DIGESTION OF
ORAL CAVITY
AND STOMACH
1
ORAL CAVITY
PHYSIOLOGICAL EVENTS
1. Ingestion
2. Mechanical digestion
3. Chemical digestion
4. Propulsion voluntary stage of
swallowing
2
ORAL CAVITY
1. Ingestion of food is
simply voluntarily taking
food into the digestive
tract through the oral
cavity.
3
ORAL CAVITY
2. MECHANICAL PROCESSES
Mastication
As food enters the oral cavity the
cheeks and the closed lips hold
food between the teeth, the
tongue mixes the food with saliva
to soften it, and the teeth cut and
grind it into a bolus. Suitable for
swallowing
Mastication is both voluntary and
partly reflexive.
4
ORAL CAVITY
3. Chemical processes
Chemical digestion of starch is begun by salivary amylase present in saliva.
Saliva (1-1,5 liters per day) is a slightly acid solution of salts and organic
substances secreted mainly by 3 pairs of salivary glands (parotid, buccal,
submandibular glands).
Basic saliva components:
• Water 99.5%
• Ions: Na+, K+, Ca2+, Cl–, HCO3–
• Proline-rich proteins for protection of teeth enamel:
- Enzymes: ptyalin (from salivary glands),
**lingual lipase (secreted from glands on the tongue).
- Immunoglobolins: IgA
- Mucin: glycoproteins for lubrication of food and protection of oral mucosa
- Lysozyme, lactoferrin, thiocyanate ions
pH of saliva is about 7
Salivary flow ranges between 0.5 ml/min during basal flow and 5ml/min during
maximum flow
5
ORAL CAVITY
Other important (non-digestive) functions of saliva:
 Cleansing – Mouth and teeth kept free of debris, ect.
 Protection – Leucocytes, the enzyme lysozyme and
antibodies act against some bacteria.
 Moistening and Lubricating – soft parts of mouth
kept pliable for speech. Cells of oral mucosa
protected from drying.
 Excretory – many organic substance (e.g. urea,
sugar) and inorganic substance (e.g. mercury, lead)
can be excreted in saliva.
6
ORAL CAVITY
4. PROPULSION
The voluntary phase of
deglutition is initiated
by the tongue. The tip
of the tongue is place
on the hard palate, and
then contracts which
forces the bolus into
the oropharynx.
7
Cerebral cortex
Salivary center
in medulla
Other inputs
Conditioned
reflex
Autonomic nerves
Pressure receptors
and chemoreceptors
in mouth
Simple reflex
Autonomic nerves
Salivary glands
Salivary secretions 8
PHARYNX
PHYSIOLOGICAL EVENTS
1. Chemical digestion
Carbohydrate digestion continues. This is due
to fact that the pH of the pharynx is slightly
acid to neutral as is the oral cavity.
No other marcomolecule begins chemical
digestion.
9
PHARYNX
2. PROPULSION
The pharyngeal phase of deglutition
is initiated by food in the
oropharynx. The presence of food
causes the tongue to blocks off
the oral cavity, the soft palate to
rise and close off the
nasopharynx.
In addition, the larynx to rise so that
the epiglottis covers the opening
into the respiratory system, and
the upper esophageal sphincter to
relax and open.
10
Esophagus

Bolus (moistened ball of chewed up
food) is forced into the pharynx.
 The epiglottis prevents food from
entering the trachea during
swallowing, and passes bolus into the
esophagus
 The esophagus is a muscular tube
that connect pharynx to the stomach.
 The series of rhythmic contractions &
relaxations is called peristalsis.
Peristalsis pushes the bolus through
the esophagus into the stomach.
11
The Swallowing Process
Is also called deglutition
Can be initiated voluntarily, Proceeds automatically
Is divided in 3 phases:
buccal phase – Compression of bolus against hard palate, Retraction of
tongue forces bolus into oropharynx:
pharyngeal phase – Bolus contacts: arches and posterior pharyngeal
wall
esophageal phase - Contraction of pharyngeal muscles forces bolus
through entrance to esophagus Primary Peristaltic Waves
12
STOMACH

3 muscle layers: oblique, circular, longitudinal
 Regions:




Cardiac sphincter
Fundus
Antrum (pylorus)
Pyloric sphincter

Vascular
 Inner surface thrown into folds – Rugae

Contains enzymes that work best at pH 1-2
13
Functions of stomach



Mix food
Reservoir
Start digestion of
- Protein
- Nucleic acids
- Fats




Activates some enzymes
Destroy some bacteria
Makes intrinsic factor – B12 absorption
Absorbs
- Alcohol
- Water
- Lipophilic acid
- B12
14
Exocrine gastric glands

Golbet cells
mucus;
 Pariental cells
hydrochloric acid (HCl);
 Chief (or zymogenic) cells
pepsinogen,



an inactive form of the protein-digestive enzime pepsin;
Enterochromaffin-like (ECL) cells
histamine and serotonin
as paracrine regulalators of the GI tract;
G cells
gastrin into the blood;
D cells
hormone somatostatin.
15
STOMACH

Mechanical digestion


The walls of the stomach have several muscle
layers. These muscles work together to churn
the food, breaking up food particles and mixing
them with gastric fluid. This results in a mixture
called chyme. Chyme moves from the stomach
to the small intestine.
Gastric glands release gastric juice, a mixture of
mucus, digestive enzymes, and hydrochloric acid.
16
STOMACH

Gastric fluid carries out chemical
digestion in the stomach



Hydrochloric acid ensures a low pH
in the stomach, dissolves minerals
and kills bacteria
An enzyme called pepsin begins the
break down of proteins into peptide
chains (chains of amino acids).
Pepsin functions in a pH of about 2.
Mucus coats the stomach and
protects it from HCl & digestive
enzymes
• When the mucus coating breaks down
allowing digestive enzymes to eat
through part of the stomach lining, the
result is called an ulcer.
17
STOMACH
PROPULSION
After a meal, peristalsis begins
near the cardiac region and
moves toward the pyloric
sphincter. The intensity of the
movements are due to the
increase in the number of
muscle layers of the stomach.
18
STOMACH
The pyloric region of the
stomach holds about 30 ml of
chyme. It allows only liquids
and small particles of chyme,
about 3 ml, to pass through
the valve for each peristaltic
wave. The contractions of
the pylorus decrease the
opening of the valve. This
results in the remaining
chyme being remixed again
and again.
19
STOMACH
The rate of peristaltic waves
is constant 3/min., however,
the intensity can be modified.
This contractile rhythm is set
by the spontaneous activity of
pacemaker cells located in the
longitudinal smooth muscle
layer. This cells establishes
the basic electrical rhythm of
the stomach.
20
STOMACH
The stomach usually
empties completely
within 4 hours after a
meal. The rate of
gastric emplying
depends on the
contents of the
duodenum as on what
is happening in the
stomach.
21
Mechanism for secretion of
hydrochloric acid
Extracellular
fluid
Pariental cell
Lumen of canaliculus
22
Stomach neurological control
23
Stomach neurological control
1. CEPHALIC PHASE
Slight, thought, taste, or
smell of food causes
stimulation of the vagus.
The vagus stimulates
the production of gastric
juice.
24
Stomach neurological control
2. GASTRIC PHASE
Vagovagal
VAGOVAGAL
REFLEX
reflex
Stomach distention
will act locally or
evoke the
vagovagal reflex.
25
Stomach neurological control
3. INTESTINAL PHASE
26
27
Stomach hormonal control
MECHANICAL DIGESTION
1. Gastrin--stimulate gastric emptying
2.
3.
4.
5.
Serotonin--contraction ofsmooth muscle
Somatostatin--inhibits motility and emptying
Secretin--inhibits gastric motility
Gastric Inhibitory Peptide--inhibits gastric
motility
28
Stomach hormonal control
CHEMICAL DIGESTION
1.
2.
3.
4.
5.
Gastrin--stimulates gastric secretions
Histamine--stimulates HCl formation
Somatostatin—inhibits gastric secretions
Secretin--inhibits gastric secretions
Gastric inhibiory peptide--inhibits gastric
secretions
6. Vasoactive intestinal peptide-inhibits HCl
production
29
Stomach hormonal control
PROPULSION
1. Gastrin--stimulates emptying
2. Somatostatin--inhibits gastric motility and
emptying
3. Secretin--inhibits gastric motility and
emptying
4. Gastric Inhibitory Peptide—inhibits gastric
motility and emptying
30
Mouth
break up food
digest starch
kill germs
moisten food
Stomach
break up food
digest protein
kill germs
store food
31