Histology Flashcards
Three layers of GI mucosa?
- epithelium
- lamina propria
- muscularis mucosa
Where is Meissner’s plexus found? Histo?
- loose areolar CT of submucosa
- neurons with large pale nucleus, prominent nucleolus, basophilic cytoplasm
Where is Auerbach’s myenteric plexus found? Histo?
- between inner circular and outer longitudinal smooth muscle of muscularis externa
- motor neurons
Where are cardiac glands found in esophagus? Function?
- lamina propria of beginning/end of esophagus
- protect non-kerat stratified squamous epithelium
What muscle is absent in upper 1/3 of esophagus?
muscularis mucosa (longitudinal in remainder of esophagus)
What is unique about submucosa in esophagus?
submucosal glands of mucoid nature throughout
How is muscle distributed in the esophageal muscularis externa?
- upper 1/3 = skeletal
- middle 1/3 = mix
- lower 1/3 = smooth
What are the surface epithelial cells of the stomach? How does it interact with mucosa?
- simple columnar
- invaginates to form gastric pits which are continuous with mucosal glands (cardiac) in mucosa
What mucosal layer is almost non-existent in the stomach?
lamina propria (tightly packed mucosal glands)
Three layers of muscularis externa in stomach?
- innermost oblique layer
- middle circular (thickening = pyloric sphincter)
- outer longitudinal
What three cell types are found in the gastric glands of the stomach?
- mucous neck cells
- parietal cells
- chief cells
Function of mucous neck cells in stomach?
- secrete acidic mucous
Function of parietal cells in stomach? Location/histo?
- lie between mucus neck cells
- large round cells with central nucleus and pale acidophilic cytoplasm
- secrete HCl and IF
Function of chief cells in stomach? Location? Control?
- lower region of glands
- basophilic cytoplasm (rER)
- make pepsinogen
- controlled by secretin and vagus nerve
What cell type produces peptide hormones in the gut? Distribution?
- enteroendocrine cells
- dispersed throughout epithelium from stomach to colon, usually near base
Where do enteroendocrine cells release hormone?
- NOT into the lumen
- secrete basally in a paracrine fashion or into underlying capillaries of lamina propria
Two mucosal specializations that increase SA of small intestine?
- plicae circularis = semicircular folds of mucosa that extend into lumen (core = submucosa)
- villi = outgrowths of mucosa (epi and LP)
Where are plicae circularis best developed?
jejunum (tall villi too)
What composes the core of villi?
- loose CT
- central blind-ended lymphatic lacteal
Which layer does NOT extend into the villi?
muscularis mucosa
What are microvilli?
tiny evaginations of the apical membrane of enterocytes
What are the crypts of Lieberkuhn?
- intestinal glands
- tubular invaginations of epithelium down into the lamina propria
How do secretions of intestinal glands reach the lumen?
- epithelium of glands is continuous with that of villi
- small openings between villi
What is the predominant cell type covering the villi? Histo?
- enterocytes
- tall columnar with basal nuclei and dense glycocalyx covering microvilli
How are enterocytes secured? life cycle?
- junctional complexes between neighboring cells
- live for a few days during which they move from crypt to villus top to be sloughed
Where are goblet cells found? Function?
- between enterocytes
- increase in number from duodenum to ileum
- secrete acidic mucous (lubricate, protect from panc enzymes/bact) = 80% carb, 20% protein
Where are paneth cells found? Life span?
- base of crypts
- 20 days
What 3 compounds are released by Paneth cells? Function?
- lysozyme stored in acidophilic granules
- TNF-alpha
- defensins
- function is to control intestinal flora
What 2 hormones are released by enterendocrine cells in the stomach?
gastrin, somatostatin
Where are enteroendocrine cells found in the small intestine? 4 secretions?
- concentrated in lower region of crypts
- CCK, GIP, motilin, secretin
What substances cross apical membrane of enterocytes by facilitated diffusion?
AA’s and monosaccharides
What substances cross apical membrane of enterocytes passively?
small lipids (larger through pinocytosis)
How are lipids processed in the enterocytes?
- monoglycerides and FA’s collect in EC sER where they are resyn into triglycerides and assembled into chylomicrons
- chylo’s are packaged into vesicles by Golgi and moved to basolateral membrane for exocytosis –> lymph capillaries
What happens to AA’s, mono’s, and small FA’s in the enterocyte?
cross basolateral membrane to reach lamina propria where they enter blood and lymphatic capillaries
How does lamina propria change prox - distal in the small intestine? Unique structure in ileum?
- inc in lymphoid tissue due to inc epithelial permeability
- Peyer’s patches
What specific submucosal glands are found only in the duodenum? Function?
BRUNNER - serous/mucus alkaline fluid that raises pH of intestinal chyme
What initiates activity of the muscularis externa in the small intestine?
distension
What two things are NOT found in the LI?
villi, Paneth cells
What cell type increases prox - distal in the LI?
goblet cells
Two unique morphological characteristics of appendix?
- complete ring of lymphoid tissues in lamina propria
- complete outer longitudinal muscle layer
Difference in epithelial cell type of cutaneous lip vs. red region at vermillion border? Accessory structures?
- both strat squamous
- kerat vs. non-kerat
- cutaneous contains hair follicles, seb and sweat glands
- red contains BV’s responsible for color
Function of lip/cheek submucosa? What does it contain?
- binds mucosa to overlying muscle in order to prevent formation of folds during mastication (dec risk of biting cheek)
- glands
Gingiva cell type? How are the gums bound to alveolar bone?
- kerat strat squamous
- lamina propria contains thick collagen fibers that blend with periosteum
- no glands, no submucosa
Epi cell type in hard vs. soft palate?
- kerat strat squamous
- non-kerat strat squamous
How is the hard palate mucosa attached to bone?
- lamina propria binds periosteum
- forms mucoperiosteum
What additional fibers are found in soft palate?
skeletal muscle
Four types of lingual papillae found on anterior 2/3 of tongue?
filiform, fungiform, circumvallate, foliate
Composition of tongue?
- mass of skeletal muscle covered by mucosa
- muscle fibers in long, transverse and oblique planes
Most numerous type of papillae?
filiform
Which papillae has narrow, conical shape, is present on entire ant 2/3, lacks taste buds, and is keratinized?
FILIFORM
Fungiform taste bud location? What happens to these papillae with age?
- apical surface
- surface keratinizes with age
How is the lamina propria arranged in fungiform papillae?
- extends into papilla
- BV’s reach close to surface
Which papillae type is rare in adult humans?
Foliate
Buds and location of foliate papillae?
- richly endowed
- posteriorly on lateral borders of tongue
Where are circumvallate papillae found? Cell type?
- 8-12 ant to sulcus terminalis
- strat squamous epithelium
What is found on lateral wall of circumvallate papillae?
numerous taste buds
What special structure is associated with circumvallate papillae? Function?
- serous con Ebner’s glands which bathe taste buds in fluid - wash out tastants
- ducts open into floor of each circular furrow
Developmental progression of taste bud cells?
basal –> supporting –> receptor
Lifetime of taste receptor cells?
10-14 days
What CN’s contribute to taste receptor cell AFF nerve terminal?
VII, IX, X
Which 2 aspects of salivary gland organization are surrounded by myoepithelial cells?
acinus and intercalated duct
Why are the striated ducts ‘striated’?
- has lots of basal infoldings due to plentiful mito
- energy require for lots of ion exchange modifying composition of secretory product
At what point does the salivary duct system become purely conductive?
- interlobular ducts
- inc CT component, absent striations
Secretory products of the salivary glands?
- submandibular = mixed
- sublingual = mucous
- parotid = serous
What percentages of saliva are contributed by the glands?
- Parotid = 30%
- submandibular = 60%
What happens to the parotid glands over time?
invaded by adipose after 40 years
What covers dentin?
- superiorly enamel
- inferiorly cementum
How is tooth held in socket?
periodontal ligament attaches to uncalcified outer layer of cementum
What cells line the pulp cavity? Function?
- odontoblasts
- make dentin = 2nd hardest compound in body (after enamel)
Secretions of odontoblasts?
- secrete apically
- Type I collagen, proteoglycans, glycoproteins = ORGANIC dentin
When does mineralization of pre-dentin secreted apically by odontoblasts occur?
- when matrix vesicles containing calcium and phosphate are released from odontoblasts
Percent composition of enamel?
96% mineral
What composes the 4% organic component of enamel?
- NO collagen
- keratin-like glycoproteins = amelogen, enamellin
What cells secrete enamel? When?
- ameloblasts (reversed polarity from odontoblasts)
- only during tooth development
What does cementum consist of?
- calcified collagenous fibrils and trapped osteocyte-like cementocytes
