Digestive System and GI Tract – 2010
The digestive tract is basically a muscular tube about 30 feet in length that extends from
the lips to the anus. It is the site for ingestion, digestion, absorption, and elimination of
the food we take into our mouths. Associated with this muscular tube are several
accessory digestive organs that include salivary glands, tongue, teeth, gall bladder, liver
These so called accessory organs are vital.
The muscular tube begins
with the mouth which leads to the esophagus which drains into the stomach.
stomach empties into the small intestine which consists of three parts: the duodenum,
the jejunum, and the ileum.
The ileum drains into the large intestine through the
The colon leads to the rectum and thence to the anus.
Refer to the
attached basic diagram of the muscular tube.
The tube consists of four concentric
layers, sometimes referred to as tunicae (sing. tunica).
Beginning from the luminal
surface, these layers are:
: a. epithelium; b. lamina propria (loose CT with lots of lymphs and lymphoid
muscularis mucosae (a thin layer of smooth muscle).
membrane is synonymous with mucosa or tunica mucosae. So, the mucosa of the GI
tract consists of three tissues:
epithelium, the lamina propria, and the
(We will see that the mucosa of the respiratory, urinary, and
reproductive tracts consists of just the epithelium and lamina propria).
Of all the four
layers, the mucosa is the most variable in terms of structure and function
dense CT containing vessels, nerves (Meissner’s plexus), and
places in the GI tract where mucous exocrine glands
are present in the
. These two places are the
esophagus and the
proximal duodenum. All other glands in GI tract are located in the mucosa.
: two layers of smooth muscles, inner layer is circular (i.e. it goes around
the tube), outer layer is longitudinal (runs up and down the tube); between these muscle
layers is CT with vessels,
nerves and neurons (Auerbach’s plexus or myenteric plexus).
a thin layer of CT covered by simple squamous cells (mesothelium).
Within the abdominal cavity, the serosa on each side of the digestive tube fuses together to
form the suspensory structure called the mesentery through which blood vessels, lymphatic
vessels, and nerves run.