final exam

• The organs of the digestive system perform their specific functions, allowing you to use the food you eat to keep you going

  
• 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, the main function of which is to nourish the body
• Accessory digestive organs


  Critical for orchestrating the breakdown of food and the assimilation of its nutrients into the body

  
• Layers of the alimentary canal


  • Mucosa
  • Submucosa
  • Muscularis
  • Serosa
• Mucosa


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


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


  The third layer of the alimentary canal, made up of smooth muscle that promotes mechanical digestion and moves 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


  Intrinsic innervation of much of the alimentary canal, containing approximately 100 million motor, sensory, and interneurons
• Myenteric plexus


  Lies in the muscularis layer of the alimentary canal and is responsible for motility, especially the rhythm and force of the contractions of the muscularis

  
• Submucosal plexus


  Lies in the submucosal layer and is responsible for regulating digestive secretions and reacting to the presence of food
• Autonomic nervous system


  Provides extrinsic innervation of the alimentary canal, including both sympathetic and parasympathetic nerves
• Sympathetic activation


  Restricts the activity of enteric neurons, thereby decreasing GI secretion and motility
• Parasympathetic activation


  Increases GI secretion and motility by stimulating neurons of the enteric nervous system
• Peritoneum


  A broad serous membranous sac made up of squamous epithelial tissue surrounded by connective tissue that holds the digestive organs within the abdominal cavity in place

  
• Mesenteric arteries


  Supply blood to the small and large intestines
• Hepatic portal system


  Venous network that takes nutrient-rich blood from the small intestine into the liver
• The blood drained from the alimentary canal viscera circulates back to the heart after being processed in the liver
• About one-fourth of the blood pumped with each heartbeat enters arteries serving the intestines during "resting and digesting"
• Peritoneum


  Broad serous membranous sac that holds the digestive organs in place within the abdominal cavity

  
• Regions of the peritoneum


  • Parietal peritoneum (lines the abdominal wall)
  • Visceral peritoneum (envelopes the abdominal organs)

  
• The peritoneal cavity is the space bounded by the visceral and parietal peritoneal surfaces

  
• A few millilitres of watery fluid act as a lubricant to minimize friction between the serosal surfaces of the peritoneum
• Major peritoneal folds


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


  Location of certain digestive structures (duodenum, pancreas, portions of large intestine) that remain completely or partially posterior to the peritoneum during fetal development

  
• Peritonitis


  Inflammation of the peritoneum
• Causes of peritonitis


  • Chemical peritonitis (breach in alimentary canal wall)
  • Hemorrhagic peritonitis (ruptured tubal pregnancy, traumatic injury)
  • Bacterial infections (appendicitis, diverticulitis, pelvic inflammatory disease)
• Peritonitis is life-threatening and often requires emergency surgery and intensive antibiotic therapy
• Improvements in surgery, anesthesia, critical care, and antibiotics have greatly improved the mortality rate from peritonitis, but it still ranges from 30-40%
• Nerve plexuses


  • Interact with the central nervous system and other nerve plexuses
  • Prompt several types of reflexes
• Types of reflexes


  • Extrinsic nerve plexuses orchestrate long reflexes (involve central and autonomic nervous systems, respond to stimuli from outside digestive system)
  • Intrinsic nerve plexuses orchestrate short reflexes (regulate activities in one area of digestive tract, coordinate local peristaltic movements and stimulate digestive secretions)
• Sight, smell, and taste of food


  Initiate long reflexes that stimulate cells in stomach to secrete digestive juices
• Food distending the stomach


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


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


  • Secretin (stimulates pancreatic bicarbonate secretion)
  • Cholecystokinin (CCK) (stimulates pancreatic enzyme and bile secretion, releases bile from gallbladder)
  • Gastric inhibitory peptide (inhibits gastric secretion and slows gastric emptying and motility)
• Endocrinocytes


  Specialized epithelial cells in mucosal epithelium of stomach and small intestine that secrete GI hormones
• GI hormones enter the bloodstream to reach their target organs
• The immune system is the complex collection of cells and organs that destroys or neutralizes pathogens that would otherwise cause disease or death

  
• The mouth, pharynx, and esophagus are the three main organs of the upper alimentary canal

  
• The lymphatic system is the system of vessels, cells, and organs that carries excess fluids to the bloodstream and filters pathogens from the blood