GIT Histo

• Parts of the gastrointestinal tract

  First part = Pharynx

  2nd part = Esophagus

  3rd part = Stomach

  4th part = Small Intestine

  5th part = Cecum and appendix

  6th part = Large intestine

  7th part = Rectum/Anus
• Operational GIT scheme

  • Ingestion = 2L/day
  • Absorption = 8.8L/day
  • Secretions = 7L/day
  • Feces = 0.2L/day
• Secretions of the GIT

  • Saliva:1L
  • Stomach: 2L
  • Bile: 1L
  • Pancreas: 2L
  • Small intestine:1L
• Four basic distinct layers in the GI tube

  • Mucosa (made up of epithelium, lamina propria & muscularis mucosae)
  • Submucosa (made up of submucosal plexus AKA plexus of meissner)
  • Muscularis externa (made up of myenteric plexus AKA plexus of auerbach)
  • Serosa (thin layer of connective tissue)

  
• Epithelium in different parts of the GI tract

  • Nonkeratinized Stratified Squamous = mouth, pharynx, esophagus & anus
  • Simple Columnar = stomach, small intestine & large intestine
• Folds of the epithelium in different parts of the GI tract

  • Esophagus: none
  • Stomach: Rugae, gastric pits
  • Small Intestine: Plicae circulares, Villi, Crypts of Lieberkuhn, microvilli
  • Large Intestine: Haustra, Intestinal glands
• The mucosa of the GIT

  • General pattern: epithelial lining, lamina propria of loose ct & muscularis mucosae of smooth muscle
  • Forms a selectively permeable barrier to the contents of the digestive tract
  • Involved in the digestion of food and the transport of nutrients (absorption) into the body in the stomach and small intestine
• Specialized structures in the submucosa of the GIT

  • Esophagus: Submucosal mucous glands
  • Duodenum: Brunner's glands
  • Ileum: Peyer's Patches
  • Stomach & Large Intestine = None
• Submucosa of the GIT

  Loose connective tissue with blood and lymph vessels, and nerve plexuses (Meissner's plexus). Glands and Lymph nodules may also be present in this layer.
• Smooth muscle layers in the muscularis externa of the GIT

  • Esophagus, Small intestine & Large Intestine: 2 (circular and longitudinal)
  • Stomach: 3 (oblique, circular, and longitudinal)
• Muscularis externa

  Smooth muscle layer with inner circular and outer longitudinal bands,

  • Contains a myenteric (Auerbach's) nerve plexus and blood and lymph vessels
  • C.T. lies between these two layers
• The muscularis mucosae causes movements of the mucous layer only, independent of the rest of the digestive tract
• Serosa of the GIT

  Thin layer of loose connective tissue, rich in blood and lymph vessels and adipose cells, containing fluid-producing cells

  • Stomach, Small Intestine & Large Intestine: Visceral Peritoneum; covered externally by mesothelium (simple squamous)
  • Oesophagus & Anus: Adventitia (because there are not in a cavity)
• The mesothelium tissues are the layer (membranes) that surround and protect organs of the chest, abdominal cavity, and pelvis
• GIT nerve plexus

  GIT wall contains two intrinsic nerve plexuses that are part of the autonomic nervous system

  ❖Submucosal nerve plexus & Myenteric nerve plexus

  ❖Regulate mobility and secretory activity of the GI tract organs
• Esophagus

  • Straight tube, ~25 cm long
  • Expandable lumen: extensive muscularis mucosa, elastic fibers in submucosa
  • Protective epithelium (stratified squamous non-keratinized)
  • Muscularis externa: upper 1/3 = striated (skeletal) muscle, middle 1/3 = mixed smooth and striated, lower 1/3 = smooth muscle
  • Delivers food and liquid from pharynx to stomach
• Structure found in the oesophagus

  • Lymphatic nodules (part of GALT) may be present in the lamina propria and/or submucosa of the esophagus
  • Esophageal glands (submucosal) secrete acidic mucous which lubricates the luminal wall; ducts carry secreted mucous to the lumen
• Specializations in esophageal tissues

  1. Tubuloacinar mucus-secreting glands (esophageal glands proper) are present in the submucosa. Their ducts extend to the esophageal lumen.
  2. Small branched mucus-secreting glands (in the lamina propria near the stomach). These are called esophageal cardiac glands.
  3. The muscular layer of the esophagus changes from striated muscle near the mouth, to smooth muscle near the stomach.
  4. A serosal layer (simple squamous) as the outermost layer is only found in the peritoneal cavity, below the diaphragm, and near the stomach.
• Gastroesophageal junction

  There is abrupt epithelial transition from stratified squamous non-keratinized (esophagus) to simple columnar (stomach)

  <|>Cardiac glands of the esophagus (in lamina propria) secrete neutral mucous to protect the oesophagus from stomach acid

  <|>Inferior esophageal sphincter prevents reflux of stomach contents into oesophagus
• Medical conditions associated with gastroesophageal junction

  • Pyrosis (heartburn; acid reflux)
  • Dysphagia (difficulty in swallowing)
  • Achalasia (failure to relax; lack of peristalsis in the lower esophagus due to loss of myenteric neurons)
• Inferior esophageal sphincter

  • Physiological sphincter, pressure difference between esophagus and stomach, diaphragmatic contraction, unidirectional peristalsis, prevents reflux of stomach contents into esophagus
• Lymph nodule (Ly) and infolded epithelium (Ep*) are present at the gastroesophageal junction
• Medical conditions associated with gastroesophageal junction

  • Barrett's esophagus/Intestinal metaplasia: change in esophageal mucosa from squamous to columnar, result of prolonged injury, pre-cancerous
  • Esophageal cancer: squamous cell carcinoma (carcinogenesis of basal cells), adenocarcinoma (progression of Barrett's esophagus or from submucosal glands)
• Stomach regions

  • Cardia (cardiac stomach)
  • Body (corpus) and fundus
  • Pylorus (pyloric stomach)
• Stomach glands

  • Cardia = Cardiac glands;
  • Fundus & Corpus = Gastric glands
  • Pylorus = Pyloric glands
• Rugae & Pits of the stomach

  • Rugae: Longitudinal folds in the stomach mucosa that allow distention
  • Pits (foveolae): invaginations of mucosal epithelium (similar to intestinal crypts*); continuous with the lumen of underlying glands
• Stomach (Cardiac Region)

  • Mucosa: simple columnar with oval nuclei, mucous secreting cardiac glands in lamina propria;
  • Submucosa: connective tissue;
  • Muscle layer: inner circular, outer longitudinal;
  • Serosa: simple squamous epithelium
• Stomach (Fundic Region)

  • Mucosa: simple columnar with oval nuclei, presence of gastric glands in lamina propria;
  • Cells: mucous neck cells, parietal cells, chief cells, enteroendocrine cells, undifferentiated cells;
  • Submucosa: blood vessels, lymphatics, Meissner's plexus;
  • Muscularis Externa: inner oblique, middle circular, outer longitudinal layer;
  • Serosa: mesothelial cells, loose connective tissue
• Stomach (Pyloric Region)

  • Mucosa: pyloric glands in lamina propria & deeper gastric pits;
  • Muscularis Externa: inner circular (thickened to form pyloric sphincter) and outer longitudinal layer;
  • Submucosa & Serosa: same as fundic part
• Small Intestine

  • Mucosa: plicae circulares, villi, microvilli, goblet cells, crypts of Lieberkuhn;
  • Submucosa: blood vessels, lymphatics, Meissner's plexus;
  • Muscularis Externa: outer longitudinal & inner circular layers
  • Serosa/Adventitia
• Small Intestine

  • Duodenum: Presence of Brunner's glands in submucosa
  • Jejunum: Villi are tongue-shaped. Absence of Brunner’s glands.
  • Ileum: Presence of Peyer's patches, villi are short and finger-like
• Large Intestine

  • Mucosa = Absence of plicae circulares and villi, Presence of microvilli, crypts of Lieberkuhn, abundant goblet cells;
  • Submucosa;
  • Muscularis Externa: thin inner circular, outer longitudinal (taenia coli);
  • Adventitia: appendices epiploicae (peritoneum forms pouch-like processes filled with fat)
• Vermiform Appendix

  • A small blind-ending diverticulum.
  • Large accumulations of lymphoid tissue, absence of villi, poorly formed crypts, thin muscularis externa, absence of taenia coli
• Rectum

  • The dilated distal portion of the alimentary canal.
  • Presence of transverse rectal folds in upper part, straight intestinal glands, continuous longitudinal muscle, absence of taenia and appendices epiploicae
• Anal Canal

  • Epithelium: Upper part - simple columnar, middle part - stratified squamous non-keratinized, lower part - keratinized skin;
  • Mucosa has anal columns (longitudinal folds) and pectinate line (smucosal folds between the anal columns)
  • Muscularis externa circular muscle forms involuntary internal anal sphincter
• large intestine

  ❖It consists of appendix, colon, rectum and anal canal.
• Large intestine – transition to anal canal

  • Colorectal zone: simple columnar epithelium with goblets cells
  • Anal transition zone: transition between the simple columnar epithelium of the rectal mucosa and the stratified squamous epithelium of the perianal skin
  • Squamous zone: stratified squamous becomes keratinized (note: lymphatic nodule & sphincters)