GI - Glands

From Iusmhistology

  • started here on 02/16/11 at 2PM.


  • Be careful veryifying one's knowledge with online resources because they can be wrong.

Contents

[edit] Glands

  • We'll do salivary, pancreas, and liver

[edit] Salivary glands

  • Saw these with epithelium.
  • Defined serous and mucus.
  • Serous cells are only found in acinar, not in tubular.
  • Mucus usually in tubular, sometimes in acinar strctures.
  • Demilunes
    • Here serous cells are found
  • Two types of ducts:
    • Intercalated
    • Striated
  • Also there are interlobular ducts in the connective tissue.
    • Also called excretory

[edit] Image(s)

  • Acinars are spherical so they will always be cut round.
  • Tubules can get cut round or longitudinally (to be long).
  • Recall that serous cells can have highly concentrated stuff in their granules so they stain dark but mucus canot be conncentrated in mucus cells.
  • Tubules and acinar empty into intercalated tubes.

[edit] Parotid glands

  • Have lots of serous acini
    • Nuclei on the outside, granuels on the inside.
  • Terculated ducts:
    • Hard to find
    • Tubular so they get longtudinally
    • Smaller in diamter than acin
  • Striated ducts
    • Have lots of mt that sometimes give striations
      • Not prominent
    • Larger than terculated ducts

[edit] Salivary

  • Three major are parotid (almost all serous cells), submandibular (mixed serous and mucous) and sublingual (more mucus than serous so will often look just mucus).

[edit] Saliva

  • Low in Na because it helps the taste bud fxn.
  • Alkaline, has bicarb to buffer acid
    • Helps keep tooth decay reduction
  • High in calcium and phosphate
    • Helps re-mineralize the teeth.
    • Mini-cavities form from bacteria but if you get it cleaned off, you can remineralize
  • Protein components:
    • alpha-amylase: starts breaking down carbs
    • Proline rich protiens
      • Abundant
      • Antibacterial
      • Help coat the tooth and keep bacteria off
    • Lysozyme
      • Lyses bacteria
    • Mucus
      • Lubrication
    • Immunoglobulins
      • Mostly IgA
      • Secreted by epithelium into forming saliva
  • Fear or nervousness can change the saliva
    • Gets thicker

[edit] Secretion

  • Serous produce fluid, protein, and zymogens
  • Mucus produces mucins
  • The products mix and then pass through intercalated ducts and then striated duct.
  • Striated ducts are most important for removing most Na+.

[edit] Summary

  • Most important is to know all glands have intercalated and striated and to know which type of secretion they generate.

[edit] Pancreas

  • Two portions: endocrine and exocrine (acinar).

[edit] Endocrine

  • Islets of langerhans (pancreatic islands) are groups of cells that produce insulin, glucagon, and somatostatin.
  • Islets make up only 1-2% of pancreas the rest is exocrine.
  • Beta = insulin
  • Alpha = glucagon
  • Alaph and beta make up most of the mass
  • Delta = somatostatin
  • alpha (20%), beta (70), d (5-10), F (1)
  • F cells generate pancreatic polypeptide.

[edit] Exocrine pancreas

  • Looks like the parotid in that it is made of acini.
    • But has not fatty tissue
    • Has no striated ducts
  • Cholesystokinin = the hormone that moves the gallbladder
    • Causes pancreas to secrete it's exocrine stuff.
    • Makes sense because the two should operate at the same time.
  • Proteases are the main product of serous cells in the pancreas:
    • Trypsin
    • Elastases
    • Protease E
    • Kallikrine
    • alpha amylases
    • Lipases
    • nucleases
  • Volume of fluid (water and salt) is secreted by ductal cells
  • Secretin stimulates ductal cells to generate the volume (water and salt)
  • Bicarb is scrected to keep the alkalinity hihg.
  • Acute pancreatitis (inflammation or plugging of duct) is bad for the panreas
    • When the cells break down the enzymes are let loose and they go nuts, destroying tissue.
  • The ducts extend up itno the acinus
    • Centroacinar cells = ductal cells that are up in the acinus
    • Have a poorly staining cytoplasm and a light nucleus.
    • Hard to find, honestly.
  • Acinar cells:
    • Well staining cyto and open nuc
    • These cells have lots of rER and secretory granules.

[edit] Liver

  • Largest gland in the body.
  • Exocrine product is called bile.
  • Bile is a nasty fluid:
    • Amphopathic salts = bile acids, a form of detergent.
    • Allow fat droplets to break up into small droplets
    • Also contains waste products like pharma and bilirubin.
  • Liver sees all the products from the GI tract before it gets to the blood.
    • An importnat monitor and processor
  • As blood passes through:
    • Hepatocytes process: store, add, remove
    • Microcirculation of the liver is special to facilitate secretion of albumins into blood. (Think sinusoidal caps).
  • 70-80% of the blood comes from the hapatic portal vein.
  • The rest is oxygenated and comes from the hapatic artery.

[edit] Hepatic blood flow

  • Blood flows between cords (a string of cells) or plates of hepatocytes.
  • Blood spaces are sinusoids, a form of sinusoidal capillary
    • Incompletely lined with endothelium; the endothelial cells don't bind to one another
    • Makes them leaky
  • Blood comes in in the hepatic vein or the hepatic artery, then flows together and mixes in the sinusoid.
  • Then collected in central veins.
  • Hepatocytes along the sinusoid is processing the lbood (taking things out and putting things in).
    • They are also producing bile that goes the other direction as blood.
  • The bile dumps into the bile duct system via the bile canaliculus.
  • The bile in the canaliculus is simply flowing between cells, it is not within a structure.
  • Portal triads are the hepatic veinule, the hapatic arteriole, and a branch of the bile duct.
    • There may be more than one of each of these.
    • Look for smooth muscle to identify the arteriole
    • Look for simple cuboidal epithelium to ID the bile duct.
    • The other things are the venules.
  • When you see large spaces in the liver, consider it a blood sinusoid.
  • Portal spaces also contain lymph vessels and nerves.
    • CAn see vessels
      • Usually look like empty space with practically no lining.
    • Cannot see nerves

[edit] Blood flow passed hepatocytes

  • Hepatocytes and blood are separated by the perisinusoidal space = space of Disse.
    • Can get enlarged upon fixation.
  • Fat storing cesll of Ito are in the perisinusoidal space.
  • Kupffer cells are macrophages of the liver that reach into the sinusoidal spaces from the perisinusoidal space.
  • Hepatocytes:
    • Large nucleili
    • Well staining cyto
  • Kupfer cells are foundin the blood flowing sinusoid area

[edit] Formation of bile

  • Bile flows within canaliculi which are formed by the hepatocytes themselves.
  • At the edges of a lobule canaliculi merge into bile ductules.
    • Ductules are lined with an epithelium.
    • The small ones are called canals of Hering.
    • These are the ducts that will add to the triad.
  • The canaliculi show up as pin-holes between cells.
    • They are NOT LINED with any cell except the neighboring hepatocytes.
    • Tight junctions separate the membranes to form the canaliculus.
  • In contrast, the ducts of hering and the larger ducts of the triad ACTUALLY HAVE an epithelial lining.
  • Three ways to understand how hepatocytes filter blood and produce and bile:
    • Liver can be lobulated:
      • The classic lobule description
      • The liver is divided into lobules that have protal veins, hepatic arteries and ducts at one side and
    • Portal lobule
      • Lobule is defined as all the hepatocytes that contribute bile to a given bile duct
    • Hepatic acinus
      • Lobule defined by hepatocytes' blood source
      • Has zones: zone 1 is highly oxygenated and zone 3 is least oxygenated.
      • After a meal, zone 1 will have the highest glucose level and zone 3 will have the lowest access to glucose.
      • Also, metabolites generated by hepatocytes will be the opposite (highest in 1 and lowest in zone 3).

[edit] The hapatocyte

  • Does lots of stuff.
  • Produces bile salts:
    • Detergents
    • Made in sER
    • Secreted across membrane of bile canaliculus
    • Conjugated wtih glycine and taurine
    • 90% of the bile salt flowing out of a healthy liver is being recycled because they have been reabsorbed in the gut, then by the perisinusoidal membrane of the hepatocytes as blood from protal vein flows by.
  • Many pharmaceuticals are secreted from the liver
    • Often chemically transformed and then secreted into the bile
    • Take some relative lipids soluble thing into your body, hepatocytes will get it from the blood, add a sugar onto it, then secret it into the bile.
    • Includes bilirubin
  • The processing often includes making the fat-soluble waste product water soluble so it can be carried to the kidney to be secreted via the urine.
    • This is common and relevant to pharma.
  • Hepatocytes also store glucose as glycogen
  • Hepatocytes also produce most of the important serum proteins:
    • Albumin:
      • Can get secreted through sinusoidal cap wall
    • lipoprotiens, glucose, urea.

[edit] Gallbladder

  • The point is to store and concentrate the bile until fatty foods are present.
  • Epithlium of gall bladder are simnple columnar epithelium
    • Has brush border
    • Absorb salt and water to concentrate the detergent bile
  • Lamina propria is the CT below the epithelium
    • Glands only found at the neck of the glall bladder.
  • Muscularis:
    • Sometimes a pouch of epithelium pokes thorugh and LOOKs like a gland but isn't.
  • True serosis is present
  • Bile gets sent to gall bladder because the commmon bile duct is usually constricted to cause back up into the bladder.


  • stopped here on 02/16/11 at 2:03PM.
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