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SGU: GI Tract

Histology: GI Tract

What does the GI tract consist of? alimentrary canal, tongue, teeth, salivary glands, pancreas, liver, gall bladder
What lines the GI tract? mucosa
What is found in mucosa? epithelium, lamina propria-loose vascular CT, and muscularis mucosa
What is found deep to the mucosa? submucosa
What is found in submucosa? dense irregular CT, blood vessels and meissner's plexus
What surrounds the submucosa? muscularis externa
What is the muscularis externa composed of? inner circular, Auerbach's/myenteric plexus and other longitudinal
What surrounds the muscularis externa? serosa- simple squamous epithelium (intraperitoneal), adventitia-extraperitoneal
What is tongue composed of? striated muscle and fat between bundles
The surface of the tongue is divided by the sulcus terminalis into anterior 2/3 and posterior 1/3
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
Where are filiform papillae found entire anterior dorsal surface
Are taste buds present on Fungiform papillae? yes, in epithelium/dorsal surface
Describe fungiform papillae mushroom-shaped and numerous near the tip
Where are fungiform papillae found on the dorsal surface everywhere, more concentrated near the tip
Describe circumvallate papillae large, dome-shaped,
Where are the circumvallate papillae located? located just anterior to sulcus terminalis
How many circumvallate papillae do humans have? 8-12
What surround circumvallate papillae? moat-like space lined with stratifeid squamous epith.
What surface of circumvallate contains tastebuds? lateral surface epithelium
What is deposited in the moat of circumvallate papillae? von ebner's glands deposit a serous secretion (ducts of lingual salivary glands)
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)
Mucosa-lamina propria functions? loose CT, contains glands, componenets of the immune system, have vessels to receive absorbed substances
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)
Location of mucosa-muscularis mucosae between mucosa and submucosa, deepest portion of mucosa
Layers of muscosa-muscularis mucosae inner circular, outer longitudinal
What is special about the muscularis mucosae? can produce movements of mucosa independent of movement of entire gut wall
What kind of CT is found in submucosa? moderately dense irregular CT
What is found in submucosa? dense irregular CT, larger blood vessels, lympathics, glands, nerve plexuses
Where do glands of submucosa occur? esophagus and initial part of duodenum
What is the name of the nerve plexus of the submucosa called and it's function? meissner's plexus, innervate smooth muscle
Describe muscularis externa two concentric thick layers of smooth muscle, contains myenteric plexus aka auerbach's plexus (enteric ANS) inbetween
Describe layers of muscularis inner circular layer-tight spiral, outer longitudinal layer-loose spiral
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
Describe serosa mesothelium - membrane containing simple squamous epithelium
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
Describe the esophagus narrowest part of alimentary path, most muscular, collapsed by tonus of muscularis externa, mucosa in longitudinal folds, 4-layered tube
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
Describe the lamina propria of the esophagus dense elastic CT, esophageal cardiac glands are present at the esophageal-gastric junction, have diffuse lymph nodules
Function of cardiac glands provide slimy mucous that enables food to slide off into stomach
Where in the esophagus are the esophageal glands? submucosa
Function of the submucousal esophageal glands? lubricate
What is found in the submucosa of the esophagus? large blood vessels, submucousal glands, Meissner's plexus, lymphatics
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
Where are the lymphatic nodules in the esophagus? lamina propria
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
Describe the esophageal glands proper occur in submucosa, majority in upper 1/2, slightly acidic mucous that lubricates lumen
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
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
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)
Describe the stomach 4 layers - mucosa, submucosa, muscularis and serosa. Inner surface has rugae, absorbs water, salts, lipid-soluble drugs, alcohol, certain drugs
What kind of epithelium is found in the Stomach simple columnar surface mucus cells
What kind of blood vessels are found in the lamina propria? fenestrated
What are gastric pits/foveolae? simple columnar epithelium that is invaginated into the lamina propria that split into tubular gastric glands
What are the the 3 histological regions of the stomach? cardia, pylorus, fundus
Describe the muscularis mucosa of the stomach well developed and at the base of the gastric glands
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
Describe the muscularis externa three thick layers of smooth muscle, inner oblique, middle circular and outer longitudinal
What forms the pyloric sphincter? the middle circular layer of the muscularis externa
Where is the myenteric plexus in the stomach? between the circular and longitudinal layers
When do rugae form? when the stomach is empty
Describe the cardia of the stomach near esophagus, contains cardiac glands
How many glands per pit is there in cardia? 1 gland per pit
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
Describe the pylorus of the stomach proximal to pyloric sphincter, contains pyloric glands
Describe the fundus of the stomach largest part, between cardia and pylorus, contains fundic glands called gastric glands
How many glands per pit is there in the fundus? up to 4 glands per pit
Describe the mucous secreting cells of the stomach cardiac glands short duct segment, connects gland with shallow gastric pits
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
Describe the gastric pits of fundus glands pits shorter, glands longer, has several fundic glands
Describe the base of fundic glands divides into 2 or 3 branches that may be coiled near muscularis mucosae
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
Describe the mucous surface cells of the fundis surface of epithelium, secrete thick, viscous mucous to protect the epithelial lining.
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
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
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
What is the function of gastric intrinsic factor? glycoprotein which binds vitamin B12 in the lumen of the stomach for absorption in the ileum
What stimulates acid secretion by parietal cells? cholinergic nerve endings by histamine and gastrin
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
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)
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
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
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
What are the 3 main complications of peptic ulcers perforation, haemorrhage and obstruction
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
What are the functions of the small intestine? passage of unabsorbed material, hormone production, principle site of digestion and absorption
Where do the enzymes of the small instestine come from? pancreas and liver
Describe the lining of the small intestine amplification of absorptive surface area by tissue and cell specializations: plicae circulares, villi
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
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
What is found in the lamina propria villi? blind ended lymphatic capillary called a central lacteal, smooth muscle accompanies lacteal
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
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
Describe the columnar absorptive cells closely-packed microvilli with tight junctions, lateral membranes form interdigitations,
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
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
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
what is found in the epithelium of the crypts of Lieberkuhn? regenerative cells, paneth cells, enterendocrine cells and goblet cells
What do the regenerative cells differentiate into? enterocytes, goblet cells, enteroendocrine cells, paneth cells
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
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
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
What causes the movement of the each villi? muscularis mucosa that course up into villus and contract several times per minutes
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
What kind of cell bodies are in Meissner's and Auerbach's plexus? postganglionic parasympathetic cell bodies
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
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
Describe distinguishing features of jejunum long prominent villi, more goblet cells, no submucosal glands
Describe distinguishing features of ileum short villi, lots of goblet cells, peyers patches covered by M Cells (epithelium)
M cells description microfold cells, take up macromolecules/antigen from lumen by endocytosis and transports it via exocytosis to lymphocytes
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
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
Function of absorptive cells absorb water and electrolytes
Function of goblet cells secrete lots of mucous to eliminate waste material
The muscularis externa of large intestine 3 longitudinal bands called taeniae coli which make haustra
What large intestine parts have a complete serosa? cecum, appendix, transverse colon and sigmoid colon
What large intestine parts have an anterior serosa and posterior adventitia? ascending and descending colon
What are the small pendulous protuberances of adipose tissue on the large intestine called? appendices epiploicae
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)
What happens with early acute appendicitis? ulceration of the mucosa, inflammatory exudates, pus in lumen, vague central abdominal pain
Describe gangrenous appendicitis continued inflammation, necrosis of muscle layer, perforation and peritonitis, pus in peritoneal cavity, no treatment - septicemia, shock, death
Describe the rectum no teniae coli, dilated, presence of transverse rectal fold
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
Submucosa of anus has large plexus of veins which form what when excessively dilated? hemorrhoids
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
What kind of epithelium is at the anal canal? stratified squamous non-keratinized
What kind of epithelium is at the anal orifice? stratified squamous keratinized
Three zones of the anal canal? colorectal zone (simple columnar), anal transition zone (simple columnar to stratified squamous), squamous zone (stratified squamous keratinized)
Created by: mnoronha



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