Digestive System

• Name the type of papillae on the dorsal surface of the tongue and state their respective locations on the tongue
  • Filiform papillae: anterior dorsal tongue
  • Fungiform papillae: Tip of the tongue
  • Circumvallate papillae: Anterior to the sulcus terminalis
  • Foliate papillae: Lateral edges of the tongue
• Name the cell types of the taste bud
  • Neuroepithelial (Sensory) cells: Elongated cells that have microvilli on their apical surface and are connected with afferent endings of CN VII, CN IX and CN X at their base
  • Supporting cells: Similar to sensory but they do not synapse with afferent nerve endings.
  • Basal cells: Stem cells for sensory and supporting cells.
• Describe the histological structure of the ductal and secretory part of a mixed salivary gland
  • Secretory part: Mucous cells with Serous demilunes (Fr. half-moon)
  • Ductal part
    • Intercalated ducts
      • Low cuboidal lining
      • Bicarbonate secretion and Cl- absorption
      • *Carbonic anhydrase activity
    • Striated ducts
      • simple cuboidal lining that gradually becomes columnar
      • Na+ reabsorption
      • K+ and bicarbonate secretion
    • Excretory ducts
      • simple cuboidal → pseudostratified columnar/ stratified cuboidal → stratified squamous lining
      • Opens into the oral cavity
• Describe the histological structure of the oesophagus
  • Mucosa
    • Non-keratinizing stratified squamous epithelium
    • Diffuse lymphatic tissue the in lamina propria
    • Muscularis mucosa (longitudinal smooth muscles)
  • Submucosa
    • Dense irregular connective tissue
    • Submucosal (Meissner’s) plexus
  • Muscularis Externa
    • Longitudinal and circular muscle layers
    • Myenteric (Auerbach’s) plexus
  • Adventitia (thoracic part) or Serosa (Visceral peritoneum in the abdominal part)
• Describe the histological appearance of the parenchyma of the parotid gland
  1. Acinus
     • Serous acini
     • Pyramid shaped serous cells
  2. Intercalated duct
     • Well developed
     • Low cuboidal epithelial cells
  3. Striated duct
     • Well developed
     • Simple cuboidal epithelium that gradually becomes columnar as it approaches the excretory duct – basal infoldings w/elongated mitochondria and basolateral folds
  4. Excretory duct
     • simple cuboidal → pseudostratified columnar/stratified cuboidal → stratified squamous epithelium
• Describe the gastric pit and gland with reference to the distribution of cells and function
  • Gastric pits (foveolae) are openings visible on the stomach mucosa at higher magnifications.Surface:
    • Surface mucous cells: Mucin secretion
    Isthmus
    • Undifferentiated adult stem cells: regeneration
    Neck
    • Parietal cell: HCl and Intrinsic factor secretionMucous neck cells: Mucin secretionEnteroendocrine cells: Hormone secretion
    Fundus
    • Chief cells: Zymogen secretionParietal cellsEnteroendocrine cells

• Describe the parts and respective functions of the ductal system of salivary glands
  • Intercalated ducts: Leads from the acinus
    • Low cuboidal lining
    • Bicarbonate secretion and Cl- absorption
    • *Carbonic anhydrase activity
  • Striated ducts: because of the presence of striations in the basal aspect
    • simple cuboidal lining that gradually becomes columnar
    • Na+ reabsorption
    • K+ and bicarbonate secretion
  • Excretory ducts: larger ducts that empty into the oral cavity
    • simple cuboidal → pseudostratified columnar/ stratified cuboidal → stratified squamous lining
    • Opens into the oral cavity
• Name the cell types of the gastric gland epithelium and state their respective functions
  • Mucous neck cells – mucin secretion
  • Chief cells – pepsinogen and weak lipase secretion
  • Parietal cells – HCl and intrinsic factor secretion
  • Enteroendocrine cells – hormone secretion
  • Undifferentiated adult stem cells – regeneration

State the structural differences in parietal cells between its active and inactive forms

• Name the cell types of the duodenal epithelium and state their respective functions
  • Enterocytes – absorption
  • Goblet cells – mucin secretion
  • Paneth cells – antimicrobial substance secretion
  • Enteroendocrine cells – produce various paracrine and endocrine hormones
  • M cells (Microfold cells) – selective endocytosis of antigens and transport to intraepithelial lymphocytes and macrophages which then travel to lymphoid tissue to mount immune responses
• Describe the lamina propria of the small intestine
  • Mucosal glands: extend into the lamina propria
  • Blood and lymphatic vessels: Fenestrated capillaries and lymphatic capillaries that absorb metabolites, lipids, and proteins
  • Lymphatic tissue: Lymphocytes, plasma cells, macrophages, eosinophils, mast cells
    • Diffuse lymphatic tissue (GALT): Diffusely arranged Lymphocytes and plasma cells
    • Peyer’s patches: Aggregated lymphocytes that occupies the lamina propria and submucosa.
• What is a “collagen table’ in the large intestines? State its significance
  • A thick layer of collagen and proteoglycans that lies between the basal lamina of the epithelium and that of the fenestrated absorptive venous capillaries
  • Regulates water and electrolyte transport from the intercellular compartment of the epithelium to the vascular compartment
• Describe the mucosa of the rectum and give one clinical correlate
  • Glands: Straight, tubular intestinal glands
  • Epithelium: Simple columnar epithelium
  • Lamina propria: Has a collagen table, pericryptal fibroblast sheath, GALT and lymphatics
  • Clinical correlate: Colorectal cancer

With the aid of diagrams outline the classification of liver lobules

• Classic Liver Lobule (A): Based on blood flow pattern, with the central vein as the axis
• Liver acinus (B): Based on susceptibility to injury. Has 3 zones
• Portal lobule (C): Based on biliary drainage, with the portal triad as the axis

Illustrate the zonation of a liver acinus

• Describe the following regarding the liver: Space of Disse, Kupffer cells, Ito cells, Glisson’s Capsule, Space of Mal
  • Space of Disse: Perisinusoidal space. Found between the hepatocytes and sinusoids
  • Kupffer cells: Phagocytic macrophages within the lumen of liver sinusoids
  • Ito cells: Hepatic stellate cells that store vitamin A, and differentiate into myofibroblasts during pathological conditions (eg. cause bridging fibrosis by secreting collagen – a feature of liver cirrhosis)
  • Glisson’s capsule: Fibrous connective tissue enclosing the liver
  • Space of Mal: Periportal space between the stroma of the portal canal and outermost hepatocytes
• What are the histological peculiarities of the gall bladder wall
  • Absent muscularis mucosae
  • Absent submucosa
  • Rokitansky-Aschoff sinuses extend through the muscularis externa. They are pathological changes.
  • Smooth muscle bundles in muscularis externa are randomly oriented
• Name the principal cell types of the islets of Langerhan and state their respective secretions
  • A cells – Glucagon production
  • B cells – Insulin production
  • D cells – Somatostatin production
  • PP cells (F cells) – pancreatic polypeptide secretion
  • D1 cell – Vasoactive intestinal polypeptide secretion
  • EC cell – secretin, motilin and substance P production
  • Epsilon cell – Ghrelin production