GI Histology Flashcards
what is the basic organizational structure of the digestive system?
a modified, layered tube
list the tunics of the GI tract and which plexus innervates them
- tunica mucosa: has lamina epithelialis, lamina propria, and +/- lamina muscularis/muscularis mucosae (submucosal plexus)
- tunica submucosa (submucosal plexus)
- tunica muscularis (myenteric plexus)
- tunica adventita/serosa (myenteric plexus)
describe the tunica mucosa of the GI tract
lamina epithelialis: completely surrounding luminal space
lamina propria: connective tissue subadjacent to epithelium, usually loosely organized and containing immune/inflammatory cells
lamina muscularis: thin smooth muscle layer that acts to move the mucosal layer, may have 2-3 layers, NOT ALWAYS PRESENT; if absent = propria submucosa
describe the tunica submucosa of the GI tract
CT layer beneath tunica mucosa; thickness varies
if submucosal glands are absent, this layer is thin
if submucosal glands are present, this layer is thick
describe the tunica muscularis of the GI tract
thick muscle layer with inner circular and outer longitudinal layer; moves luminal contents in a single direction
describe the tunica adventitia/serosa of the GI tract
outermost layer of loosely arranged CT that blends into surrounding fascia; if enclosed by mesothelium = tunica serosa
describe the tongue
a muscular organ covered by a mucus membrane;
stratified squamous epithelium whose keratinization varies, possesses a variety of bumps, ridges, and protrusions called lingual papillae
what are the 2 types of lingual papillae?
- mechanical: facilitate the movement of ingesta and grooming
- gustatory papillae: contain taste buds for perception of taste; at their apex open to epithelial surface (taste pore)
list and describe the 3 types of mechanical papillae
- filiform: most numerous, slender threadlike structures covered by stratified squamous epithelium with a thick stratum corneum (in felines have two prominences and a keratinized spine)
- conical: larger than filiform, usually not highly keratinized, occur on the root of the tongue in dogs, cats, and pigs
- lenticular: flattened, lens shaped, and located on the torus linguae of ruminants (a lateral swelling on the tongue that pushes food against the hard palate)
list and describe the 3 types of gustatory papillae
- fungiform: scattered among mechanical filiform, dome shaped like a mushroom; covered by nonkeratinized stratified squamous epithelium
- valate or circumvalate: large flattened structures just rostral to root of tongue, surrounded by epithelial lined sulcus
- foliate: parallel folds located on the margin of the tongue just rostral to the palatoglossal arch
describe taste buds (6)
- ellipsoidal clusters of specialized epithelial cells
- associated with gustatory papillae but also dispersed throughout oral cavity and pharynx
- at their apex is a taste pore where dissolved food particulates are sensed
- chemoreceptor/taste cells: chemical transducers of specific taste modalities
- sustentacular cells: supportive cells
- basal cells: stem cells
list and describe the 2 types of teeth
- brachydont: short crowns with well-developed roots that cease growth after full eruption; have a crown, a neck, and 1 or more roots, found in humans, carnivores, the incisor teeth of ruminants, and the canines of horses
- hypsodont: tall/long crowns with short roots, continuous growth throughout most of if not all of adult life; found in horse incisors and cheek teeth, and the cheek teeth of ruminants
describe the basic structure of a brachydont tooth (5)
- enamel: produced by ameloblasts along the external surface of the developing tooth, are 99% mineral (hydroxyapatite) and 1% organic material, nonviable and nonregenerative because ameloblasts are lost with tooth eruption
- dentin: synthetic product of odontoblasts along the internal surface of developing tooth, forms the tooth root and crown and gets thicker with age as the pulp cavity gets smaller
- cementum: covers the outer surface of tooth root, harder than loose irregular CT (like a kind of bone); has lacunae with canaliculi and lamellae, produced by cementoblasts that are called cementocytes once in lacunae; sharpey’s fibers from the periodontal ligament embed in the cementum to hold the tooth in the socket/alveolus
- periodontal ligament: functions as a specialized periosteum for the alveolar bone and a type of suspensory ligament for the tooth (fixed to the cementum); made of thick collagen and elastic fibers that radiate perpendicular to the surface of the root and the bone
- pulp cavity: filled with dental pulp (CT, blood and lymphatic vessels, nerves); odontoblasts live here
describe the tunica mucosa of the esophagus
- lamina epithelialis: stratified squamous epithelium with varying degrees of keratinization based on species and diet (ruminants are highly keratinized bc eat hard shit)
- lamina propria: CT often denser than that of t. submucosa
- lamina muscularis: longitudinally oriented along the length of the esophagus; absent in the cranial end/cervical region of dogs and pigs; cats, horses, and ruminants have isolated bundles of smooth muscle near the pharynx that increase in number as approach the glandular stomach
describe the tunica submucosa of the esophagus
loose irregular CT with longitudinally oriented arteries, veins, nerves, and glands
glands vary greatly among species but secrete a mucous to seromucous product
