Explain the difference between cells (chief, mucuous, G cells, perital cells), tissues (smooth, loose, nervous, columnar epithelium), and organs and systems (digestive) found in the stomach. Include references. 

Cells are the basic structural units of all living organisms. A group of cells form tissues, groups of tissues form organs, and groups of organs form systems. The stomach, an organ which consists of four main tissues and four main types of cells, is the main organ of the digestive system.

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The four main types of cells found in the stomach are the chief, parietal, mucous, and endocrine cells.

  1. Chief cells can be gastric chief cells (also called peptic cells) that release the proenzymes pepsinogen and chymosin; parathyroid chief cells, which can be chief cells (they secrete PTH or the parathyroid hormone) and oxyphil cells; and type 1 chief cells.
  2. Parietal (oxyntic) cells secrete hydrochloric acid, as well as intrinsic factor, which helps the body absorb cobalamin or vitamin B12. Parietal cells are therefore essential when it comes to the proper functioning of the gastrointestinal tract.
  3. Mucous cells can be found in the stomach, the salivary glands, and the esophageal glands. The main function of the mucous cells is to protect the epithelium from digestive acid and enzymes.
  4. G cells are endocrine cells located in the duodenum and the pancreas that secrete gastrin. Gastrin stimulates the stomach to release acid and absorb essential vitamins and proteins from the food, as well as to destroy harmful bacteria that come with the food.

There are four main types of tissues in the stomach: serosa, muscularis, submucosa, and mucosa.

  1. The serosa is the outer layer, which separates the internal organs from the abdominal cavity.
  2. The muscularis (muscle layer) consists of layers of smooth muscle that move the food through the gut.
  3. The submucosa is where the nervous tissue or digestive nerve plexus ensures that there is normal and smooth muscle contraction and movement and regulates the synthesis and secretion of digestive substances.
  4. The mucosa, or the mucous membrane of the stomach, is composed of the simple columnar epithelium (which has gastric pits and glands and a single layer of columnar cells, and its main function in the stomach is to protect it from bacteria), lamina propria (which is a layer of loose connective tissue), and muscularis mucosae (which is layer of smooth muscle).

The abdominal area is the part where all of the digestive organs are located; these include the organs of the gastrointestinal (GI) tract—mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum, and anus, as well as the pancreas, the liver, and the gallbladder. Together, they compose the human digestive system.

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