The Stomach - The Key Organ of Digestion
The stomach is a muscular, hollow, dilated part of the digestion system which functions as an important organ of the digestive tract in some animals, including vertebrates, echinoderms, insects (mid-gut), and molluscs. It is involved in the second phase of digestion, following mastication (chewing).
The stomach is located between the esophagus and the small intestine. It secretes protein-digesting enzymes and strong acids to aid in food digestion, (sent to it via oesophageal peristalsis) through smooth muscular contortions (called segmentation) before sending partially digested food (chyme) to the small intestines.
The word stomach is derived from the Latin stomachus which is derived from the Greek word stomachos, ultimately from stoma (στόμα), "mouth". The words gastro- and gastric (meaning related to the stomach) are both derived from the Greek word gaster (γαστήρ).
Role in Digestion
Bolus (masticated food) enters the stomach through the oesophagus via the oesophageal sphincter. The stomach releases proteases (protein-digesting enzymes such as pepsin) 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 wall called peristalsis – reducing the volume of the fundus, before looping around the fundus and the body of stomach as the boluses are converted into chyme (partially digested food). Chyme slowly passes through the pyloric sphincter and into the duodenum, where the extraction of nutrients begins. Depending on the quantity and contents of the meal, the stomach will digest the food into chyme anywhere between forty minutes and a few hours.
Anatomy of the Stomach
The stomach lies between the esophagus and the duodenum (the first part of the small intestine). It is on the left upper part of the abdominal cavity. The top of the stomach lies against the diaphragm. Lying behind the stomach is the pancreas. The greater omentum hangs down from the greater curvature.
Greater omentum and stomach; Two sphincters keep the contents of the stomach contained. They are the esophageal sphincter (found in the cardiac region, not an anatomical sphincter) dividing the tract above, and the Pyloric sphincter dividing the stomach from the small intestine.
The stomach is surrounded by parasympathetic (stimulant) and orthosympathetic (inhibitor) plexuses (networks of blood vessels and nerves in the anterior gastric, posterior, superior and inferior, celiac and myenteric), which regulate both the secretions activity and the motor (motion) activity of its muscles.
In adult humans, the stomach has a relaxed, near empty volume of about 45 ml. Because it is a distensible organ, it normally expands to hold about one litre of food, but can hold as much as two to three litres. The stomach of a newborn human baby will only be able to retain about 30 ml.
The stomach is located between the esophagus and the small intestine. It secretes protein-digesting enzymes and strong acids to aid in food digestion, (sent to it via oesophageal peristalsis) through smooth muscular contortions (called segmentation) before sending partially digested food (chyme) to the small intestines.
The word stomach is derived from the Latin stomachus which is derived from the Greek word stomachos, ultimately from stoma (στόμα), "mouth". The words gastro- and gastric (meaning related to the stomach) are both derived from the Greek word gaster (γαστήρ).
Role in Digestion
Bolus (masticated food) enters the stomach through the oesophagus via the oesophageal sphincter. The stomach releases proteases (protein-digesting enzymes such as pepsin) 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 wall called peristalsis – reducing the volume of the fundus, before looping around the fundus and the body of stomach as the boluses are converted into chyme (partially digested food). Chyme slowly passes through the pyloric sphincter and into the duodenum, where the extraction of nutrients begins. Depending on the quantity and contents of the meal, the stomach will digest the food into chyme anywhere between forty minutes and a few hours.
Anatomy of the Stomach
The stomach lies between the esophagus and the duodenum (the first part of the small intestine). It is on the left upper part of the abdominal cavity. The top of the stomach lies against the diaphragm. Lying behind the stomach is the pancreas. The greater omentum hangs down from the greater curvature.
Greater omentum and stomach; Two sphincters keep the contents of the stomach contained. They are the esophageal sphincter (found in the cardiac region, not an anatomical sphincter) dividing the tract above, and the Pyloric sphincter dividing the stomach from the small intestine.
The stomach is surrounded by parasympathetic (stimulant) and orthosympathetic (inhibitor) plexuses (networks of blood vessels and nerves in the anterior gastric, posterior, superior and inferior, celiac and myenteric), which regulate both the secretions activity and the motor (motion) activity of its muscles.
In adult humans, the stomach has a relaxed, near empty volume of about 45 ml. Because it is a distensible organ, it normally expands to hold about one litre of food, but can hold as much as two to three litres. The stomach of a newborn human baby will only be able to retain about 30 ml.
Sections of the Stomach
Cardia - The cardia is the anatomical term for the part of the stomach attached to the esophagus. The cardia begins immediately distal to the z-line of the gastroesophageal junction, where the squamous epithelium of the esophagus gives way to the columnar epithelium of the gastrointestinal tract.
Just proximal to the cardia at the gastroesophageal (GE) junction is the anatomically indistinct but physiologically demonstrable lower esophageal sphincter. The area termed the cardia overlaps with the lower esophageal sphincter; however, by definition, the cardia does not contain the lower esophageal sphincter. Although the topic was previously disputed, current consensus affirms the cardia is indeed part of the stomach.
The cardia overlaps with but specifically does not contain the lower esophageal sphincter (LES) (also termed cardiac sphincter, gastroesophageal sphincter, and esophageal sphincter; which is the opening in the stomach from the esophagus). This is in contrast to the "upper esophageal sphincter" contained in the hypopharynx (area extending from the base of the tongue to the cricoid cartilage) and consists of striated muscle controlled by somatic innervation.
Fundus - The fundus of the stomach is the left portion of the stomach's body, and is marked off from the remainder of the body by a plane passing horizontally through the cardiac orifice.As the rounded part of the upper stomach, it allows for an accumulation of stomach gases produced by chemical digestion. It will also store undigested food for up to 1 hour.
It will also store undigested food for up to 1 hour.
Body or Corpus - The Body of the Stomach (Lat. corpus gastricum) often just called the body or corpus is an anatomical region of the stomach in humans. The boundaries of the body of the stomach are shown in the diagram to the right, with the dotted line stemming from the cardiac notch separating the body from the fundus, while the lower boundary is defined by a line perpendicular to the lesser curvature of the stomach from the angular notch. The line drawn from the angular notch thus divides the body of the stomach to yield an antrum section, which goes on to drain into the duodenum via the pyloric sphincter.
Pylorus - The pylorus ( /paɪˈlɔərəs/ or /pɨˈlɔərəs/; from the Greek πυλωρός, "gate guard") is the region of the stomach that connects to the duodenum (the beginning of the small intestines). It is divided into two parts:
A. ) The pyloric antrum, which connects to the body of the stomach.
B. ) The pyloric canal, which connects to the duodenum.
The pyloric sphincter, or valve, is a strong ring of smooth muscle at the end of the pyloric canal which lets food pass from the stomach to the duodenum. It receives sympathetic innervation from the celiac ganglion.
Cardia - The cardia is the anatomical term for the part of the stomach attached to the esophagus. The cardia begins immediately distal to the z-line of the gastroesophageal junction, where the squamous epithelium of the esophagus gives way to the columnar epithelium of the gastrointestinal tract.
Just proximal to the cardia at the gastroesophageal (GE) junction is the anatomically indistinct but physiologically demonstrable lower esophageal sphincter. The area termed the cardia overlaps with the lower esophageal sphincter; however, by definition, the cardia does not contain the lower esophageal sphincter. Although the topic was previously disputed, current consensus affirms the cardia is indeed part of the stomach.
The cardia overlaps with but specifically does not contain the lower esophageal sphincter (LES) (also termed cardiac sphincter, gastroesophageal sphincter, and esophageal sphincter; which is the opening in the stomach from the esophagus). This is in contrast to the "upper esophageal sphincter" contained in the hypopharynx (area extending from the base of the tongue to the cricoid cartilage) and consists of striated muscle controlled by somatic innervation.
Fundus - The fundus of the stomach is the left portion of the stomach's body, and is marked off from the remainder of the body by a plane passing horizontally through the cardiac orifice.As the rounded part of the upper stomach, it allows for an accumulation of stomach gases produced by chemical digestion. It will also store undigested food for up to 1 hour.
It will also store undigested food for up to 1 hour.
Body or Corpus - The Body of the Stomach (Lat. corpus gastricum) often just called the body or corpus is an anatomical region of the stomach in humans. The boundaries of the body of the stomach are shown in the diagram to the right, with the dotted line stemming from the cardiac notch separating the body from the fundus, while the lower boundary is defined by a line perpendicular to the lesser curvature of the stomach from the angular notch. The line drawn from the angular notch thus divides the body of the stomach to yield an antrum section, which goes on to drain into the duodenum via the pyloric sphincter.
Pylorus - The pylorus ( /paɪˈlɔərəs/ or /pɨˈlɔərəs/; from the Greek πυλωρός, "gate guard") is the region of the stomach that connects to the duodenum (the beginning of the small intestines). It is divided into two parts:
A. ) The pyloric antrum, which connects to the body of the stomach.
B. ) The pyloric canal, which connects to the duodenum.
The pyloric sphincter, or valve, is a strong ring of smooth muscle at the end of the pyloric canal which lets food pass from the stomach to the duodenum. It receives sympathetic innervation from the celiac ganglion.