histopathology

• Components of the GI tract

  • Oesophagus - carries food to stomach
  • Stomach → acid & enzymes breakdown proteins
  • Small intestine→ digestion& absorption of nutrients
  • Large intestine → absorption of water

  
• Functions of the GI Tract or Digestive System

  • Ingestion
  • Mechanical digestion
  • Chemical digestion (secretion)
  • Absorption
  • Excretion

  
• The GIT basic architecture

  • Muscular tube about 8 meters long, lined with epithelium
  • Epithelium may be specialised for protection, absorption &/or secretion
  • Tube is enwrapped by connective tissue with blood vessels and nerves
  • Made up of layers

  
• Layers of the GI tube

  • Mucosa
  • Submucosa
  • Muscularis
  • Serosa

  
• The general structure is common to different parts of the GI tract with some variation dependent on the function of each part.

  
• The GI Four distinct functional layers

  • Mucosa: Epithelium (protection, secretions), Lamina propria (supporting), Muscularis mucosa (local mucosal folding& movement)
  • Submucosa: Loose collagen, provides mucosal support, contains large blood vessels, lymphatics and nerves
  • Muscularis propria: Inner circular smooth muscle layer, Outer longitudinal smooth muscle layer
  • Adventitia (Serosa): Loose supporting tissue (major vessels& nerves)

  
• Autonomic, Parasympathetic system controls GI secretions and blood flow in the submucosa (Meissner's plexus) and GI movements in the muscularis propria (Auerbach's plexus)
• Meissner's plexus


  Small clusters of ganglion cells in the submucosa

  
• FNM [025] Histology of the Gastrointestinal tract

  
• Objectives


  By the end of this session and the practical one students should be able to:

  • list and describe the main functions of the oesophagus, stomach, small intestine, large intestine
  • state whether the epithelial lining of the gut, in any given region, is secretory, absorptive or protective
  • list the major histological features of epithelium in that region
• Components of the GI tract

  • Oesophagus - carries food to stomach
  • Stomach → acid & enzymes breakdown proteins
  • Small intestine→ digestion& absorption of nutrients
  • Large intestine → absorption of water

  
• Components & functions of the digestive system

  • Ingestion
  • Mechanical digestion
  • Chemical digestion (secretion)
  • Absorption
  • Excretion

  
• The GIT basic architecture

  • MUSCULAR TUBE about 8 meters long, lined with epithelium
  • Epithelium may be specialised for protection, absorption &/or secretion
  • Tube is enwrapped by connective tissue with blood vessels and nerves
  • Made up of LAYERS

  
• Layers of the GI tube

  • Mucosa
  • Submucosa
  • Muscularis
  • Serosa

  
• Mucosa


  • Epithelium (protection, secretions)
  • Lamina propria (supporting)
  • Muscularis mucosa: local mucosal folding& movement

  
• Submucosa


  • Loose collagen, provides mucosal support
  • Contains large blood vessels, lymphatics and nerves

  
• Muscularis propria


  • Inner circular smooth muscle layer
  • Outer longitudinal smooth muscle layer
• Adventitia (Serosa)


  Loose supporting tissue (major vessels& nerves)
• Autonomic, Parasympathetic system controls GI secretions and blood flow (Meissner's plexus) and GI movements (Auerbach's plexus)
• Submucosa


  Loose CT with scattered Ganglion cells
• Auerbach/ Myenteric plexus is demonstrated by S-100 immune stain to show neurons
• The oesophagus carries food to the stomach
• Functions of oesophageal layers

  • MUCOSA: Stratified squamous epithelium provides protection, Mucous glands→ mucus to lubricate the esophagus and help shield the mucosa from stomach acid
  • SUBMUCOSA: provides blood and nerve supply
  • MUSCULARIS PROPRIA: allows contraction and expansion to move substances
  • ADVENTITIA: outer covering, loose attachment of esophagus to surrounding organs

  
• The mucosal lining of the oesophagus is non-keratinized stratified squamous epithelium

  
• The submucosal gland (G) of the oesophagus consists of mucous cells (D is the duct)

  
• The gastro-oesophageal junction is a medically important region where dysphagia, acid reflux, and Barrett's oesophagus can occur
• Metaplasia


  A change of one type of mature differentiated tissue into another type of the same category
• Intestinal metaplasia


  A change of the stratified squamous epithelium into simple columnar intestinal type epithelium to accommodate for the chronic irritation by the acid
• Intestinal metaplasia in Barrett's oesophagus is precancerous and can lead to intestinal type adenocarcinoma
• Functions of the stomach

  • Storage: 1500ml capacity (holds about 4 l), collapsible and expandable (rugae)
  • Forms→ semifluid chyme (a paste of food mixed with stomach acid and enzymes)
  • Protection: HCl→ kills bacteria, Mucous→ prevents damage to stomach from alcohol, aspirin, NSAIDs, etc.
  • Absorption: Small amounts of H2O, alcohol, drugs
  • Mechanical digestion: via muscles
  • Secretions: enzymes and hormones

  
• Layers of the gastric (stomach) wall

  • Mucosa
  • Submucosa
  • Muscularis externa
  • Serosa

  
• The gastric mucosa has gastric pits and gastric glands
• The gastric mucosa contrasts with the oesophageal mucosa

  
• Secretions of the gastric glands

  • HCL
  • Pepsinogen
  • Gastric lipase
  • Mucous
  • Intrinsic factor
  • Gastrin
• Other less identified cells in the gastric mucosa include ECL cells and stem cells
• The cell types and distribution in the gastric mucosa change according to the gastric site
• Cell types, site and function in the gastric mucosa

  • Mucous Cells
  • Endocrine cells
• Chronic gastritis affecting the antrum is caused by H pylori infection in 90% of patients
• Complications of H pylori infection

  • H pylori gastritis → increased acid secretion → peptic ulcer of the stomach or duodenum
  • H. pylori infection leads to increased risk of gastric cancer
• Pathogenesis of H pylori gastritis

  • Flagella, allowing bacterial motility in the viscous mucus
  • Urease enzyme: generates ammonia from endogenous urea → elevating the pH around the organisms thus protecting them from the high gastric acidity
  • Adhesins: enhance bacterial adherence to surface cells
  • Toxins may be involved in ulcer or cancer development