PHYSIOLOGY of Digestive System

1. Physiology of Digestive system
1

2. Introduction
Gastrointestinal Tract (GIT)
• Called alimentary canal, continuous tube that
extends from the mouth to the anus.
• length of the GIT about 5–7 meters
2

3. Accessory Digestive Organs
• teeth
• tongue
• salivary glands
• liver
• gallbladder
• pancreas
3

4. Organs of the digestive system 4

5. Functions of the Digestive system
Motility
• mix & move food along its length with the
processes of:
A. Ingestion :Taking food & liquid into the mouth.
B. Mastication: Grinding & mixing food with saliva.
C. Deglutition :Swallowing food.
D. Peristalsis: Rhythmic & wavelike contractions
along GIT
5

6. Cont.
• Peristalsis cause food to move forward along GIT at an
appropriate rate for digestion & absorption
Cause of Peristalsis
• Stretch of GIT wall due to distention
• Chemical or physical irritation of the epithelial lining in
the GIT.
• Acetyl choline from postganglionic parasympathetic
neuron
• Peristalsis occurs only weakly or not at all in the
congenital absence of the myenteric plexus
6

7. Mechanism of Peristalsis
1. Stimuli (mechanoreceptors or chemoreceptor) on the
segment of the GIT initiates peristalsis
2. Contractile ring begins on the oral side of the distended
segment & moves toward the distended segment,
pushing GIT content
3. At the same time GI relaxes several centimeters
downstream toward the anus (receptive relaxation)
• This action is called myenteric (Peristaltic reflex).
• Peristaltic reflex & anal direction of peristaltic
movement is called law of the gut
7

8. Peristalsis 8

9. Segmentation (Mixing Movement)
• Intermittent GIT smooth muscle contractions
occur simultaneously at different GIT
segments.
• Serves to mix the food or chyme with digestive
juice
9

10. Segmentation contraction
10

11. Secretion
About ~ 7 liters of
• water, HCl, HCO3-
• And digestive enzymes secreted into the lumen
of GIT /day from digestive organs
• Besides, Stomach & small intestine secrete
hormones that help to regulate the digestive
system.
11

12. Mechanical Digestion
• The teeth cut , tear and grind food
• Contraction of smooth muscles of the stomach &
intestine breakdown the food.
• As a result, food molecules become smaller, dissolved &
mixed with saliva, digestive juice & enzymes.
Chemical Digestion
• Carbohydrate , lipid, protein, & nucleic acid in the food
hydrolyzed into their monomers by digestive enzymes.
12

13. Absorption
• Entrance of ingested & secreted fluids, into the
epithelial cells of the GIT , blood or lymph.
Storage
GIT temporarily store food, chyme & feces
Defecation
• Elimination of
– indigestible food
– bacteria
– cells sloughed from the lining of the GIT, & end
products that are not absorbed
13

14. Immune Barrier
• Epithelial cells that lines GIT provides a physical
barrier to the penetration of microorganisms
and their toxins.
• Mucosa-associated lymphatic tissue (lymphatic
nodules) located in lamina propria of GIT
contain immune cell which prevent disease.
14

15. Layers of the Gastrointestinal Tract
• The GIT from the esophagus to the anal canal
is composed of four layers ( tunics).
mucosa
submucosa
muscularis
Serosa (adventitia)
15

16. 16

17. The layers of the digestive tract 17

18. Salivary Gland
• Is an exocrine gland, secret saliva into the oral
cavity.
• Mucous membrane of the mouth & tongue
contains small salivary glands that secret less
saliva into oral cavity.
• Eg. Lingual gland located in the tongue, secrete
mucus, watery fluid & lipid digesting enzyme:
lingual lipase
• Most saliva is secreted by the major salivary
glands: parotid, submandibular & sublingual
glands
18

19. Parotid, sublingual& submandibular Salivary
glands 19

20. Composition of Salvia
• Saliva is 99.5% water and 0.5% solutes.
• Between 1 and 1.5 L of saliva per day is produced
by continuous secretion of the three salivary
glands
• Na+,K+,Cl-,HCO3
-, phosphate ion, mucus, IgA,
lysozyme enzyme , salivary amylase .
• Sex steroids are also secreted in saliva
(testosterone, estrogen, progesterone)
20

21. • Parotid gland (25%)
– secrete only a watery (serous) fluid & salivary
amylase
• Submandibular gland (70%)
– secrete more serous, salivary amylase & small
amount of mucus.
• Sublingual gland (5%)
– secret more mucus & small amount of salivary
amylase & watery fluid
21

22. two stages of Saliva secretion
1. acini of salivary gland secrete isotonic solution
resembling interstitial fluid contain ptyalin (a-
amylase) & mucus
2. these secretion flows through salivary ducts
22

23. Cont.
1. Na+ reabsorbed & K+ secreted actively from
salivary ducts
2. Excess Na+ reabsorption over K+ secretion
creates electrical negativity of about -70 mV in
the salivary ducts; this in turn causes Cl-
passive reabsorption.
3. HCO3
- are passively secreted by the ductal
epithelium into the lumen of the duct in
exchange of Cl-.
4. Therefore, Saliva has low Na+ & Cl- & high K+ &
HCO3
-
23

24. 24

25. Regulation of Salivary Secretion
• Salivary glands are mainly controlled by
parasympathetic nervous signals from the
salivatory nuclei in the medulla & pons
• It is excited by both taste & tactile stimuli from
the tongue , mouth & pharynx.
25

26. Cont.
• Parasympathetic stimulation of salivary gland
cause production of abundant watery saliva &
enzymes.
• Sympathetic nerves originate from the superior
cervical ganglia innervate salivary glands.
• Sympathetic nerve stimulation cause secretion
of smaller volume of thick & mucoid saliva
26

27. Function of Saliva
• water in saliva dissolves food
• Cl- in the saliva activate salivary amylase
• HCO3
- & phosphate ions buffer acidic foods that
enter the mouth & acid produced by oral bacteria.
– saliva pH: 6–7
– This prevent dental carries ,
– optimal for salivary amylase action
• Mucus lubricates food, moved easily in the
mouth, formed into bolus & swallowed
27

28. Digestion In the Mouth
1. Mechanical Digestion
Mastication (Chewing)
• slicing, tearing, grinding, & mixing with saliva
• increase surface area for digestive enzymes
action
28

29. 2.Chemical Digestion
Carbohydrate:
• Salivary amylase catalyze hydrolysis of starch
into maltose, maltotriose & a –dextrin ( short-
chain glucose polymers )
• Protein and lipid – No chemical digestion
29

30. Esophagus
muscular tube, about 25 cm
Function
1. Conduct food from the pharynx to the stomach
through peristalsis
2. Secrete mucous ,provide lubrication during swallowing
& protect the mucosa from damaging by food & acidic
gastric juices
• Pharyngoesophageal sphincter (UES) –remains
contracted & preventing air entrance into the
esophagus during respiration.
• Gastroesophageal sphincter (LES) - prevent the stomach
contents from regurgitating into the esophagus
30

31. Peristalsis in the Esophagus 31

32. Disorders of the Esophagus
Achalasia
• difficulty in swallowing (Dysphagia)
• Failure of the LES to relax, resulting in swallowed food
being retained in the esophagus
• Caused by abnormalities in the enteric nerve
• Peristaltic waves are weak
Gastroesophageal reflux disease (GERD)
• LES doesn’t maintain tone
• Acid reflux damages esophageal epithelium
32

33. Stomach
• J-shaped & the
most distensible
organ of GIT.
• Connects
esophagus with
duodenum of the
small intestine
33
Physiologic anatomy of the stomach.

34. Function of Stomach
34

35. 1.2. Mixing & Propulsion of Food
• Chyme- semifluid food mixed with
– saliva ,and gastric secretions in the stomach.
• Food in the stomach cause weak peristalitic &
mixing waves begin in the fundus & body of
the stomach so that it moves toward antrum
about 1/ 15 -20 Second
• Result: mix & digest food.
35

36. Cont.
• Within 2 - 4 hours after eating a meal, the
stomach has emptied its contents into the
duodenum.
Stomach emptying
• Foods rich in carbohydrate spend the least
time in the stomach
• High protein foods remain somewhat longer
and
• Emptying is slowest after a fat-loaded meal
containing large amounts of triglycerides.
36

37. 2.Gastric Secretion
• Mucosa of the stomach has folds called
rugae.
• The cells that line these folds form the gastric
pit & glands
• Gastric pits - openings of the gastric glands
into the stomach lumen
37

38. Gastric pits and gastric glands of the mucosa 38

39. Cells of gastric glands 39

40. 1. Parietal cells
• Secrete HCl & intrinsic factor
• Stimuli: acetylcholine , gastrin & histamine
stimulation
Function of HCl:
1. Makes gastric juice very acidic : pH < 2
2. Activates pepsinogen & kill Microorganisms
3. Denature protein, their tertiary structure
altered so that they become more digestible.
Intrinsic factor
Facilitates absorption of vitamin B12
40

41. The activation of pepsin by HCl 41

42. 2. Chief Cells
• secrete pepsinogen, inactive form of pepsin
• Stimuli: acetylcholine , gastrin & histamine
• Pepsinogen is initially converted to active pepsin by
acid.
• Active pepsin continues the process.
• Pepsin is active only in the acid pH medium of the
stomach.
42

43. 3. G cells
• secretes gastrin into the blood
• Stimulus: presence of amino acids in the
stomach lumen from partially digested proteins
& acetylcholine from vagus nerve
4. D cells
• secretes somatostatin in response to acid
• Somatostatin is universal inhibitor
• Somatostatin :inhibits parietal, and G cell
secretion
43

44. 44

45. 45

46. 46

47. 47

48. Control of acid secretion
There are 3 natural substances that stimulate parietal
cells:
• Acetylcholine (ACh), acting as a transmitter; release is
stimulated by sight/smell of food and reflexly in
response to stomach distension (vagovagal reflex).
• Locally released histamine; stimulated by Ach and
gastrin
• The hormone gastrin; stimulated by release of GRP
• As stomach pH falls, somatostatin (SST) is released,
which inhibits gastrin and reduces acid secretion
(feedback regulation of acid secretion).
48

49. 3.Digestion in the Stomach
1. Mechanical digestion
2. Chemical Digestion
2.1 Carbohydrate Digestion
• Starch digestion begins in the mouth with the
action of salivary amylase
• But, salivary amylase inactivated by acidic
gastric juice (PH < 4).
49

50. Protein Digestion in the Stomach
• Proteins partially digested in the stomach by
pepsin enzyme
• Pepsin is most active at a pH of 2.0 - 3.0 &
inactive at a pH above about 5.0.
• Pepsin digests the collagen protein,
• Collagen is a major constituent of the
intercellular connective tissues.
50

51. Lipid Digestion in the Stomach
• lingual & gastric lipase becomes activated in
the acidic environment of stomach:
• Hydrolyzes triglycerides into fatty acids,
• But, amount of fat digestion is less than 10%
• Essentially all fat digestion occurs in the small
intestine. 51

52. Absorption In stomach
• The stomach is a poor absorptive area of the
GIT because:
1. It lacks the villus , absorptive membrane &
2. Junctions between the epithelial cells are
tight junctions.
• Only a few highly lipid soluble substances,
such as alcohol and some drugs like aspirin,
are absorbed in stomach.
52

53. Liver
• Location: right upper abdominal cavity
• The 2nd largest organ in the human body, mass
about 1.3 -1.5 kg
liver lobule
• The basic structural & functional unit of the liver
• Are 50,000 to 100,000 in human liver
• Function : Secrete bile into gallbladder or/and
duodenum
53

54. Relation of the pancreas among liver,
gallbladder & duodenum.
54

55. Secretion of Bile
• Liver secret 250 - 1,500 ml of bile/day
• Bile is a yellow, brownish, or yellow-green
liquid, pH of 7.6–8.6
Gall Bladder:
• Is a saclike organ attached to the inferior &
posterior surface of the liver
• 7 to 10 cm long
• stores, concentrates & release bile into
duodenum 55

56. Composition of Bile
1. Water - more than 90%
2. Bile pigment (bilirubin)
3. Bile salts made up of cholesterol (converted to
cholic acid, ) , glycine or taurine & Na+
4. Phospholipids : lecithin, cholesterol, fatty acid
5. Metabolite of hormone, drug & proteins
6. Na+, K+,Ca2+
,Cl-,HCO3
-
56

57. Cont.
• Bile is secreted in two stages by the liver:
1. Hepatocytes secret
 bile acids, cholesterol, bilirubin & other organic
substances into bile canaliculi
2. Secretory epithelial cells that line bile
canaliculi & ducts
 secret H2O, Na+, HCO3-
57

58. Gallbladder Emptying
1. Fatty foods in the duodenum leads to
secretion of CCK
2. CCK causing the gallbladder contractions &
releasing of bile into duodenum via sphincter
of Oddi
3. Gallbladder contraction also stimulated by
acetylcholine from vagus
58

59. Stimulation of bile secretion & gallbladder emptying
59

60. Function of Bile
• Bile serves two important functions:
1. fat digestion & absorption
– Emulsify the large fat particles into many minute
particles , increase surface area for action of
pancreatic lipase
– Aid absorption of fatty acids, monoglycerides &
cholesterol from intestine
2. means for excretion of wastes from the blood.
E.g. Bilirubin & cholesterol
60

61. Pancreas
• Is a soft, glandular organ that has both exocrine &
endocrine gland
Endocrine Gland
• Pancreatic islets (islets of Langerhans),secrete
the hormones insulin, glucagon etc. into the
blood.
Exocrine Gland
• Pancreatic acini & duct cells secretes pancreatic
juice through the pancreatic duct into the
duodenum. 61

62. Cont.
• Pancreatic juice contains of HCO3
- & Water,
enzymes for the digestion of proteins ,
carbohydrates , and fats.
• HCO3- neutralize acidity of the chyme
Protein digesting pancreatic enzymes:
• Trypsin (abundant), chymotrypsin &
carboxypeptidase
• They hydrolyzed proteins into peptides, amino
acids
62

63. Cont.
Carbohydrate Digesting Pancreatic
Enzymes
• Pancreatic amylase hydrolyzes starches,
glycogen, other carbohydrates (except
cellulose) in to disaccharides & trisaccharides.
63

64. Fat Digesting Pancreatic
Enzyme
1. Pancreatic lipase - hydrolyzing triglycerol
into fatty acids & monoglycerol
2. Cholesterol esterase hydrolyze cholesterol
from its bound with other molecules.
3. Phospholipase -splits fatty acids from
phospholipids
64

65. Regulation of Pancreatic Secretion
What stimulis are causing for pancreatic
secretion?
1. Acetylcholine
• Released from postganglionic parasympathetic
neuron of vagus nerve & cholinergic neuron of
enteric nervous system
2. Cholecystokinin
65

66. Cont.
• Acetylcholine & Cholecystokinin stimulate
acinar cells to produce pancreatic digestive
enzymes , water, and electrolytes
3. Secretin
• Stimulates secretion of water , Na+ & HCO3
- by
the pancreatic ductal epithelial cells
66

67. Regulation of pancreatic secretion 67

68. Small Intestine
• Portion of the GIT between the pyloric sphincter
& ileocecal valve
• Is about 3.25 m long, 2.5 cm in diameter
• It divided into three regions:
1. Duodenum : it starts from pyloric sphincter,
about 25cm long
2. Jejunum: about 1 m long ;extend to ileum
3. Ileum: about 2 m long, joins the large intestine
at ileocecal sphincter (smooth muscle
sphincter) 68

69. Cont.
• Absorption of monosaccharaides, lipids,
amino acids, Ca2+ , & iron occurs primarily in
the duodenum & jejunum.
• Bile salts, vitamin B12 , water, and electrolytes
are absorbed primarily in the ileum.
69

70. Villi & Microvilli
• Villi - a fingerlike fold of mucosa that projects
into the intestinal lumen
• Cells that line these villi have folded plasma
membrane called microvilli (brush border)
• Digestive enzymes are embedded within the
microvilli
• These increases the surface area for secretion
, digestion & absorption
70

71. Secretions in the Small Intestine
• Epithelial layer of the small intestinal mucosa is
composed of simple columnar epithelium that
contains different types of cells
1. Absorptive Cells
– Digest & absorb nutrients from small intestinal
chyme.
2.Goblet cells
 secrete mucus that lubricates & protects the
intestinal mucosa.
71

72. 3. Stem cells
• Divide by mitosis to replace themselves &
produce different cells of intestinal mucosa.
4. Paneth cells:
• Secrete lysozymes, a bactericidal enzyme which
has phagocytic purpose.
• Regulating number of microorganisms in small
intestine.
72

73. Cont.
5. Enteroendocrine cells
1. S cells - secrets secretin
2. I cells = secrets cholecystokinin
Duodenal (Brunner’s) glands:
• Secrete an alkaline mucus that helps neutralize
gastric acid in the chyme.
73

74. Cells of intestinal mucosa 74

75. Intestinal Enzymes
• Plasma membranes of the microvilli contain
intestinal (brush border) enzymes that
hydrolyze disaccharides & polypeptides.
• These include:
1. Disaccharides: Sucrase, Maltase & Lactase
2. Peptidase: Aminopeptidase & enterokinase
3. Intestinal lipase - small amounts
75

76. Cont.
• These enzymes are not secreted into the
lumen,
• But instead remain attached to the plasma
membrane with their active sites exposed to
the chyme
• Enterokinase activate trypsinogen into
trypsin: protein-digesting pancreatic enzyme
76

77. Location of brush border enzymes 77

78. Digestion in Small intestine
1. Digestion of Carbohydrates
• Carbohydrates converted into maltose & small
glucose polymers by pancreatic amylase
• They hydrolyzed into monosaccharides by
intestinal digestive enzymes:
1. lactose Lactase glucose + galactose
2. Sucrose sucrase glucose + Fructose
78

79. Cont.
3. Maltose maltase glucose + Glucose
4. small glucose polymers a-dextrinase glucose +
glucose
• Thus, the final products of carbohydrate
digestion are all monosaccharides.
• They are all water soluble and are absorbed
immediately into the portal blood.
79

80. 2. Protein Digestion in small intestine
1. Trypsin & chymotrypsin split protein into small
polypeptides
2. Carboxypeptidase split individual amino acids
from carboxyl terminal.
3. Aminopeptidase & dipeptidases split
polypeptides into tripeptides, dipeptides &
amino acid
80

81. Cont.
• Amino acids, dipeptides & tripeptides are
absorbed into enterocyte.
4. In the cytosol of enterocyte dipeptides &
tripeptides hydrolyzed into amino acid by
other dipeptidases & tripepdidases
81

82. Digestion of lipid In Small Intestine
• Emulsification of Fat by Bile Acids and Lecithin
1. Physical breakdown of fat globules into very
small sizes so that the water-soluble digestive
enzymes can act on the globule
2. This process is called emulsification of the
fat, and it begins in the stomach.
3. Most of the emulsification occurs in the
duodenum under the influence of bile,
82

83. Cont.
• Pancreatic lipase hydrolyzed triglycerol in to
free fatty acids & monoglycerol.
• Intestinal lipase split triglycerol into glycerol
and fatty acids
83

84. Absorption in the Small Intestine
Water Absorption
• Water is transported through the intestinal
cell membrane entirely by diffusion
Hypotonic (Dilute Chyme)
• Water is absorbed through the intestinal
mucosa into the blood of the villi almost
entirely by osmosis.
• Hyperosmotic Chyme -Water diffuse from
plasma into the chyme
84

85. Absorption of Carbohydrates
• All carbohydrates in the food are absorbed in the
form of monosaccharides
• Most abundant of the absorbed
monosaccharides is glucose , more than 80%.
• Remaining 20% monosaccharides are galactose
from milk & fructose sugar cane.
• Absorbed via facilitated diffusion or active
transport . 85

86. Cont.
• Glucose & galactose are absorbed by 2o
active transport: Na+ co-transport mechanism
from small intestine.
• Na+/K+ ATPase: actively transports of Na+ via
basolateral membranes of intestinal cells into
the blood
• Na+ & glucose or galactose combines with a
carrier protein & transported together into
the interior of the cell
86

87. Cont.
• Glucose & galactose transported by facilitated
diffusion via cell’s basolateral membrane into
tissue space & blood capillaries.
• Fructose is absorbed by facilitated diffusion all
the way through the intestinal epithelium into
blood.
87

88. Absorption of Proteins
• Proteins after digestion, are absorbed into
intestinal epithelial cells in the form of
dipeptides, tripeptides & a few free amino acids.
• Via Na+ - amino acid , dipeptide or tripeptide
symporters ,2o active transport
• Peptide or amino acid & Na+ bind with carrier
protein in microvillus membrane,
88

89. Cont.
• Then Na+ moves down its electrochemical gradient
to the interior of the cell along amino acid or
peptide.
• Dipeptides & tripeptides also absorbed into
intestinal epithelial cells via H+ - dipeptide or
tripeptide symporters = 2o active transport
• Dipeptides & tripeptides are hydrolyzed into
amino acids, then absorbed into the blood
89

90. Absorption of Lipid
• Fatty acids & monoglycerides form micelles in
the small intestinal lumen , absorbed by
epithelial cells & converted into triglycerides in
endoplasmic reticulum.
• Then combined with protein to form
chylomicrons, which enter into lymphatic vessels
(lacteals) of the villi.
90

91. Cont.
• Lymphatic vessels transport chylomicrons to
the thoracic duct then into subclavian vein.
• Small quantities of short & medium-chain
fatty acids are absorbed directly into the
portal blood rather than lymphatic vessels.
91

92. Cont.
• Reason: short-chain fatty acids are more
water-soluble & mostly are not reconverted
into triglycerides by endoplasmic reticulum
• This allows diffusion of these short-chain fatty
acids from the intestinal epithelial cells
directly into the capillary blood of the
intestinal villi.
92

93. Fat absorption 93

94. Large Intestine
• Is the terminal portion of the GI tract
• Size: 1.5 m long & 6.5 cm in diameter
• Four regions of the large intestine are :
• cecum, colon, rectum & anal canal
• The epithelium of large intestinal mucosa is
composed of absorptive and goblet cells
• In large intestine there is no folds (villi); but,
microvillus are present on the absorptive cells
94

95. Anatomy of large intestine 95

96. Large Intestinal glands & cell types
96

97. Function of large Intestine
1. Secretion
2. Digestion : large intestine has little digestive
function
3. Absorption
4. Production of vitamin.
5. Feces formation
6. Defecation
97

98. Secretion in Large intestine
• Mucus by goblet cells
• Bicarbonate ions ….by non–mucus-secreting
epithelial cells that neutralizes acid formed by
bacteria
• Water also secreted by large intestine .
• Mucus secretion is stimulated by enteric &
parasympathetic NS in response to tactile stimuli
& irritation
98

99. Mucus
1. lubricates the passage of the colonic contents
2. Protects the large intestine wall against
bacterial activity
3. Provides an adherent medium for holding
fecal matter together
99

100. Digestion in large Intestine
Mechanical Digestion
• Constriction of muscular wall of large
intestine: haustration & peristalsis physically
breach down chyme
Chemical Digestion
• Final stage of digestion occurs in the colon
through the activity of bacteria
100

101. Function of Bacteria In the large
Intestine
1. Ferment remaining of carbohydrates &
release H2 , CO2, and CH4 gases: flatus.
2. Convert proteins to amino acids, break down
amino acids into H2S, :odor of flatus.
3. Decompose bilirubin to stercobilin, which
gives feces their brown color
4. Produce vitamin K
101

102. Absorption In large Intestine
• Large intestine absorb water ,electrolytes ,
vitamin B complex & vitamin K.
• About 200 ml of fluid excreted in the feces.
102

103. Cont.
• Most of the absorption in the large intestine
occurs in the proximal one half of the colon
,called absorbing colon
• Distal colon store feces until it defecate ,
called the storage colon.
• Na+ & Cl- absorption by actively and
passively from large intestine respectively.
103

104. Cont.
• Mucosa of the large intestine secretes HCO3
-
& absorbs equal number of Cl- in an exchange
transport process.
• HCO3
- neutralize the acidic end products of
bacterial action in the large intestine.
• Absorption of Na+ & Cl- creates an osmotic
gradient, causes absorption of water.
104

105. Regulation of the Digestive system
• extrinsically by the autonomic nervous system
& endocrine system and
• Intrinsically by the enteric nervous system
Enteric Nervous System
– The gastrointestinal tract has its own nervous
system called the enteric nervous system
105

106. Cont.
• It lies entirely in the wall of the GIT , beginning
in the esophagus & extending all the way to the
anus.
• The number of neurons in this enteric nervous
system (ENS) is about 100 million
Function : ENS controls gastrointestinal
movements & secretion.
Include: myenteric & submucosal plexus
106

107. Cont.
• Myenteric plexus controls GIT movements,
and
• Submucosal plexus controls GIT secretion &
local blood flow.
• Composition: ENS made up of sensory
interneurons, motor neurons, glial cells &
astrocytes
107

108. Neural control of GIT
108

109. Organization of the enteric nervous system 109

110. Autonomic Nervous System Control of
the Digestive system
• Sympathetic & parasympathetic NS has
connection with both myenteric & submucosal
plexus
• SNS inhibit GIT motility , inhibit digestion
• PSNS - stimulate GIT motility & secretion,
promote digestion
110

111. Hormonal Control of Digestive System
• GIT secretion and motility is also control by
hormones . These are:
1. Gastrin
• Secreted by G- cell of gastric gland in response to
stomach wall stretch & presence of digestive
products of protein in the stomach.
Function
 Gastrin stimulates secretion of HCl & gastric
motility
111

112. Cont.
2.Cholecystokinin
• Secreted by I cells of duodenum & jejunum in
response to fatty substances in the chyme
• Inhibit gastric emptying when excess quantities
of acidic or fatty chyme are available in the
duodenum.
• Increase contraction of gallbladder
• Relaxes sphincter of oddi
112

113. 3.Secretin
• Secreted by S cells from duodenal mucosa in
response to acidic chyme in the duodenum
• Inhibit gastric emptying,
• stimulate pancreatic acini to produce
bicarbonate.
113

114. 4.Gastric Inhibitory Peptide (GIP)
• Released from K cells of upper small intestine in
response to fat & carbohydrates: glucose
Function
1. Decreasing gastric motility , secretion & emptying
2. Stimulates secretion of insulin from pancreatic islets
5.Motilin
– Is secreted by the upper duodenum during fasting
– Increase gastrointestinal motility.
114