The GI tract is a series of hollow organs joined in a long, twisting tube from the mouth to the anus. The hollow organs that make up the GI tract are the mouth, esophagus, stomach, small intestine, large intestine, and anus. The liver, pancreas, and gallbladder are the solid organs of the digestive system

1. GASTROINTESTINAL
TRACT

2. The gastrointestinal tract, also known as the gut or alimentary canal, is
a tube by which bilaterian animals (including humans) transfer food to
the digestion organs. In large bilaterians, the gastrointestinal tract
generally also has an exit, the anus, by which the animal disposes of
solid wastes. Some small bilaterians have no anus and dispose of solid
wastes by other means (for example, through the mouth). Animals that
have gastrointestinal tracts are classified as either protostomes or
deuterostomes.Protostomes include arthropods, molluscs, and
annelids, while deuterostomes include echinoderms and chordates.
INTRODUCTION

4. Esophagus
The esophagus or oesophagus, commonly known as the foodpipe or
gullet, is an organ in vertebrates which consists of a fibromuscular tube
through which food passes, aided by peristaltic contractions, from the
pharynx to the stomach. The wall of the esophagus from the lumen
outwards consists of mucosa, submucosa (connective tissue), layers of
muscle fibers between layers of fibrous tissue, and an outer layer of
connective tissue. The mucosa is a stratified squamous epithelium of
around three layers of squamous cells, which contrasts to the single
layer of columnar cells of the stomach. The transition between these two
types of epithelium is visible as a zig-zag line. Most of the muscle is
smooth muscle although striated muscle predominates in its upper two
thirds. It has two muscular rings or sphincters in its wall, one at the top
and one at the bottom. The lower sphincter helps to prevent reflux of
acidic stomach content.
TISSUE LAYERS

5. Most of the tissue in the digestive tract itself has four layers. These layers are
called the mucosa, the submucosa, muscularis externa, and the serosa. The layer in
the innermost part of the digestive tract is called the mucosa. The mucosa serves
to line the cavity of the tract. The mucosa consists of three sub-layers called the
epithelium, the lamina propria, and the muscularis mucosae.The epithelium also
contains many cells that secrete mucus. This mucus lubricates the digestive tract.
The lamina propia is a sub-layer that is made of loose connective tissue. The
muscularis mucosae is a sub-layer of smooth muscle.The next layer after the
mucosa is called the submucosa. This layer is a thick layer of loose connective
tissue. Although this layer does not have any sub-layers, it does have blood vessels,
vessels belonging to the lymphatic system, and nerves, some of which control
digestion. In some places, such as the small intestine, the submucosa also contains
cells that secrete mucus onto the surface of the tract.
DIGESTIVE TRACT

6. After the submucosa is a layer called the muscularis externa. Except for the upper
portion of the esophagus, this layer consists of smooth muscle. This layer has two
sub-layers of smooth muscle called the inner circular layer and the outer
longitudinal layer. The cells of the inner circular layer, which is closer to the
submucosa layer, wrap around the digestive tract like a ring. The cells of the outer
longitudinal layer, which is closer to the serosa, run lengthwise along the digestive
tract. These muscles are involved in the peristaltic action that moves food through
the digestivEven though the muscularis externa layer has 2 sub-layers of smooth
muscle in most of the digestive tract, the muscularis externa layer varies in the
esophagus and the stomach. Unlike the other organs in the digestive tract, the
muscularis externa layer in the upper portion of the esophagus is made of striated
muscle instead of smooth muscle. The muscularis externa layer in the stomach
consists of three sub-layers instead of two. These layers include an outer
longitudinal sub-layer, a middle circular sub-layer, and an inner oblique sub-layer.
The inner oblique sub-layer provides the stomach with added strength so that it
can mix food better.e tract.
DIGESTIVE TRACT

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