Regional Histology of the GIT PDF

Regional histology of the GIT YBOD200 Ms M Mahasha Learning Objectives  Identify, describe, and discuss the general components of the tubular organs unique to each region  Compare and contrast the microanatomy of each region of the tubular organs of the...

Regional histology of the GIT YBOD200 Ms M Mahasha Learning Objectives  Identify, describe, and discuss the general components of the tubular organs unique to each region  Compare and contrast the microanatomy of each region of the tubular organs of the gastrointestinal tract  Describe and discuss how the unique microanatomy is suited for specific function in the:  Oesophagus  Stomach  Duodenum  Jejunum and ileum  Appendix  Colon  Introduction  Gastrointestinal tract functions to break down food for absorption into the body  Gastrointestinal tract is regionally specialized to serve the changing functions of the tract from mouth to anus  At four points along the tract the mucosa undergoes abrupt transitions: 1. Oesophago-gastric junction – distal oesophagus joins proximal stomach 2. Gastroduodenal junction – pyloric stomach joins duodenum of the small intestines 3. Ileocecal junction – ileum of small intestines joins cecum of large intestine 4. Rectoanal junction – between the rectum and anal canal Oesophagus  Oesophagus  Muscular tube that carries food from the pharynx to the stomach  In a relaxed state the oesophageal mucosa is deeply folded, which allows marked distension during passage of the bolus  Lumen of oesophagus is lined with stratified squamous epithelium, with a narrow lamina propria that contains scattered lymphoid tissue  Submucosa is quite loose with several elastin fibres and also contains E – Stratified squamous epithelium G – Serous mucous glands seromucous glands, similar to the salivary glands CM – Inner circular muscle LM – Outer longitudinal muscle  Muscularis propria is thick and contains the outer longitudinal muscle MM - Muscularis mucosa Ly – Lymphoid aggregates and inner circular muscle layers SM – Submucosa  Oesophagus  Oesophagus is subdivided into three:  Upper portion – Mascularis externa is entirely skeletal muscle, and this is essential for swallowing under voluntary control  Middle portion – Mascularis externa is made up of both skeletal and smooth muscle Sk – Skeletal muscle Sm – Smooth muscle  Lower portion – Mascularis externa is entirely smooth muscle  Oesophago-gastric juction  At junction of oesophagus with stomach the mucosa undergoes a transition  Stratified squamous epithelium is now replaced with simple columnar epithelium forming a tightly packed glandular secretory mucosa  Muscularis mucosae is continuous; however, not easily seen in the stomach where it is directly beneath the glands  Submucosa and muscularis propria continue uninterrupted beneath the mucosal junction GM – Glandular secretory mucosa MM – Muscularis mucosae MP – Muscularis propria  Muscularis propria does not form a defined anatomical sphincter, rather a SE – Stratified squamous epithelium SM - Submucosa physiological sphincter mechanism is described Stomach  Stomach  Portion of GI tract that partially digests food to form chyme  Anatomical divided into 4 parts : Cardia, fundus, body and pylorus  Histologically divided into 3 parts ;  Cardia – small area of mucous secreting glands surrounding the entrance of the oesophagus  Body/Fundus – major histological region of the stomach(histologically, fundus and body are identical)  Pylorus – most distal part of the stomach  Body of Stomach  Mucosa is thrown into regular folds (rugae) and consists of regular gastric glands that extend from muscularis mucosae to open in the stomach lumen – occurs via gastric pits or foveolae  Inner circular layer of the muscularis propria has another added reinforcement layer – inner oblique layer  Submucosa is relatively loose and contains larger blood vessels C – Inner circular layer of muscularis propria GP – Gastric pits/foveolae L – Outer longitudinal layer of muscularis propria  Serosal layer, which covers peritoneal surface, is thin and barely M – Mucosa visible MM – Muscularis mucosae O – Inner oblique layer of muscularis propria SM - Submucosa  Gastric gland  Secrete gastric juice containing hydrochloric acid and the pepsin  Glands are divided into three parts: Isthmus, neck and base  Gastric gland  Consists of 3 major cell types:  Parietal cells – secrete gastric acid as well as intrinsic factor (a glycoprotein required for the uptake of vitamin B12 in the small intestine)  Neck mucous cells – have larger secretory granules and secrete a more acidic mucin substance o Stem cells – give rise to all other gastric gland cells  Chief (Peptic) cells – secrete pepsin, can be seen by their strongly basophilic granular cytoplasm o Neuroendocrine cells - secrete serotonin PC - Parietal cells CC - Chief cells E - Neuroendocrine cells  Pylorus of Stomach  Glands in the pyloric region are branched and coiled, gastric pits occupy about half the thickness of the mucosa.  Glands are lined by mucous-secreting cells and a small number of acid-secreting cells (parietal cells)  Prominent muscularis mucosae separated glands from underlying submucosa.  Scattered among pyloric cells are G cells which secrete G – G cells gastrin (peptide hormone) which promotes secretion of pepsin MM – Muscularis mucosae P – Gastric pits and acid by gastric glands to enhance gastric motility.  Pylorus of Stomach  Pyloric sphincter marks a transition from glandular secretory type mucosa of the stomach to the villous absorptive type mucosa of the duodenum  Brunners glands, which secrete a thin, alkaline mucous, are found in the submucosa of the duodenum and often extend into the mucosa  Pyloric sphincter has a thickening of the circular layer of the B – Brunners glands muscularis propria at the gastroduodenal junction CM – Inner circular layer D – Duodenum LM – Outer longitudinal layer  Circular and longitudinal layers of muscularis propria are PS – Pyloric sphincter continuous between pylorus and duodenum S - Stomach Small Intestine  Small intestine  Mucosa and submucosa of the small intestine are arranged in circular folds termed plicae circulares – particularly numerous in the jejunem  Mucosal surface made up of several Villi which then has several microvilli present on the luminal surface of the enterocytes CM – Circular layer  Enterocytes are columnar epithelial cells which cover the villi E – Columnar epithelium LM – Longitudinal layer MM – Muscularis mucosae Mv – Microvilli PC – Plicae circulares SM – Submucosa  Small intestine  Muscularis mucosae lies beneath crypts and seperates mucosa from submucosa  Vascular submucosa extends into and forms core of plicae circulares  Peritoneal aspect of muscular propria is invested by loose collagenous serosa CM – Circular layer E – Columnar epithelium LM – Longitudinal layer MM – Muscularis mucosae Mv – Microvilli PC – Plicae circulares SM – Submucosa  Duodenum  Duodenal mucosa is typical to the rest of the small intestine.  Numerous elongated villi are present, between which are crypts of Lieberkuhn  Height of villi decreases as we move along the small intestine  Unique feature of duodenum is extensive mass of coiled branched tubular Brunners glands.  Pale-stained Brunners glands occupy the entire submucosa which is deep to the muscularis mucosae.  Small portion sometimes found in lamina propria where duct C – Crypts of Lieberkuhn MM – Muscularis mucosae and gland empties into the crypts V - Villi  Duodenal Epithelium  Duodenal epithelium has goblet cells present with mucigen granules  Next to the mucin granules are golgi apparatus and rough endoplasmic reticulum  Surrounding the goblet cells are several enterocytes G – Goblet cells  These enterocytes have less prominent rough endoplasmic Go – Golgi apparatus reticulum but have high numbers of free ribosomes and M – Mitochondria R – Ribosomes mitochondria rER – Rough endoplasmic reticulum  Intestinal Villi  Lined by simple columnar epithelium which is continuous with that of the crypts  Lamina propria extends between crypts and into core of each villus and contains a rich vascular and lymphatic network – absorption of digestive products  Muscularis mucosae is immediately beneath crypts C – Crypts of Lieberkuhn LP – Lamina propria MM – Muscularis mucosae V - Villi  Intestinal Villi  Epithelium of small intestine includes variety of cell types:  Enterocytes - columnar cells with microvilli that serve an absorptive role  Goblet cells - mucin for lubrication  Paneth cells - defensive role  Stem cells  Intraepithelial lymphocytes - are mostly T-cells  Neuroendocrine cells - regulate gastric motility and secretion PC – Parietal cells CC – Chief cells E – Neuroendocrine cells  Ileocecal junction  Abrupt transition in lining of the valve from the small intestinal villiform pattern to the glandular form of the large intestine  Consists of thickened extension of the muscularis propria which provides strong support for the mucosa  Lymphoid tissue in the form of large Peyers patches is found in the mucosa Ly – Lymphocytes MP – Mascularis propria Appendix  Appendix  General structure of appendix is similar to that of large intestine  Suspensory mesoappendix is continuous with the outer serosal layer of the appendix  Appendix has presence of masses of lymphoid tissue within the mucosa and submucosa. This lymphoid tissue occasionally forms follicles which then bulge into the lumen of the appendix F – Follicles LP Lamina propria  Mucosal glands are less closely packed than large intestine M – Mesoappendix S – Serosal layer Large Intestine  Colon  Muscularis propria of large intestine consists of inner circular and outer longitudinal muscle, except in the rectum where the outer longitudinal muscle forms three separate longitudinal bands – taeniae coli  Mucosa is same from caecum to rectum – folded in non-distended state but does not have distinct plicae circulares  Muscularis mucosae is a prominent feature of this mucosa CM – Circular layer LM – Longitudinal layer  Mucosa has two types of cells: Ly – Lymphoid tissue MM – Muscularis  Absorptive cells mucosae  Mucous secreting goblet cells  These cells are closely packed in straight crypts that extend into the muscularis mucosae  Anorectal junction  Rectal mucosa is same as rest of large bowel except that much more goblet cells are present  At the anorectal junction an abrupt transition occurs in which stratified squamous epithelium is now present in the anal canal  Branched tubular circumanal glands open at the anorectal junction into small pits at the distal ends of the columns of Morgagni – which are longitudinal folds formed by the mucosa J – Anorectal junction RM – Rectal mucosa SS – Stratified squamous epithelia  At anal sphincter the epithelium undergoes a gradual change to skin containing sebaceous and apocrine glands Resources 1. Wheater’s functional histology, seventh edition. 1 2. Netter’s essential histology, third edition.  IT’S For any queries or questions A please feel free to contact me: [email protected] WRAP