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GI Tract I,II

UBSDM 2015 Histology

QuestionAnswer
Organs of the Gastrointestinal Tract Oral Cavity, pharynx, esophagus, stomach, small/large intestine rectum, anal canal, gallbladder, pancreas, liver
Oral Cavity – Epithelium Oral Mucosa is nonkeratinized stratified squamous epithelium which is always wet.
Oral Cavity – Connective Tissue Thin superficial layer of loose connective tissue(Lamina propria) with papillae that meet epithelial pegs and submucosal collagen bundles. May be over muscle or bone
Tongue – Structure Instrinsic muscles of the tongue consist of superior and inferior longitudinal,vertical and transverse fibers. Covered by nonkeratinized stratified squamous epithelium
Tongue - Connective tissue Lamina propria, is between the epithelium and intrinsic muscle. The anterior 2/3 dorsal surface of the tongue has many small surface projections called papillae. The dorsal posterior 1/3 surface of the tongue contains the lingual tonsil.
Filiform Papillae Finger-like shape with no taste buds. Partially keratinized. Scrape food off tongue
Fungiform Papillae Mushroom Shaped, Not Keratinized, Taste Buds may be scattered on epithelial surface
Circumvallate Papillae Posterior boundary of ant. 2/3. Flying V arrangement anterior to sulcus terminalis. Large, 6-12 count, submerged to tongue surface. Taste buds surrounded by saliva moat.
Glandes of Von Ebner Salivary glands in Cirvumvallate Papillae. Lie beneath salivary moat to wash food out to keep taste buds reactive to new chemical stimuli
Teeth There are 20 deciduous teeth and 32 permanent teeth with different morphology to serve different functions. If you don’t know this you are in trouble ;)
Enamel most calcified tissue in the human body (95-98%). Enamel matrix is secreted by ameloblasts and calcified by enamel rods bound together by interrod enamel. Enamel is formed over the crown, cannot be replaced - the ameloblasts die at tooth eruption.
Dentin calcified tissue (approximately 70% mineralized) secreted by odontoblasts. It is initially secreted in an unmineralized state called predentin
Cementum covers the dentin of the root of the tooth. It is similar to bone, but it lacks Haversian systems and blood vessels
Tooth pulp loose connective tissue with odontoblasts, fibroblasts, thin collagen fibers and ground substance
Periodontal Ligament Dense connective tissue forming periosteum of alveolar bone that attaches to cementum. Allows some movement during mastication. High rate of protein turnover.
Pharynx Foregut derivative, Three regions=naso/oro/laryngo-pharynx. Lined by stratified keratinized epithelium. Controlled by CN-X the Vagus Nerve.
Four Layers of the GI Tract Mucosa, Submucosa, Muscularis Externa, Serosa.
GI Mucosa Epithelial Muscosal selective membrane from lumen to body. Secretes enzymes, regulate pH. Absorbs products, Secretes protective mucus, Secretes local hormones.
GI Lamina Propria Supports Mucosal layer epithelium. Contains small vessels and lymphatics(lacteals in S.intestine) Lymphoid glands, smooth muscle, and local immune mechanisms. ie; macrophages, lymphocytes, plasma cells etc.
GI Muscularis Mucosae Layer of smooth muscle between submucosa and lamina propria. Moves the mucosae, creates folds and rugae
GI Submucosa layer of loose connective tissue that contains larger diameter collagen fibers than does the lamina propria, large vessels, Nervous plexi (Meissner’s) which provides neural regulation of digestion.
GI Mucus Glands Found in the submucosa of esophagus and duodenum. Protect the mucosal surface
GI Lymphoid Nodules Found in the mucosa and submucosa anywhere along the GI tract. Aggregates are called Peyer’s Patches. Activate immune response to antigens in the GI tract.
GI Muscularis Externa Smooth Muscle next to submucosa in a circular layer. Outer layer is longitudinal. Responsible for the mass movement of food.
Myenteric Plexu (Auerbach’s) Autonomic neurons located between the two layers of Muscalaris externa. Supported by thin layer of LCT. Initiates/coordinates contractions of smooth muscles to move food.
GI Muscularis Externa Exceptions Upper esophagus has skeletal muscle, Cardiac of stomach has incomplete 3rd layer, pyloric sphincter has thick circular layer, colon has 3 longitudinal bands (taenia coli), 3rd layer in anal canal
GI Serosa Single layer of squamous epithelium & connective tissue with large blood, lymph, nerve supply. Called mesothelium. Fluid provides lubrication for gut movement.
Number of organs located in peritoneal cavity 0, zero, none, zilch, 0/n, zip, nil, cero, нула, אֶ֫פֶס, số không
Adventitia Organs that don’t have serosa (retroperitoneal) have adventitia. Fascia with adipose, blood vessels, nerves that form outer layer of organ and connects it to other stuff.
Esophagus – Mucosa Non-keratinized stratified squamous epithelium. Superior/inferior mucosal glands that secrete high concentration of proteoglycan mucus.
Esophagus – Submucos Submucosal Glands (esophageal) present throughout organ. These glands plus the stratified epithelium are how to identify esophagus.
Esophagus – Muscularis Externa Inner circular layer of muscle and outer longitudinal layer. Skeletal in upper 1/3 of organ. Mixed in middle 1/3. Smooth in lower 1/3.
Esophagus Adventitia Thick tunic of connective tissue binding it to trachea. No peritoneum.
Stomach – Mucosa Irregular folds called rugae. Simple columnar epithelium – secrete protective mucus
Stomach – Glands – Cardiac Region Simple or branched tubular cardiac glands, secrete neutral glycosaminoglycans protective mucus.
Stomach – Glands – Fundus Mucous Neck Cells, Stem Cells, Parietal Cells, Chief Cells, Enteroendocrine cells,
Stomach – Glands – Mucous Neck Cells Only in the neck of the gland, secrete acidic mucus. Shorter and contain fewer secretory droplets than surface cells
Stomach – Glands – Stem cells In the neck of each gland near the base of the pit. Mitotic division to form new epithelial(3-5day lifespan) and gland cells.
Stomach – Glands – Parietal Cells Secrete HCl to reduce pH to 1.5. Located in the upper part of the body of gastric glands. Large, pale, Round/Pyramidal shape. 1or2 nuclei. Acidophilic cytoplasm. Numerous mitochondria.
Parietal Cell Intracellular Canaliculs Deep invagination visible on EM. HCl secretion occurs here. Non-functional cell has tubulovesiculr system near this. Active cells is microvilli.
Stomach – Glands – Chief Cells Zymogenic (produce enzymes) in the lower portion of the body of glands. Smaller than parietal, basophilic cytoplasm. Secrete pepsinogen. Granules in the apical cytoplasm contain the inactive proenzyme pepsinogen. Secretes gastric lipase and rennin.
Stomach – Glands – Enteroendocrine Cells Tiny glands that secrete more than 20 hormones. Well known polypeptides secreted by these cells include
Stomach – Glands – Pylorus Long Gastric pits and short endpeices. Secrete mucus and lysozyme. Predominant enteroendocrine cell produces Gastrin (G-cells) found at the base of the gland.
Stomach – Muscularis Mucosae Separates mucous membrane from Submucosa.
Stomach – Submucosa Typical connective tissue with blood supply and submucosal plexus.
Stomach – Muscularis Externa Inner oblique layer(cardiac/body of stomach), Middle circular, outer longitudinal. Middle circular is thick in pyloric region forming sphincter.
Small Intestine Mucosa Simple Columnar Epithelium responsible for digestion and absorption. Contains Absorptive cells, goblet cells, and intestinal glands (Crypts of Lieberkühn).
Small Intestine – Mucosa – Absorptive Cell Predominant cell type. Simple Columnar. Polarized with~3000 microvilli (Striate or Brush Border) Covered in glycocalyx.
Small Intestine – Mucosa – Goblet Cells Gradually increase toward ileum. Secrete high concentration proteoglycan mucus for protection. Apical surface concentrated with mucinogen granules. Bottom is narrow.
Small Intestine – Intestinal Glands – Enteroendocrine Cells In the small intestine, these cells secrete many products including secretin, cholecystokinin, gastric inhibitory peptide, and motilin into the lamina propria
Small Intestine – Intestinal Glands – Paneth Cells Found in the base of each gland. Secrete lysozyme.
Small Intestine – Intestinal Glands – M Cells (membranous Epithelial Cells) Flat cells over lymphoid nodules. Apical surface has small folds. Endocytose antigens and pass to lymphoid tissue.
Small Intestine – Intestinal Glands – Stem Cells In lower ½ of gland. Continual mitosis. Creates all cell types in epithelium. Entire epithelium is renewed in 3-7 days.
Small Intestine – Lamina Propria lacteals (lymph vessels) are present and a prominent muscularis mucosae. Projecting into the mucosa and lamina propria are many lymphoid nodules. These are prevalent in the small intestine (particularly the ileum) and are called Peyer’s patches.
Small Intestine – Peyer’s Patches Lymphatic tissue aggregations running the length of the intestines. Basophilic staining.
Small Intestine – Submucosa – Brunner’s Glands In the duodenum. Secrete alkaline mucus to increase pH to neutral.
Small Intestine – Muscularis Externa Typical - Inner circular layer and outer longitudinal. Covered in serosa.
Large Intestine Crypts of Lieberkühn lead into tubular glands that containing simple columnar cells, many goblet cells, and enteroendocrine cells.
Large Intestine – Mucosa two predominant cell types; goblet and simple columnar cells, a lamina propria. Lymphoid nodules are present
Large Intestine – Submucosa Typical – Blood Vessels, nerves, lymphatics
Large Intestine – Muscularis Externa Complete inner circular layer of smooth muscle. 3 bands of consolidated longitudinal smooth muscle bands called taenia coli.
Large Intestine – Serosa Covered by normal serosa or visceral peritoeneum.
Gut Associated Lymphoid Tissue GALT
GALT lymphoid tissue is in the form of lymphoid nodules, as well as loosely organized lymphocytes, macrophages, eosinophils, and plasma cells in the lamina propria. M-Cells overly Peyer’s Patches. Stimulate antigen response.
Created by: speedy2782