GIT HISTOLOGY unveiled the microscopic study of the GIT
- 1. 1 Oral cavity • Oral cavity is lined with stratified squamous epithelium, keratinized or nonkeratinized, depending on the region • The keratin layer protects the oral mucosa from damage during masticatory function • The keratin layer is present in the gingiva and hard palate • Nonkeratinized stratified squamous epithelium covers the soft palate, lips, checks and the floor of the mouth 1
- 2. 2 Tongue • The tongue is a mass of striated muscle covered by a mucous membrane • The dorsal surface of tongue is rough due to presence of papillae • The ventral surface of tongue is smooth • The posterior one-third of dorsal surface is separated from the anterior two-thirds by a V-shaped boundary 2
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- 4. 4 Papillae Papillae are elevations of epithelium and lamina propria. There are four types of papillae: • Filiform papillae - slender, conical shape, most numerous, cover the entire dorsal surface • Fungiform papillae - less numerous, have broad round surface resemble mushrooms • Foliate papillae – poorly developed in humans • Circumvallate papillae – large circular papillae with flattened surfaces, distributed in the V region in the posterior portion of the tongue 4
- 6. 6 Muscles of tongue (Anterior part of tongue) • The tongue consists of criss-crossing bundles of skeletal muscle • The muscles are longitudinal, transverse or oblique • The connective tissue around the muscle bundle contain blood vessel • Anterior lingual gland – lies in the lower half of the tongue and opens on the ventral surface of the tongue 6
- 7. 7 Anterior region of the tongue 7
- 8. 8 Posterior tongue behind circumvallate papilla • Dorsal surface of posterior region exhibits large mucosal ridges • Nonkeratinized stratified squamous epithelium covers the mucosal ridges • Lamina propria of the mucosa is wider but similar to that in the anterior two-thirds • Lamina propria contains diffuse lymphatic tissue, accumulation of adipose tissue, nerve fibers and blood vessels • Skeletal muscle lies beneath the lamina propria • The posterior lingual gland opens onto the dorsal surface 8
- 9. 9 Posterior tongue behind circumvallate papillae 9
- 10. 10 Teeth • Called “dentition” (like dentist) • Teeth live in sockets (alveoli) in the gum- covered margins of the mandible and maxilla • Chewing: raising and lowering the mandible and moving it from side to side while tongue positions food between teeth
- 11. 11 Teeth • Two sets – Primary or deciduous • “Baby” teeth • Start at 6 months • 20 are out by about 2 years • Fall out between 2-6 years – Permanent: 32 total • All but 3rd set of molars by end of adolescence • 3rd set = “wisdom teeth” – Variable – Some can be “impacted” (imbedded in bone)
- 12. 12 Teeth are classified according to shape and function • Incisors: chisel-shaped for chopping off pieces • Canines: cone shaped to tear and pierce • Premolars (bicuspids) and • Molars - broad crowns with 4-5 rounded cusps for grinding incisor canine premolar molar Cusps are surface bumps
- 13. 13 Tooth structure • Two main regions A. Crown (exposed) B. Root (in socket) C. Meet at neck • Enamel – 99% calcium crystals – Hardest substance in body • Dentin – bulk of the tooth (bone-like but harder than bone, with collagen and mineral) • Pulp cavity with vessels and nerves – Root canal: the part of the pulp in the root A B C
- 14. 14 Tooth structure • Cementum – bone layer of tooth root – Attaches tooth to periodontal ligament • Periodontal ligament – Anchors tooth in boney socket of the jaw – Continuous with gingiva (gums) • Cavities or caries - rot • Plaque – film of sugar, bacteria and debris A B C
- 15. 1. In adult humans there are 32 permanent teeth. 2. These are preceded during childhood by 20 deciduous teeth. 3. The tooth lies in a bony socket, the alveolus, that is covered my an oral mucosa called the gingiva (gums) that consist of, a. keratinized stratified squamous epithelium b. lamina propria of loose connective tissue that lies directly adjacent to the bone of the alveolus. eeth
- 16. a. the crown - the portion that protrudes above the gum line. b. the root - the portion that extends into the alveolus. Internally, the tooth consists of a layer of dentin that surrounds a pulp consisting of loose connective tissue, nerves and blood vessels. In the dentin, directly adjacent to the pulp is a layer of specialized cells called odontoblasts - secrete organic matrix that calcifies and forms the dentin. The tooth consists of two major parts,
- 17. Dentin is covered by a layer of calcified organic matrix - the enamel a. Hardest substance in body b. Formed by ameloblasts before tooth “erupts” from socket Root region Dentin is covered by calcified organic matrix - the cementum - similar to bone, but no haversian system Between the cementum and the bone of the socket lies the peridontal ligament - consists of fibroblasts and collagen fibers with glycosaminoglycans in between. a. forms cushion between tooth and bone b. Attaches tooth to bone - Sharpey’s fibers Crown region
- 18. Salivary Glands • Three major paired salivary glands: 1. Submandibular 2. Sublingual 3. Parotid glands. • They differ from one another in the relative abundance of serous and mucous acini • and in the length of the various kinds of ducts.
- 19. Major Glands • Parotid: so-called watery serous saliva rich in amylase, proline-rich proteins – Stenson’s duct • Submandibular gland: more mucinous – Wharton’s duct • Sublingual: viscous saliva – ducts of Rivinus; duct of Bartholin Minor glands • Minor salivary glands are not found within gingiva and anterior part of the hard palate • von Ebner lies below the sulci of the circumvallate and folliate papillae of the tongue. they are Serous glands • Glands of Blandin-Nuhn: lies in the ventral part of the tongue • Palatine, glossopalatine glands are pure mucus • Weber glands
- 20. Functions of Saliva • Protection – lubricant – barrier against noxious stimuli; microbial toxins and minor traumas – washing non-adherent and acellular debris – formation of salivary pellicle • calcium-binding proteins: tooth protection; plaque • Buffering (phosphate ions and bicarbonate) – bacteria require specific pH conditions – plaque microorganisms produce acids from sugars
- 21. • Digestion – neutralizes esophageal contents – dilutes gastric chyme – forms food bolus – brakes starch • Antimicrobial – lysozyme hydrolyzes cell walls of some bacteria – lactoferrin binds free iron and deprives bacteria of this essential element – IgA agglutinates microorganisms
- 22. • Maintenance of tooth integrity – calcium and phosphate ions ionic exchange with tooth surface • Tissue repair – bleeding time of oral tissues shorter than other tissues – resulting clot less solid than normal – remineralization • Taste – solubilizing of food substances that can be sensed by receptors – trophic effect on receptors
- 23. Salivary glands are compound tubuloalveolar gland surrounded by a moderately dense connective tissue capsule From the capsule, septa enters the parenchyma dividing the gland into lobes and lobules.
- 24. • Each lobule consist of secretory end pieces which is made up of a more or less spherical mass of cells called an acinus and a branching duct system. The secretory end pieces present two types of secretory cells “serous and mucous well as the non- secretory myoepithelial cells. The acini can be either serous or mucous.
- 25. Serous cells • The cells are usually pyramidal in shape • Their apex have short, irregular microvilli directed toward the lumen and their base resting on a basement membrane. • They have rounded nuclei that lies towards the basement membrane.
- 26. • The secretion of serous cells is thin, watery and proteinaceous. • Serous cells stained darkly because of the presence of zymogen granules in their cytoplasm. • They are joined near their apical surfaces by junctional complexes.
- 27. Mucous cells • Mucous cells secrete a viscous, glycoprotein-rich product, which is stored as mucinogen granules. • The nuclei are typically flattened against the base of the cells. • Mucous cells stains lightly thus looking pale and appear empty in standard histological sections, because their granules are lost during preparation.
- 28. Myoepithelial cells • Are contractile cells • Also called basket cells lie between the basement membrane and the plasma membrane of the secretory cells. • They are also found in the proximal part of the duct system. • Myoepithelial cells posses many actin-containing microfilaments, which squeeze on the secretory cells and move their products toward the excretory ducts
- 29. • The myoepithelial cells of the intercalated ducts are more spindled-shaped and fewer processes • Ultrastructurally very similar to that of smooth muscle cells • Functions of myoepithelial cells – Support secretory cells – Contract and widen the diameter of the intercalated ducts – Contraction may aid in the rupture of acinar cells of epithelial origin
- 30. Duct systems • Secretions produced in the secretory end pieces empty into the intercalated ducts, lined by cuboidal epithelial cells. • Several of these short intercalated ducts join to form striated or secretory ducts. Secretory ducts reasorb sodium and secrete potassium. • Both intercalated and secretory ducts are found within the parenchyma of the gland and are therefore intralobular ducts.
- 31. Intercalated Ducts • Small diameter • Lined by small cuboidal cells • Nucleus located in the center • Well-developed RER, Golgi apparatus, occasionally secretory granules, few microvilli • Myoepithelial cells are also present • Intercalated ducts are prominent in salivary glands having a watery secretion (parotid).
- 32. Striated duct • The striated ducts of each lobule converge • and drain into ducts located in the connective tissue septae separating the lobules, • where they become interlobular, or excretory ducts. • They are initially lined with pseudostratified or stratified cuboidal epithelium,
- 33. • but more distal parts of the excretory ducts are lined with stratified columnar epithelium containing a few mucus-secreting cells. • The main duct of each major salivary gland ultimately empties into the oral cavity • and is lined with nonkeratinized-stratified squamous epithelium
- 34. • Vessels and nerves enter the large salivary glands at the hilum and gradually branch into the lobules. • A rich vascular and nerve plexus surrounds the secretory and ductal components of each lobule. • The capillaries surrounding the secretory end pieces are very important for the secretion of saliva, stimulated by the autonomic nervous system.
- 35. • Parasympathetic stimulation, usually through the smell or taste of food, promotes vasodilation and a copious watery secretion content. • Sympathetic stimulation produces small amounts of viscous saliva, rich in organic material
- 36. Parotid gland • The parotid salivary gland is a compound, acinar, serous gland. • Unlike all other salivary glands, the parotid includes no mucous cells • its secretory portion is composed exclusively of serous cells containing secretory granules • that are rich in proteins and have a high amylase activity.
- 37. Parotid gland • This activity is responsible for most of the hydrolysis of ingested carbohydrates. • Individual acini are drained by small intercalated ducts. • These in turn drain into striated (or "secretory") ducts, whose cells are specialized for concentrating the secretory product.
- 38. • Cells lining the striated duct pump water and ions across the epithelium, from the duct lumen and into interstitial fluid. • each acinus is surrounded by a thin envelope of capillaries and connective tissue. • As in other large salivary glands, the connective tissue contains many plasma cells and lymphocytes.
- 39. • The plasma cells secrete IgA, which forms a complex with a secretory component synthesized by the serous acinar, intercalated duct, and striated duct cells. • The IgA-rich secretory complex released into the saliva is resistant to enzymatic digestion • and constitutes an immunological defense mechanism against pathogens in the oral cavity • adipocytes are also common in the parotid gland
- 40. HISTOLOGY OF PAROTID GLAND The parotid salivary gland is a compound, acinar, serous gland. Unlike all other salivary glands, the parotid includes no mucous cells its secretory portion is composed exclusively of serous cells containing secretory granules that are rich in proteins and have a high amylase activity.
- 41. • Features: • Serous - compound tubuloacinar gland. • Surrounded by conn.tissue capsule-septa-lobes-lobules. • Each lobule-of serous acini- pyramid cells, basophilic cytoplasm and secretory granules present. • Serous acini surrounded by myoepithelial cells. • Serous acini open into intercalated ducts-striated ducts- interlobular • excretory ducts-interlobar ducts- oral cavity.
- 42. HISTOLOGY OF SUBMANDIBULAR GLAND
- 43. serous secretory unit 2 - mixed secretory unit 3 - intercalated excretory duct 4 - striated excretoy duct 5 - interlobular excretory duct 6 - interlobular connective tissue septa 7 - mucous part of mixed secretory unit 8 - serous part (serous demilune) of mixed secretory unit Features: Mixed-Compound tubuloacinar gland. Predominantly serous acini present. Serous acini: small,dark staining pyramidal cells with secretory granules at apex. Mucous acini: cells large with pale staining or colourless cytoplasm Mixed acini(serous and mucus):Are mucus acini capped by serous demilumes. Duct system-Interobular intercalated ducts – striated ducts
- 44. Submandibular salivary gland • The submandibular gland is a branched tubuloacinar gland • its secretory portion contains both mucous and serous cells. • Its mucous acini are quite frequently capped with a serous demilune,. • In humans, 90% of the end pieces of the submandibular gland are serous acinar, • whereas 10% consist of mucous tubules with serous demilunes.
- 45. • Serous cells are responsible for the weak amylolytic activity present in this gland and its saliva. • The cells that form the demilunes in the submandibular gland secrete the enzyme lysozyme, whose main activity is to hydrolyze the walls of certain bacteria. • Some acinar and intercalated duct cells in large salivary glands also secrete lactoferrin, which binds iron, a nutrient necessary for bacterial growth.
- 46. 1 - mucous part of mixed secretory unit 2 - serous part (serous demilune) of mixed secretory unit 3 - serous secretory unit 4 - mucous secretory unit 5 - myoepithelial cells Features: Compound mixed tubuloacinar gland. Predominantly mucus acini and mucus acini capped with serous demilumes present. Serous acini few. Myoepithelial cells surround acini. Typical intercalated ducts infrequent/absent. Nonstriated intralobular excretory ducts present.
- 47. • The sublingual gland, like the submandibular gland, is a branched tubuloacinar gland formed of serous and mucous cells. • Mucous cells predominate in this gland; • serous cells are present almost exclusively on demilunes of mucous tubules • cells that form the demilunes in this gland secrete lysozyme. • Intralobular ducts are not as well developed as in other major salivary glands.
- 48. Features: 1.Pancreas has an exocrine part and an endocrine part. Exocrine part: Contains serous acini with zymogenic cells surrounding a lumen. The excretory duct extends into centroacinar cells. Centroacinar cells are continous with intercalated ducts which open into interlobular ducts.
- 49. Endocrine part:comprises of Pancreatic islets.(Islets of Langerhans) Endocrine cells are in clumps separated by conn tissue fibres. A capsule separates islets from the serous acini. Contains Alpha cells-stain pink- peripherally located-secrete Glucagon Betacells-cytoplasm stains blue,costitute 70%,more deeper- secrete Insulin. Delta cells-variable cell type, occur anywhere in the islet. secrete Somatostatin. Numerous capillaries are present in the islets.
- 50. The Pancreas • A thin capsule of connective tissue covers the pancreas. • Septa extending from the capsule divide the pancreas into poorly defined lobules. • A stroma of loose connective tissue surrounds the lobules. • Larger blood vessels, nerves and ducts lying between the lobules are surrounded by more abundant connective tissue.
- 51. Endocrine Pancreas: • The islets of Langerhans make up about 2% of the pancreas, and are most numerous in the tail. • There are three principal cells types in the islets. • B cells, which make up 60-70% of the islets, secrete insulin. • A cells (15-20%) secrete glucagon, • and D cells (5-10%) secrete somatostatin. • Minor cell types, which secrete a number of other peptides, make up about 5% of the islets.
- 52. Exocrine Pancreas: • The exocrine portion of the pancreas is a compound acinar gland, similar in structure to the parotid gland. • The cells that make up the serous acini of the pancreas are pyramidal in shape with a broad base and a narrow luminal surface. • In the apical cytoplasm, they contain acidophilic zymogen granules.
- 53. • These granules contain a number of digestive enzymes in their inactive form • trypsinogen, chymotrypsinogen, procarboxypeptidase (all for digesting proteins), • ribonuclease, deoxyribonuclease, triacylglycerol lipase, phospholipase A2, elastase, and amylase. • These products are conveyed by ducts to the small intestine, where enterokinases from the glycocalyx activate trypsinogen by converting it to trypsin.
- 54. • Trypsin in turn activates all the inactive enzymes, including trypsinogen. • The activation of trypsinogen within pancreatic cells is inhibited by trypsin inhibitor.
- 55. • The duct system in the pancreas begins within the acini themselves. • Cells of the smallest ducts, the intercalated ducts, penetrate right into the center of the acinus. • In sections, they can be identified as centroacinar cells or CA cells. • The intercalated ducts are also called intralobular collecting ducts, which have a cuboidal epithelium.
- 56. • The intralobular collecting ducts drain into larger interlobular or excretory ducts, • which are lined with low columnar epithelium. • Enteroendocrine cells and an occasional goblet cell can be found in these ducts. • There are no secretory (striated) ducts in the pancreas. • The interlobular ducts drain directly into the main pancreatic duct, which runs the length of the pancreas parallel to its long axis and joins the common bile duct before entering the duodenum.
- 57. • Two hormones secreted by enteroendocrine cells in the duodenum are major regulators of exocrine pancreatic activity. • Secretin stimulates the release of the bicarbonate rich fluid from the intercalated ducts, • while cholecystokinin (CCK) stimulates the acinar cells to release their proenzymes. • The release of secretin and CCK is stimulated by the entry of acidic chyme into the duodenum.
- 59. 1.Hepatic lobules with a central vein separated by septa. 2.Hepatocytes radiate from the central vein. 3.Sinusoids lined by endothelial cells are separated from the hepatocytes by a perisinusoidal space of Disse. 4.Hepatocytes secrete bile into bile canaliculi which converge at the periphery of each lobule into portal areas as bile ducts. 5.The connective tissue forms portal triads/portal areas ,It contains branches of hepatic artery,hepatic portal vein,and bile duct. 6.Bile ducts drain into the hepatic duct. 7.Specialized phagocytes called Kupfer cells present.
- 60. 4.Hepatocytes secrete bile into bile canaliculi which converge at the periphery of each lobule into portal areas as bile ducts. 5.The connective tissue forms portal triads/portal areas ,It contains branches of hepatic artery,hepatic portal vein,and bile duct. 6.Bile ducts drain into the hepatic duct. 7.Specialized phagocytes called Kupfer cells present.
- 61. The Liver • The liver is the largest internal organ, and the body’s second largest, after the skin Functions of the liver Digestive and Metabolic Functions • synthesis and secretion of bile • storage of glycogen and lipid reserves • maintaining normal blood glucose, amino acid and fatty acid concentrations • synthesis and release of cholesterol bound to transport proteins • inactivation of toxins • storage of iron reserves • storage of fat-soluble vitamins
- 62. Non-Digestive Functions • synthesis of plasma proteins • synthesis of clotting factors • synthesis of the inactive angiotensinogen • phagocytosis of damaged red blood cells • storage of blood • breakdown of circulating hormones (insulin and epinephrine) and immunoglobulins • inactivation of lipid-soluble drugs
- 63. General organization of the liver. • Liver may be regarded as a modified exocrine gland. • The liver is covered by a thin connective tissue capsule (Glisson's capsule) that becomes thicker at the hilum, • The portal vein and the hepatic artery enter the organ and the right and left hepatic ducts and lymphatics exit at the hilium. • Structurally the liver is divided into lobules by loose connective tissue septae from the Glisson’s capsule
- 64. The Liver Lobule • hexagonal in shape. • The angles of the hexagon are called portal areas (or portal canals, or portal tracts). • The basic structural component of the liver is the liver cell, or hepatocyte. • arranged in stacks of anastomosing plates, one or two cells thick, radiating from a central vein at the centre of the lobule towards the periphery. • The plates of cells are separated by an anastomosing system of sinusoids.
- 65. Inside the sinusoids • The liver sinusoids are irregularly dilated capillaries • fenestrated endothelial cells. • space of Disse or perisinusoidal space. • The sinusoids also contain phagocytic cells derived from monocytes, known as Kupffer cells • A third cell type, called the Ito cell (or lipocyte or adipose cell) is found right inside the perisinusoidal space. • These cells store fat, and accumulate exogenously administered vitamin A, which is transported to the retina for the synthesis of visual pigments • they also store vitamins D, E, K and B12.
- 68. Portal canal • Three structures are found grouped together in the loose connective tissue surrounding the plates of hepatocytes. • These include branches of the hepatic artery, • the hepatic portal vein (venule) • and the intralobular bile ductule. • This group of three structures has been called a portal triad but now is called a portal canal.
- 69. Features: 1.GB consists of the following layers: Mucosa-Exhibits temporary folds,Lining Epithelium-Simple tall columnar epithelium. Laminapropria contains loose connective tissue and diffuse lymphatic tissue. Fibromuscular layer:with smooth muscles and loose connective tissue rich in elastic fibres. Perimuscular connective tissue:contains blood vessels, Lymphatics and nerves. Serosa-outermost layer.
- 70. HISTOLOGY OF GALL BLADDER
- 71. • The gall bladder receives bile from the liver. Bile is composed of bile salts that emulsify fats forming water-soluble complexes with lipids (micelles) to facilitate the absorption of fat. • Bile salts in the small intestine also activates lipases in the intestine. Functions of the gall bladder. • storage of bile • concentration of bile • acidification of bile • send bile to the duodenum in response to cholecystokinin secreted by from enteroendocrine cells in small intestine;
- 72. • Mucosa: When the gall bladder is empty, this layer is extremely folded. • The folds are called rugae. When full, this layer is smoother but still has some short folds. • there are no goblet cells in the epithelium of gall bladder. The folds may branch and anastomose with one another. • Epithelia: composed of simple columnar epithelial cells with numerous microvilli on their luminal surfaces • lamina propria: composed of loose connective tissue rich in reticular and elastic fibers , may contain simple tubuloalveolar glands • Muscularis mucosae: not present • Submucosa: present and typical
- 73. • Muscularis: contains much smooth muscle, poorly organized • Serosa: present and typical • Contraction of the smooth muscle of the gallbladder • Is induced by cholecystokinin, a hormone produced by enteroendocrine cells located in the epithelial lining of the small intestine. • Release of cholecystokinin is, in turn, stimulated by the presence of dietary fats in the small intestine