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THE STOMACH
Features functions and cells
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STOMACH
An important organ in the body part of the digestive system which has several important
functions in the digestion of food.
Features
 Stomach Wall
Consists of several layers, the mucosa, sub-mucosa, muscularis external, and the serosa.
The Mucosa has three layers (mucosal epithelium,lamina propria and muscularis
mucosa).
The sub-mucosa contains layers of muscle tissue and a dense irregular connective tissue
with a network of blood vessels and nerves.
The outer layer, the serosa has an epithelial layer and connective tissue that connect to
other organs.
The muscular stomach walls consisting of longitudinal and circular muscles aids
peristalsis which assists in the mechanical breakdown of food and propelling it forward.
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
The two sphincters perform an important function of controlling the movement of food in
and out of the stomach. The cardiac sphincter controls the food entering the stomach
while the pyloric sphincter controls the movement of food out of the stomach.

Cells
o The inner wall of the stomach is lined by a mucous membrane known as the
gastric mucosa covered by a layer of thick mucus that is secreted by tall columnar
epithelial cells. The mucus prevents injuries to the stomach by lubricating the
contents in the stomach and chemical injuries due to the corrosive gastric juices.
o Mucoid cells - Secret gastric mucus used for lubrication.
o Zymogenic or chief cells - located in the fundic portions of the stomach, these
cells secrete pepsinogen, inactive gastric enzyme converted to pepsin, a digesting
enzyme.
o Parietal cells – secret hydrochloric acid which converts pepsinogen to pespsin and
also provides a conducive environment for digestion where digestive enzymes are
activated and help break down food into simpler components for the body to use.
o Endocrine cells - located throughout the body of the stomach, these cells secret
several substances, including the hormones histamine, endorphins, serotonin,
cholecystokinin and somatostatin.
How they work together:
Masticated food enters the stomach through the lower esophageal sphincter. The stomach then
releases protease and hydrochloric acid which kills or inhibits bacteria and provides the acidic
pH of two for the proteases to work. Food is churned by the stomach through muscular
contractions of the stomach walls. The Chyme then slowly passes through the pyloric sphincter
into the duodenum where the extraction of nutrients begins.
Why each organ requires different cell types:
The smallest units in the body are cells which share certain characteristics. These cells collect to
form tissues which in turn collect to form organs. These organs depend on these small blocks
working together to perform the task required. The stomach is an organ but with a collection of
different cell types that perform different tasks but in the end help the stomach as an organ
perform the task of digestion.
An organ cannot comprise of a single cell since it needs to perform a much more complex task
than a single cell. Therefore for an organ to function fully it has to comprise of different cells in
order to work together to accomplish a more complex task.
The advantage of having different cell types is that each cell gets to perform a certain task
according to its specialization and these cells working together can accomplish an even more
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complex task. Compared to a single-celled animal, a multi-celled animal can perform more
complex tasks due to the variety of cells it has.
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