Physiology of the Gastrointestinal Tract (GIT)

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The gastrointestinal tract (GIT) includes both the alimentary canal and accessory glands.


The parotid gland is an example of an accessory organ in the digestive system.


There are 3 layers in the muscularis of the gastrointestinal tract: circular, longitudinal, and fibrous.


The liver is considered an organ of the digestive system but is not part of the alimentary canal.


The ascending colon is located before the transverse colon in the gastrointestinal tract.


The primary functions of the GIT include secretion, digestion, absorption, and osmoregulation.


The visceral peritoneum allows for free movement of organs within the abdominal cavity.


Mesenteries are peritoneal extensions that suspend the length of the intestine outside the abdominal cavity.


Sphincter muscles play a crucial role in preventing the backward flow of food.


Gastrin, a hormone from the stomach, inhibits gastric motility and secretion.


Secretin, released from the small intestines, stimulates pancreatic enzyme secretion and gall bladder contraction.


The myenteric or Auerbach’s plexus controls the secretory activity and contraction of sphincters in the gastrointestinal tract.


Study Notes

Structural Organization of the GIT

  • The GIT (alimentary canal) extends from the mouth to the anus and includes accessory organs that release secretions to help digest food.
  • The alimentary canal includes the mouth, pharynx, esophagus, stomach, small intestine, and large intestine.
  • Accessory organs include salivary glands, liver, gall bladder, and pancreas.

Layers of the GIT

  • Mucosa: the innermost layer with mucosal glands and Meissner's nerve plexus.
  • Submucosa: with submucosal glands and blood vessels.
  • Muscularis: with two layers of muscle (circular and longitudinal) for movements of food through the canal (mixing and peristalsis).
  • Serosa: the outermost layer with a fibrous coating, visceral peritoneum, and intestinal peritoneal extensions (mesenteries).

Sphincter Muscles

  • Definition: a strong circular muscle that prevents regurgitation of food.
  • Locations: between the esophagus and stomach (gastroesophageal sphincter), stomach and small intestine (pyloric sphincter), small and large intestine (ileocecal valve), and large intestine to outside (internal anal sphincter and external anal sphincter).

Digestive Processes

  • Ingestion: taking food into the mouth (eating).
  • Movement of food: muscular contractions that move food through the gastrointestinal (GI) tract (swallowing and peristalsis).
  • Secretion: digestive juices (enzymes, bile, mucus, hormones) are released into the GI tract.
  • Digestion: the breakdown of food by chemical and mechanical means.
  • Absorption: the transport of digested food (vitamins, minerals, water, etc.) from the GI tract into the bloodstream and lymph for distribution to cells.
  • Defecation: the elimination of undigested material (feces) from the GI tract.

Control of GI Functions

  • Nervous control: extrinsic (autonomic) and intrinsic (enteric nervous system).
  • Hormonal control: gastrin, CCK, and secretin regulate GI functions (secretions and motility).

Types of Movements

  • Mixing movements: to mix food with digestive enzymes and secretions.
  • Propulsion movements: to move food through the GI tract (peristalsis).

Learn about the structural organization, functions, movements, secretions, and regulatory mechanisms of the gastrointestinal tract (GIT) including the alimentary canal and accessory glands. Explore how digestion, absorption, and motility are controlled in the GIT.

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