Download Digestion 1

Title: Overview of the Digestive System
1- Introduction: Two groups of organs make up the digestive system, these include
the gastrointestinal (GI) tract organs and the accessory digestive organs
a- The GI tract or Alimentary (Latin for nourishment) Canal is a continuous
hollow tube that extends from the mouth to the anus through the ventral
(front) body cavity.
b- The organs of the GI tract include: mouth, most of the pharynx,
esophagus, stomach, small intestine (duodenum, ilium, and jejunum) and
the large intestine (ascending colon, transverse colon, descending colon,
rectum, anus)
c- In a cadaver the entire length of the digestive system is about 30 feet – it is
considerably shorter in the living person because the muscles are in a state
of sustained contraction.
d- The accessory digestive organs include: teeth, tongue, salivary glands,
liver, gallbladder and pancreas.
1- Of these accessory organs only the teeth and the tongue actually come
in physical contact with the food
2- Secretions from the other accessory organs flow from those organs
into the GI tract through ducts and aid in the chemical breakdown of
food
2- The Digestive System performs six basic functions
a- Ingestion –
b- Secretion –
c- Mixing and propulsion
d- Digestion –
e- Absorption –
f- Defecation –
3- The walls of the GI tract from the lower esophagus to the anal canal has, the same
basic four layered arrangement of tissue. From deep to superficial they are 1)
mucosa, 2) submucosa, 3) muscularis and 4) serosa
a- Within the mucosa you find the
1- Epithelium – (NKSSE, SCE, CSCE)
2- Mucosa associated lymphatic tissue (MALT) -
3- Muscularis Mucosae –
b- Within the submucosa you find the blood vessels and the lymphatic
drainage and the submucosal plexus (plexus of Meissner) and the
myenteric plexus (plexus of Auerbach). These two enteric plexuses contain
100 million neurons and have local control over the GI tract and is often
called the “brains of the gut”
c- The muscularis is the muscle of the digestive tract. The mouth, pharynx,
esophagus and anus is composed of skeletal muscle the remainder is
smooth muscle
d- The serosa is a membrane surrounding the digestive tract that secretes
watery fluid that allows the digestive organs to glide over the other organs
in the body
e- Diagram: