Histology of Esophagus, Stomach, and Duodenum

What nerve plexus is contained in the submucosa of the stomach?

Meissner's plexus

The stomach has three gland types - what are they?

cardiac, pyloric, gastric

The stomach turns the stores/churns/and digests food, turning it into _______

chyme

Where are the esophageal glands proper located? What type of glands are they? what kind of mucous do they produce (pH wise)?

esophageal glands proper are in the submucosa. they are mucous glands and produce an acidic mucous

Good view of Auerbach's plexus. How can you tell a ganglion cell on histo?

ganglion cell = big nucleus, little nucleolus [I'm in a GANG, you better be NERVOUS...I got my EYES on you - look like little eyes!]

which sphincter prevents gastric reflux?

inferior esophageal sphincter

What's special about the mucosal surface of the stomach?

it has many pits called foveolae. these pits are the openings of several branched tubular glands. The necks of the glands are the narrow portions that connect with the pits. [I feel it in the PIT of my STOMACH.]

What's distinct about the muscularis mucosa in the esophagus?

it's thick and has only ONE layer of longitudinal SM

Where does the enteric nervous system extend from?

lower esophagus - internal anal sphincter

What is the purpose of the muscularis mucosae?

mix contents of lumen

What two things to do parietal cells secrete?

parietal cells secrete HCl and intrinsic factor

What is the function of the muscularis externa?

peristalsis - slow rhythmic *waves* of contraction that constrict and shorten the tube to propel food along the GI tract

What are the rugae? Are they present when the stomach is empty or full?

rugae = longitudinal folds of the internal surface of the stomach (specifically the muscularis mucosa); flatten out as the stomach fills

Through what structures do parietal cells secrete HCl?

secretory canaliculi (canals) - open up into lumen of gastric gland, lined by microvili

Where would you find Meissner's plexus (part of enteric NS)?

-submucosa (Meind ur own Business - suBmucosa)

What are the muscle types in the different portions of the muscularis externa of the esophagus?

-upper 1/3 = skeletal muscle, BUT INvoluntary! -middle 1/3 = mix of smooth and skeletal muscle -lower 1/3 = smooth muscle

In the intestine, the mucosa forms intestinal ________

-vili = fingerlike projections to increase SA for digestion and absorption in the SI -also note the other labeled features in the pic

Enteroendocrine/APID cells are part of this large family of cells

DNES = Diffuse Neuroendocrine System = present in GI sys, resp sys, thyroid gland, pituitary gland, prostate

What GI organs have submucosal glands?

Esophagus and Duodenum (ED, ED, + EDdie have sublevel intelligence - Esophagus and Duodenum have glands in in SUBmucosa)

Extrinsic component also consists of ________ (pre/post gang) sympathetic fibers from which ganglia?

Extrinsic component also consists of POSTGANGLIONIC sympathetic fibers from which celiac, superior mesenteric, and inferior mesenteric ganglia. [I'm sorry CERYAK, I do feel SYMPATHETIC towards you, but you never taught me what a mesentery is!]

Extrinsic component consists of _________ (pre/post gang) parasympathetic fibers from ______ and ________ __________ nerves

Extrinsic component consists of PREGANGLIONIC parasympathetic fibers from VAGUS and PELVIC SPLANCHNIC nerves

What is GALT? Where might you find it within the gut wall?

GALT = gut associated lymphoid tissue; found in the lamina propria

For each of these hormones - what type of cells are they secreted by? Are they endocrine or paracrine? What is their function? gastrin histamine somatostatin

GASTRIN -true hormone - endocrine (Think of this as the purest one) -secreted by G cells -stimulates acid secretion HISTAMINE -paracrine -secreted by ECL cells throughout the GI mucosa (Think when you're having a histamine allergy attack - throat closes - ECL) -stimulates gastric acid secretion SOMATOSTATIN -paracrine -secreted by D cells (think D cells - somatostatin - Downregulates stuff) -inhibits secretory activity of neighboring enteroendocrine cells

Gastric glands -pits make up what fraction of the mucosa? -are the glands straight or coiled?

Gastric glands -pits make up 1/3 of the mucosa -glands are STRAIGHT (think you have a ton of room in the body) -also contain stem cells in the isthmus

What comprises the enteric nervous system?

-Auerbach's/myenteric plexus -Meissner's/submucosal plexus -can function on its own although it is influenced by extrinsic system

Another histo pic of small intestine. What structure looks like a floating island of tissue? So if you see it, where do you know you are?

-VILUS looks like island of floating tissue! So if you see one you know you're in the small intestine

What is the pathophys of ulcer formation?

-action of HCl and pepsin -> digest the mucosa -often happens from H pylori infection bc it can survive in an acidic environment and causes an inflammatory rxn that degrades the epithelium (also increased acid secretion, chronic aspirin usage)

Parietal cells look different when they are actively secreting vs. resting. What are the differences?

-active secretion - secretory canaliculi -resting - *tubulovesicular system* contains *membrane reserve* that can form microvili when needed

histo of a chief cell

-big nucleus towards base of cell -lots of RER bc we are producing enzymes

Surface mucous cells are constantly being shed into the lumen. How are they replaced?

-by stem cells in the isthmus = lower portion of the pit just superior to necks of glands.

What are the four major regions of the stomach?

-cardiac region -fundic region (go OUT and have fun! - outer upper edge!) -body of the stomach -pyloris

Where do enteric sensory neurons receive their info from?

-chemoreceptors (from nerve endings in epithelium) -mechanoreceptors (from nerve endings in SM)

Where are chief cells located? How are they stimulated? What is their function?

-chief cells are located in the basal half of glands (PARIETal as the PRIORity) -they are stimulated the same way parietal cells are - ACh, Histamine, Gastrin -they secrete pepsinogen ( -> gets converted to pepsin -> cleaves peptide bonds at acidic pH's) and lipase (hydrolyzes fats)

What are the physiological effects of contracting the inner circular layer of the muscularis externa? What about contracting the outer longitudinal layer?

-contract inner circular layer -> constricts the lumen -contract outer longitudinal layers -> shortens the tube

histo of intestinal gland. How do Paneth cells appear?

-dark bright red granules - ready to fight bacteria!

What 2 cell types do enteric motor neurons innervate? What are the functions of each?

-enteric motor neurons innervate SM -> stimuate peristalsis -enter motor neurons stimulate enteroendocrine cells (in ep) -> secrete hormones

Enteroendocrine/APUD cells are another cell type in gastric glands. Where are they located? Are they big or small? What do they secrete? What is the function these cells?

-enteroendocrine cells = small cells located throughout the epithelium of the GI tract -they secrete hormones that either enter the bloodstream (endocrine) or act locally (paracrine) -these cells regulate the secretory activity of cells throughout the GI system

What kinds of glands are in the esophagus? Where can the esophageal cardiac glands be found?

-esophagus contains mucous glands (Esophagus - gotta think mucous) -cardiac esophageal glands are in the lamina propria at the lower end of the esophagus - produce mucous with a neutral pH (I am a neutral nerd cuz I have all this mucous...it's so LAME! No one HEARTS me and I'm at the lowest end of the totem pole)

What organs would have an adventitia rather than a serosa?

-esophagus/ anal canal /anything retroperitoneal when stuck to abd wall [Also, side note: adventitia merges with CT of adjacent structures]

What structures are located with the lamina propria of the small intestine?

-fenestrated capillaries which are permeable to macromolecules like short chain fatty acids -central lacteal = lymphatic capillary, imp for fat absorption (long chain FA's) -there's also some surrounding SM in the muscularis mucosa that allows the vili to scrunch up and mix contents of lumen

What is the most numerous gland in the stomach? In what parts of the stomach are they located?

-gastric glands - located in body and fundus of stomach

What hormones do enteroendocrine cells secrete?

-gastrin -histamine -somatostatin

What is the gastroesophageal sphincter? Where is it located? What is its function?

-gastroesophageal sphincter = inferior esophageal sphincter -prevents gastric reflux by creating a pressure differential (increases esophageal pressure -> collapses the esophagus -> no reflux of stomach contents)

What are the three main functions of HCl in the gastric juice?

-initial protein digestion (by denaturing them) -cleaves pepsinogen into pepsin which further digests proteins via hydrolysis -destroys most ingested bacteria

What is intrinsic factor? What does it do? What happens if you have a deficiency in intrinsic factor?

-intrinsic factor = a glycoprotein secreted by parietal cells -binds to vitamin B12 in the duodenum and allows for B12 absorption by the ileum -deficiency in IF -> deficiency in B12 -> defective RBC formation -> pernicious anemia

nice overview of isthmus - what other types of cells can it replace? Which does it do quicker?

-isthmus cells can travel up to replace surface mucous cells - quicker -OR can travel down to replace longer-lived gland cells - slower

What is the outermost layer of the esophageal wall?

-most of the esophagus is surrounded by adventitia because it's attached to body wall -lowest 2-3 cm of esophagus is located in the abdominal cavity and thus is covered by serosa

What are the four major layers of the GI tract wall? What types of cells are in each?

-mucosa = ep, LP (loose CT), ~2 layers of SM = muscularis mucosae -submucosa = dense, irregular CT -muscularis externa = inner circular, outer longitudinal -adventitia/serosa: serosa = visceral peritoneum = CT + mesothelium (simple squamous epithelium, makes things slippery so that organs can slide past each other); adventitia = just CT

What are mucous neck cells? Where are they found?

-mucous neck cells = can be found in the necks of the glands shoved between parietal cells (big pink cells) -they produce a SOLUBLE mucous - more soluble than that produced by the surface mucous cells (Think: gotta be soluble to get stuff up to the pit)

What are some other functions of the stomach?

-mucous production -begin protein digestion

Enteroendocrine cells can be open or closed types. What are the differences?

-open types = exposed to the lumen; microvili can sample the local environment -closed types = buried in other cells -> only contact the BM, not exposed to the lumen. Stimulated by the motor component of the enteric NS

Good pic of mucous neck and parietal (aka oxyntic) cells in the neck of a gland. Why are parietal cells so pink? Where are they primarily located?

-parietal cells are pink bc they're loaded with mito - HCl v energy intensive (you use a lot of ATP dependent membrane transporters). Parietal cells are primarily in the necks of the glands

Cardiac glands of the stomach -where do they occur? -are they coiled or straight? -what is the depth of their pits? -what type of cells do they contain?

Cardiac glands of the stomach -occur within the first 4 cm from the cardiac orifice -these glands are coiled (think - it's not a v free space) -pits are shallow - 1/4 the thickness of the mucosa (think: love is shallow) -contain primarily mucous cells

More on Crypts of Lieberkuhn -what kind of epithelium are they lined by? -what additional cell types are located in the crypts?

Crypts of Lieberkuhn -simple columnar epithelium -has stem cells at the base, located above Paneth cells (lysozymes) [Sasha has taken classes with Dr. Panjrath]

good overview of intestinal mucosa

Crypts of Lieberkuhn = intestinal glands located at the bases of the vili (think of LITTLE sasha LIBERman in the small intestine)

Do gastric glands have just one cell type?

No! Contain - enzyme-, acid-, hormone-, and mucous- secreting cells!

Does much absorption happen in the stomach?

No! Water and lipid-soluble drugs are absorbed by the surface mucous cells. aspirin and alcohol are also absorbed -> but they disrupt the mucosal epithelium

Moving onto the small intestine! -there are four levels of structural specialization that allow the small intestine to increase its surface area for reabsorption. What are they?

Plicae circulares (permanent folds in mucosa/submucosa) -> vili and Crypts of Lieberkuhn (glands btwn the base of the vili) -> microvili -> glycocalyx (integral membrane glycoproteins/digestive enzymes)

Pyloric glands of the stomach -wheat's the depth of the pits? -primary cell type? -are the glands straight or coiled?

Pyloric gland of stomach -longer pits than cardiac glands = 1/2 the depth of the mucosa -primary cell type is mucous glands are coiled

What's unique about the muscularis externa of the stomach? Also, what nerve plexus can be found here?

THREE (not two) smooth muscle layers -inner oblique (not present along lesser curvature) -middle circular (thickens to form pyloric sphincter) -outer longitudinal [Think to get through all the stomach histo you need a lot of muscle!] -Auerbach's plexus can be found btwn circular and longitudinal layers - coordinates motility

Innervation of the GI is _______ (autonomic/somatic)

autonomic

Where is the myenteric/Auerbach's plexus located?

btwn the 2 layers of muscularis externa [Remember that myenteric = Auerbach bc of Arnold swarzenegger with the big myenteric muscles]

What type of epithelium does small intestine have?

simple columnar

What type of epithelium does the stomach have?

simple columnar

The circular layer of the muscularis externa thickens to form __________

sphincters

Histological organization of the esophagus: what kind of epithelium is in the mucosa?

stratified squamous unkeratinized. It's thick!!!

Duodenum has what special type of gland? Located where? What's their function?

submucosal Brunner's gland (DUOdenum part of BRUDDERS) -secrete alkaline mucosa -> ducts open into the bases of the crypts

What are the specialized cells in the stomach epithelium? What is their function?

surface mucous cells (Remember: mucous is a big deal in the stomach) - they secrete bicarbonate rich mucous (gotta neutralize stomach acid) and they cover the pits.

How would you describe the gastroesophageal junction?

things change abruptly! Go from very thick esophageal ep (on the right) to all of a sudden simple columnar. Occurs at the cardiac orifice of the stomach

What types of cells are in the isthmus?

undifferentiated, low columnar stem cells