Histology: GI Tract
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| What does the GI tract consist of? | alimentrary canal, tongue, teeth, salivary glands, pancreas, liver, gall bladder
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| What lines the GI tract? | mucosa
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| What is found in mucosa? | epithelium, lamina propria-loose vascular CT, and muscularis mucosa
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| What is found deep to the mucosa? | submucosa
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| What is found in submucosa? | dense irregular CT, blood vessels and meissner's plexus
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| What surrounds the submucosa? | muscularis externa
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| What is the muscularis externa composed of? | inner circular, Auerbach's/myenteric plexus and other longitudinal
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| What surrounds the muscularis externa? | serosa- simple squamous epithelium (intraperitoneal), adventitia-extraperitoneal
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| What is tongue composed of? | striated muscle and fat between bundles
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| The surface of the tongue is divided by | the sulcus terminalis into anterior 2/3 and posterior 1/3
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| Describe the features of the filiform papillae | most numerous and smallest, elongate projections of CT covered with strat. squam. epith., NO taste buds, partly keratinized
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| Where are filiform papillae found | entire anterior dorsal surface
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| Are taste buds present on Fungiform papillae? | yes, in epithelium/dorsal surface
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| Describe fungiform papillae | mushroom-shaped and numerous near the tip
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| Where are fungiform papillae found | on the dorsal surface everywhere, more concentrated near the tip
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| Describe circumvallate papillae | large, dome-shaped,
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| Where are the circumvallate papillae located? | located just anterior to sulcus terminalis
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| How many circumvallate papillae do humans have? | 8-12
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| What surround circumvallate papillae? | moat-like space lined with stratifeid squamous epith.
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| What surface of circumvallate contains tastebuds? | lateral surface epithelium
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| What is deposited in the moat of circumvallate papillae? | von ebner's glands deposit a serous secretion (ducts of lingual salivary glands)
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| Functions of the mucosa epithelium | facilitate passage of the bolus, provide a selectively permeable barrier between body and external environment, absorbs products of digestion (for transport to vascular)
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| Mucosa-lamina propria functions? | loose CT, contains glands, componenets of the immune system, have vessels to receive absorbed substances
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| Describe the vessels that absorb substances in the lamina propria of the mucosa | fenestrated, absorption occurs in small and large intestine, many lymphatic capillaries (receive lipids and some proteins)
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| Location of mucosa-muscularis mucosae | between mucosa and submucosa, deepest portion of mucosa
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| Layers of muscosa-muscularis mucosae | inner circular, outer longitudinal
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| What is special about the muscularis mucosae? | can produce movements of mucosa independent of movement of entire gut wall
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| What kind of CT is found in submucosa? | moderately dense irregular CT
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| What is found in submucosa? | dense irregular CT, larger blood vessels, lympathics, glands, nerve plexuses
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| Where do glands of submucosa occur? | esophagus and initial part of duodenum
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| What is the name of the nerve plexus of the submucosa called and it's function? | meissner's plexus, innervate smooth muscle
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| Describe muscularis externa | two concentric thick layers of smooth muscle, contains myenteric plexus aka auerbach's plexus (enteric ANS) inbetween
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| Describe layers of muscularis | inner circular layer-tight spiral, outer longitudinal layer-loose spiral
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| Describe Hirschsprung disease | mutations in one to four genes, arrest in migration of neural crest cells to one segment of colon, absence of enteric nervous system
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| Describe serosa | mesothelium - membrane containing simple squamous epithelium
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| What organs do not have a serosa and what do they have instead? | extraperitoneal organs - esophagus, duodenum, ascending and descending colon. Covered by loose CT - adventitia
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| Describe the esophagus | narrowest part of alimentary path, most muscular, collapsed by tonus of muscularis externa, mucosa in longitudinal folds, 4-layered tube
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| Describe the epithelium of the muscosa of the esophagus | stratified squamous non-keratinized epithelium: basal layer is columnar attached to basement membrane via hemidesmosomes, further up are cuboidal and final is squamous
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| Describe the lamina propria of the esophagus | dense elastic CT, esophageal cardiac glands are present at the esophageal-gastric junction, have diffuse lymph nodules
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| Function of cardiac glands | provide slimy mucous that enables food to slide off into stomach
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| Where in the esophagus are the esophageal glands? | submucosa
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| Function of the submucousal esophageal glands? | lubricate
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| What is found in the submucosa of the esophagus? | large blood vessels, submucousal glands, Meissner's plexus, lymphatics
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| Where in the esophagus is the think striated muscular layer and what is its function? | in muscularis externa,in upper portion to propel food rapidly by peristalsis
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| Where are the lymphatic nodules in the esophagus? | lamina propria
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| Describe the different sections of the esophagus with respect to the muscularis externa | upper 1/3 is striated muscle, middle third is striated and smooth muscle interwoven, last third is smooth muscle continuous with rest of gut
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| Describe the esophageal glands proper | occur in submucosa, majority in upper 1/2, slightly acidic mucous that lubricates lumen
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| Describe the esophageal cardiac glands | occur in lamina propria, similar to cardiac glands in stomach, present in terminal parts of esophagus, produce neutral mucous to protect against regurgitated material
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| What is the function of the circular muscle layer of the muscularis externa at the gastro-esophageal junction? | acts as a physiological sphincter and prevents regurgitation of food once it enter the stomach
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| Describe Barret's Esophagus | abnormal change in cells of the lower end of the esophagus caused by damage from chronic acid exposure, normal lining is replaced by intestinal-type lining (squamous - columnar)
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| Describe the stomach | 4 layers - mucosa, submucosa, muscularis and serosa. Inner surface has rugae, absorbs water, salts, lipid-soluble drugs, alcohol, certain drugs
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| What kind of epithelium is found in the Stomach | simple columnar surface mucus cells
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| What kind of blood vessels are found in the lamina propria? | fenestrated
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| What are gastric pits/foveolae? | simple columnar epithelium that is invaginated into the lamina propria that split into tubular gastric glands
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| What are the the 3 histological regions of the stomach? | cardia, pylorus, fundus
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| Describe the muscularis mucosa of the stomach | well developed and at the base of the gastric glands
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| Describe the submucosa of the stomach | dense irregular CT with blood vessels, lymphocytes, macrophages and mast cells. Has the meissners plexus. Produces ridges/folds called rugae
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| Describe the muscularis externa | three thick layers of smooth muscle, inner oblique, middle circular and outer longitudinal
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| What forms the pyloric sphincter? | the middle circular layer of the muscularis externa
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| Where is the myenteric plexus in the stomach? | between the circular and longitudinal layers
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| When do rugae form? | when the stomach is empty
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| Describe the cardia of the stomach | near esophagus, contains cardiac glands
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| How many glands per pit is there in cardia? | 1 gland per pit
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| Describe cardiac glands of the stomach | near esophagus orifus, secretes with esophagus cardiac glands, contributes to gastric juice, tubular, tortuous, branched, composed of mucus secreting cells, some interspersed enterendocrine cells
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| Describe the pylorus of the stomach | proximal to pyloric sphincter, contains pyloric glands
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| Describe the fundus of the stomach | largest part, between cardia and pylorus, contains fundic glands called gastric glands
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| How many glands per pit is there in the fundus? | up to 4 glands per pit
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| Describe the mucous secreting cells of the stomach cardiac glands | short duct segment, connects gland with shallow gastric pits
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| Describe the fundic glands of the stomach | produce digestive juice, present throughout gastric mucosa (except where cardiac and pyloric glands are), simple branched tubular, extend from bottom of gastric pits to muscularis mucosae, long neck segment and short wide base/fundic segment
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| Describe the gastric pits of fundus glands | pits shorter, glands longer, has several fundic glands
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| Describe the base of fundic glands | divides into 2 or 3 branches that may be coiled near muscularis mucosae
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| Fundic glands are composed of 5 functional cell types which are | (PM CAR) mucous neck cells, chief cells, parietal cells/oxyntic cells, enteroendocrine cells, undifferentiated cells
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| Describe the mucous surface cells of the fundis | surface of epithelium, secrete thick, viscous mucous to protect the epithelial lining.
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| Describe the mucous neck cells of fundis glands | located in neck region, shorter than surface mucous cells, do not exhibit prominent mucous cap, nucleus spherical, secretes a watery/soluble mucous for transport of other gastric gland secretions
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| Describe the parietal cells of fundic glands | fried egg appearance, secrete HCl and intrinsic factor, numerous microvilli, located in neck, numerous in upper and middle sections, gives epithelium beaded apprearance, large binucleate cells, extensive intracellular canalicular system
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| Describe the intracellullar canalicular system of parietal cells of fundic glands | communicates with lumen of fundic gland, numerous surface microvilli project from canaliculi, HCl produced in lumen of intracellular caniculi
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| What is the function of gastric intrinsic factor? | glycoprotein which binds vitamin B12 in the lumen of the stomach for absorption in the ileum
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| What stimulates acid secretion by parietal cells? | cholinergic nerve endings by histamine and gastrin
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| What is pernicious anemia | absence or loss of parietal cells (ulcers), inadequate intrinsic factor production, and vitamen B12 not absorbed, vit B12 is required for hemapoesis
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| Describe the chief cells of fundic glands | typical protein-secreting cells in deepest part of fundic gland, cuboidal/low columnar, cells are easily identified by intense basophilia (RER and apical granules), secrete pepsinogen/a weak lipase (zymogens)
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| Describe the enterendocrine/APUD cells of fundic glands | located at any level of gland, small cells that sit on the basal lamina, clear cytoplasm, small membrane limited granules, produce gastrin and serotonin, secrete into lamina propria
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| What occurs during peptic ulcers | majority caused by helicobacterium pylori, destruction of mucus layer erosion of mucusa, submucosa, and muscularis, caused by an inbalance between damaging factors and protective factors and if unchecked can erode through the wall
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| What is produced by the peptic ulcer? | urease which makes a NH4 cloud increasing the alkalinity of the stomach causing parietal cells to secrete more HCl
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| What are the 3 main complications of peptic ulcers | perforation, haemorrhage and obstruction
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| Describe the pyloric glands of the stomach | in pyloric antrum, branched tubular and coiled, cells similar to surface mucous cells, neuroendocrine cells interspersed, glands empty into deep gastric pits that occupy 1/2 the thickness of the mucosa
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| What are the functions of the small intestine? | passage of unabsorbed material, hormone production, principle site of digestion and absorption
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| Where do the enzymes of the small instestine come from? | pancreas and liver
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| Describe the lining of the small intestine | amplification of absorptive surface area by tissue and cell specializations: plicae circulares, villi
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| Decribe the plicae circulares | valves of Kercking, permanent transvers folds that contain a core of submucosa, each fold circularly arranged, extends around half to 2/3 circumference of lumen, found in the distal duodendum, entire jejunum and proximal ileum
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| Describe the epithelium of the small intestine | simple columnar with villi and goblet cells, core of villus consists of a) extenstion of the lamina propria and b) network of fenestrated capillaries beneath epithelium
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| What is found in the lamina propria villi? | blind ended lymphatic capillary called a central lacteal, smooth muscle accompanies lacteal
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| Describe the microvilli of enterocytes | major amplification of luminal surface, each enterocyte has several thousand, in light microscopy give apical region of cell a striated appearance
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| What are the cells found in the mucosa of the small intestine? | (GP CAR) Goblet cells, Paneth cells, Columnar absorptive cells, APUD cells, Regenerative/stem cells
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| Describe the columnar absorptive cells | closely-packed microvilli with tight junctions, lateral membranes form interdigitations,
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| Function of columnar absorptive cell | secretes glycoprotein enzymes, absorps amino acids, monosaccharides, water, minerals and electrolytes, inside SER the TAGs are formed and relaeased as chylomicrons into the extracellular space where they are transported by lacteals
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| Describe the Goblet cells in the small intestine | mucous secreting cells that protect and lubricate the epithelial lining, more in the ileum than the jejunum or duodendum, have an accumulationg of mucin granules apically, mucous secreted covers the glycocalyx, basal cytoplasm full of RER
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| Describe the small intestine Crypts of lieberkuhn | intestinal glands in lamina propria entends from villous base to muscularis mucosae, lined by single layer of columnar epith., constantly renewed, cells slough into lumen
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| what is found in the epithelium of the crypts of Lieberkuhn? | regenerative cells, paneth cells, enterendocrine cells and goblet cells
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| What do the regenerative cells differentiate into? | enterocytes, goblet cells, enteroendocrine cells, paneth cells
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| Structure and function of Paneth cells of the small intestine | large pyramidal cells, at base of glands with eosinophilic granules which contain lysozyme secreted into the lumen of intestine to act as a bacteriocide. May also regulate bacterial flora of small intestine
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| Describe the enterocytes in the small intestine | tall columnar cell with a basal nucleus with a striated border on luminal surface which are microvilli, secretes glycocalxy which helps in the break down of food
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| Describe the APUD/enteroendocrine cells and their function | secrete into lamina propria, situated in lower part of the crypts then migrate and found at all levels, secrete secretin, cholecystokinin and motilin to increase liver and gallbladder activity and decrease gastric secretions
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| What causes the movement of the each villi? | muscularis mucosa that course up into villus and contract several times per minutes
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| Describe the submucosa of the duodenum | dense irregular CT with immune cells, blood vessels and nerve cell bodies of meissner's plexus. Has brunner's glands that connect into the base of the crypts
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| What kind of cell bodies are in Meissner's and Auerbach's plexus? | postganglionic parasympathetic cell bodies
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| Describe the submucosa of the ileum | dense irregular CT with immune cells, blood vessels and nerve cell bodies of meissner's plexus. Peyer's patches
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| Describe distinguishing features of duodenum | distinguishing plicae circularis, long prominent villi, few goblet cells, presence of brunner gland in submucosa, and 2nd and 3rd part have adventitia on posterior surface and serosa on anterior
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| Describe distinguishing features of jejunum | long prominent villi, more goblet cells, no submucosal glands
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| Describe distinguishing features of ileum | short villi, lots of goblet cells, peyers patches covered by M Cells (epithelium)
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| M cells description | microfold cells, take up macromolecules/antigen from lumen by endocytosis and transports it via exocytosis to lymphocytes
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| Describe celiac disease | autoimmune disease caused by hypersensivity to gluten, inflammatory process causes loss of villus, causes weight loss, steatorrhea, hyperplasia, flat small bowel mucosa, increase in intraepithelial lymphocytes
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| mucosa of large intestine | no villi, straight tubular intestinal glands, no paneth cells, epithelium has columnar absorptive cells with many goblet cells, lamina propria is rich in immune cells
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| Function of absorptive cells | absorb water and electrolytes
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| Function of goblet cells | secrete lots of mucous to eliminate waste material
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| The muscularis externa of large intestine | 3 longitudinal bands called taeniae coli which make haustra
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| What large intestine parts have a complete serosa? | cecum, appendix, transverse colon and sigmoid colon
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| What large intestine parts have an anterior serosa and posterior adventitia? | ascending and descending colon
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| What are the small pendulous protuberances of adipose tissue on the large intestine called? | appendices epiploicae
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| Describe the appendix | extension of cecum, has one complete layer of longitudinal muscle in the muscularis, large numbers of lymphatic nodules with fecal matter, star-shaped lumen, no taeniae coli (converge at appendix)
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| What happens with early acute appendicitis? | ulceration of the mucosa, inflammatory exudates, pus in lumen, vague central abdominal pain
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| Describe gangrenous appendicitis | continued inflammation, necrosis of muscle layer, perforation and peritonitis, pus in peritoneal cavity, no treatment - septicemia, shock, death
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| Describe the rectum | no teniae coli, dilated, presence of transverse rectal fold
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| Describe the anal canal | contains vertical folds produced by infolding of mucous membrane around submucosa known as rectal columns of morgagni, has depressions between columns anal sinuses
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| Submucosa of anus has large plexus of veins which form what when excessively dilated? | hemorrhoids
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| Describe the muscularis externa of the the anus | circular layer of smooth muscle constitutes the internal anal sphincter with more superficial skeletal muscle forming the external anal sphincter
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| What kind of epithelium is at the anal canal? | stratified squamous non-keratinized
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| What kind of epithelium is at the anal orifice? | stratified squamous keratinized
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| Three zones of the anal canal? | colorectal zone (simple columnar), anal transition zone (simple columnar to stratified squamous), squamous zone (stratified squamous keratinized)
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