Nasopharynx
 Oropharynx
 Laryngopharynx
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24. PharynxPharynx
 Nasopharynx: Superior portion of pharynx.
 Important for respiration.
 Oropharynx: Intermediate portion of pharynx.
 Laryngopharynx: Inferior portion of pharynx
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25. EsophagusEsophagus
 Muscular collapsible tube
 25 cm long
 2 cm in diameter
 lies posterior to trachea
 It continuous with pharynx &
connected to stomach.
 Upper & lower ends are closed
by sphincter.
 Upper esophageal sphincter (UES)
 Lower esophageal sphincter (LES)
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Esophagus

26. EsophagusEsophagus
 Upper esophageal sphincter (UES):
 Regulates the movement of food from pharynx to
esophagus.
 Lower esophageal sphincter (LES):
 Regulates the movement of food from esophagus to
stomach.
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27. DeglutitionDeglutition
 Swallowing (deglutition):
 Movement of food from mouth into stomach is called as
swallowing
 Facilitated by the secretion of saliva & mucus
 It occurs in the mouth, pharynx, & esophagus
 Complex but fast process completed within seconds
 3 phases,
 Buccal swallowing
 Pharyngeal swallowing
 Esophageal swallowing
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28. DeglutitionDeglutition
 Buccal stage: The bolus is passed from oral cavity into
the oropharynx
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29. DeglutitionDeglutition
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 Pharyngeal stage: The bolus passes from pharynx into
the esophagus

30. DeglutitionDeglutition
 Esophageal stage: The bolus passes from the esophagus
into the stomach
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31. StomachStomach
 Enlargement of GI tract
 J shaped organ
 Connecting organ between
esophagus & duodenum
 Divided into 4 parts
 Cardia
 Fundus
 Body
 Pylorus
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Stomach PartsStomach Parts
 Cardia: Located near the opening
 Fundus: Rounded portion
 Body: Large central portion
 Present below the fundus
 Greater curvature: Concave border
 Lesser curvature: Convex border
 Pylorus: Present below the body
 Pyloric antrum: Connects to the body of
stomach
 Pyloric canal: Connects to the
duodenum

33. FunctionsFunctions
 Act as a reservoir of food
 With the peristaltic movement it causes mixing of food with
gastric juice
 Mucosal lining is responsible for absorption of water, alcohol
& glucose to the blood stream
 Causes secretion of 1-2 liter of gastric juice every day
 Gastric lipase: Lipolytic activity
 Pepsin: Breakdown of proteins to peptones
 Mucus from mucus cell prevents mechanical injury to
stomach
 HCl: Kills bacteria in food & gives protection
 It forms intrinsic factor requires for absorption of vitamin B12.
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34. Gastric JuiceGastric Juice
 Clear colorless juice
 Acidic in nature
 2 liters of gastric juice secreted daily by gastric glands in the mucosa
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35. Composition of Gastric JuiceComposition of Gastric Juice
 It consists of,
 Water: Liquefies the swallowed food
 Mineral salts:
 Mucus secreted by goblet cells: Prevents mechanical injury
to stomach
 Hcl secreted by parietal cells: Kills the ingested M.O.
 Intrinsic factor in gastric glands: Absorption of vitamin B12
 Pepsinogen enzyme secreted by chief cells
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Small intestineSmall intestine
 It continues from stomach to large
intestine
 Thin & long (4 m in length)
 It lies in the abdominal cavity
surrounded by large intestine
 Most enzymatic digestion occurs
 Most enzymes secreted by
pancreas
 Almost all absorption of nutrients
 3-6 hour process

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 Small intestine has 3 subdivisions
• Duodenum – Superior portion (25 cm long)
• Jejunum – Middle portion (1.5 m long)
• Ileum – Terminal portion (2 m long)
Small intestineSmall intestine

38. Histology of Small IntestineHistology of Small Intestine
 Wall of SI is made up of four layers
 Mucosa
 Sub-mucosa
 Muscularis
 Serosa
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39. HistologyHistology
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40. MucosaMucosa
 Innermost mucosa forms fingerlike projections & they
increase surface area for absorption.
 Simple columnar cells
 Four types of cells present
 Absorptive cells with brush border of microvilli: increases SA for
absorption and secrets enzymes
 Goblet cells: Secrets mucus
 Enteroendocrine cells: S cells, K cells and CCK cells, secrets
secretin
 Paneth cells: Phagocytic in nature & contains lysozyme enzyme
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41. Intestinal JuiceIntestinal Juice
 About 1-2 liters of juice secreted every day
 Clear yellow fluid, alkaline in nature (pH 7.6 to 8.0)
 It consists of
 Water
 Mucus
 Mineral salts
 Consist of several digestive enzymes:
 Peptidases: breaks proteins to amino acids
 Amylase: breaks starch to maltose
 Lactase : breaks maltose to glucose
 Lipase: Breaks glycerides, fatty acids and glycerol
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42. Mechanical Digestion in SIMechanical Digestion in SI
 Two types of movements of small intestine
 Segmentation
 Peristalsis
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43. Mechanical DigestionMechanical Digestion
 Segmentation:
 These are rhythmical altering contraction and relaxation of SI.
 These movements mixes the chyme with the food & bring
food particles into contact with mucosa for absorption
 Digestion & absorption are promoted
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44. Mechanical DigestionMechanical Digestion
 Peristalsis:
 Entry of food into SI stimulates stretch receptors .
 Stretch receptors covey message to CNS,
 PNS stimulates contraction of intestine
 SNS stimulate relaxation of intestine, decrease the motility of
SI.
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45. Chemical Digestion in SIChemical Digestion in SI
 Digestion of carbohydrates:
 Pancreatic amylase converts all polysaccharides to
Monosaccharides
 Digestion of proteins:
 Enzymes like trypsin, chymotrypsin, carboxypeptidase
converts all proteins to amino acids
 Digestion of fats:
 The enzyme lipase converts fats to fatty acid and glycerol
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46. Large IntestineLarge Intestine
 Terminal portion of the GI tract
 Functions:
 Completion of absorption
 Production of certain vitamins
 Formation of feces
 Expulsion of feces from the body
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47. Large IntestineLarge Intestine
 1.5 m long and 2.5 cm in diameter
 Extends from ileum to anus
 It forms arch around the coiled small intestine
 It is divided into,
 Caecum
 Ascending colon
 Transverse colon
 Descending colon
 Sigmoid colon
 Rectum
 Anus
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48. Large IntestineLarge Intestine
 Caecum:
 First part of colon
 Elevated portion of LI below the ileocaecal sphincter is
Caecum
 Twisted coiled tube is attached called as appendix or
vermiform appendix.
 Colon:
 The remaining part of LI is called as colon
 Divided into four parts
• Ascending colon
• Transverse colon
• Descending colon
• Sigmoid colon
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49. Large IntestineLarge Intestine
 Rectum:
 Dilated portion of LI
 13 cm long
 Starts from sigmoid colon and ends in the anus
 Stores feces which consists of undigested part of food, water,
inorganic salts and bacteria, etc.
 Anus:
 Short passage
 3.8 cm long
 Starts from rectum to the exterior
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50. Function of LIFunction of LI
 Absorption:
 Absorption of water by osmosis, continues until the semisolid consistency
of faeces is achieved.
 Mineral salts, vitamins and some drugs are also absorbed into the blood
capillaries
 Microbial activity:
 The large intestine is heavily colonised by bacteria which synthesize
vitamin K & folic acid i.e. E. coli, S. faecalis.
 Harmless in human
 Defecation Reflex:
 Mass peristalsis movements push faecal material from sigmoid colon into
the rectum.
 Distension of rectal wall stimulates stretch receptors which initiates
defecation reflex that empties the rectum.
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Histology – large intestineHistology – large intestine
 No villi
• Fewer nutrients absorbed
 “Columnar cells” =
absorptive cells
• Take in water and
electrolytes
 Goblet cells for mucus
• Lubricates stool

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LiverLiver
 Largest gland in the body
 1.4 kg average weight
 Over 500 functions
 Upper part of abdominal cavity
 Right and Left lobes
 Right lobe is again divided into;
 Caudate lobe
 Quadrate lobe
 Covered by peritoneum
 Falciform ligament
• A fold of peritoneum

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Liver histologyLiver histology
 Made up of many functional units called as liver lobules
(about one million)
• Hexagonal structure consists of special cells called as
hepatocytes (liver cells) around a central vein
• Corners of lobules have “portal triads”
(see next pic)

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 Portal triad
• Portal arteriole
• Portal venule
• Bile duct
 Carries bile away
 Liver sinusoids
• Large capillaries
between plates of
hepatocytes
 Kupffer cells
• Liver macrophages
• Phagocytic in nature,
removes dead cells,
bacteria & foreign
matter in the blood
Liver histologyLiver histology

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Functions of liverFunctions of liver
 Carbohydrate metabolism
 Fat metabolism
 Protein metabolism
 Activation of vitamin-D
 Excretion of bilirubin: Excreted in bile
 Stores some vitamins (A, B12, D, E & K)
 Breakdown of RBCs & phagocytosis
 Detoxification of poisons & drugs
 Production of heat

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GallbladderGallbladder
 Small pear shaped organ
 Attaches to the liver at
back side
 7-10 cm long
 It has 3 parts
 Fundus: Expanded portion
 Body: Main part
 Neck: connects to cystic
duct
 Functions:
 Reservoir for bile
 Released stored bile

57. BileBile
 Secreted by liver
 Stored in gall bladder
 500-1000 ml of bile are secreted
 Bile has pH= 8 (Alkaline)
 Composition:
 Water, Mineral salts, Mucus, Bile salts, Bile pigments &
cholesterol
 Functions:
 Bile salts emulsify fats in small intestine
 Bile salts make cholesterol & fatty acid soluble.
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PancreasPancreas
 Yellowish in color
 Elongated leaf shaped gland lying
below the stomach
 12-15 cm long & 2.5 cm thick
 Three parts
 Head: Expanded portion lies near the
curve of duodenum
 Body: Central portion
 Tail: Tapering portion
 Pancrea divided into 2 parts;
 Exocrine pancrea
 Endocrine pancrea

59. Histology of pancreaHistology of pancrea
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Exocrine PancreaExocrine Pancrea
 Small clusters of glandular
epithelium
 99% are arranged in clusters
called as acini
 Sac-like structure
 Acinar cells make 22 kinds of
enzymes
• Stored in zymogen granules
• Grape-like arrangement

61. Endocrine pancreaEndocrine pancrea
 Remaining 1% cells are arranged in clusters called as
pancreatic islets (Islets of Langerhans).
 They secrete hormone insulin, glucagon are responsible for
maintaining blood sugar level.
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Endocrine pancreaEndocrine pancrea
 Islets of Langerhans are the hormone secreting cells
 Insulin (from beta cells)
• Lowers blood glucose (sugar)
 Glucagon (from alpha cells)
• Raises blood glucose (sugar)

63. Pancreatic JuicePancreatic Juice
 1.2 to 1.5 L of pancreatic juice
 Clear, colorless liquid
 Composition:
 Water, Salts, Sodium bicarbonate, Several enzymes
 Amylase: Carbohydrate digesting enzymes
 Trypsin, Chymotrypsin, Elastage: Protein digesting enzymes
 Lipase: Triglyceride digesting enzymes
 Ribonuclease & deoxyribonuclease: Nucleic acid digesting
enzymes
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64. Function of pancreatic juiceFunction of pancreatic juice
 Neutralizes acidic contents of chyme in duodenum due to
presence of sodium bicarbonate.
 Pancreatic juice provides alkaline pH for enzyme action.
 Pancreatic α-amylase digests Glycogen, starch & other
complex carbohydrate to disaccharides.
 Enzyme nucleotides digest nucleoproteins.
 Proteins are converted to amino acid by enzyme pancreatic
trypsin & elastase.
 Pancreatic lipase converts fats to fatty acid & glycerol.
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65. Disorders of digestive tractDisorders of digestive tract
 Dental caries/Tooth decay:
 It involves a gradual demineralization (softening) of the enamel and
dentin.
 If untreated micro-organism may invade the pulp causing inflammation
and infection with subsequent death of the pulp and abscess of the
alveolar bone surrounding the root apex requiring root canal therapy.
 Periodontal disease:
 It is a collective term for a variety of conditions characterized by
inflammation and degeneration of the gingivae, alveolar bone,
periodontal ligament and cement.
 Periodontal diseases are often caused by poor oral hygiene, by local
irritants such as bacteria, impacted food cigarette smoke.
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66. Disorders of digestive tractDisorders of digestive tract
 Peptic ulcer diseases (PUD):
 It is a lesion of membrane that develop in areas of gastrointestinal tract
exposed to acidic gastric juice are called as peptic ulcer.
 Complications of peptic ulcer is bleeding which can lead to anaemia if
enough blood is lost.
 Causes:
 The bacteria Helicobacter pylori
 Non-steroidal anti-inflammatory drugs
 Hypersecretions of HCl
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67. Disorders of digestive tractDisorders of digestive tract
 Diverticular diseases:
 In Diverticular disease, saclike outpouching of the wall of colon termed as
diverticula.
 Development of diverticula called as diverticulosis.
 Diverticula showing inflammation called as diverticulitis.
 The condition may be characterised by pain either constipation or
increased frequency of defecation, nausea, vomiting and low grade fever.
 Colorectal cancer:
 Cancer of colon and rectum called as colorectal cancer.
 Intake of alcohol and diet high in proteins and fats are associated with
increased risk of colorectal cancer.
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68. Disorders of digestive tractDisorders of digestive tract
 Hepatitis:
 It is an inflammation of the liver that can be caused by viruses, drugs and
chemicals including alcohol.
 Types of hepatitis.
 Hepatitis-A
 Hepatitis-B
 Hepatitis-C
 Hepatitis-D
 Hepatitis-E
 Anorexia Nervosa:
 Anorexia is chronic disorder characterized by self induced weight loss,
negative perception of body image and physiological changes that results
from nutritional depletion.
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