2. • Main function: the GIT provides the body with
a supply of water, nutrients, electrolytes and
vitamins.
• Actions:
• 1) Digestion of the food
• 2) Absorption of digestive products
• 3) Regulation of various functions
3. • PHYSIOLOGY OF MOUTH
• Functions:
• 1. Mechanical and chemical digestion of the food.
• Mechanical activity – mastication (chewing)
• The anterior teeth – a cutting action
• The posterior teeth – a grinding action
• Innervations of the muscles of chewing – 5th, 8th,
12th cranial nerves
• Mechanism of mastication (Chewing reflex or
Opening-jaw reflex):
4.
5. Chewing reflex :
The presence of a bolus of food in the mouth
(It compresses on the teeth surface causes
reflex inhibition of the muscles of mastication,
which causes dropping the lower jaw.
The sudden drop in turn stimulates contraction
of the jaw muscles.
This automatically raises the lower jaw to
cause closure of the teeth.
The bolus is compressed again on the teeth
surface, which allowing the jaw to drop and this
is repeated again and again.
Mastication can occur reflexively and voluntary
6. • Functions of the mastication:
• *grinding the food
• *mixing with saliva
• *prevention of excoriation of GIT
• *making easy swallowing
• *It is especially important for most fruits and
raw vegetables which have indigestible
cellulose wall and it must be broken before the
food reach the stomach.
• *It acts as a stimulus for the reflex secretion of
saliva and other GIT juice.
7. SALIVARY SECRETION
The salivary glands:
Secretion of the saliva:
-Basal :800 – 1500 ml/day
-Superadded during intake of food (8-20 folds the
basal levels).
Types of secretion:
Serous secretion containing ptyalin (a -amylase)
Mucous secretion secreted by the mucous cells
10. • Control of salivary secretion
Only nervous mechanisms by conditioned and
unconditioned reflex
No hormonal regulation is present
11. • The unconditioned reflex:
• It is an inherent reflex (not depending on
previous training or the presence of cerebral
cortex).
Stimulus:
Chemicals or
mechanical
inside the mouth
Salivary
centers
Afferent :VII,
IX and X
Sympathetic and
parasympathetic
Salivary glands
14. • Functions of saliva:
Articulation: Moistening of the buccal cavity and helps speech
Antibacterial action through:
• a- The saliva washes away the pathogenic bacteria and the
food particle.
• b- It contains antibodies that can destroy oral bacteria.
• c- Saliva also contains factors that destroy bacteria
Digestion: It has amylase can hydrolyze the starch into maltose.
Deglutition: Lubrication helps the swallowing.
Dilution : It dilutes the irritating substances
Excretion: of Some drugs as mercury, iodides
Regulation of water balance:
Regulation of body water: Dryness of the mouth stimulates thirst
receptor and increases water intake.
Regulation of oral ph:
• Regulation of body-temperature:
Solvent dissolves foods to stimulate the taste buds.
Deficiency in salivation is called xerostomia.
15. DEGLUTITION (SWALLOWING)
Definition transferring the food from the mouth
into the stomach.
Stages:
1-Oral – voluntary (First) phase:
The tongue is moved upwards and
backwards as a result of contraction of
myelohyoid muscle. Therefore, the bolus
is moved downwards into the pharynx.
.
16. 2-Pharyngeal involuntary (Second) stage:
1-The mouth cavity is shut by contraction of the
myelohyoid muscle,
2-Protective reflexes are:
a-Elevation of the soft palate to close the posterior
nares to prevent food from entering the nasal cavity.
b- Elevation of the Larynx upward and anteriorly to
be covered by epiglottis and by the vocal cord
approximation, so the opening of the larynx is
closed. To prevent passage of food into the trachea.
c- Inhibition of respiration
3-Stretches the opening of oesophagus.
4-The constrictor muscle of the pharynx-contracts to
push the food to oesophagus
17. 3- oesophageal involuntary (third) phase:
It consists of the passage of food through the
oesophagus to the stomach.
• Mechanism: two types of peristaltic movements:
1- Primary peristalsis: is a continuation of the peristaltic
wave that begins in the pharynx and spread into the
oesophagus
2- Secondary peristaltic: If the primary peristaltic wave
fails to move all the food into the stomach, secondary
peristaltic waves occurs continues until all the food
has emptied into the stomach.
18.
19. Disorders of the swallowing include:
1-dysphagia – pain during swallowing.
2-achalasia:
• It's a condition in which the food
accumulates in the oesophagus with its
dilatation.
• It's due to: 1-weak oesoph. peristalsis,
• 2-increased tonus of cardiae
3-lower oes. sphincter incompetence or
gastrooesophageal reflux
20. STOMACH
• The stomach is the most dilated part of the
alimentary canal.
Functions of gastric secretion:
1-Pepsin.
• It is a proteolytic enzyme secreted from the peptic
cells in inactive form pepsinogen and activated by
HCl to pepsin.
• Its optimum pH is 1.5-2.0.
• Pepsin hydrolyzes the proteins into peptones, and
polypeptides.
• 2-Gastric hydrochloric acid:
• Activate pepsinogen into active pepsin.
• Provides the optimum pH for the action of pepsin (pH
1:5-2.0).
• Antibacterial function.
• Important for the absorption of calcium and iron.
21.
22. • Regulation of gastric secretion
• Gastric secretion occurs in 3 phases:
• 1-Cephalic phase (Nervous):
• It occurs before food enters the stomach.
• The gastric juice secreted during the nervous phase is
copious, rich in acid, pepsin and mucin. It is about 1/10 of
the gastric secretion.
• 2-Gastric phase (hormonal phase):
• When food enters the stomach, it stimulates the secretion of
gastrin H
• Site of secretion: Pyloric (antral) mucosa.
Factors increase gastrin:
1-Distention of the stomach
2-Secretagogues: chemical substances that have the power to
stimulate secretion as: extracts of meat, vegetable extracts,
partially digested proteins (peptides and amino-acids), alcohol
and caffeine.
23. • Actions of gastrin hormone:
• -Stimulate HC1 secretion (8 folds) while increase
enzyme secretion 2-4 folds.
• Stimulate gastric motility.
• Trophic action: Stimulate the growth of the mucosa of
the stomach and small and large intestines.
• 3-Intestinal phase (humoral phase)
• The presence of food in the duodenum firstly
stimulates gastric secretion and later on inhibits
gastric secretion.
• A) Stimulation of gastric secretion during intestinal
phase is produced by:
• 1-Intestinal gastrin
• 2- Duodenal mucosa secrets entero-oxyntin
24. • B) Inhibition of gastric secretion during
intestinal phase is produced by:
• Hormonal factors as:
• Enterogastrone.
• Secretin & cholecystokinin (pancreozymin)
hormones, Gastric inhibitory peptide (GIP),
vaso active intestinal polypeptide (VIP) and
somatostatin inhibit gastric acid secretion
either by direct inhibition of parietal cells or by
inhibiting the release of gastrin hormone.
25. VOMITING
Definition: It is the outward expulsion of the gastric contents,
through the oesophagus, pharynx and mouth.
• It is controlled by the vomiting center in the medulla oblongata.
Causes of vomiting:
1-Reflex (Peripheral) vomiting:
• Stimulation of the posterior part of the tongue and soft palate or
pharynx.
• Chemical: irritation of the gastric and duodenal mucosa
• Toxic or irritant substances in food.
• Stimulation of labyrinth in rapidly changing movements of the
body (motion sickness).
• Vomiting may accompany sever pain as:
-Renal colic. -Biliary colic.
Appendicitis -Coronary thrombosis
• Intestinal obstruction or gastroenteritis.
26. • II- Central vomiting:
• Drugs as morphine and apomorphine can
directly stimulate the chemoreceptor trigger
zone and initiate vomiting.
• High altitudes.
• Increased intracranial tension.
• The morning sickness of pregnancy.
• Various psychic stimuli.
• Visual stimuli
• Head injury.
• Brain tumor.
27. • Vomiting mechanism: occurs in 4 steps:
• First step: Vomiting is preceded by unpleasant
sensation of nausea and profuse salivary secretion.
• Second step: Includes deep inspiration to decrease
intrathorax pressure, elevation of larynx to be
covered by the epiglottis and rising of palate to close
the posterior nares.
• Third step: A strong downward contraction of the
diaphragm, all of the abdominal muscle and (pelvic
floor) to raise the intragastric pressure.
• Fourth step: the large pressure difference develops
between intrathorax and intragastric + relaxation of
gastroesophageal sphincter thus allowing expulsion
of the gastric contents upward through the
oesophagus.
28. • Effect of vomiting:
1. Dehydration due to loss of water.
2. Alkalaemia due to loss of HCL.
3. Potassium depression due to potassium loss.
4. Tetany due to alkalaemia.
31. PANCREATIC SECRETION
(EXOCRINE)
Functions of pancreatic enzymes:
A) Proteolytic enzymes as:
-Trypsin & Chemotrypsin are activated by enterokinase
secreted from the duodenal mucosa- in the presence o
ca++ ions.
The optimum pH for trypsin activity is 8-9.
It converts proteins to proteoses peptones, polypeptides.
Carboxypeptidase: is activated by trypsin.
It act on C- terminal of polypeptides and release free AC.
B) Pancreatic lipase:
It converts neutral fats (triglyceride) into glycerol and fatty
acids. Bile salts accelerate its action several folds.
32.
33. • C) Pancreatic amylase:
It hydrolyzes starch. Its action is similar to
salivary amylase, but it is more powerful than
it, because it can act on cooked and uncooked
starch. Chloride ion accelerates its action.
• D) Secretion of trypsin inhibitor: prevents
the activation of all of pancreatic proteolytic
enzymes inside the pancreas until they are
secreted in the intestine.
• Prevention of autodigestion
34. Regulation of pancreatic Secretion
• I- The nervous control:
• by vagus stimulation (vagus juice) is very rich
in enzyme.
• II- The hormonal control:
• A- Secretin:
• Site of secretion: Mucosa of the duodenum
and jejunum in an inactive form prosecretin.
• Stimulus: Acids and digested protein cause
release of prosecretin and its activation to
secretin.
• It stimulates secretion of juice rich in alkali.
35. • Other Functions of secretin:
• Helps to neutralize the acid chym in the
duodenum.
• The bicarbonate secretion provides a suitable
pH for the action of the pancreatic enzyme.
• Decreases gastric acid secretion and motility.
• Increase the intestinal motility.
• Increases bile secretion by the liver.
• Stimulates mucous secretion from the
duodenum that helps in neutralization of HCl.
• Trophic action: Stimulate the growth of the
mucosa of the stomach and small and large
intestine
36. • B) Cholecystokinin:
• Site of secretion: Duodenal and jejunal mocosa.
Stimulus: contact of fats and partial digested
protein stimulates its secretion. Then it reaches the
pancreas through its arterial supply to stimulate the
secretion of juice rich in enzymes.
Other functions:
• Stimulate gall bladder evacuation.
• Inhibit gastric emptying.
• increase secretion of enterokinase.
• Increase motility of the small intestine and colon.
37. I-Bile salts
• Functions of bile salts:
• 1-Digestion: They aid the emulsification of fat
by decreasing the surface tension of fat
globules and breaks them into fine particles.
Therefore, the surface area increased.
38.
39.
40. • 2-Absorption: Bile salts are important for the
absorption of fatty acids and fat soluble
vitamins.
• 3-Choleretics: Bile salts are the best stimulant
of bile secretion by the liver.
• 4-Solvents: They help to keep cholesterol in
solution. So, they prevent their precipitation in
the gall bladder and the formation of gallstone.
• 5-Stimulant of peristalsis: Bile salts stimulate
the movement of small and large intestine.
• 6- Anti-putrefactive: This effect is secondary
to stimulation of fat absorption.
41. Functions of gall bladder
1- Storage of bile: Bile is continually secreted by the liver cells.
The sphincter of odd is closed in between meals and so bile
passes from hepatic to cystic duct to be stored into bladder until
needed in the duodenum.
2- Concentration of bile: The total secretion of bile is 1-1.5
liter/day and the maximum volume of the gall bladder is 60 ml.
During the storage of bile water chloride sodium and
bicarbonate are absorbed by the gall bladder mucosa while bile
salt, bile pigments, and cholesterol: are concentrated up to 10
times.
3- Acidification of liver bile: The absorption. of Naco3 by the gall
bladder causes the pH of liver bile (pH: 8-8.6) to be less
alkaline (pH: 7). This prevents precipitation of calcium
4- Equalization of pressure Concentration of bile decreases the
pressure in the biliary passages because the hepatic cells can
not secrete against a high pressure.
5- Secretion of mucus white milk. The gall bladder secretes from
its mucous surface a large quantity of mucus helps to protect
the mucosa of gall bladder and ducts from highly concentrated
bile.
42.
43. JAUNDICE
Definition: jaundice means a yellow colouration
of the sclera, mucous membrane, deep tissues
and skin caused by hyperbilirubinemia.
44.
45. SMALL INTESTINE
• Functions of small intestine:
• Digestion: completes the process of digestion
of food mainly in the upper half of small
intestine, through secretion of succus entericus
by crypts of Lieberkun.
• Absorption: Absorption of digestive products
mainly in the lower half of small intestine.
• Secretion: Secretion of hormones.
• Intestinal motility: For propagation of food and
for helping digestion and absorption
46. • Functions of large intestine:
• 1- Absorption: of the water and electrolytes are absorbed
in the proximal colon..
2- Secretion: of mucin that responsible for:
• - Neutralization acids produced by bacterial fermentation.
• - Protection the mucosa.
• - Binding the fecal particles together.
• - Lubrication the feces.
• Mucin is secreted in response to the mechanical or chemical
irritation.
3- Bacterial action: synthesize the following:
• Vitamins: Vitamin K, vitamin B12, thiamin and riboflavin.
• Gases that causes the flatus in the colon.
• 4- Storage of feces: Stools are stored in the pelvic colon till
the time of defecation.
