Gut Hose Flashcards
What are the four main layers of the gut wall?
- mucosa
- submucosa
- muscularis externa
- serosa/adventitia
What layers are contained within the mucosa?
- epithelium
- lamina propria
- muscularis mucosae
(T/F) Muscularis mucosa is unique to the GI tract.
T
What is the function of the muscularis mucosa?
- contains a thin layer of smooth muscle
- mediates local movements of the mucosa
What is the major role of the mucosa in the GI tract?
-absorption of nutrients
What is contained within the submucosa?
- denser connective tissue (than lamina propria)
- blood vessels
- Lymphatics/immune cells
- glands (duodenum and esophagus)
- submucosal/meissner’s nerve plexus
Where is meissner’s nerve plexus located?
-the submucosa
What is the muscularis externa composed of?
- smooth muscle
- connective tissue between layers
- has an inner circular and an outer longitudinal component
- myenteric/auerbach nerve plexus
Where is the myenteric/auerbach nerve plexus located?
-connective tissue of the muscularis externa
What is the function of the muscularis externa?
-mixes and propels luminal contents along the GI tract
What is contained within the serosa/adventitia?
- loose connective tissue
- blood and lymphatic tissues
- adipose tissue
- simple sqamous covering called the mesothelium
What is the mesothelium?
-a simple squamous covering around the serosa/adventitia
How often do cells in the epithelium of the small intestine turn over?
every 3-5 days
What are the two portions of GI epithelium? Which portion do stem cells tend to live in?
- Villus
- Crypt
-Stem cells live in crypt
When does secondary peristalsis occur?
when food gets stuck, the tube neetds continuous peristalsis to unstick it
What is retroperistalsis?
throwing up
What is receptive relaxation of the stomach?
-the relaxation of smooth muscle layers to allow food to expand the stomach
What is pyloric grind?
When the pyloric sphincter contracts and circulates the food around the stomach.
What is the migrating motor complex (MMC)?
- a sweeping that travels through the stomach and intestine which clears anything out that was left over from digestion
- occurs every 90 minutes
What are the two movements of the stomach that involve movement of the epithelium?
- Mucosal squeeze: Up and down motion
- Mucosal Flutter: horizontal wave-like motion that coccurs in the muscularis mucosa to aid the stomach in digestion
What is segmentation?
Local mixing in the small intestine and large intestine
What is segmentation called in the colon? Why?
- haustration
- Called this because there is consolidation of fecal matter
What occurs in the large intestine insteadof MMC?
-mass movements, which consolidate things into poop
Why doesn’t mucosal flutter occur in the large intestine?
-because of the big bolus of poop, it wouldn’t accomplish much
What is the vagovagal reflex?
- response to an expansion of the stomach
- tells us to poop
What cells are the pacemaker of the gut, and where are they located?
- interstitial cells of Cajal
- A part of the myenteric plexus of the enteric nervous system
What type of epithelium is present in the esophagus?
-non-keratinized stratified squamous epithelium
Why is the lamina propria of the esophagus interdigitated with down growths of epithelium?
-to prevent food we swallow from scraping off our epithelium
Why does the epithelium of our esophagus have melanocytes?
- thought to have more of a free-radical detox role
- can still get melanoma here
Why isn’t there a very pronounced muscluaris mucosa in the esophagus?
-food doesn’t spend much time in the esophagus for digestion
What do esophageal cardiac glands do and where are they present?
- near the transition of the esophagus and the stomach
- it produces mucous which helps prevent stomach acid from damaging the esophagus near the stomach
Describe the muscle types found in the muscularis externa of the esophagus.
- upper 1/3 is skeletal
- middle 1/3 is mixed skeletal and smooth
- -lower 1/3 is smooth
Which nerve plexus is responsible for pirmary, secondary, and reverse peristalsis in the esophagus?
-myenteric plexus
Does the esophagus have serosa or adventitia?
- both
- most is adventita
- distal 1-2cm has serosa
What is the function of the upper esophageal sphincter?
- prevents air form entering into the esophagus during breathing
- prevents reflux of esophageal contents into the pharynx
What is the function of the lower esophageal sphincter?
-protects the esophagus from gastric contents
Are the upper and lower esophageal sphincters made of smooth or skeletal muscle?
- upper: skeletal (not voluntary)
- Lower: smooth
What is the gastroesophageal junction, and what signifies its presence histologically?
- it is the transition point between the esophagus and the stomach
- the epithelium changes from squamous to columnar at the Z-line
What is esophageal Varices?
- dilation of veins from the deep submucosa when the liver is failing
- usually caused by portal hypertension
- Veins can rupture and bleed into esophagus
- means your liver is fucked
What is GERD?
- gastro esophageal reflux disease
- abnormal relaxation of the lower esophageal sphincter allows stomach acid to come up from the stomach
What is Barrett’s Esophagus?
- occurs after chronic exposure of the esophageal epithelium to shomach acid
- involves a histological change in the epithelium so that it looks like the stomach or small intestine
- metabplasia of squamous epithelium to simple columnar increases the risk of a cancer called esophageal adenocarcinoma
What are the overall functions of the stomach?
- stretch to accommodate food bolus
- perform mechanical digestion
- perform chemical digestion
What are rugae?
- large longitudinally directed folds of mucosa and submucosa
- take part in receptive relaxation
Does the stomach have a serosa or an adventitia? What is it made up of? What is its function?
- serosa
- connective tissue, blood vessels, mesothelium
- it protects the stomach from friction as it expands to mix and propel food
What are the three layers of muscularis externa in the stomach?
- outer longitudinal
- middle circular
- inner oblique
What defines the pyloric sphincter histologically?
-a thickening of the middle circular layer of the muscularis externa
What makes up the submucosa of the stomach?
- connective tissue
- LARGE blood and lymphatic vessels
- diffuse lymphoid cells (macrophages and mast cells)
What type of epithelium is present in the stomach?
-simple columnar
What cell types are present in the epithelium of the stomach?
- surface mucous cells
- RARELY you’ll find an intraepithelial T lymphocyte, but its not really considered part of the epithelium
What are the three portions of gastric glands?
- Gastric pit
- Isthmus
- branched tubular gastric glands
What are the two major types of cells in the cardial and pyloric gastric glands?
- mucous cells
- enteroendocrine cells
What are the 5 major types of cells in the body and fundus gastric glands?
- Mucous Neck cells
- Parietal Cells
- Chief Cells
- Enteroendocrine cells
- Stem Cells
What do surface mucous cells do?
- they line the stomach lumen and secrete a thick adherent viscous mucous layer
- this mucous is rich in bicarb which protects the stomach from the low pH of the lumen
What do mucous neck cells do?
- line the neck/isthmus of gastric glands.
- They produce mucous here that is less alkaline than that of the surface mucous cells
What is mucous made of?
-mostly the glycoprotein mucin
what type of secretion is mucous secreted by?
-merocrine
What do parietal (oxyntic) cells do?
- the are located among the mucous neck cells and deeper in the gland
- they produce HCL
- also secrete intrinsic factor, which binds B12
What stimulates the secretion of HCl by parietal cells?
- parasympathetic innervation
- histamine and gastrin from the DNES
What do Chief (zymogenic) cells do?
- located in lower region of gastric glands
- secrete proteins including pepsinogens and gastric lipases
Where are enteroendocrine cells located in the stomach?
they are scattered around the gastric mucosa
What can cause stomach ulcers?
- reacting of acid and pepsin with epithelium
- H. Pylori is a bacteria known to cause ulcers
- NSAIDs
- Steroids
- Stress
What type of epithelium is in the small intestine?
-cytokeratin positive simple columnar
What 5 cell types are present in the small intestine epithelium?
- enterocytes
- goblet cells
- paneth cells
- enteroendocrine cells
- stem cells
What is the epithelium of the small intestine organized into?
-Villi and crypts
What is contained within the lamina propria of the small intestine?
- fibroblasts and loose connective tissue
- continuous fenestrated capillaries with diaphragms
- meissner’s plexus
- lymphatics and immune cells, producing IgA, G and M
What makes up the brush border of the small intestine?
-microvilli and glycocalyx
On which cells in the small intestine is the brush border located?
-enterocytes
Which part of the small intestine has the highest density of enterocytes?
-the duodenum
What do enterocytes do?
- they are absorptive columnar cells
- produce disaccaridases and peptidases
What is the function of small intestine goblet cells?
-secrete glycoproteins to form mucous, which protects the GI lining and lubricates chyme
What do paneth cells do? Where do they live?
- part of the innate immune system
- secrete lysozymes, phopholipase A, and defensins
- protects stem cells
-live at the base of intestinal crypts
What do enteroendocrine cells of the small intestine do?
- control motility and secretion of enzymes
- control our sense of satiety
Where are stem cells of the small intestine located?
-the bottom of the intestinal crypts
What is the turnover rate of the epithelium of the villi in the small intestine?
-3-5 days
What is the turnover rate of the crypts in the small intestine?
30 days to 1 year
What is mucositis-ulceration and what can cause it?
- an influx of inflammatory cells to the lamina propria, with a loss of epithelial cell and mucosal structure
- disrupts large areas of the epithelial lining of the small intestine
-side effect of chemotherapy
What is adenocarcinoma?
-the most common type of small intestine cancer, though still extremely rare
What are enteric pathogens?
-any microbe that is able to cause enteric disease
What are plicae circularis and where are they located?
- submucosa that is thrown into circular/semilunar folds to increase surface area
- located in the submucosa of the small intestine
What are the two shapes of the plicae circularis, and where are they respectively found?
- leaf in duodenum
- finger in ileum
What lies between the inner circular and outer longitudinal layer of smooth muscle in the small intestine?
-myenteric (auerbach) nerve plexus
What are Brunner’s Glands and where are they located?
- branched tubular glands that produce a mucous product that is very alkaline
- they are located in the mucosa and submucosa of the proximal duodenum
What are peyer’s patches and where are they located?
- they are a part of the GALT, specifically the lymphoid nodules
- contain M cells (not motillin) which are specialized epithelial cells that have a porous basement membrane with pockets that contain lymphocytes and dendritic cells.
-located in the small intestinal mucosa of the ileum
What are the three layers of the mucosal barrier of the small intestine?
- mucous
- epithelium
- GALT
What is the histological finding in celiac disease?
- accumulation of T and Plama cells in the lamina propria of the small intestine
- whats left of the enterocytes have fat globules inside, and a stratified nucleus, with no brush border and an increase in crypt mitotic cells
What cells are contained within the epithelium of the large intestine?
- Goblet cells
- Colonocytes
- DNES cells
- stem cells
- Lymphocytes
What do colonocytes do?
- absorptive columnar cells
- absorb water
Describe the intestinal glands of the large intestine.
- tubular glands in epithelium that extend into the lamina propria
- Lined by goblet cells and colonocytes
- thin brush border
- stem cells in bottom 1/3 of gland
Describe the muscularis mucosa of the large intestine.
-has distinct inner circular and outer longitudinal layers
How is the outer longitudinal layer of the muscularis externa different in the large intestine?
-it is present as 3 equally spaced bands of smooth muscle called Teniae Coli.
What are omental appendages?
- suspended masses of adipose tissue on the large intestine
- small and pendulous
- protrude from the serosal surface
What compromises the distal end of the large intestine?
- rectum
- rectoanal junction
- anal canal
- anus
What type of epithelium does the Rectum have vs the anal canal?
- rectum is simple columnar
- anal canal is stratified squamous epithelium
Where are anal columns present?
the anal canal
What are anal columns?
- longitudinal folds of mucosa and submucosa located in anal canal
- contain a rectal venous plexus
What is the pectinate line?
-the transition from the simple columnar epithelium of the rectum to the stratified squamous epithelium of the anal canal
What is the appendix composed of?
- inner and outer muscularis externa
- filled with lymphoid tissue
- houses normal bacterial flora
What is Hirshsprungs disease?
- caused by heterogeneous defects in migration and survival of neuroblasts. Leads to an altered distribution of interstitial cells of cajal
- complications include distention of proximal colon with muscular wall hypertrophy/rupture
Which contains villi, the small intestine or the large intestine?
-only small
Are there paneth cells in the large intestine?
-no
What is the relative lengths of the crypt of glands in the small intestine vs large intestine?
-small intestine has shorter crypts than large intestine
How is the lymphoid tissue of the submucosa organized in the small intestine compared to the large intestine?
Small intestine:
-organized peyer’s patches
Large Intestine:
-diffuse lymphoid nodules
Compare/contrast the microvilli and glycocalyx in the small and large intestine.
Small intestine:
-extensive microvilli and glycocalyx
Large Intestine:
-patchy microvilli and no glycocalyx
