Secretory Function of Alimentary Tract Digestive juice: 1. Saliva 2. Gastric juice 3. Intestinal juice 4. Pancreatic juice 5. Bile

1. DIGESTION
Digestive juice secretions
Md. Saiful Islam
Dept. of Pharmaceutical Sciences
North South University
Facebook Group: Pharmacy Universe
YouTube Channel: Pharmacy Universe

2. Secretory Function of Alimentary Tract
Digestive juice:
• 1. Saliva
• 2. Gastric juice
• 3. Intestinal juice
• 4. Pancreatic juice
• 5. Bile

3. Salivary Glands; Characteristics of Saliva.
• Salivary Glands; Characteristics of Saliva.
• The principal glands of salivation are the parotid,
submandibular, and sublingual glands; in addition, there are
many very small buccal glands.
• Daily secretion of saliva normally ranges between 800 and
1500 milliliters,
• Saliva contains two major types of protein secretion: (1) a
serous secretion that contains ptyalin (an a-amylase), which
is an enzyme for digesting starches, and (2) mucus secretion
that contains mucin for lubricating and for surface protective
purposes.
• The parotid glands secrete almost entirely the serous type of
secretion, while the submandibular and sublingual glands
secrete both serous secretion and mucus.
• The buccal glands secrete only mucus. Saliva has a pH
between 6.0 and 7.0, a favorable range for the digestive
action of ptyalin.

4. Function of Saliva for Oral Hygiene.
• Under basal awake conditions, about 0.5 milliliter of saliva, almost entirely of the
mucous type, is secreted each minute; but during sleep, secretion becomes very
little.This secretion plays an exceedingly important role for maintaining healthy oral
tissues. The mouth is loaded with pathogenic bacteria that can easily destroy tissues
and cause dental caries. Saliva helps prevent the deteriorative processes in several
ways.
• First, the flow of saliva itself helps wash away pathogenic bacteria as well as food
particles that provide their metabolic support.
• Second, saliva contains several factors that destroy bacteria. One of these is thiocyanate
ions and another is several proteolytic enzymes—most important, lysozyme—that (a)
attack the bacteria, (b) aid the thiocyanate ions in entering the bacteria where these
ions in turn become bactericidal, and (c) digest food particles, thus helping further to
remove the bacterial metabolic support.
• Third, saliva often contains significant amounts of protein antibodies that can destroy
oral bacteria, including some that cause dental caries. In the absence of salivation, oral
tissues often become ulcerated and otherwise infected, and caries of the teeth can
become rampant.

5. Composition
A. Water: 99.5%
B. Solid:0.5%
1. Organic
• Enzyme (Ptyalin, Lysosome)
• Mucin
• Urea
• Cholesterol
• Amino acid
2. Inorganic
( Various ion)
3. Cellular constituent
(Yeast, bacteria)
4. Gases (N2, O2)

6. Function:
• It keeps the mouth moist and helps in speech.
• It facilitates swallowing
• It helps in preparing food stuff into bolus
• It acts as a lubricant
• By dissolving food stuff, saliva helps in taking the taste of food.
• It breaks down boiled starch into maltose due to the presence of
enzyme ptyalin.
• It excretes urea heavy metals, certain drugs.
• It helps in acid-base balance
• It has bacteriolytic property

7. Structure of stomach
The stomach is an expanded section of the
gastrointestinal tract between the esophagus and the
duodenum of the small intestine.
• The stomach is on the left side of the abdominal cavity
with the most superior part laying against the diaphragm
• The major regions of the stomach are the cardia, fundus,
body and the pylorus.
• Additionally it has the greater and lesser curvatures, which
are the right and left sides of the stomach, respectively.
• The esophageal sphincter is contained within the cardia
region. The esophageal sphincter controls the flow of
material coming into the stomach.
• The fundus is the section of the stomach that is formed by
the upper curvature .
• the body is the main area of the stomach.
• The final part of the stomach is the antrum where the
pylorus, the exit of the stomach and entrance to the
duodenum of the small intestine is located.
• Within the pylorus is the pyloric sphincter that controls
what leaves the stomach into the duodenum.

8. Gastric Anatomy

9. • The inside of the stomach is composed of four layers,
from the innermost layer to the outermost layer:
• muscosa, submuscosa, muscularis externa, and the
serosa.
• The muscosa is where stomach acid is produced and
secreted into the stomach.
• The submuscosa is layer composed of connective
tissue that separates the muscosa from the
muscularis externa.
• The muscularis externa is composed of three layers
of smooth muscle: inner oblique, middle circular, and
outer longitudinal. These are the muscles that are
primarily responsible for mixing material that has
come into stomach with digestive enzymes and
moving the material through the stomach.
• The final layer is the serosa, which is a layer of
connective tissue that attaches and is continuous
with the peritoneum, the lining of the abdominal
cavity.

10. • There are three types of gastric gland present in the stomach:
1. Cardiac gland: Mucus secreting cell
2. Gastric gland or oxyntic gland:
a. Mucus neck cell: Secrets mainly mucus but also some pepsinogen
b. Peptic/Chief cell: Secret large quantities of pepsinogen, gastric renin.
c. Parietal/Oxyntic cell: Secret HCl and intrinsic factor.
d. Enterochromaffin like cell: Secret gastrin and histamin
3. Pyloric gland: secret mucin and hormone gastrin
Gastric secretion

11. Gastric Glands and secretions

12. Composition and function of gastric secretions
1. HCl
 converts pepsinogen to pepsin for chemical digestion
 provides optimal pH environment for pepsin
 destroys some bacteria
 stimulates the small intestinal mucosa to release
secretin and CCK (Cholecystokinin from Greek chole,
"bile"; cysto, "sac"; kinin, "move) is a peptide hormone
of the gastrointestinal system responsible for stimulating
the digestion of fat and protein)
 promotes the absorption of Ca2+ and Fe2+ in small
intestine

13. 2. Pepsinogen (precursor of pepsin)
 digestion of proteins
3. Mucus
 forms a protective barrier: Mucus-bicarbonate
barrier
4. Intrinsic factor
 combines with vitamin B12 to make it
absorbable
5. Gastrin
Stimulates gastric acid secretion
6. Histamine
Stimulates gastric acid secretion

14. Gastric acid secretion
• The Figure shows schematically
the functional structure of a
parietal cell (also called oxyntic
cell), demonstrating that it
contains large branching
intracellular canaliculi. The
hydrochloric acid is formed at
the villus-like projections inside
these canaliculi and is then
conducted through the
canaliculi to the secretory end
of the cell.

15. The chemical mechanism of hydrochloric
acid formation consists of the following
steps:
1.Chloride ion is actively transported from the
cytoplasm of the parietal cell into the lumen of
the canaliculus, and sodium ions are actively
transported out of the canaliculus into the
cytoplasm of the parietal cell.
These two effects together create a negative
potential of -40 to –70 millivolts in the
canaliculus, which in turn causes diffusion of
positively charged potassium ions and a small
number of sodium ions from the cell cytoplasm
into the canaliculus. Thus, in effect, mainly
potassium chloride and much smaller amounts
of sodium chloride enter the canaliculus.
2. Water becomes dissociated into hydrogen ions
and hydroxyl ions in the cell cytoplasm.
The hydrogen ions are then actively secreted
into the canaliculus in exchange for potassium
ions: this active exchange process is catalyzed
by H+,K+- ATPase.

16. In addition, a separate sodium pump actively
reabsorbs the sodium ions. Thus, most of the
potassium and sodium ions that had diffused into
the canaliculus are reabsorbed into the cell
cytoplasm, and hydrogen ions take their place in
the canaliculus, giving a strong solution of
hydrochloric acid in the canaliculus.
The hydrochloric acid is then secreted outward
through the open end of the canaliculus into the
lumen of the gland.
3. Water passes into the canaliculus by osmosis
because of extra ions secreted into the
canaliculus. Thus, the final secretion from the
canaliculus contains water, hydrochloric acid,
potassium chloride and a small amount of sodium
chloride.
4. Finally, carbon dioxide, either formed during
metabolism in the cell or entering the cell from
the blood, combines under the influence of
carbonic anhydrase with the hydroxyl ions (from
step 2) to form bicarbonate ions. These then
diffuse out of the cell cytoplasm into the
extracellular fluid in exchange for chloride ions
that enter the cell from the extracellular fluid and
are later secreted into the canaliculus.

18. Secretion and Activation of Pepsinogen
Several slightly different types of pepsinogen are secreted by the
peptic and mucous cells of the gastric glands.
When pepsinogen is first secreted, it has no digestive activity.
However, as soon as it comes in contact with hydrochloric acid, it is
activated to form active pepsin.
In this process, the pepsinogen molecule, having a molecular weight
of about 42,500, is split to form a pepsin molecule, having a
molecular weight of about 35,000.
Pepsin functions as an active proteolytic enzyme in a highly acid
medium (optimum pH 1.8 to 3.5), but above a pH of about 5 it has
almost no proteolytic activity and becomes completely inactivated in
a short time.
So, Hydrochloric acid is as necessary as pepsin for protein digestion in
the stomach;

19. Secretion of Intrinsic Factor.
• The substance intrinsic factor, essential for absorption of
vitamin B12 in the ileum, is secreted by the parietal cells
along with the secretion of hydrochloric acid.
• If the acid-producing parietal cells of the stomach are
destroyed, which frequently occurs in chronic gastritis, the
person develops not only achlorhydria (lack of stomach
acid secretion) but often also pernicious anemia because
of failure of maturation of the red blood cells in the
absence of vitamin B12 stimulation of the bone marrow.

20. Pyloric Glands—Secretion of Mucus
and Gastrin
• The pyloric glands are structurally similar to the oxyntic glands
but contain few peptic cells and almost no parietal cells.
• Instead, they contain mostly mucous cells that are identical
with the mucous neck cells of the oxyntic glands.
• These cells secrete a small amount of pepsinogen, and an
especially large amount of thin mucus that helps to lubricate
food movement, as well as to protect the stomach wall from
digestion by the gastric enzymes.
• The pyloric glands also secrete the hormone gastrin, which
plays a key role in controlling gastric secretion.

21. Regulation of Pepsinogen Secretion
• Regulation of pepsinogen secretion by the peptic cells in the oxyntic
glands is much less complex than regulation of acid secretion; it
occurs in response to two types of signals:
1) stimulation of the peptic cells by acetylcholine released from the
vagus nerves or from the gastric enteric nervous plexus, and
2) stimulation of peptic cell secretion in response to acid in the
stomach. Therefore, the rate of secretion of pepsinogen, the
precursor of the enzyme pepsin that causes protein digestion, is
strongly influenced by the amount of acid in the stomach.
In people who have lost the ability to secrete normal amounts of acid,
secretion of pepsinogen is also decreased, even though the peptic
cells may otherwise appear to be normal.

22. Regulation of gastric secretion :Phases of Gastric Secretion
1. Cephalic Phase
2. Gastric Phase
3. Intestinal Phase

23. 1. The taste or smell of food, tactile
sensations of food in the mouth, or
even thoughts of food stimulate the
medulla oblongata (green arrow).
2. Parasympathetic action potentials
are carried by the vagus nerves to
the stomach (pink arrow).
3. This impulse stimulate
secretion by parietal and chief cells
and stimulate gastrin secretion by
endocrine cells.
5. Gastrin is carried through the
circulation back to the stomach
(purple arrow), where it stimulates
secretion by parietal and chief cells.
Cephalic Phase
Gastrin
Circulation
Secretions
stimulated
Taste or smell of food
Tactile sensation in mouth
Medulla oblongata
Vagus nerves
Stomach
1
2
3
5
4
Regulation of gastric secretion :Phases of Gastric Secretion

24. The taste or smell of food, tactile sensations of food in the mouth, or even thought of
food sends nerve signals to the medulla oblongata (green arrow).
Taste or smell of food
Tactile sensation in mouth
Thought of food
Medulla oblongata
Cephalic Phase

25. Parasympathetic action potentials are carried by the vagus nerves to the
stomach (pink arrow).
Vagus nerves
Cephalic Phase

26. Cephalic Phase
This impulse stimulate secretion by parietal and chief cells and stimulate gastrin
secretion by endocrine cells.
Gastrin
Stomach

27. Cephalic Phase
Gastrin is carried through the circulation back to the stomach (purple arrow), where it
stimulates secretion by parietal and chief cells.
Gastrin
Circulation
Secretions
stimulated

28. Cephalic Phase:Summary
• Stimulated by sight, smell, and taste
of food.
• Activation of vagus:
– Stimulates chief cells to secrete
pepsinogen.
– Directly stimulates G cells to
secrete gastrin.
– Directly stimulates ECL cells to
secrete histamine.
– Indirectly stimulates parietal
cells to secrete HCl.
• Continues into the 1st 30 min. of a
meal.

29. Stomach
Local reflexes
stimulated by
stomach distention
Distention
Secretions
stimulated
Vagus nervesMedulla
oblongata
1. Distention of the stomach activates a
parasympathetic reflex. Action potentials
are carried by the vagus nerves to the
medulla oblongata (green arrow).
2. The medulla oblongata stimulates stomach
secretions (pink arrow).
3. Distention of the stomach also activates
local reflexes that increase stomach
secretions (purple arrow).
Gastric Phase
1
2
3

30. Local reflexes
stimulated by
stomach distention
Distention
Vagus nervesMedulla
oblongata
Distention of the stomach activates a parasympathetic reflex. Action potentials are
carried by the vagus nerves to the medulla oblongata (green arrow).
Gastric Phase
Stomach

31. Gastric Phase
Secretions
stimulated
The medulla oblongata stimulates stomach secretions (pink arrow).
Vagus nerves
Stomach
Decreased
gastric
secretions

32. Gastric Phase
Local reflexes
stimulated by
stomach distention
Distention of the stomach also activates local reflexes that increase stomach
secretions (purple arrow).
Stomach
Distention

33. • Arrival of food in stomach stimulates
the gastric phase.
• Gastric secretion stimulated by:
– Distension.
– Chemical nature of chyme (amino acids
and short polypeptides).
• Stimulates G cells to secrete gastrin.
• Stimulates chief cells to secrete
pepsinogen.
• Stimulates ECL cells to secrete
histamine.
– Histamine stimulates secretin of
HCl.
Gastric Phase

34. 1. Chyme in the duodenum with
a pH less than 2 or containing
fat digestion products (lipids)
inhibits gastric secretions by
three mechanisms.
2. Sensory vagal action potentials
to the medulla oblongata
(green arrow) inhibit motor
action potentials from the
medulla oblongata (pink arrow).
3. Local reflexes inhibit gastric
secretion (orange arrows).
4. Secretin, gastric inhibitory
polypeptide, and cholecystokinin
produced by the duodenum
(brown arrows) inhibit gastric
secretions in the stomach.
Intestinal Phase
Secretin, gastric inhibitory
peptide, cholecystokinin
Circulation
pH<2
or lipids
Local
reflexes
Decreased
gastric
secretions
Medulla oblongata
Vagus
nerves
Vagus
nerves
1
2
3
4

35. Chyme in the duodenum with a pH less than 2 or containing fat digestion
products (lipids) inhibits gastric secretions by three mechanisms.
pH<2
or lipids
Intestinal Phase

36. Intestinal Phase
They cause impulses to go to the medulla oblanga to decrease parasympathetic
stimulation of the gastric glands.
pH<2
or lipids
Medulla
oblongata
Vagus
nerves
Vagus
nerves
Mechanism One
Decreased
gastric
secretions

37. Intestinal Phase
Secondly they set up local reflexes, via neuron in the wall of the gut,
that inhibit gastric secretion (orange arrows).
pH<2
or lipids
Local
reflexes
Decreased
gastric
secretions
Mechanism Two

38. Thirdly, they cause the release of 3 local hormones: Secretin, gastric inhibitory
polypeptide, and cholecystokinin from the duodenum (brown arrows) which
travel via circulation to the gastric gland and inhibit gastric secretions in the
stomach.
Secretin, gastric inhibitory
peptide, cholecystokinin
pH<2
or lipids
Decreased
gastric
secretions
Circulation
Mechanism Three
Intestinal Phase

39. Control Of Gastric
Secretions: The
Intestinal Phase

40. 3.Pancreatic juice
Composition
A.Water: 98.5%
B.Solid:1.5%
a. Organic:
i. Proteolytic enzyme: Trypsin,chemotrypsin
ii. Carbohydrate splitting enzyme: Pancreatic amylase
iii. Fat splitting enzyme: Pancreatic lipase,phospholipase
b. Inorganic: Various ions
• Function:
1. Due to the presence of high concentration of different enzyme,
pancreatic juice digest all three types of food-Proteins,
carbohydrate and fats.
2. Pancreatic juice contain large quantities of bicarbonate which
plays an important role neutralizing the acid emptied by the
stomach into the duodenum

41. 4. Intestine Juice
Composition
I) Water – 98.5%
II) Solid – .5%
a) Inorganic e.g. Na+, K+, Ca++ etc.
b) Organic-Various enzymes
-Mucin
Functions:
• It helps in digestion of food like protein, fat, carbohydrate.
• Due to the presence of mucin, it protects intestinal mucosa.
• Due to its abundant water content it-
-helps in the transport of food particles, ready for absorption.
-provides the ready supply of water, needed for hydrolysis of food
particles.
-dissolves substances like vitamins.
-It helps in water balance
-It helps in absorption.

42. 5. BILE
Functions of Bile
• Digestive function:
– Bile helps in the digestion of fat and to a lesser extent
of proteins and carbohydrate.
• Absorptive function:
– Bile helps in the absorption of fat and other
substances like fat soluble vitamins, iron, Ca++ etc.
– Laxative function: Bile salts increases peristalsis and
thereby help in defecation.

43. THANK YOU