The Human StomachNicole KummerSeptember 11, 2013BIO 120-WW10

The Stomach

Location• The stomach is located in the left upper quadrant. Also

contained in this quadrant is the spleen, left kidney, a small portion of the liver, the majority of the pancreas, and a portion of the small intestines and colon.

• The stomach is held within the abdominal cavity which is on the anterior or ventral side of the body. Within the abdominal cavity is the peritoneum, a two layer membrane. The outer layer the lines the abdominal cavity is the parietal peritoneum, and the inner layer that encases the stomach is the visceral peritoneum.

• The stomach is inferior to the diaphragm, and superior to the small intestines.

Medical Terminology• The following medical terminology terms and

abbreviations pertain to the stomach:▫ Gastr/o= Stomach▫ Gastroenterology= Study of the stomach and small

intestines▫ Gastroenterologist= One who studies the stomach and

small intestines▫ Hypogastric= Under the stomach▫ Epigastric= Above the stomach▫ GI= Gastrointestinal▫ LUQ= Left Upper Quadrant

Digestive System• The stomach is a part of the Digestive System.• Other structures that make up the Digestive System

include▫ Oral cavity▫ Pharynx▫ Esophagus▫ Small intestine▫ Colon▫ Liver▫ Gallbladder▫ Pancreas▫ Salivary glands

Structure• The stomach is a J-shaped muscular organ that is composed of three

parts: the fundus (upper region), the body (main portion), and the antrum (lower portion).

• The cardiac sphincter keeps food from going back into the esophagus. The pyloric sphincter regulates the passage of food into the small intestines.

• The stomach varies from 15 to 25 cm long, and its diameter and volume depend on how much food is within it. When totally distended the stomach can hold about 4 Liters of food.

• The stomach contains muscle fibers, nerve tissues, and epithelial tissue. The lining of the stomach is simple columnar epithelium tissue composed entirely of mucous cells. Deep gastric pits are all over the lining and lead to gastric glands which secrete gastric juice.

Structure

Layers of Muscle• There are four layers of muscle in the stomach:

▫ Mucosa- Innermost layer. Made of mucous membrane containing epithelial tissue which has gastric pits which secrete mucus and digestive enzymes.

▫ Submucosa- Second layer. Made of connective tissue, nerves, and blood vessels.

▫ Muscularis Externa-Three layers of smooth muscle: Inner Oblique Layer, Middle Circular Layer, and Outer Longitudinal Layer.

▫ Serosa- Layers of connective tissue, continues into peritoneum. Secretes serous fluid to protect stomach from damage when expanding in the body.

Function• The stomach completes the following tasks:

▫ Receives food from the esophagus.▫ Stores the food we eat.▫ Mixes Hydrochloric Acid and other gastric juices into

food to break it down into chyme. Hydrochloric acid is secreted from gastric pits.

▫ Slowly empties contents into the small intestines for further digestion. Chyme is passed very slowly into the small intestines due to the fact that it is highly acidic and needs time to be neutralized.

▫ The stomach usually takes around 4 hours to empty after a meal. Liquids pass through more quickly than solids.

More on Gastric Juice▫ Neural and hormonal mechanisms control gastric secretion.

This happens in three phases: 1.)Cephalic Reflex- This happens before food enters the

stomach. Aroma, taste, sight, and thought are all relayed to the hypothalamus in the brain and after a process of nerve and motor impulses being transferred , the stomach glands are stimulated.

2.) Gastric- This phase starts once food hits the stomach, lasts three to four hours, and provides 2/3rds of the gastric juice provided. Gastric juices are increased because of stomach distension and low acidity level. Low acidity levels happen when proteins enter the stomach raising the pH level.

3.)Intestinal- As food begins to enter the small intestines, the intestines release Intestinal Gastrin, which encourages gastric glands to continue their activity.

Mucosal Barrier• If the stomach is so acidic, why doesn’t it eat itself?

▫ The stomach is able to withstand all of the acid it produces without being damaged itself because of the layer of mucus within it.

▫ Three factors make up this barrier: 1.) A thick coating of bicarbonate-rich mucus builds on the

stomach wall (bicarbonate neutralizes acid). 2.) Cells are joined together by tight junctions (which do not

allow things to pass through). Therefore gastric juice can not leak into underlying layers.

3.) Damaged cells on the lining are shed and replaced very quickly.

Stomach Ulcers• Gastric Ulcers are erosions of the stomach wall. • 90% of recurrent ulcers are caused from a bacteria called

Helicobacter Pylori. These bacteria drill through the mucus and destroy mucosal layer.

• H. Pylori can lead to stomach cancer, but can also be treated with antibiotics if found.