Digestive system

• Digestive system


  Group of organs that break down the food we consume into smaller forms that can be used by our cells
• GI tract


  One continuous tube extending from the esophagus to the anus, ranges from about 17-23ft
• Organs of the digestive system


  • Esophagus
  • Stomach
  • Small intestine
  • Large intestine (colon)
  • Rectum
• Accessory structures


  • Teeth
  • Tongue
  • Salivary glands
  • Liver
  • Gall bladder
  • Pancreas
• Digestive processes


  • Ingestion
  • Secretion
  • Motility
  • Digestion
  • Absorption
  • Defecation
• Layers of the GI tract


  • Mucous
  • Submucous
  • Muscular layer
  • Serosa
• Enteric Nervous System


  "Brain of the gut"
• Neural plexuses


  • Submucosal plexus
  • Myenteric plexus
• Roles of the Autonomic Nervous System

  • Parasympathetic (increases digestive canal secretions and motility)
  • Sympathetic (decreases digestive canal secretions, typically in responses to emotional states like anger, stress, fear, and anxiety)
• GI reflex pathways

  Regulate GI secretion and motility in response to stimuli within the GI tract
• Peritoneum


  Largest serous membrane in the body, can be further subdivided into parietal and visceral portions
• Peritoneal folds

  • Greater omentum
  • Lesser omentum
  • Falciform ligament
• Mouth

  Begins the digestion process by breaking foods apart and mixing with saliva
• Salivary glands

  • Parotid
  • Submandibular
  • Sublingual
• Saliva

  Lubricates, dissolves, and breaks down foods through enzymes
• Tongue

  Participates in chewing, swallowing, and speech
• Types of teeth

  • Incisor
  • Canine
  • Premolar
  • Molar
  • Wisdom
• Mechanical digestion

  First step in the digestion process, chewing (mastication) chops and mixes food with saliva and forms a bolus which can be easily swallowed
• Chemical digestion

  Salivary amylase converts polysaccharides to disaccharides, lingual lipase mixes with food and becomes activated in the acidic stomach to breakdown fats and oils
• Pharynx

  Funnel shaped tube that extends from the internal nares to the esophagus posteriorly and to the larynx anteriorly
• Esophagus

  Collapsible, muscular tube that lies posterior to the trachea and connects the pharynx to the stomach
• Deglutition

  Act of swallowing or moving food from the mouth to the stomach, has 3 phases: oropharyngeal, pharyngeal, and esophageal
• Peristalsis

  Progression of coordinated muscle contractions and relaxations of the muscularis layer
• Gastroesophageal Reflux Disease

  Occurs when lower esophageal sphincter fails to close adequately after food has entered the stomach, causing stomach contents to reflux back to esophagus
• Stomach


  1. shaped enlargement of the GI tract where the bolus is further broken down into a more liquid material called chyme
• Regions of the stomach

  • Cardia
  • Fundus
  • Body
  • Pylorus
• Functions of the stomach

  Mixes saliva, food, and gastric juice to form chyme, serves as a reservoir for food before release into the small intestine, secretes gastric juice containing HCl, pepsin, intrinsic factor, and gastric lipase
• Intrinsic factor is a glycoprotein that helps with the absorption of B12 vitamins, non-functional IF can cause pernicious anemia
• The stomach secretes gastrin into the blood, which helps promote growth of stomach lining, stimulate gastric motility, and release of gastric acid
• 1.ingestion – taking food into the mouth

  2. secretion – water, acid, buffers, and enzymes

  3. motility – churning and movement of food through the digestive canal

  4. digestion – mechanical and chemical breakdown of foods

  5. absorption – passage of digested products from digestive canal to lymph and plasma

  6. defecation – elimination of what is remaining from the digestive canal
• 1.mucous – mucous membrane lining inside of digestive canal (regrow every 5-7 days

  2.submucous – binds the mucosa to the muscularis layer, contains blood and lymphatic vessels

  3.muscular layer – production of voluntary swallowing and defecation. Smooth muscle in this layer will move food along the digestive canal and mix digestive secretions

  4.serosa – most superficial layer consisting of a serous membrane
• 1.Submucosal plexus – found in the submucosa. Mostly deals with receptors detecting change such as the stretch of the stomach or chemicals in foods

  2. Myenteric plexus – located between the smooth muscle layers. Mostly deals with motility or movement of food
• Gastric Lipase is produced by chief cells and released when fatty acids are present.
• Chief cells secrete pepsinogen.
• Automatic nervous system: Parasympathetic – works to increase digestive canal secretions and motility

  Sympathetic – causes a decrease in digestive canal secretions, typically in responses to emotional states like anger, stress, fear, and anxiety
• 1.Greater omentum – largest of the folds and consists of many lymph nodes that prevent illness in the digestive canal

  2. Lesser omentum – connects the stomach and part of the intestine to the liver. Pathway for blood vessels entering the liver

  3. Falciform ligament – attaches the liver to the abdominal wall and diaphragm
• The gallbladder stores bile until it’s needed to emulsify lipids in the small intestine. It also concentrates bile from the liver.
• Bile ducts carry bile from the liver into the small intestine. The common hepatic duct carries bile from both lobes of the liver and joins with the cystic duct which drains the gallbladder. Together they form the common bile duct which empties into the first portion of the small intestine called the duodenum.
• Pancreas produces enzymes that break down carbohydrates, proteins, and lipids. Pancreatic juice flows through the main pancreatic duct into the duodenum where it helps to neutralize acidity and activate enzymes.