GI - Small intestine through anus

From Iusmhistology

  • started here on 02/14/11 at 2PM.

Contents

[edit] GI - Small intestine through anus

[edit] Esophagus review

  • All parts of the gut have four layers: mucosa (epithelia, lamina propria, and muscularis mucosi), submucosa, muscularis externa, serosa
  • In the esophagus:
    • epithelial is stratified squamous non keratinized
    • No glands in the esophagus
    • muscularis has longitudinal bundles that are discontinuous
    • Sub mucosa has glands that secrete mucus
    • Muscularis externa is composed of 1/3 skeletal, 1/3 mixed, 1/3 smooth muscle
      • Each third has inner circular and out longitudinal
    • Serosa: adventitia through thorax b/c not in pleural space, then once thorugh the diaphragm it gets a mesothelial covering

[edit] Stomach

  • Has cardia region: a ring just around entry.
    • We don't ahve to recognize this.
    • Contains mucus glands.
  • Fundus and body are next, and are similar.
    • Have mucosal grlands: fundic glands = gastric glands = oxyntic glands (acid secreting)
    • Cell types withing glands include stem cells, mucus neck cells, and parietal cells
  • Stem cells:
    • Reproduce all other types
    • Live in the neck of the gland
  • Mucus neck cells:
    • Usuaqlly in neck
    • Can't be distinguished versus stem cells
    • Produce mucus
  • Parietal cells = oxynctic cells
    • In the neck
    • Make acid and intrinsic factor
    • Intrinsic factor binds b12 to protect fromn degradation so it can be absorbed later.
    • Without factor I you have pernicious anemia (because it is hard to fix)

[edit] Stomach images

  • Pits have the same surface mucuus cells.
  • Glands have a different type of cell lining them.
  • Neck region is the lighter staining area
    • Neck cells include: parieta, mucosla, and stem cells.
  • The neck region lives in the lamina propria.
  • Need to identify the neck.
  • Parietal cells:
    • Tend to bulge out from the walls of the gland
    • Look like fried eggs.
  • Acid secretion:
    • Occurs by fusion of tubulovesicles with a secretory canaliculus.
    • Think of pushing your finger into the cyto; an invagination.
    • When the tubulovesicles fuse they release lots of proton pumps that pump acid out into the ECF.
    • Have lots of mt b/c make lots of proton pumps.
    • Note that potassium is moved along with acid.
    • Bicarb moves in the opposite direction of acid.

[edit] Chief cells

  • Produce, store, and then secrete pepsinogen (a zymogen).
  • Pepsinogen cleaves itself into pepsin.
  • Breaks up proteins.
  • Because of the zymogen granules they stain well with H.
  • Granules are generally kept at the apical surface.


  • Pairetal cells live in both the neck and the base of the gland.
[edit] Enteroendocrine cells
  • ADUP-type (amine precursur uptake and decarobxylation): the name for production of hormone produced by these cells.
  • Scattered through epithelium
  • Produce ltos of endocrine secretion for local or global action.
  • We cannot see these cells in our stains.
  • There are several types:
    • Defined as opened when apical surface reaches into the gland
    • Open or closed
    • Endocrine cells secrete toward the blood (their base) not toward the gland.

[edit] Pylorus

  • Has deeper pits and shorter glands.
  • Has lot sof mucus cell sint eh glands.
  • In the pylorus, gastrin is secreted.


  • Gland types:
    • Cardiac, fundus, body: gastric glands
    • Pylorus: deepr pits and mostly just mucus glands

[edit] Small intestine

  • Has vili and crypts.
  • The si is 12 to 24 feet as part of its specialization for absorption.
  • There are folds to increase surface area (plicae circulares = valves of kerkring).
  • There are vili (finger-like extensions of the epithlium) out into the lumen.
  • There are absorptive cells with microvilli at their apical membrane.
  • Absorptive cells are called enterocytes.
  • Lots and lots of surface area!
  • The muscularis mucosa and lamina propria are folded within the plicae circulares.
  • The enterocytes are specialized for moving salt, water, amino acids, vitamins, sugar, etc.
  • the caps within will carry the nutrients away.
  • The cell interior of the enterocyte is usally negative (via Na/K atpase) so that the electro gradient can be used to run active transport of all the nutrients.
  • Vilus is impt for nutrient absoprtion.
    • Each has it's own arteries and veins.
    • So within each is an isolated region.
    • So as active enterocytes pump lots of nutrients in, the concentration of nutrients actually causes diffusion of nutrients from the vein to the arteries and vice versa for water.
    • This causes a higher concentration of nutrient at the distal end.
  • Enterocytes also absorb fat
    • Absoprtion can only be performed as free fatty acids.
    • Fat must be dispersed, not in the drops of fat as chyme has caused them to form into.
    • So bile salts disrupt these droplets to form smaller pieces.
    • Then smaller parts can be moved into apical membrane of the enterocyte, where they are put back into tAGs, put them into chylomicrons, and then secrete the chylomicrons through the basal membrane into the lymph system!
    • Note that caps in the vili are pretty leaky (fenestrated) but not leaky enough for chylomicrons to get through, hence they gro throug the lymp.
    • the central lacteal is where the chylomicrons of all the enterocytes of a singl3e lacteal are entering the lymph

[edit] Goblet cells

  • Found on the surface of the vili
  • Secret mucin

[edit] M cells

  • Found at peyer's patches
  • help transport antigens and abs for immune surveillance.
  • Lymphocytes can migrate out between enterocytes, too.
  • Lymphocytes can actually congregate somewhat inside the M cells, too.

[edit] Enteroendocrine cell

  • Don't worry about table 15-1; don't memorize it!
  • Don't worry about the table in the slides either.

[edit] Glands of the si

  • These are simple tubular glands
  • Called crypts of lieberkuhn.
  • In both si and li but different.
  • SI:
    • crypts are the locaiton of stem cells
    • Look for mitotic figures because this is where cells are dividing.
    • At the very base are paneth cells
      • Somewhat mysterious
      • Have antibacterial agents, lysozymes, and defensins in eosinophilic granules.
      • These are really eosinophilic.
      • We think these chemicals released help control who gets to live in the gut.
      • may be important for crohn's disease.
  • Submucoals glands found only in the duodenum
    • Called Brunner's glands
    • Mostly mucus glands
    • Mostly alkaline secretion (to counteract the acid secretion)
  • Muscularis externa:
    • Inner cicrular, outer longitudinal.
  • Serosa of the SI:
    • Retroperitoneal parts don't have mesophthelium but most does
  • Nerve plexuses:
    • Myenteric plexus = auerbach's: between the two layers 9of the musculara externa (inner cirular, outer longitudinal)
    • Meissner's plexus = submucosa: runs within the submucosa
    • Both are found in the large and small intestine.
    • A plexus has little bundles that have nerve cells and then nerve material that connect them in a complicated way.
    • Sometimes called the "little brain" of the gut because this is what controls the coordination of the muscle.
    • Brain just says to speed up or slow down.

[edit] Large intesstine

  • Cecum and colon are very similar.
  • In the LI there are many long cryps of lieberkuhn and no submucosal glands
  • Mucosa:
    • There are simple columnar absorptive epithelial cells
    • No paneth cells but instead there are undifferentiated cells
    • There are lots of globlet cells which are easy to see.
    • Colon has no vili that stick out but still has crypts.
    • Colon serves to dry the feces and maintain salt balance.
    • Also lubricates the feces with goblet cells.
  • Muscularis externa:
    • Has outer longitudinal muscle with special bands called tenia coli.
    • Haustra are pouches that are formed.
    • This is a thickening of outer longitudinal muscle bands.
    • the poutches help hold the food material as it is turned into feces.

[edit] Appendix

  • Looks much like colon.
  • Exception: lots of lymphid molecules.

[edit] Rectum

  • Lots of goblet cells.
  • Moves from simple columnar to the stratified squamous of the skin.

[edit] Cell turnover

  • 3-6 days in SI
  • 4-8 days in LI
  • Methotrexate experiment
    • Causes cells to stop dividing:
    • Dark cells are dividing
    • Height of vili gets smaller when division is inhibited
      • Vili slough off cells constantly so if they aren't replaced digestive problems occur.
      • Both problems with uptake and with processing.
    • After 4 days, division begins again; by 8 we are back nearly to normal structure.


  • stopped here on 02/14/11 at 3PM.


[edit] Lab

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