1. Gastrointestinal Functions

2. Small intestinal digestion Large intestinal digestion Absorption
Introduction
Mouth digestion
Stomach digestion
Small intestinal digestion
Large intestinal digestion
Absorption

3. Section 1 Introduction
Physiological characteristics of digestive smooth muscle
Secretion of digestive gland
Neural control of digestive tract
Gastrointestinal hormones

4. Gastrointestinal system
consists of
Gastrointestinal (GI) tract
Accessory glandular organs
LARYNX pharynx

5. Anatomy and functions of the GI tract
mouth, pharynx, esophagus,
stomach, small intestine,
large intestine, anus
Accessory Glandular Organs
salivary glands, liver, gallbladder, pancreas

7. 1. Definition
- Digestion
It shows the large molecular substances were
changed into the small molecular substances.
- Absorption
It indicates the small molecular substances were
absorbed to blood & lymph.
2. Digestive modes
- Mechanical digestion:
by smooth muscles of digestive tracts
- Chemical digestion:
by digestive enzyme

9. Physiological Characteristics of Digestive Smooth Muscle
1. General characteristics
- The intestinal wall is composed of 5 layers.
- Excitation is lower, contraction is slow.
- Have autorhythmicity, but is not stable.
- Have large dilation.
- It is not sensitive to electric stimulus and is
sensitive to stretch, T and chemical stimulus

10. Longitudinal muscle layer
Layers of Alimentary Canal
Submucosa
Mucosa
Serosa
Circular muscle layer
Longitudinal muscle layer

11. Layers of Alimentary Canal
Myenteric
plexus
Serosa
Mucosa
Submucosal
plexus
Longitudinal
muscle
Submucosa
Circular muscle

12. 2. Characteristic of electrical activity muscle
- Resting potential: - 50 ~ - 60 mV
- Slow wave potential:
it is not AP, it is undulating changes in the RP, about 10 ~ 15 mV.
- Action or spike potential:
They occur when the RP becomes more positive than about – 40 mV, the channels responsible for the AP allow Ca ions an Na ions enter.

13. Cells and Electrical Events in the Muscularis
Insert fig

15. Secretion of Digestive Gland
1. Component:
Water, digestive enzyme, mucus and antibody
ets.
2. Function:
- digest food
- provide pH,
- dilute food
- protect mucosa of digestive tract.

17. Neural Control of Gastrointestinal Function
1. Enteric nervous system
- The Myenteric plexus, or Auerbach’s plexus
Stimulation causes increased “tone” of the gut
wall, increased intensity and rate of rhythmical
contractions
- The submucosal plexus, or Meissner’s plexus
It is mainly concerned with controlling function
within the inner wall of each minute segment of
the intestine.

19. CNS to gut connections BRAIN STEM nodose ganglion SPINAL CORD Vagal
efferent
SPINAL CORD
Vagal
afferent
dorsal root ganglion
Spinal
afferent

20. 2. Autonomic nerve
The parasympathetic nerves
- It increases the activity of the enteric nervous system. This in turn enhances the activity of most gastrointestinal functions.
The sympathetic nervous
- to a slight extent by a direct action that inhibits the smooth muscles of gastrointestinal wall.
- to a major extent by an inhibitory effect on the neurons of the enteric nervous system.
3. Gastrointestinal reflexes

21. The Reflex Pathway of the Digestive System
Central nervous system
Sympathetic, parasympathetic nerve
Enteric nervous system
smooth muscle (GI) secreting cells endocrine cells
Stretch, chemical,
T receptor

23. Gastrointestinal Hormones
1. Gastrointestinal tract produces many hormones
All known GI hormones are peptides with mole-
cular weights in most cases ranging between
2,000 to 5,000.
2. Effects:
- Regulate secretion of digestive glands and motility
of digestive tract.
- Regulate the other hormone release.
- Trophic action
3. The three major hormones are in the below table:

24. Three Major GI Hormones
Hormone Effects Site
Gastrin Stimulates acid secretion G cells
and promote digestive
motility.
CCK Stimulates gallbladder con-
traction and pancreatic I cells
enzyme secrete
Secretin Stimulates HCO3- and water S cells
secrete of pancretic liquid.

25. Section 2 Mouth and Esophagus
Saliva & function
Digestion of food in mouth

26. Saliva & Function 1. Saliva - Secretion
Saliva is secreted by three pairs of large glands,
the parotid, submaxillary, and sublingual gland.
- Components:
Water 99%, ptyalin, bacteriolysis enzyme, mucus,
Ig A, Na+, K+, HCO3- , pH 6.6 ~ 7.1.
Control of secretion
- It includes conditional and unconditional reflex.
- It is controlled mainly by vagus and sympathetic
signals.

27. Salivary gland Anatomy Parotid glands submandibular glands
submaxillary glands
smaller glands in mucosa of tongue, palate, etc.
Secretory unit (salivon)
Acinus - initial secretory process
intercalated duct - initial portion of duct
striated duct - modification of secretory product
myoepithelial cells
surround acinus and intercalated duct
contraction moves saliva, prevents development of back pressure

28. 2. Functions of saliva
- The serous secretion contains ptyalin ( an α-amylase ), which is an enzyme for digesting starch.
- Mucous secretion contains mucus for surface protection and lubrication.
- Solubilizes dry food
- Keep oral hygiene: bacteriolysis enzyme, Ig A.

29. Esophagus peristaltic contractions
During swallowing, boluses of food
are propelled through the esophagus
by strong peristaltic contractions.

30. Section 3 Gastric Digestion
Functional structure of the stomach
Gastric secretion
Regulation of gastric secretion
Motor functions of the stomach

31. Functional Anatomy of Stomach
Oesophagus
Fundus
Lower Oesophageal
Sphincter
Fundus
Storage
Body
Storage
Mucus
HCl
Pepsinogen
Intrinsic factor
Duodenum
Pylorus
Body
Antrum
Antrum
Mixing/Grinding
Gastrin

32. Functional Structure of Stomach
Region Cell type Secretion
Cardiac gland Mucous cells Mucus, HCO3-
(fundus)
Oxyntic gland Parietal cells, HCl, intrinsic factor
(body) Chief cells Pepsinogen,
Pyloric gland G cells Gastrin
(antrum) Mucus cells Mucus
D cells Somatostatin

34. Gastric Secretion 1. Gastric acid ( HCl) 1.1 Secretion
- It is secreted by parietal cells, pH 0. 9 ~ 1. 5.
- Excreting volume:
Basal acid secretion : 0 ~ 5 mmol / h
fasting overnight
The maximal secretion: 20 ~ 25 mmol / h
- Determine acid content
Normal value: total HCl 10 ~ 50 u

35. Proton
pump
Alkaline
tide

36. 1.2 Effects
- turning pepsinogen into activated pepsin,
- changing the character of the protein,
- killing many swallowed virulent organisms,
- promoting absorption of ferrum and Ca2+,
- promoting secretion of pancreas and bile.
2. Pepsinogen
- It is secreted by chief cell, and is activated to the active form pepsin by HCl.
- It hydrolyzes protein molecules to form proteoses, peptones.

37. 3. Intrinsic factor
- It is a glucoprotein secreted by the parietal cell.
- It is essential to absorption of vitamin B12 in the ileum.
4. Mucus
- The surface epithelial cells of the stomach secrete a viscous mucus, they also secrete HCO3-.
- It is widely believed that mucus and bicarbonate form a mucus bicarbonate barrier.
- The mucus bicabonate barrier serves an important
role in protecting the epithelium from acid - pepsin
and other chemical insults.

39. Regulation of Gastric Secretion
1. Stimulating factor of gastric secretion
- Ach
It excites secretion of gastric secretion.
- Gastrin
G cells secrete gastrin which stimulates pariatal cells strongly and peptic cells to a lesser extent.
- Histamine( enterochromaffin like cell)
It can enhances acid secretion by stimulating
parietal cells.

40. 2. There are three phases of gastric secretion
Cephalic phase
- It is 30% of all gastric juice, HCl and pepsinogen
are higher.
- Vagus directly stimulates parietal cells and G
cell releasing gastrin.
Gastric phase
- It is 60 % of all gastic juice, HCl is high but
pepsinogen is lower than cephalic’.
Intestinal phase
- It is 10%, HCl and pepsinogen are low.

41. Cephalic
phase
Gastric
phase

43. enterochromaffin-like cell

44. 3. Inhibitory factor of gastric secretion
- Excess acid
When the pH of gastric acid falls, gastrin secretion
decrease by inhibit G cells and nervous reflex.
- Chyme ( acid in the upper intestine, protein break down products, or the irritation of the mucosa ) in the small intestine inhibits secretion.
- Hormones
Secretin, bulbogastrone, enterogastrone, gastric
inhibitory peptide are especially important in the
inhibition of gastric secretion.

45. Motor Functions of the Stomach
1. Motility in head region
- The stomach relaxes when food enters it. This is
called receptive relaxation.
- Its function is storage of food.
2. Motility in tail region
- Peristalsis:
It occurs when food enters stomach, 3 times / min.
“Retropulsion” is an important mixing mechanism
of the stomach.
- It can propels food into the duodenum.
- Migrating motility complex

46. Gastric Motility Peristaltic waves: Body  Antrum Body
Thin muscle  weak contraction
 No mixing
Antrum
Thick muscle  powerful contraction
Mixing
Contraction of pyloric sphincter 
Only small quantity of gastric content (chyme) entering duodenum
Further mixing as antral contents forced back towards body

47. C: phase of retropulsion and grinding
The contraction of the gastric pump can be differentiated into three phases:
A: phase of propulsion,
B: phase of emptying,
C: phase of retropulsion and grinding
Phase of propulsion
Phase of retropulsion
Phase of emptying
Bulge
Rapid flow of liquids with
suspended small particles
and delayed flow of large
particles towards pylorus
Emptying of liquids with
small particles whereas
large particles are retained
in the buldge of the terminal
antrum
Antrum
Retropulsion of large
particles and clearing
of the terminal antrum

48. Thin wall, holds large volumes of food by receptive relaxation
Thick wall with strong and
contraction that mix and
propel food into duodenum.
cartoon

49. 3. Empting of food:
- The food is emptied into small intestine at a rate suitable for proper digestion and absorption.
- Promoting empting factor:
Gastric factor promotes gastric emptying.
- Inhibitting empting factor:
Gastric emptying is inhibited by enterogastric reflexes from the duodenum and cholecystokinin which is released from the mucosa of the jejunum in response to fatty substances.

50. Section 4 Digestion of the Small Intestine
Pancreatic secretion
Bile secretion
Secretion of the small intestine
Movement of the small intestine

53. Pancreatic Secretion 1. Pancreatic fluid: pH 7.8 ~ 8.4, 1 ~ 2 L/day.
1.1 Digestive enzymes
- For digestion of proteins are chymotrypsin,
trypsin.
- For carbohydrates is pancreatic amylase which
hydrolyzes starches to form disaccharides.
- For fat is pancreatic lipase which hydrolyzes
neutral fat into fatty acids and monoglycerides.
1.2 Bicarbonate ions and water
They are secreted by epithelial cells of ductules.

56. Bile Secretion 1. Components:
Bile acids, cholesterol, bile salt, lecithin, bilirubin,
electroytes. Bile contains no digestive enzyme.
2. Secretion:
- Bile synthesized in the liver and is acidic as it
flows through the bile ducts, is alkalescent in
gallbladder.
- Bile is concentrated about fivefold to tenfold in
the gallbladder.

58. 3. Action of bile salts:
- promotes fat digestion (fat droplet)
- help to emulsify the large fat particles into minute particles that can be attacked by the lipase enzyme.
- promotes fat , fatsoluble vitamins absorption.
4. Regulation of bile:
- Fatty foods that enter the duodenum cause CCK to be released from the local glands.
- CCK cause rhythmical contractions of the gallbla-
dder and simultaneous relaxation of the sphincter
of Oddi.

62. Movements of the Small Intestine
1. Motility patterns
- Segment contraction
It promotes mixing of the solid food particles with
the secretions of the small intestine.
- Peristalsis
Chyme is propelled through the small intestine by peristaltic waves at a velocity of 0.5 to 2.0 cm/s.
2. Regulation
- Nervous signals are caused by the chyme into the duodenum but also by a gastroenteric reflex.
- Hormonal signals: Gastrin, CCK enhance; secretin inhibits.

66. Secretion of the Large Intestine
1. Secretion: pH
- Most of the secretion in large intestine is mucus.
- Mucus protects the intestinal wall against friction
and bacterial activity, provides the adherent
medium for fecal matter and barrier to keep acids
from attacking the intestinal wall.
2. Bacterias action
It can synthesize vitamine B ( B1, B2, B12 ), K and
folacin by ferment and decay of bacterias.

68. Section 6 Absorption in the Gastrointestinal Tract
The site of the absorption
Absorption of foods

69. The site of Absorption - in the Small Intestine
- The folds of plica, villi, and microvilli increase the
mucosal absorptive area. The total area of the
small intestinal mucosa is 250m2 about the surface
area of a tennis court.
- Foods have been digested to small molecules.
- Foods stay in small intestine for long time, about 3 to 8 hours.
- Every villi has a capillary and lymph duct, also has
smooth muscle.

75. Absorption of Foods 1. Absorption of carbohydrates
- Essentially all carbohydrates are absorbed in the
form of monosaccharides. The most abundant of
the absorbed monosaccharides is glucose which
is absorbed to blood.
- Glucose is transported by a sodium co-transport
mechanism.
- It is secondary active transport.

77. (secondary active transport)
Carbohydrate and protein absorption
(secondary active transport)
ATP
cartoon

78. 2. Absorption of proteins
- Most proteins are absorbed to blood through the membranes of the intestinal epithelial cells in the form of dipeptide, tripeptide, and a few free amino
acids.
- The energy for most of this transport is supplied by a sodium co-transport mechanism in the same way that sodium co-transport of glucose occurs.

80. 3. Absorption of fats
- Monoglycerides and fatty acids diffuse passively to the interior of the enterorocyte.
- After entering the enterocyte, the fatty acids and monoglycerides are mainly recombined to form new triglycerides.
- The reconstituted triglycerides that contain choles-terol and phospholipids. These globules are called chylomicrons which enter the lymph, then upward through the thoracic duct to be emptied into the great veins of the neck.

82. Chylomicron

85. chylomicron

87. - Sodium: active transport by Na+ pump
4. Electrolytes
- Sodium: active transport by Na+ pump
- Iron: Fe Fe2+
Except the Vitamine C, HCl can dissolved iron,
thereby helping absorption of iron.
- Ca2+
HCl can promote Ca2+ dissociate, vitamine D make Ca2+ dissolve.
Vit C

88. 5. Absorption of water ( in the large intestine)
- The proximal half of the colon is important for absorption of electrolytes and water.
- It can absorb a maximum of about 5 to 7 L of fluid
and electrolytes each day .
- It is passive and follows the absorption of osmotic
particles.