Histology of the Gastrointestinal Tract PDF

Histology of the Gastrointestinal Tract Joyce El-Haddad [email protected] @orientatewithjoyce Lecture Outline GIT overview Textbook references used: Ovalle, W.K. and Nahirney, P.C., 2020. Netter's Essential Histology E-Book: With Correlated Histopathology. Elsevier Health Sciences. Stevens...

Histology of the Gastrointestinal Tract Joyce El-Haddad [email protected] @orientatewithjoyce Lecture Outline GIT overview Textbook references used: Ovalle, W.K. and Nahirney, P.C., 2020. Netter's Essential Histology E-Book: With Correlated Histopathology. Elsevier Health Sciences. Stevens, R., 2006. Gray’s Anatomy for Students Main histological features of the anatomical subdivisions of GIT Gastrointestinal Tract LAYERS OF THE GIT Mucosa: Ø Epithelium Ø Lamina Propria Ø Muscularis Mucosae Submucosa: Ø Loose areolar CT Ø Submucosal plexus Muscularis: Ø Inner circularis mm Ø Outer Longitudinal mm Ø Myenteric Plexus Serosa/Adventitia Ø Loose areolar CT @orientatewithjoyce Mucosa • Mucous membrane: • Epithelium. Different types based on the region of GIT you are in. • Lamina propria (loose areolar connective tissue) • Muscularis mucosae (inner circular, outer longitudinal layer of smooth muscle). Submucosa • Made of loose areolar connective tissue • The goodies - blood and lymph vessels, submucosal (Meisnner’s) nerve plexus – enteric nervous system (ENS). Muscularis • Skeletal muscles in the mouth, pharynx, upper and middle parts of oesophagus, and external anal sphincter. • Smooth muscle in other regions • Muscularis: internal (circular) and external (longitudinal); • Myenteric (Auerbach’s) nerve plexus (ENS). Serosa • Also called visceral peritoneum • Serous (wet and glossy) membrane (covered by serous fluid) around GI organs below diaphragm Areolar conn. tissue contains blood and lymph vessels, simple squamous epithelium (mesothelium). • • There are a few exceptions along the tract of the GIT Summary Esophagus Gross anatomy of the esophagus. 0 Histology of the esophagus at different levels. Stratified squamous epithelium Lamina propria Superficial glands Duct of gland Muscularis mucosae Submucosa Circular muscle Longitudinal muscle Striated Incisor teeth Oropharynx Epiglottis Average length in centimeters Oesophagus Pharyngoesophageal constriction 16 Thoracic (aortobronchial) constriction 23 Thyroid cartilage Cricoid cartilage Cricopharyngeus (muscle) part of inferior pharyngeal constrictor Trachea Arch of aorta Left main bronchus Diaphragmatic constriction (inferior esophageal 38 “sphincter”) 40 Abdominal part of esophagus Cardiac part of stomach Longitudinal section: Upper end of esophagus (H&E,! 25) Stratified squamous epithelium Lamina propria Muscularis mucosae Submucosa Esophageal glands (deep) Duct of gland Smooth Circular muscle Longitudinal muscle Intermuscular connective tissue (containing myenteric plexus) Diaphragm Fundus of stomach Lumen Stratified squamous epithelium Lamina propria Muscularis mucosae Submucosa Esophageal glands (deep) Circular muscle Longitudinal muscle Longitudinal section: Lower third of esophagus (H&E, ! 25) * Ep LM of a The secreto tightly pack submucosa the muscul crosses the (*). Epitheliu epithelium is richly vas lymphatic c predominan esophageal SM MM Duct H&E. MA BV MA Ly Duct Oesophagus • The upper third of the oesophagus has skeletal muscle fibres; the middle third, a mixture of smooth and skeletal muscle; and the lower third, only smooth muscle. • The oesophageal mucosa consists of nonkeratinized stratified squamous epithelium (continuous with that of the pharynx), underlying lamina propria, and prominent muscularis mucosae. • Cells can become keratinized if exposed to a degree of trauma • Oesophagus upper = skeletal m • Middle – both skeletal and smooth • Lower – smooth Cardiac glands of stomach Superficial (cardiac) glands of esophagus Peritoneum 282 Cardio-oesophageal junction Zigzag (Z) line: juncture of Upper Digestive System esophageal and gastric Longitudinal esophageal muscle mucosa Esophageal mucosa Circular esophageal muscle Gastric epithelium (columnar) Gradual muscular thickening Esophageal epithelium (stratified squamous) Diaphragm Gastric folds (rugae) Muscularis mucosae Esophagogastric junction. Three layers of gastric musculature Two layers of esophageal musculature Juncture of esophageal and gastric epithelium Cardiac glands of stomach Superficial (cardiac) glands of esophagus Peritoneum Zigzag (Z) line: juncture of esophageal and gastric mucosa Muscularis mucosae Esophagogastric junction. Three layers of gastric musculature Two layers of esophageal musculature Gastric folds (rugae) SSE LM of the esophagogastric junction. An abrupt transition occurs at this squamocolumnar junction (arrow). Nonkeratinized stratified squamous epithelium (SSE) of the esophagus changes to simple columnar epithelium (SCE) of the stomach. Gastric epithelium contains surface mucous cells. Small gastric glands—cardiac glands (CG)—are in underlying lamina propria (LP), are associated with gastric epithelium, and contain mucus-secreting cells. 240×. H&E. SCE LM of the esophagogastric junction. An abrupt transition occurs at this squamocolumnar junction SCE (arrow). Nonkeratinized stratified squamous epithelium SSE (SSE) of the esophagus changes to simple columnar epithelium (SCE) of the stomach. Gastric epithelium contains surface mucous cells. Small gastric glands—cardiac glands (CG)—are in underlying lamina propria (LP), are associated with gastric epithelium, and contain mucus-secreting cells. 240×. H&E. CG LP CG LP Cardio-oesophageal junction • An abrupt transition occurs in the epithelial lining at the esophagogastric junction. This serrated border, called the Z line, is clinically important, as it is the most common site of oesophageal carcinoma (cells are easily confused) • At the Z line, nonkeratinized stratified squamous epithelium of the oesophagus changes to simple columnar epithelium of the stomach, and only basal cells of the oesophageal epithelium continue into simple epithelium of the stomach Mucous membrane of the stomach. Cardiac glands * Isthmus Mucosa e on rd Neck Serosa Fund us Ca z iac 287 ME dy Bo Pylo rus SM Body Rugae MM Mucus * Mucous cell Pyloric glands Gastric or fundic glands Submucosa Mucosa * Chief cell Solitary lymph nodule Neuroendocrine G cell Muscularis mucosae Submucosa Light micrograph (LM) of the stomach wall showing four concentric layers at low magnification. A thick mucosa (formed mostly of tightly packed gastric glands) lines the lumen (*). The rectangle indicates a ruga consisting of a submucosal connective tissue core covered by mucosa. A thick layer of mucus secreted by surface cells forms a barrier over the mucosa for protection of tissues from acid and proteolytic enzymes 288 Parietal cell (between a mucous cell and a chief cell) Lower Digestive System BV LM of a gastric ruga at low magnification. The mucosa is prominent; underlying submucosa is richly vascularized connective tissue. The gastric lumen (*) is above. 10×. H&E. Surface epithelial cell LM of the gastric mucosa. Short gastric pits on Stomach Pits Lower Digestive System Tortora Stomach Parietal cells are most numerous in the body of the glands but are also mixed with mucous neck cells in neck areas or with chief cells in basal areas of glands. Parietal cells (HCl + Intrinsic factor) are most numerous in the body of the glands but are also mixed with mucous neck cells in neck areas or with chief cells in basal areas of glands. deeply eosinophilic cytoplasm is due to abundant mitochondria and relative rareness of rough endoplasmic reticulum. (intrinsic factor; glycoprotein that facilitates vitamin B12 absorption in the proximal small intestine) Cuboidal to columnar chief cells, mostly in basal parts of glands, have a round basal nucleus. Their basal cytoplasm is basophilic; secretory (zymogenic) granules make their apical cytoplasm look more granular. ( pepsinogen (inactive pepsin)+ HCl = pepsin) Gastric glands also contain less numerous enteroendocrine cells, scattered with the other cells, that produce gut hormones and are hard to see in routine sections. Special immunocytochemical or electron microscopic methods are needed to identify them with certainty. More than 30 gastrointestinal hormones are produced. The muscularis externa of the stomach is made of three layers of smooth muscle: outer longitudinal, middle circular, and inner oblique Lower Digestive System Gastro-duodenal junction Lymphoid nodules Pylorus of stomach First part of duodenum Pyloric sphincter Villi Gastric pit Pyloric gland Lymphoid nodule LMs of the gastroduodenal junction. Above, The transition from pylorus (left) to duodenum (right) shows many lymphoid nodules and a prominent pyloric sphincter. Pyloric glands (Left) are densely packed, shorter, and more tortuous than are fundic glands. Gastric pits in the pylorus are also deeper than in other parts of the stomach. Mucus-secreting cells that resemble mucous neck cells of fundic glands line pyloric glands. Duodenal mucosa (Right) consists of villi and intestinal glands (crypts). Draining into crypts are Brunner’s glands, which reach the submucosa. Above: 5×; Left and Right: 60×. H&E. Crypts Brunner’s gland 295 Gastro-duodenal junction • The gastroduodenal junction. Its gross anatomy is well delineated, but its histology is not. • In contrast to the esophagogastric junction—a discrete squamocolumnar junction • The gastroduodenal junction shows a gradual transition from gastric mucosa of the pylorus to villous epithelium of the duodenal mucosa. SMALL INTESTINE Mucosa of the intestine • Numerous crevasses lined by glandular epithelium – intestinal glands • Cells: • Absorptive: most common cell type; tall columnar, brush border. Function = absorption • Goblet: secrete mucous. • Enteroendocrine: secrete hormones, same as stomach. • M cells (microfold cells) modified absorptive, located over enlarged lymph nodes, carry antigens to MALT. • Paneth: secrete anti-microbial lysozymes. Located in the base of intestinal glands. Small intestine - Duodenum • Simple columnar epithelium • Presence of permanent macro folds – villi • Mucous secreting glands 297 Lower Digestive System Duodenal bulb and mucosal surface of duodenum. Duodenum * Mu ME SM LM of the duodenum showing a plica circularis. Plicae are crescent-shaped folds made of a core of submucosal connective tissue (SM) covered by mucosa (Mu). The mucosa features many closely packed villi that project into the lumen (*). The muscularis externa (ME) consists of two layers of smooth muscle. Figure below shows an area similar to that in the rectangle at higher magnification. 15×. H&E. Crypts BG MM BG Villi LM of the mucosa and submucosa of the duodenum. Secretory acini of a mucosal Brunner gland (BG) pierce the muscularis mucosae (MM) to lie deep in submucosa (to the left). Small ducts of the gland drain into bases of intestinal crypts. Villi are outpocketings of mucosa covered by simple columnar epithelium. Brunner glands are prominent in the proximal duodenum and slowly disappear in more distal areas. 80×. H&E. Duodenum • Simple columnar epithelium, made of enterocytes and goblet cells, covers the villi. • Between the villi, the epithelium dips down to form simple, tube-like invaginations called intestinal glands, • Because it is near the stomach, the proximal duodenum has distinctive duodenal mucus-secreting glands (to protect from stomach acid) Small intestine - Jejunum • Main site of absorption • Plicae circularis – folding of both the mucosa and the submucosa • Presence of lacteal vessels 298 Jejunum 298 Lower Digestive System Lower Digestive System Vi * En Vi * Lamina propria En IC La SM Lamina propria ME IC Cap GC Se La LM of the jejunum at low magnification. Tall, slender villi (Vi) and intestinal crypts (IC) occupy the mucosa. The lumen (*), submucosa (SM), muscularis externa (ME), SM and serosa (Se) are indicated. 15×. H&E. SM ME Se Cap En GC LM of the jejunum at low magnification. Tall, slender villi (Vi) and intestinal crypts (IC) occupy the mucosa. The lumen (*), submucosa (SM), muscularis externa (ME), and serosa (Se) are indicated. 15×. H&E. Lacteal Cap En SM LM of the tip of a jejunal villus in longitudinal section. Simple columnar epithelium composed of enterocytes (En) and goblet cells (GC) covers the surface. The lamina propria, a highly cellular connective tissue, contains a central lacteal (La), blood capillary (Cap), and tufts of smooth muscle cells (SM). 300×. H&E. GC Jejunum • The jejunum has the largest surface area for luminal secretion and absorption • It has a thicker wall and a wider lumen compared to the ileum • Plicae circulares are thicker, taller, and more numerous in the jejunum • Most of the cells found in the simple columnar epithelium are enterocytes – tall columnar absorptive cells and contain oval shaped nuclei that are located basally • Apical border usually striated in appearance • The core of each villus = highly vascularized lamina propria, systemic capillaries, and one larger lymphatic lacteal (for the transport of fats to the liver) Lower Digestive Digestive System System Lower Ileum Digestive System 299 LM of of part partLower of the the ileum. ileum. Club-shaped stubby villi villi (Vi), LM of Club-shaped stubby (Vi), short intestinal intestinal crypts, crypts, and and highly highly cellular cellular lamina lamina propria propria short (LP) characterize characterize the the mucosa. mucosa. The The submucosa submucosa (SM) (SM) isis (LP) fibrous connective connective tissue. tissue. The The rectangle rectangle delineates delineates the the fibrous LMseen of part of themagnification ileum. Club-shaped villi (Vi), H&E. area seen at higher higher magnification (Below).stubby 80×. H&E. area at (Below). 80×. short intestinal crypts, and highly cellular lamina propria (LP) characterize the mucosa. The submucosa (SM) is fibrous connective tissue. The rectangle delineates the area seen at higher magnification (Below). 80×. H&E. Vi Vi Vi Vi Vi Vi Crypt Crypt LP LP LP 299 299 SM SM Crypt LM LM of of the the bases bases of of crypts crypts in in the the ileum. ileum. At At the the bases bases of of the the crypts crypts are are clusters clusters of of Paneth Paneth cells cells (PC), (PC), which which have have distinctive distinctive eosinophilic eosinophilic granules. granules. The The lamina lamina propria propria (LP) (LP) isis richly richly vascularized; vascularized; underlying underlying muscularis muscularis LM of the bases of crypts in the ileum. At theH&E. mucosae (MM) consists of muscle. 280×. H&E. mucosae (MM) consists of smooth smooth muscle. 280×. bases of the crypts are clusters of Paneth cells (PC), which have distinctive eosinophilic granules. The lamina propria (LP) is richly vascularized; underlying muscularis mucosae (MM) consists of smooth muscle. 280×. H&E. SM IV IV Pl Pl IV LP LP Pl LP Colonoscopic Colonoscopic views views of of the the ileum ileum (Left) (Left) and and ileocecal ileocecal valve valve (Right). (Right). Plicae Plicae circulares circulares (Pl) (Pl) are are aa main main feature feature of of the the ileum. ileum.The The ileocecal ileocecal valve valve (IV) (IV) between between ileum ileum and and cecum cecum isis aa sphincter sphincter formed formed by by semilunar semilunar Colonoscopic views of the ileum (Left) and folds folds of of mucosa mucosa supported supported internally internally by by thickened thickened ileocecal valve (Right). Plicae circulares (Pl) are a main smooth smooth muscle. muscle. feature of the ileum. The ileocecal valve (IV) between ileum and cecum is a sphincter formed by semilunar folds of mucosa supported internally by thickened smooth muscle. 13.14 HISTOLOGY OF THE ILEUM MM MM MM PC PC PC all parts of the small intestine but are especially numerous in the Ileum • The ratio of goblet cells:enterocytes is the greatest in ileum • Large amounts of gut associated lymphoid tissue (GALT) MALT • Peyers patches (aggregated lymphoid nodules) in the LP – most common in the distal ileum • Function = immune response and serve as a source of plasma cells (but diminish in size and number with age) • Secretory Paneth cells occur in all parts of the SI but ^ in ileum at bases of crypts (role in aiding epithelial renewal by secreting antimicrobial agents e.g. lysozyme into the intestinal crypts Specialisations • Duodenum: villi are often leaf or ridge shaped; Brunner’s glands. • Jejunum: the main absorptive site, most complex finger like villi. • Ileum: greatest development of gut-associated lymphoid tissue – Peyer’s patches; may have leaf like villi. Layers Mucosa Duodenum Jejunum Ileum Simple columnar Simple columnar The highest number of absorptive cells. Most absorption occurs here. Submucosa Has duodenal glands (Brunner’s glands) Invaginates with mucosa – High concentration of Gut plicae circularis Associated Lymphoid Tissue (GALT) (Payer’s Presence of lacteal vessels Patches Muscularis Inner circular Outer Longitudinal Inner circular Outer Longitudinal Inner circular Outer Longitudinal ✅ ✅ ✅ Serosa Simple Columnar Histology of Colon Cross-section of large intestine. Lumen Mucosa Muscularis mucosae ding Submucosa ic taenia d by hook) Circular muscle nia bera) Visceral peritoneum Longitudinal muscle Enterocyte/ Columnar absorptive cell Intestinal glands (crypts) Mucosa oid mesocolon oid colon Crypts MC LN Neuroendocrine cell and adjacent capillary SECTION 8 LP Submucosa Part of muscularis externa SM coli. These outward bulges are important surgical landmarks. Between them, the colon wall has crescent-shaped projections into the lumen called plicae semilunares. Appendices epiploicae, another unique feature of the colon, are subserosal pockets of adipose tissue that form pendulous bulges shaped like grapes. CLINICAL POINT Diverticulosis is the presence of diverticula, or herniations of mucosa and submucosa through the muscularis externa of the colon. Of unknown cause, it is most prevalent in developed countries where low-fiber diets are common. Inflammation of diverticula, or diverticulitis, can lead to perforations, tears, bleeding, and infection. Early symptoms are cramps, bloating, and constipation, often followed by blood in the stool. Antibiotic treatment is usually successful, but severe cases may need surgery. A high-fiber (25-30 g/day) diet may prevent the disorders. Goblet cell 1158 Lymphoid follicle Fig. 66.51 The microstructure of the colonic wall and its epithelial cells. Note the aggregations of lymphocytes (blue) and undifferentiated epithelial cells (white). y Free taenia (taenia libera) Visceral peritoneum Sigmoid mesocolon En Histology of Colon Sigmoid colon G Crypts MC EP LP G Lower Digestive System LN En 305 Lumen G Mucin granules G Striated Striated border border Crypt Crypt Goblet cell LP Gob cel LP Enterocyte BV LM of the colonic mucosa. Surface epithelium containing goblet cells (G) and enterocytes (En) invaginates to form an intestinal crypt. The lamina propria (LP), with capillaries (arrows) and larger blood vessels (BV), is richly cellular. 600×. Toluidine blue. hat is 1.5 m long ocecal junction estinal contents , bile acids, and ion and lubricastion of foods. It Lamina propria SM BV Cap 5 µm EM of the colonic mucosa. Enterocytes have an apical striated border of microvilli that project into the lumen. These cells occur with goblet cells, which have apical mucin granules. The lamina propria contains a capillary (Cap). 3400×. coli. These outward bulges are important surgical landmarks. * * Between them, the colon wall has crescent-shaped projections into LM of intestinal crypts in the colonic mucosa. The the lumen called plicae semilunares. Appendices epiploicae, crypts, sectioned transversely, appear as regularly oriented, circular profiles surrounded by lamina propria. Simple columnar epithelium lines lumina (*). 600×. H&E. pockets of another unique feature of the colon, arecryptsubserosal adipose tissue that form pendulous bulges shaped like grapes. * LM of the colonic mucosa. Surface epithelium containing goblet cells (G) and enterocytes (En) invaginates to form an intestinal crypt. The lamina propria (LP), with capillaries (arrows) and larger blood vessels (BV), is richly cellular. 600×. Toluidine blue. Lamina propria Cap 5 µm CLINICAL POINT Crypts of Lieberkühn fossa VermiformRetrocecal Appendix Mu LN ME * LN LN SM SM LM of the appendix in transverse section. Prominent mucosa (Mu) shows multiple lymphoid nodules (LN) bulging into a narrow stellate lumen (*). Connective tissue makes up a submucosa (SM); the muscularis externa (ME) contains two layers of smooth muscle. 8×. H&E. LP LM of part of the appendix. Mucosa contains richly cellular lamina propria (LP) infiltrated with lymphoid nodules (LN) that extend into submucosa (SM). Shallow invaginations of the surface—intestinal crypts (arrows)—vary in length. The submucosa has some adipose tissue. 85×. H&E. Histology of colon (large intestine) • The colon lacks villi • Columnar (absorptive) cells Columnar (absorptive) cells are the most numerous of the epithelial cell types. Although there is some variation in their structure, they all bear apical microplicae (microvilli) which are shorter and less regular than those on enterocytes in the small intestine. • Mucous (goblet) cells Mucous cells have a similar structure to those of the small intestine but they are more numerous. They are outnumbered by absorptive cells for most of the length of the colon but they are equally frequent towards the rectum, where their numbers increase. • Microfold (M) cells Microfold cells are similar to those of the small intestine. En Lumen G Mucin granules G Crypt Goblet cell LP Enterocyte BV LM of the colonic mucosa. Surface epithelium containing goblet cells (G) and enterocytes (En) invaginates to form an intestinal crypt. The lamina propria (LP), with capillaries (arrows) and larger blood vessels (BV), is richly cellular. 600×. Toluidine blue. Lamina propria Cap 5 µm Striated Striated border border 308 Rectum and Anal Canal Histology 308 308 Lower Digestive System LowerDigestive DigestiveSystem SystemRectum and anal canal. Lower Rectum and anal canal. Rectum and anal canal. Anal gland and duct • At anorectal junction we start to see a change in epithelium from simple columnar to stratified squamous epithelium below the pectineal line • Lower end of the anal canal is continuous with the perianal skin…this should give us clues on what epithelial lining we can expect. Anal glandinto opening Anal gland and duct anal crypt and duct opening into opening into anal crypt anal crypt Transition from Transition squamous Transition tosquamous columnar from from squamous epithelium columnar to to columnar epithelium well above epithelium well above pectinate line well above Rectal mucosa Rectal Rectal mucosa mucosa Anal Analcolumn Anal column column SHSH pectinate line pectinate line Pectinate Pectinate Pectinate line line line SH IH IHIH Internal Internal Internal sphinctersphincter sphincter HiH ltioltno’ n’s Hilto s whwhit n’s ite lei linewhit Anal Anal ne e line Anal canal canal canal External sphincter External sphincter Thinning down Thinning down of squamous of squamous Thinning down epithelium epithelium at at of squamous pectinate line at pectinate line epithelium pectinate line Hair follicles Hair follicles and sweat and sweat Hairpresent follicles glands present glands perianal skin; and sweat in in perianal skin; absent anal absent in in anal glands present canal canal in perianal skin; absent in anal canal Endoscopic view anorectal Endoscopic view of of thethe anorectal junction. The transition from rectum junction. The transition from rectum to to anal canal near serrated pectinate anal canal is is near thethe serrated pectinate (arrows), which shows a color change Endoscopic view ofa color the anorectal lineline (arrows), which shows change on surface. It marks squamocolumnar onjunction. thethe surface. thethe squamocolumnar TheIt marks transition from rectum to External sphincter Skin with hair follicles Skin with hair follicles and sebaceous glands and sebaceous glands Skin with hair follicles and sebaceous glands anorectal junction LMLM of of thethe anorectal junction in in longitudinal section. rectum leads longitudinal section. TheThe rectum (at(at top)top) leads anal canal (at bottom). The squamocolumnar intointo thethe anal canal (at bottom). The squamocolumnar LM of the anorectal junction in junction occurs above pectinate line. Other junction occurs wellwell above thethe pectinate line. Other longitudinal section. The rectum features indicated. Superior (SH) inferior(at top) leads features areare indicated. Superior (SH) andand inferior into thevenous anal canal (at bottom). The squamocolumnar hemorrhoidal venous plexuses—thin-walled (IH)(IH) hemorrhoidal plexuses—thin-walled junction occurs well above the line. Other veins filled with blood—lie both sides ofpectinate the veins filled with blood—lie on on both sides of the features are H&E.indicated. Superior (SH) and inferior pectinate line. H&E. pectinate line. 5×.5×. (IH) hemorrhoidal venous plexuses—thin-walled veins filled with blood—lie on both sides of the