digestive

• Digestive System


  The system responsible for the digestion of food, absorption of digested substances, and excretion of undigested materials
• Components of the Digestive system

  • Digestive tract
  • Digestive glands
• Functions of the Digestive system

  • Digestion of food
  • Absorption of digested substances
  • Excretion of undigested materials
• General histologic layers of the digestive tract

  • Mucosa (mucous membrane)
  • Submucosa
  • Muscularis externa
  • Adventitia/Serosa
• Mucosa (Tunica mucosa, mucous membrane)


  Consists of three layers: Epithelium, Lamina propria, Muscularis mucosa
• Submucosa


  Consists of two relatively thick smooth muscle coats or layers: Inner layers (muscle fibers are arranged circularly), Outer layers (muscle fibers are arranged longitudinally)
• Adventitia/Serosa

  Outermost layer of the digestive tract. In those that are covered by peritoneum the outer covering is lined by mesothelium known as serosa.
• Oral Cavity (Mouth)


  Initial segment of the digestive tract and divided into two regions: Vestibule, Oral Cavity proper
• Histologic layers of the Oral Cavity

  • Mucosa
  • Submucosa
  • Muscularis externa
  • Adventitia
• Tongue


  A muscular organ that plays an important role in mastication, deglutition and speech. Sulcus terminalis is the inverted "V" shaped shallow furrow that separates the anterior to the posterior part of the tongue. The apex of the "V" is called the Foramen cecum.
• Lingual Papillae


  Projections of the mucosa that are confined to the dorsal surface of the anterior tongue. Consist of core of connective tissue that are lined externally with Stratified Squamous Non-Keratized Epithelium.
• Types of Lingual Papillae

  • Filiform Papillae
  • Fungiform Papillae
  • Circumvallate Papillae
• Filiform Papillae


  The most numerous papillae, slender and tapering and are found all over the dorsal surface of the anterior tongue.
• Fungiform Papillae


  Contains connective tissue which are rich in capillaries; appear as pinhead-size red dots to the naked eye. Taste buds are occasionally present on their surface.
• Circumvallate Papillae


  Arranged along the sulcus terminalis. They are the largest (1 to 3 mm in diameter) but the least (only 6 to 14) of the lingual papillae. About 200-300 taste buds are embedded on its lateral surface.
• Taste Buds


  Organs responsible for the sense of taste. They are ovoid structures that are embedded in the epithelium of circumvallate and fungiform papillae. They consist of densely-packed fusiform cells.
• Cells of the Taste Buds (Light Microscope)

  • Sustentacular or Supporting cells
  • Neuroepithelial or Gustatory cells
  • Basal Cells
• Sustentacular or Supporting Cells

  Slender, spindle shape cells whose free surface is covered by microvilli. They are darker staining cells than neuroepithelial cells.
• Neuroepithelial or Gustatory Cells


  Slender, spindle shape cells whose free surface is covered by microvilli. They are lighter staining cells than sustentacular cells.
• Basal Cells


  One of the three cell types of the taste buds seen under light microscope.
• Esophagus


  Long muscular tube (20 to 25 cm) that serves as a passageway for food from the pharynx to the stomach.
• Histologic layers of the Esophagus

  • Mucosa
  • Submucosa
  • Muscularis externa
  • Adventitia
• Mucosa of the Esophagus


  Forms longitudinal folds which flatten out when swallowed materials passes through the organ.
• Submucosa of the Esophagus


  Thicker than the lamina propria, consists of connective tissue, elastic fibers, blood vessels and esophageal glands.
• Muscularis Externa of the Esophagus

  Outer layer consists of longitudinal muscle fibers, while inner layer consists of circular muscle fibers.
• Stomach

  1. shaped hollow organ located in the left upper quadrant of the abdomen. Presents a left or lateral border (great curvature), a medial border (lesser curvature), an anterior surface and a posterior surface. Grossly subdivided into: Cardia portion, Fundus, Body, Pyloric region.
• Mucosa of the Stomach

  The mucosa and part of the submucosa forms longitudinal anastomosing folds or wrinkles (rugae). At intervals, the surface epithelium invaginates into the lamina propria to form shallow grooves (gastric foveolae or pits).
• Glands of the Stomach

  • Fundic (Gastric) glands
  • Cardiac glands
  • Pyloric glands
• Fundic (Gastric) Glands


  Located in the fundus and body of the stomach. Consists of five types of cells: Oxyntic (parietal) cells, Zymogenic (chief) cells, Mucous neck cells, Stem cells, Enteroendocrine cells.
• Parietal or Oxyntic Cells


  Pyramidal in shape with oval or round nucleus. The most easily identified cells of the fundic glands in the H&E preparation. Produce hydrochloric acid and are involved in the absorption of Vitamin B12.
• Chief or Zymogenic Cells


  Most numerous cells of the fundic glands especially in the basal region. They have secretory granules that contain pepsinogen.
• Mucous Neck Cells


  Generally confined in the neck of the fundic glands. Contains numerous secretory granules that contain mucin.
• Stem Cells


  Play an important role in renewing the cell population of the stomach. Can differentiate into surface mucous cells or gastric cells.
• Enteroendocrine Cells/Enterochromaffin Cells/Argentaffin Cells


  Hormone producing cells of glands of the stomach, large and small intestines. In the stomach the types are: G cells (secrete Gastrin), EC cells (secrete Serotonin), D cells (secrete Somatostatin), ECL cells (secrete Histamine).
• Cardiac Glands


  The least numerous of the gastric glands. Also contains all the cell types of the gastric glands.
• Pyloric Glands


  Shorter but more coiled than fundic and cardiac glands.
• Gastric Mucosal Barrier

  Prevents HCl and the gastric enzymes from damaging the mucosa of the stomach. It has three components: compact epithelium, layer of mucus, bicarbonate ions.
• Histologic Layers of the Stomach

  • Mucosa
  • Submucosa
  • Muscularis externa
  • Adventitia/Serosa
• Small Intestine


  Segment located between the stomach and the large intestine. The organ responsible for the absorption of nutrients from the digested food. Composed of three segments: Duodenum, Jejunum, Ileum.
• Lamina Propria and Muscularis Mucosae of the Small Intestine

  Consists of loose connective tissue and smooth muscle fibers. Embedded within the intestinal glands or crypts of Lieberkuhn are 5 cell types: Stem cells, Enterocytes, Goblet cells, Paneth cells, Enteroendocrine cells.