Histology_Digestive System

• If you add up marginal utility for each unit you get total utility
• The inner layer of the entire digestive tract forms an important protective barrier between the content of the tract’s lumen and the internal milieu of the body’s connective tissue and vasculature
• The digestive system is also called the gastrointestinal (GI) tract or alimentary canal
• Structures of the digestive system

  • Oral cavity
  • Esophagus
  • Stomach
  • Small intestine
  • Large intestine
• Key functions of the digestive tract

  • Ingestion
  • Mastication
  • Motility
  • Secretion
  • Hormone release
  • Chemical digestion
  • Absorption
  • Elimination
• Marginal utility

  The additional utility (satisfaction) gained from the consumption of an additional product
• During digestion

  1. Proteins, complex carbohydrates, nucleic acids, and fats are broken down into their small molecule subunits that are easily absorbed through the small intestine lining

  2. Most water and electrolytes are absorbed in the large intestine
• The digestive system consists of the digestive tract—oral cavity, esophagus, stomach, small and large intestines, and anus—and its associated glands—salivary glands, liver, and pancreas
• The function of the digestive system is to obtain from ingested food the molecules necessary for the maintenance, growth, and energy needs of the body
• General structure of the digestive tract

  • Mucosa
  • Submucosa
  • Muscularis
  • Serosa
• Structures within the digestive tract allow

  1. Ingestion, or introduction of food and liquid into the oral cavity

  2. Mastication, or chewing, which divides solid food into digestible pieces

  3. Motility, muscular movements of materials through the tract

  4. Secretion of lubricating and protective mucus, digestive enzymes, acidic and alkaline fluids, and bile

  5. Hormone release for local control of motility and secretion

  6. Chemical digestion or enzymatic degradation of large macromolecules in food to smaller molecules and their subunits

  7. Absorption of the small molecules and water into the blood and lymph

  8. Elimination of indigestible, unabsorbed components of food
• Propulsion of luminal contents forward


  Generated and coordinated by the myenteric plexus
• The digestive system consists of the tract from the mouth (oral cavity) to the anus, as well as the digestive glands emptying into this tract, primarily the salivary glands, liver, and pancreas
• Rich autonomic innervation of the enteric nervous system


  Provides an anatomic explanation of the actions of emotional stress on the stomach and other regions of the GI tract
• The stomach, small intestine, and large intestine are suspended by mesenteries that are the sites of nerves, blood vessels, and lymphatics from the stomach and intestines
• In diseases such as Hirschsprung disease or Chagas disease, plexuses in the digestive tract's enteric nervous system are absent or severely injured, disturbing digestive tract motility and producing dilations in some areas
• MALT

  Multiple free immune cells and lymphoid nodules in the mucosa and submucosa
• The mucosa-associated immune defense system provides an essential backup to the thin physical barrier of the epithelial lining
• Serosa

  A thin layer of loose connective tissue, rich in blood vessels, lymphatics, and adipose tissue, with a simple squamous covering epithelium or mesothelium
• Organs in the digestive system

  • Oral cavity
  • Tongue
  • Teeth
  • Sublingual salivary gland
  • Submandibular salivary gland
  • Liver
  • Gallbladder
  • Small intestine
  • Large intestine
  • Parotid salivary gland
  • Pharynx
  • Esophagus
  • Stomach
  • Pancreas
  • Anus
• The digestive tract normally contains thousands of microbial species, including both useful inhabitants of the gut as well as potential pathogens ingested with food and drink
• The oral cavity is lined with stratified squamous epithelium, which may be keratinized, partially keratinized, or nonkeratinized depending on the location
• Accessory digestive glands

  • Salivary glands
  • Liver
  • Pancreas
• Layers of the digestive tract

  • Epithelium
  • Lamina propria
  • Muscularis mucosae
  • Submucosa
  • Muscularis
  • Serosa
• Epithelial differentiation


  Similar to features in the epidermis and dermis
• Shed cells of nonkeratinized or parakeratinized oral epithelium retain their nuclei
• Keratinized cell layers resist damage from abrasion and are best developed in the masticatory mucosa on the gingiva and hard palate
• The lips have a well-developed core of striated muscle for mobility in ingestion, speech, and communication
• Canker sores occur in the oral cavity, while cold sores or fever blisters occur on the skin
• Lesions occur when immune defenses are weakened, allowing the virus to move into epithelial cells
• Flattened superficial cells of the oral epithelium undergo continuous desquamation, unlike those of the epidermis
• The oral cavity epithelium contains transient antigen-presenting cells and rich sensory innervation
• The muscle fibers of the tongue are oriented in all directions, allowing a high level of mobility
• The tongue is a mass of striated muscle covered by mucosa, which manipulates ingested material during mastication and swallowing
• Lining mucosa overlies a thick submucosa containing minor salivary glands and diffuse lymphoid tissue
• The red vermilion zone lacks salivary or sweat glands and is kept moist with saliva from the tongue
• The lower surface of the tongue is smooth, with typical lining mucosa
• Surfaces of the lips

  • Internal mucous surface, red vermilion zone, outer surface
• Connective tissue between muscle fascicles is penetrated by the lamina propria, making the mucous membrane strongly adherent to the muscular core
• Viral infections with herpes simplex 1 can cause vesicular or ulcerating lesions in the oral mucosa or skin near the mouth