Pharynx Esophagus and Stomach Part 2

Digestive System
Tanveer Saeed
Assistant Professor
AKU-SONAM
Pharynx
• 12-14 cm long
• Extends from the
base of the skull to
the level of 6th.
cervical vertebra.
Divided into three
parts:
• Nasopharynx
• Oropharynx
• Laryngopharynx
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Structure of Pharynx
Pharynx composed of three layers:

1. Mucosa varies slightly in different parts:
• Nasopharynx lined by ciliated columnar
epithelium.
• Oro and laryngopharynx, mucosa is formed
by squamous epithelium.
2. Fibrous tissue: middle layer
3. Muscle tissue: consists of several
involuntary constrictor muscles help in
deglutition or swallowing.
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Esophagus
• about 25 cm long,2 cm
wide extends from
pharynx to stomach.
• It lies in the median plan
in the thorax in front of the
vertebral column behind
the trachea and the heart.
• upper esophageal or
Cricopharyngeal
sphincter,regulatesfood
passing from
laryngopharynx to
esophagus
• LOS or cardiac sphincter
prevents regurgitation
from stomach to
esophagus.
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Lower esophageal sphincter controls the passage into the stomach and
only opens up when the peristaltic wave reaches this sphincter
Heart burn occurs when gastric juices regurgitate into the esophagus
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General Plan for Esophagus
The layers of the esophagus are as follows:
1. mucosa
– nonkeratinized stratified squamous epithelium
– lamina propria
– muscularis mucosae: smooth muscle
2. submucosa: Contains the mucous secreting glands

(esophageal glands).
3. muscularis externa (or "muscularis propria"): composition

varies in different parts of the esophagus, to correspond with
the conscious control over swallowing in the upper portions
and the autonomic control in the lower portions:
– upper third, or superior part: striated muscle
– middle third, smooth muscle and striated muscle,
4. adventitia
Functions of the Esophagus
• Food is passed through
the esophagus by
using the process of
peristalsis.
• The esophagus is
deeply lined with
muscle that acts with
peristaltic action to
move swallowed food
down to the stomach.
• Acid Reflux is also known as:
Gastroesophageal reflux or heart burn.
• You may feel a burning in the chest or throat
called heartburn. Sometimes, you can taste
stomach fluid in the back of the mouth. This is
acid indigestion. If you have these symptoms
more than twice a week, you may have
GERD.
Esophagus and Swallowing Reflex
• The swallowing reflex is coordinated by the medulla oblongata,
which stimulates the appropriate sequence of contraction and
relaxation in the participating skeletal muscle, sphincters, and
smooth muscle groups.
• Swallowing = deglutination
Three phases
• Buccal Phase
• Pharyngeal Phase
• Esophageal Phase
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The swallowing reflex is coordinated by the medulla oblongata, which
stimulates the appropriate sequence of contraction and relaxation in the
participating skeletal muscle, sphincters, and smooth muscle groups.
Buccal Phase
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Pharyngeal Phase Esophageal Phase
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Structure of Stomach
• J-shaped
• Located in
epigastric, umbilical
and left
hypochondriacregio
ns of the AC.
• Enlarged segment of
digestive tract.
• Lesser curvature
• Greater curvature
• Pyloric sphincter
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Stomach
Stomach consists of four parts:
• Cardiac / Cardia: Surrounds the superior • Enlarged segment of digestive

opening of the stomach. tract.
• Fundus: Rounded portion above and to • Stores up to 2 liters of food.
the left of the cardia.
• Gastric glands within the
• Body: Large central portion.
stomach produce secretions
• Pylorus: Inferior part of stomach called gastric juice.
connects to the duodenum.
• The muscular walls of the
• Pyloric Sphincter: Guards exit from stomach contract vigorously to
stomach
mix food with gastric juice,
producing a mixture called
chyme.
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Histology of the Stomach
Specialized cells in the lining of the stomach synthesize and secrete

mucous fluid, enzyme precursors, hydrochloric
Tanveer Saeed acid, and hormones.
The Layers of the Stomach
• Serous layer – the visceral layer of the peritoneum is
the outermost.
• Muscular layer – this consists of smooth muscle fibers,
the outer being longitudinal, the middle being circular and
the inner being oblique.
• Sub mucous layer – this is composed of loose areolar
tissue.
• Mucous membrane – this is honeycombed in
appearance because of the presence of the gastric
glands and their openings.
• The mucous membrane has numerous folds, called
rugae, which run longitudinally and which flatten out
when the stomach is full.
• The mucus secreted by the goblet cells helps to lubricate
the food.
The Stomach
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Layers of Stomach
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Stomach
• Rugae are the extensive folds in the
stomach lining in relaxed stomach that
allow for expansion and increases surface
area for digestion.
• These folds can stretch to accommodate
an increase in stomach volume with
consumption of a meal.
• They also help direct the food downward
toward the pylorus as a result of stomach
motility.
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Gastric Juice
Composition: 2-3 L
(2000ml- 3000ml)
• Water
• Mineral Salts
• Mucus
• Hydrochloric acid (Hcl)
• Intrinsic factor (protein
compound)
• Inactive enzyme
precursor pepsinogen
• Mucus cells secrete
mucus
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• Hcl secreted by parietal /
oxyntic cells
zymogen (chief) cells release Functions of Stomach
*pepsinogen and Food storage
*(Inactive enzyme precursor) Mixing of food with gastric juice yielding
chyme.
Chemical digestion of proteins.
• Intrinsic factor secreted by Mechanical digestion ( Churning)
cells in gastric glands. Nonspecific immune defense.
Secretion of intrinsic factor.
Onward movement of the contents to the
• Pepsinogen is converted by
pyloric end of the stomach.
HCl into pepsin ---- acts on
proteins and converts them
to polypeptided.
Pepsin: pH 1.5 ----- 3.5
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Function of Hydrochloric Acid
• Dissolves the food fibers
• Kills microorganisms
• Activate enzyme pepsin
• Acidifies the food and stops the action of

salivary amylase
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REGULATION OF GASTRIC SECRETION
The important stimulatory signals are :

• Autonomic nerves
• Release acetylcholine (Ach) Stimulates
smooth muscle contraction, also
stimulates chief and parietal cells.
Tanveer Saeed
REGULATION OF GASTRIC SECRETION
Three phases are recognized :
• Cephalic phase prepares stomach to
receive ingested material.
• Gastric phase begins with the arrival of
food in the stomach.
• Neural, hormonal, and local responses
• Intestinal phase controls the rate of
gastric emptying.
Tanveer Saeed
Tanveer Saeed
Cephalic Phase
• Occurs before food enters
the stomach; initiated by
smell, taste,sight, thought
(conditioned reflex ).
• Impulses from olfactory,
chemical and other receptors
activate the vagal nuclei in the
medulla (via Hypothalamus)
• This triggers motor impulses to
travel via the vagus nerve to
the parasympathetic
submucosal plexus this in turn
stimulate stomach glands
( gastric glands) •
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Gastric Phase
• Starts when food reaches the

stomach and responsible for
2/3 of the juice released.
• An increase in pH (thus, ‘less’
acidity), presence of
peptides,caffeine, alcohol,
activates the G-cells
• This results in Gastrin being
released. Gastrin, being a
hormone, needs to enter the
blood stream and return to the
stomach before it can act.
• Gastrin acts on parietal cells
that start secreting HCl.
• The increase in HCl promotes
pepsin production and protein
degradation.
Tanveer Saeed
Intestinal Phase
• Food in duodenum stimulates secretion of
*enterogasterone.
• EG in blood reduces gastric motility and
secretion of gastric juice.
• *Enterogasterone is a hormone complex
formed by two hormones
• Secretin and Cholecystokinin ( CCK)
Tanveer Saeed

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Pharynx Esophagus and Stomach Part 2

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Digestive System

Pharynx composed of three layers:

2. submucosa: Contains the mucous secreting glands

3. muscularis externa (or "muscularis propria"): composition

• Cardiac / Cardia: Surrounds the superior • Enlarged segment of digestive

Specialized cells in the lining of the stomach synthesize and secrete

• Activate enzyme pepsin

• Acidifies the food and stops the action of

The important stimulatory signals are :

• Starts when food reaches the

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