It is specially for nursing & allied health science.. hope it will be useful... Jaita

1. The Digestive System
1

2. Objective
• At the end of the class students will be able
to:
- explain about the structure of alimentary tract
& it’s accessory organs of digestion
- explain about various alteration in diseases
- apply & implicate the knowledge in day to
day practice

3. • Digestive system = alimentary canal +
accessory organs + variety of digestive
processes.

4. Alimentary canal or Gastrointestinal
(GI) tract
• Mouth
• Pharynx
• Oesophagus
• Stomach
• Small intestine
• Large intestine
• Rectum & Anal canal

5. The Components of the Digestive System

6. Accessory organs
• Glands situated out side of the tract;
secretions pass through ducts to enter the
tract:
- 3 pairs of salivary glands
• Parotid in front of ear
• Submandibular below lower jaw
• Sublingual below tongue
- The pancreas
- The liver & biliary tract

7. The Major Salivary Glands
7

8. Duct System

9. Digestive processes
• Ingestion:
• Propulsion:
• Digestion:
• Absorption:
• Elimination:

10. General structures/ Layers of
Digestive System

11. • Modified in different levels according to
process
• Inner Epithelial layer/ Mucosa
– Soft and pink in colour
– 3 layers
 Mucous membrane (innermost; columnar
epithelium with goblet cells; protection,
secretion, absorption)
Lamina propria (loose connective tissue;
supports blood vessels & lymphoid tissue)
Muscularis mucosa (thin outer layer;
smooth muscle)
– Secretion of enzyme and mucus

12. • Mucous membrane secrets digestive juices:
 saliva from the salivary glands
Gastric juice from gastric glands
Intestinal juice from intestinal glands
Pancreatic juice from pancreas
Bile from liver
• Also secrets mucus from goblet cells.
12

13. • Sub- mucosa
– Connective tissue (binds muscle layer to mucosa)
• Muscular layer
– Outer layer (Longitudinal muscles)
– Inner layer (Circular muscle)
Between these two layers: blood vessels, lymph vessels
& a plexus (network) of sympathetic&
parasympathetic nerves (myenteric plexus or
Auerbach’s plexus)
– Peristalsis (Segmental contraction)
13

14. • Outer Serous layer or Adventitia
– Protective function
– In abdomen organs are covered by a serous membrane
(peritoneum)
 Parietal peritoneum: lines the abdominal wall
Visceral peritoneum: covers the organs (viscera)
within the abdominal & pelvic cavities.
Home work: explain about peritoneum in detail.
14

15. Anatomy of the Mouth and Throat
15

16. Mouth or oral cavity
• Is bounded by muscles & bones:
Anteriorly: by the lips
Posteriorly: continuous with oropharynx
Laterally: by the muscles of the cheeks
Superiorly: by bony hard palate &
muscular soft palate
Inferiorly: by the muscular tongue &
soft tissues of the floor of the mouth
16

17. • Vestibule: part of mouth between gums &
cheeks.
• Remainder of the cavity: oral cavity
• Palate: forms the roof of mouth; has 2
parts
Anterior hard palate: formed by maxilla
& palatine bone
Posterior soft palate: muscular curves
from back of hard palate & blends with
the wall of pharynx at side.
17

18. • Uvula: curved fold of muscle covered with
mucous membrane, hanging down from
middle of free border of soft palate.
• Palatine tonsil: collection of lymphoid
tissue on each side between the arches.
18

19. Tongue
19

20. • Voluntary muscle structure
• Attached to hyoid bone at
base
• Attached to floor of the
mouth by a fold of its
mucous membrane
covering: frenulum
• Superior surface: numerous
papillae (small
projections); many of these
contain sensory receptors
(test buds) 20

21. Blood supply: lingual branch of external
carotid artery; venous drainage by lingual vein
Nerve supply: hypoglossal nerves (12th
cranial nerve)- supply voluntary muscles;
lingual branch of mandibular nerves (arises
from 5th cranial nerve)- pain, temperature &
touch; facial & glossopharyngeal nerves (7th &
9th cranial nerves)- nerves of taste
21

22. Functions of tongue
• Chewing (mastication)
• Swallowing (deglutition)
• Speech
• Taste
22

23. Teeth
23

24. • Embedded in the alveoli or sockets of the
alveolar ridges of the mandible & the maxilla.
• Temporary or deciduous teeth: babies born
with two sets (dentitions)
• 20 temporary teeth (10 in each jaw); erupt at
about 6 months; should be present by 24
months
• Permanent teeth begin to replace deciduous
teeth in 6th year; 32 teeth; usually complete by
21st year
24

25. Functions of the teeth
• Incisors & canine teeth: cutting teeth;
used for biting pieces of food
• Premolar & molar teeth: broad, flat
surface; used for grinding or chewing food
25

26. Structure of tooth
• Crown: part that protrudes from gum
• Root: part embedded in bone
• Neck: narrowed region between crown
& root.
• Blood supply: maxillary artery;
jugular veins
• Nerve supply: upper teeth maxillary
nerves; lower teeth mandibular nerves.
Both are branches of trigeminal nerves
(5th cranial nerve)
26

27. Salivary glands
27

28. Parotid glands
• Each side of the face just below the
external acoustic meatus.
• Each gland has a parotid duct opening in
mouth at the level of 2nd upper molar tooth.
28

29. Sub- mandibular glands
• One on each side of face under angle of
jaw.
• 2 submandibular ducts open on the floor of
the mouth (each side of the frenulum of
tongue)
29

30. Sublingual glands
• Lie under the mucus membrane of the
floor of mouth in front of submandibular
glands
• Have numerous small ducts that open into
the floor of mouth
30

31. Salivary Glands
• Produce and secrete saliva that:
– Cleanses the mouth
– Moistens and dissolves food chemicals
– Aids in bolus formation
– Chemical digestion of Food

32. Saliva
• 1-1.5 litre/day; pH slightly acidic (6.8)
Composition
• Mostly water 97 to 99.5%
• Mucus
• Mineral salts
• A digestive enzyme: salivary amylase
• Lysozyme
• Immunoglobulin
• Blood clotting factors

33. Secretion of saliva
• Secretion is under autonomic nervous system
• Parasympathetic stimulation causes: profuse
secretion of watery saliva with a relatively low
content of enzymes & other organic substances
• Sympathetic stimulation causes: secretion in
small amount of saliva rich in organic materials
specially from sub mandibular glands
33

34. Functions of saliva
• Chemical digestion of polysaccharides
Saliva contains enzyme amylase: break down
of complex sugars (starch to disaccharide
maltose)
• Lubrication of food
made a bolus ready for swallowing
• Cleaning & lubricating the mouth
prevents damage to mucous membrane by
rough & abrasive food
34

35. • Non- specific defence
lysozyme, immunoglobulin & clotting factors
combat invading microbes
• Taste
test buds are stimulated only by chemical
substances; thus dry foods only stimulate the
sense of taste after thorough mixing with
saliva
35

36. Pharynx
• Connects nasal and oral cavities with larynx &
oesophagus
• force food down during swallowing
• Divisions
 Nasopharynx (important in respiration)
 Oropharynx &
 Laryngopharynx
(both are common passage to both respiratory &
digestive system)

37. 37

38. • Blood supply: several branches of facial
arteries; venous drainage: into facial veins
& internal jugular veins
• Nerve supply: sympathetic from cervical
ganglia; parasympathetic by
glossopharyngeal & vagus nerves
38

39. Oesophagus

40. Esophagus
– 25cm long muscular tube; 2cm diameter
– From pharynx to stomach
– Behind trachea and in front of vertebral
column
– Food passes to stomach by active muscular
action
– As it passed through diaphragm it curves
upward: prevents regurgitation (backflow) of
gastric content
40

41. Oesophagus contd.
– Closed with two sphincters
(upper: cricopharyngeal or upper oesophageal
sphincter;
lower: cardiac or lower oesophageal sphincter)
– Solid food reaches stomach in 7 to 8 seconds
– Liquids reaches stomach in 2 to 3 seconds
• Functions
– Secrete mucous
– Transport food
41

42. • Blood supply:
- Thoracic region- paired oesophageal
arteries; venous drainage: azygous &
hemizygous veins
- Abdominal region- branches from inferior
phrenic arteries & left gastric branch of
coeliac artery; Venous drainage in left
gastric vein
42

43. Anatomy of the Stomach
43

44. Stomach
• Usually “J” shaped; 1.5lt or more in adult
• 2 sphincters: cardiac & pyloric
44

45. Organs associated with stomach
• Anteriorly: left lobe of liver &
abdominal wall
• Posteriorly: abdominal aorta,
pancreas, spleen, left kidney &
adrenal gland
• Superiorly: diaphragm,
oesophagus & left lobe of liver
• Inferiorly: transverse colon &
small intestine
• To the left: diaphragm & spleen
• To the right: liver & duodenum
45

46. Walls of stomach
• Consists of 3 layers instead of 2.
Outer: longitudinal fibres
Middle: circular fibres
Inner: oblique fibres
• This arrangement allows churning motion as well
as peristaltic movement.
• Circular muscle is strongest in the pylorus &
pyloric sphincter
46

47. • Mucosa of stomach:
When empty: thrown into longitudinal folds
or rugae
When full: rugae are ironed out & surface has
a smooth, velvety appearance.
Numerous gastric glands situated below
mucous membrane & open on to it: secrets
gastric juice
47

48. • Mucous membrane
– G cells – secret gastrin
– Goblet cells – secret mucous
– Gastric pit has Oxyntic gland – Parietal
cells – secret HCl
– Chief cells or Zymogenic cells
• Pepsin
• Gastric lipase
48

49. Histology of Stomach

50. • Blood supply:
Arterial supply: left gastric artery, a branch
of coeliac artery, right gastric artery &
gastroepiploic arteries.
Venous drainage: through veins of
corresponding names into the portal vein
50

51. Gastric juice
• About 2 lt of gastric juice/ day
• Consist of:
Water (by gastric glands)
Mineral salts (by gastric glands)
Mucus (mucous cells)
HCL (parietal cells)
Intrinsic factor (parietal cells)
Inactive enzyme precursors: pepsinogen by
chief cells
51

52. Functions of gastric juice
• Water further liquefies the food
swallowed
• HCL:
Acidifies the food & stops action of salivary
amylase
Kills ingested microbes
Provides acid environment needed for
effective digestion by pepsins
52

53. • Pepsinogens:
are activated to pepsins by HCL acid &
pepsins already present in the stomach
These enzymes begin the digestion of
proteins.
Pepsins are more effective at a very low pH
(1.5-3.5)
53

54. • Intrinsic factor (a protein): needed for
absorption of vit B12 from ileum
• Mucus:
prevents mechanical injury to the stomach
wall by lubricating the contents
Prevents chemical injury by acting as a barrier
between stomach wall & corrosive gastric
juice
54

55. Secretion of gastric juice
• Always a small quantity of gastric juice
present in the stomach (even if no food) =
“fasting juice”
• Max. level: about 1 hr after a meal
• Declines to fasting level after about 4 hrs.
• 3 phases of secretion of gastric juice
Cephalic phase
Gastric phase
Intestinal phase
55

56. Cephalic Phase

57. Cephalic phase
• This flow of juice occurs before food
reaches the stomach
• Due to reflex stimulation of vagus
(parasympathetic) nerves initiated by the
sight, smell or test of food.
57

58. Gastric phase
stimulated by the presence of food the in the pyloric antrum
duodenum secret gastrin (circulating in blood)
blood which supplies the stomach
stimulates the gastric glands to produce more gastric juice
Gastric phase secretion is suppressed when
the pH in the pyloric antrum falls to about 1.5
58

59. Gastric Phase

60. Gastric Phase
• Distention of the stomach activates a
parasympathetic reflex. Action potentials are
carried by the vagus nerves to the medulla
oblongata.
• Medulla oblongata stimulates further secretions
of the stomach.
• Distention also stimulates local reflexes that
amplify stomach secretions.

61. Intestinal Phase
• Chyme in the duodenum with a pH less than 2 or
containing lipids inhibits gastric secretions by 3
mechanisms
• Sensory input to the medulla from the duodenum
inhibits the motor input from the medulla to the
stomach. Stops secretion of pepsin and HCl.
• Local reflexes inhibit gastric secretion
• Secretin, gastric inhibitory polypeptide, and
cholecystokinin produced by the duodenum inhibit
gastric secretions in the stomach.
(Enterogastrone)

62. Intestinal Phase

63. Intestinal phase
• When the partially digested contents of the
stomach reach the small intestine, a hormone
complex enterogastrone is produced which slows
down the secretion of gastric juice & reduces
gastric motility.
• Two hormones forming this complex are secretin
& cholecystokinin (CCK)
• Enterogastrone (any hormone or combination of
hormones released by the intestine that inhibits
gastric secretion.)
63

64. • By slowing the emptying rate of the
stomach, the contents of the duodenum
become more thoroughly mixed with bile
& pancreatic juice.
• This phase of gastric secretion is most
marked when the meal has had a high fat
content
64

65. 65

66. Functions of Stomach
– Mix food – Limited absortion of
– Reservoir • Alcohol
– Mechanical digestion • Water
– Chemical digestion of • B 12
• Protein – Storage of food for 3
• Nucleic acids hours
• Fats
– Partial digestion of
– Activates some enzymes proteins and fats
– Destroy some bacteria
– Outward movement of
– Dissolving out iron from content of pyloric end
food
of the stomach
66

67. Small Intestine
• Extends from pyloric
sphincter  ileocecal valve
– 6 to 7 meter long, 2.5cm
diameter
– Lies in center of
abdomen
– Divided into 3 parts
• First part – Duodenum
• Second part – Jejunum
• Third part – ileum
67

68. Small Intestine
• Alkaline Secretions
– Protects from acid contents
of stomach
• Small intestine
– Mucosa
• Deeply folded to increase
the surface area (villi)
• Helps in absorption of food.
• Movements
– Segmentation
– Peristalsis 68

69. Segmentation & Peristalsis
• Peristalsis: is a radially symmetrical contraction
and relaxation of muscles which propagates in a
wave down the muscular tube, in an anterograde
fashion. In humans, peristalsis is found in the
contraction of smooth muscles to propel contents
through the digestive tract.
• Segmentation: Most areas of the small intestine
and some portions of the large intestine undergo
cycles of contraction that churn and fragment the
bolus, mixing the contents with intestinal
secretions

70. Peristalsis and Segmentation
70

71. 71

72. Small Intestine cont.
• Structural modifications of the small intestine
wall increase surface area
– Plicae circulares: deep circular folds of the
mucosa and submucosa
– Villi – fingerlike extensions of the mucosa
– Microvilli – tiny projections of absorptive
mucosal cells’ plasma membranes

73. Small Intestine

74. Structure of the Villi in the
Small Intestine
74

75. Small Intestine
• Requires pancreatic
enzymes & bile to
complete digestion
• Blood supply:
Superior mesenteric
artery; superior
mesenteric vein
75

76. Large Intestine
• Extends from ileocecal valve to anus
– 1.5meter long, 5 to 6cm diameter
• Regions
– Cecum
– Colon: Divided into 3 parts
• Right ascending colon
• Transverse colon
• Left descending colon
– Appendix (Epiploic appendages)
– Rectum
– Anal canal 76

77. Large Intestine
• Cecum
– 1st part of large intestine, Blind sac, appendix
attached
• Colon
– Ascending, transverse, descending, sigmoid
• Rectum
– Straight muscular tube, 13cm long, between
sigmoid colon & anal canal
• Anal canal: 3.8cm long
– Internal anal sphincter (smooth muscle)
– External anal sphincter (skeletal muscle)

79. Large Intestine
– No villi
– No permanent circular folds
– Longitudinal muscle is modified: collected
into 3 bands
• Taeniae coli (Haustra)
– Otherwise like rest of Gl tract
79

80. Large intestine
• Blood supply:
- Inferior mesenteric artery, middle &
inferior rectal arteries;
- Superior & inferior mesenteric vein
80

81. Functions of Large Intestine
• Absorption
• Microbial activity (large no. of microbes
synthesize vitamin K & folic acid):E. coli,
Streptococcus faecalis etc.
• Mass movement
• Defecation
81

82. Feces Formation and Defecation
• Sigmoid Colon & • Defecation
– Peristalsis pushes feces
Rectum into rectum
– Temporary storage of – Rectal walls stretch
faeces • Control
• Chyme dehydrated to
– Parasympathetic
form feces
• Feces composition – Voluntary
– Water
– Inorganic salts
– Epithelial cells
– Bacteria
– Byproducts of digestion
82

83. The Liver
• The largest gland in the body
• Performs metabolic and hematological
regulation and produces bile
• Location
– R. Hypochondrium
– Epigastric region

84. Organs associated with liver
• Superiorly & anteriorly: diaphragm & anterior
abdominal wall
• Inferiorly: stomach, bile ducts, duodenum,
hepatic flexure of the colon, right kidney &
adrenal gland
• Posteriorly: oesophagus, inferior vena cava,
aorta, gall bladder, vertebral column, diaphragm
• Laterally: lower ribs & diaphragm
84

85. Liver
• 4 Lobes
– Left
– Quadrate
– Caudate
– Right
85

86. The Liver

87. • Each lobe has lobules (tiny functional
units) – hexagonal in shape;
• Lobules contains hepatocytes: arranged in
pairs of column
• Between 2 pairs of column of cells are
sinusoids (blood vessels with incomplete
walls – Feed into central vein (mix blood
from portal vein & hepatic artery)
• Kupffer cells (Hepatic macrophages):
within sinusoids; ingest & destroy worn
out blood cells & any foreign particles
present in blood
87

90. Liver
• Dual blood supply
– Hepatic portal vein
– Hepatic artery/vein
90

91. Blood and Bile Flow

92. Liver
Functions
•Carbohydrate, fat, protein metabolism
•Synthesis of bile
•Formation of urea
•Detoxification of drugs, alcohol
•Destruction of RBC
•Storage of excess glucose in form of glycogen
•Storage of Vitamin A & D
•Storage of Hemoglobin
•Activates vitamin D
•Fetal RBC production
•Phagocytosis
•Manufacturing of prothrombin & fibrinogen
92

93. The Pancreas
• Pale gray gland; (Both exocrine & endocrine gland)
• In epigastric & left hypochondriac regions; posterior
to stomach
• Weighing 60 gm; 12-15cm long
• Parts of pancreas
– Broad Head (lies in curve of duodenum)
– Body (behind the stomach)
– Narrow Tail (infront of left kidney just reaches the
spleen)
• Abdominal aorta & inferior vena cava lie behind

94. Tail Pancreas
Body
Head
94

95. The Pancreas
• Endocrine functions
– Groups of specialized cells (pancreatic islets of
Langerhans): have no ducts; hormones diffuse
directly into blood.
– Secrets Insulin, Glucagon (controls blood glucose)

96. • Exocrine functions
– Majority of pancreatic secretions
– Consists of a large number of lobules made up
of small alveoli (walls consists of secretory
cells)
– Each lobules is drained by tiny duct (unite to
form pancreatic duct): joins with common bile
duct (forms hepatopancreatic ampulla) &
opens into duodenum
– Duodenal opening of ampulla is controlled by
hepatopancreatic sphincter (sphincter of Oddi)
96

97. The Pancreas
– Produces pancreatic juice containing enzymes
– Pancreatic juice digests
• Carbohydrate
• Proteins
• Fats

99. Pancreas
• Blood supply:
Arterial supply: splenic & mesenteric
arteries;
Venous drainage: splenic & mesenteric veins
joins to form portal vein
99

100. Biliary tract
• Consists of bile duct & gall bladder
100

101. Bile ducts
• Right & Left Hepatic ducts merge  Common
hepatic duct (7.5 cm long, 6mm diameter)
• Common hepatic duct joins Cystic duct from
gallbladder  Common Bile duct
• Bile duct joins Pancreatic duct at
Hepatopancreatic ampulla and enters duodenum
• Hepatopancreatic sphincter regulates passage of
bile and pancreatic juices into duodenum

102. 102

103. The Gallbladder
• Hollow, pear-shaped sac; attached to posterior
surface of liver
• Has a fundus (expanded end) & body (main part)
& neck (continuous with cystic duct)
• Stores, modifies and concentrates bile
• Releases bile via the cystic duct, which flows into
the bile duct
• Blood supply:
- Cystic artery (branch of hepatic artery)
- Cystic vein (joins portal vein)

104. Functions of gall bladder
• Reservoir for bile
• Secretion of mucus into the bile
• Absorption of water so that it is 10-15
times more concentrated than liver bile
• Release of stored bile
104

105. Metabolism
• Carbohydrate
• Protein
• Fat
105

106. Digestive processes
• Ingestion: taking food in GI tract (eating,
drinking)
• Propulsion: mixes & moves the contents
along GI tract.

107. Digestive processes cont.
• Digestion: Mechanical breakdown of food
(mastication) & chemical digestion (by
enzymes of secretion produced by glands
& accessory organs.

108. Digestive processes cont.
• Absorption: digested food substances pass
through the walls of some organs of GI
tract into blood & lymph capillaries for
circulation &use by body cell

109. Digestive processes cont.
• Elimination: food substances which can
not be digested & absorbed excreted as
faeces by the process of defaecation.

110. oral cavity/teeth/salivary glands
oropharynx/epiglottis
oesophagus
The path
of food: stomach
small intestine: duodenum
small intestine: jejunum
small intestine: ileum
large intestine: ascending colon
large intestine: transverse colon
large intestine: descending colon
sigmoid colon rectum anus

111. Diseases of mouth
• Inflammation: thrush, angular cheilitis,
gingivitis, stomatitis,
• Viral infection
• Tumors of mouth: squamous cell
carcinoma
• Developmental defects: cleft palate & cleft
lip
111

112. Diseases of pharynx
• Tonsillitis
• Diphtheria
112

113. Diseases of salivary glands
• Mumps
• Calculus formation
• tumors
113

114. Diseases of oesophagus
• Esophageal varices
• Inflammatory conditions
• Spontaneous rupture of oesophagus
• Tumors
• Congenital malformation
114

115. Diseases of the stomach
• Gastritis
• Peptic ulceration
• Tumors of stomach
• Congenital pyloric stenosis
115

116. Diseases of the intestine
• Appendicitis
• Microbial disease: typhoid fever,
paratyphoid fever, infection, food
poisoning, cholera, dysentery
• Inflammatory bowel disease: crohn’s
disease, ulcerative colitis, tumors, hernias,
intestinal obstruction etc
116

117. Diseases of pancreas
• Acute pancreatitis
• Chronic pancreatitis
• Tumors
117

118. Disease of liver
• Acute hepatitis
• Chronic hepatitis
• Non- viral inflammation of liver: liver
abscess, cirrhosis of liver, liver faliure,
hepatic encephalopathy, blood coagulation
defect, ascites etc.
• Tumors of the liver
118

119. Disease of gall bladder & bile
duct
• Gall stones (cholelithiasis)
• Tumors
• Jaundice
• Cholecystitis
119