Digestive

• Alimentary canal


  Also called the gastrointestinal (GI) tract or gut, a one-way tube about 7.62 meters (25 feet) in length during life and closer to 10.67 meters (35 feet) in length when measured after death, where the main function is to nourish the body
• Alimentary canal


  • Begins at the mouth and terminates at the anus
  • Food and wastes within the alimentary canal are technically considered to be outside the body
  • Only through the process of absorption do the nutrients in food enter into and nourish the body's "inner space"

  
• Organs of the alimentary canal

  • Mouth
  • Pharynx
  • Esophagus
  • Stomach
  • Small intestine
  • Large intestine

  
• Accessory digestive organs


  • Teeth
  • Tongue
  • Salivary glands
  • Gallbladder
  • Liver
  • Pancreas

  
• Accessory digestive organs


  Aid in the breakdown of food and the assimilation of its nutrients into the body

  
• The alimentary canal is composed of four tissue layers: the mucosa, submucosa, muscularis, and serosa

  
• Mucosa


  Referred to as a mucous membrane, consists of epithelium in direct contact with ingested food and a layer of connective tissue (lamina propria)
• Submucosa


  A broad layer of dense connective tissue that connects the mucosa to the underlying muscularis
• Muscularis


  Made up of a double layer of smooth muscle: an inner circular layer and an outer longitudinal layer, which promote mechanical digestion and move food along the canal
• Serosa


  The portion of the alimentary canal superficial to the muscularis, consisting of a layer of visceral peritoneum overlying a layer of loose connective tissue
• Enteric nervous system


  Runs from the esophagus to the anus, contains approximately 100 million motor, sensory, and interneurons, and is responsible for regulating digestive secretions and motility
• Autonomic nervous system


  Provides extrinsic innervation to the alimentary canal, with sympathetic activation restricting activity and parasympathetic activation increasing secretion and motility
• Peritoneum


  A broad serous membranous sac that holds the digestive organs within the abdominal cavity in place, composed of the parietal peritoneum lining the abdominal wall and the visceral peritoneum enveloping the abdominal organs

  
• Inflammation of the peritoneum is called peritonitis, which can develop from breaches in the alimentary canal wall or bacterial infections
• Visceral peritoneum


  Envelopes the abdominal organs
• Peritoneal cavity


  Space bounded by the visceral and parietal peritoneal surfaces
• A few milliliters of watery fluid act as a lubricant to minimize friction between the serosal surfaces of the peritoneum
• Peritonitis


  Inflammation of the peritoneum
• Chemical peritonitis


  1. Develops when the wall of the alimentary canal is breached, allowing the contents of the lumen entry into the peritoneal cavity

  2. For example, when an ulcer perforates the stomach wall, gastric juices spill into the peritoneal cavity
• Hemorrhagic peritonitis


  Occurs after a ruptured tubal pregnancy or traumatic injury to the liver or spleen fills the peritoneal cavity with blood
• Bacterial infections


  Associated with severe peritonitis, seen with appendicitis, colonic diverticulitis, and pelvic inflammatory disease
• Peritonitis is life threatening and often results in emergency surgery to correct the underlying problem and intensive antibiotic therapy
• The mortality rate from peritonitis still ranges from 30 to 40 percent
• Major peritoneal folds


  • Greater omentum
  • Falciform ligament
  • Lesser omentum
  • Mesentery
  • Mesocolon
• Greater omentum


  Apron-like structure that lies superficial to the small intestine and transverse colon; a site of fat deposition in people who are overweight
• Falciform ligament


  Anchors the liver to the anterior abdominal wall and inferior border of the diaphragm
• Lesser omentum


  Suspends the stomach from the inferior border of the liver; provides a pathway for structures connecting to the liver
• Mesentery


  Vertical band of tissue anterior to the lumbar vertebrae and anchoring all of the small intestine except the initial portion (the duodenum)

  
• Mesocolon


  Attaches two portions of the large intestine (the transverse and sigmoid colon) to the posterior abdominal wall

  
• During fetal development, certain digestive structures, including the first portion of the small intestine (called the duodenum), the pancreas, and portions of the large intestine (the ascending and descending colon, and the rectum) remain completely or partially posterior to the peritoneum

  
• The location of these organs is described as retroperitoneal
• Distension of the stomach

  Initiates short reflexes that cause cells in the stomach wall to increase their secretion of digestive juices
• Gastrin


  The main digestive hormone of the stomach, secreted in response to the presence of food, which stimulates the secretion of gastric acid
• GI hormones produced by the duodenum

  • Secretin (stimulates pancreatic bicarbonate secretion)
  • Cholecystokinin (CCK) (stimulates pancreatic enzyme and bile secretion, and gallbladder contraction)
  • Gastric inhibitory peptide (inhibits gastric secretion and slows gastric emptying and motility)
• GI hormones are secreted by specialized epithelial cells called endocrinocytes, located in the mucosal epithelium of the stomach and small intestine
• GI hormones enter the bloodstream to reach their target organs
• Mouth


  • Cheeks, tongue, and palate frame it
  • Also called the oral cavity or buccal cavity
• Lips


  Outer covering is skin, which transitions to a mucous membrane in the mouth proper
• Orbicularis oris muscle


  Regulates what comes in and goes out of the mouth
• Buccinator muscles


  Contract to help keep food from falling out of the mouth when eating