General Structure of Gastrointestinal Tract (GIT) - PDF

GENERAL STRUCTURE OF GASTROINTESTINAL TRACT (GIT) Dr. Amir M Ali Associate Prof of Anatomy  In general, the GIT made up of 4 principal layers: 1. Mucosa 2. Submucosa 3. Muscularis 4. Serosa Mucosa ▪ Epithelium, rest on basal lamina ▪ Lamina propria: O...

GENERAL STRUCTURE OF GASTROINTESTINAL TRACT (GIT) Dr. Amir M Ali Associate Prof of Anatomy  In general, the GIT made up of 4 principal layers: 1. Mucosa 2. Submucosa 3. Muscularis 4. Serosa Mucosa ▪ Epithelium, rest on basal lamina ▪ Lamina propria: Of loose CT rich in blood, lymph vessels and smooth muscle cell ▪ Muscularis mucosae Separating the mucosa from the submucosa Submucosa ▪ of dense CT with many blood and lymph vessels, and glands ▪ contains submucosal nerve plexus ( Meissner`s) Muscularis of two layers: 1. Inner circular layer 2. Outer longitudinal layer ▪ Creates sphincter ▪ Contains the myenteric nerve plexus (Auerbach`s) Serosa ( adventitia) ▪ Thin layer of loose CT Esophagus Mucosa: covered by nonkeratinised stratified squamous epithelium. Submucosa contains mucus-secreting glands (esophageal glands) Muscularis striated muscle in the upper third mixture of striated and smooth in the middle third smooth muscle in the lower third  Stomach Mucosa ▪ simple columnar epithelium and presence of gastric pits. – Rugae: mucosal folds allow expansion – Many intrinsic glands Goblet cells Gastric glands Stomach is divided into three regions on the basis of nature of glands: Cardiac region Fundic region (fundus & body) Pyloric region Cardiac region ▪ Conatins mucous secreting cardiac glands in lamina propria. Funadic region Contains Mucous neck cells Parietal (oxyntic) cells (HCL) Chief (peptic/zymogen) cells Submucosa of dense CT infiltrated by lymphoid cells, macrophages and mast cells  Muscularis externa – Oblique layer (inner) – Circular layer ( middle) Pyloric sphincter – Longitudinal layer (outer) Serosa, - thin, covered by mesothelium of peritoneum  Small intestine Mucosa: Lined by simple columnar epithelium with goblet cells Many modfication for absorption 1. Length – Increase surface area 2. Plicae circularis ( kerckring`s valves) – Transverse semilunar, circular, or spiral ridges of mucosa – Increase surface area – Most developed in the jejunum – Move chyme 3. Villi – Finger-like out-growth of mucosa – 0.5-1.5 mm long – Between them are the opening of the intestinal glands – Move chyme, increase contact – Contain lacteals: remove fat 4. Microvilli: – Increase surface area – Finger-like extensions of the plasma membrane of apical epithelial cell (brush border) Modifications decrease distally Lamina propria: ▪ Of loose CT ▪ Penetrate the core of villi ▪ Together with submucosa the contains aggregation of lymph nodules (Peyer`s patches) Submucosa: In the duodenal potion, contain the duodenal glands (Burner`s) Muscularis of two layers: 1. Inner circular smooth muscle fibers 2. Outer longitudinal smooth muscle fibers. Serosa Duodenum ▪ Presence of Brunner’s glands in submucosa Jejunum ▪ Villi are tongue shaped. ▪ Absence of Brunner’s glands. Ileum ▪ Presence of lymphoid aggregations in lamina propria known as Peyer’s patches. ▪ Villi are short & finger like.  Large intestine ▪ Mucosa: Absence of Plicae circulares and villi - Presence of Microvilli - Presence of Crypts of Lieberkuhn - Presence of Goblet cells in large number ▪ Submucosa ▪ Muscularis externa: ▪ Inner circular layer - thin compared to small intestine. ▪ Outer longitudinal layer- forms Taenia coli. ▪ Adventitia: Appendices epiploicae (peritoneum forms pouch like processes filled with fat) Vermiform Appendix ▪ Large accumulations of lymphoid tissue in lamina propria ▪ Intestinal villi are usually absent. ▪ Absence of taenia coli. Rectum ▪ Absence of taenia. ▪ Absence of appendices epiploicae. Anal canal ▪ Epithelium: upper part-simple columnar, middle part-stratified squamous non-keratinized, lower part-covered by true skin. ▪ Mucosa has longitudinal folds (Anal columns.) ▪ Externa-circular muscle forms involuntary internal sphincter. “May I please be excused? My brain is full !!”