Digestive System ....

It begins with our MOUTH ....... I know most of you are
familiar with this structure because you can see it , so I won’t go
into details with this. You chew the food, masticate ( mix with
saliva for easier flow of food, plus some enzymes will start some
chemical reactions )

ESOPHAGUS


The Esophagus is a hollow muscular tube , approximately 23-25
cm ( 10 inches ) in length and 2 -3 cm ( approximately 1
inch ) in diameter in adults.

The esophagus serves as a channel for food going from the mouth
to the stomach.

It is considered the third organ of digestion, after the mouth and
pharynx.

The esophagus is located behind the trachea and larynx ( organs
for breathing )

It passes through the diaphragm and into the abdomen at an
opening called the diaphragmatic hiatus.

Almost immediately after the esophagus passes through the
hiatus, it enters the stomach.

The wall of the esophagus is made up of 3 layers:
1. mucosa - mucus-producing glands
2. submucosa - loose connective tissues (fibrous, elastic)
plus blood vessels & nerve fibers
3. muscularis - inner layer- circular muscle
outer layer - longitudinal muscle fibers

UNLIKE most of the rest of the GI TRACT, the esophagus is not
surrounded by serosa.


At the upper end of the esophagus is the hypopharyngeal, or
upper esophageal sphincter (UES).

At the lower end of the esophagus, directly above the angle of
HIS, which marks the junction between the tubular esophagus,
and the stomach, is the lower esophageal sphincter (LES)


The LES ( 2-4 cm in length ) is also known as the
gastroesophageal sphincter or cardiac sphincter. It controls the
passage of ingested food to the stomach.

The above references are very important in the future
discussions of Gastroesophageal Reflux Disease (GERD)
which includes hiatal hernia ...

The esophagus receives arterial blood via the esophageal
arteries of the aorta, inferior thyroid artery, and the left gastric
artery. Blood is returned by way of the azygos, thyroid , and
left gastric veins.

The esophagus receives both sympathetic and parasympathetic
innervation. The swallowing center in the medulla initiates
peristaltic contractions ( moving action ) via the vagus nerve,
which innervates the striated muscle in the upper esophagus.


MOTILITY

At rest, both the UES and the LES are closed.

When a bolus of food is pushed through the pharynx, the UES
opens allowing the bolus to pass into the esophagus. At this
point, gravity and peristalsis combine to advance the bolus down
through the esophagus.

PERISTALSIS is defined as a distally progressive band of
circular muscle contraction. When it is initiated by swallowing,
it is known as primary peristalsis. Secondary peristalsis
originates below the hypopharynx with no antecedent swallowing
movement ---it is elicited by esophageal distention.


To recap........ when the food reaches the esophagus, peristalsis
begins in the pharynx, and moves down at a rate of 3-5 cm per
second, effectively transporting material toward the stomach.

When the bolus reaches the LES, the sphincter opens to allow the
bolus to enter the stomach and then closes to prevent a reflux of
food and acid............


Enjoy Your Thanksgiving Dinner !
Happy Thanksgiving to All !
Make sure you don't "reflux" your food !



Maria
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GLOBALHEALTH2000
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