Histology - Comp Exam

Question 1

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Question 2

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Question 3

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Question 28

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Question 29

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Question 30

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Question 31

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Question 32

Stratified squamous epithelium.

Answer 32

Question 33

Acid Fixatives

Answer 33

Acid fixatives fix chromatin, nucleoli, and spindle fibers but not mitochondria or nucleoplasm.

• Carnoy’s fluid - mixture of alcohol, chloroform, and glacial acetic acid. Good general fixative, useful for preserving glycogen in animal tissues.
• Zenker’s fluid - contains potassium dichromate, mercuric chloride, and glacial acetic acid. Good for sharp histological detail, but must be washed out carefully to prevent the precipitaion of black crystals.
• Bouin’s fluid - contains picric acid, formalin, and glacial acetic acid. Widely used general fixative that gives good cytological detail. Requires prolonged and careful washing cycles.

Question 34

Basic Fixatives

Answer 34

Basic fixatives can be used to fix tissues where mitochondrial staining is desired, but dissolves chromatin.

• Zirkle-Erliki fixative contains potassium dichromate, ammonium dichromate, copper sulfate, and distilled water. Requires a long fixing time (2 days) and washing under running water.

Question 35

How can lipids be stained and observed?

Answer 35

By using fat-soluble stains such as the Sudans, but preservation requires techniques that do not utilize alcohol for dehydration.

Question 36

Describe acid dyes.

Answer 36

• Acidic dyes bind to tissue components by forming electrostatic linkages with cationic groups such as the amino groups of proteins.
• Different types of acid dyes have slightly different properties and can be used in sequence to give different results:
  
  • Mallory’s triple stain uses 3 acid dyes sequentially: aniline blue stains collagen, acid fuchsin stains ordinary cytoplasm, and orange G stains RBCs.
• Any tissue component that reacts with an acid dye is said to be acidophilic.
• Examples: Acid fuchsin, aniline blue, eosin, orange G

Question 37

What can be used to stain RNA?

Answer 37

RNA-rich organelles may be stained with basic dyes such as toluidine blue, methylene blue, or methyl green. However, control slides must be made and incubated with ribonuclease to distinguish other basophilic substances.

Question 39

What is hematoxylin and eosin (H&E) stain used for and what are its pros and cons?

Answer 39

HE is commonly used for routine staining because they display structural features. It does not say much about the chemical characteristics of the tissues.

• There are several kinds of hematoxylin preparations that stain nuclear material and some cytoplasmic components, such as RER, dark blue to light blue or purple.
• Although not basic dye, hematoxylin behaves like one due to the properties of the mordant that is used to help it bind to the tissues.
• Derived from logwood as hematein.
• Eosin, an acid dye, stains most of the cytoplasmic components and much of the extracellular material a yellowish to pinkish color.

Question 40

What is the periodic acid-Schiff reaction (PAS)?

Answer 40

• Periodic acid is used to cleave the bonds between adjacent carbons of carbohydrates and form aldehyde groups.
• Schiff reagent reacts with the aldehyde groups and forms a deep-pinkish color.
• PAS-positive substances:
  
  • Polysaccharides (glycogen)
  • Glycosaminoglycans
  • Proteoglycans
  • Glycoproteins
  • Glycolipids

Question 41

What is Best carmine?

Answer 41

Best carmine is a dye that may also be used to demonstrate glycogen deposits.

Question 42

What is orcein and resorcin fuchsin stain used for?

Answer 42

To reveal elastic material.

Question 43

Describe the acinus structure of the glands of the pancreas.

Answer 43

Pancreas - Acinus Structure of Glands

• Acini are serous.
• Acinar cells are pyramidal serous cells:
  
  • Basal zone is basophilic and contains nucleus and RER.
  • Apical zone with zymogen granules.
    
    • Precursors of the enzymes in pancreatic juice.
    • Trypsin, chymotrypsin, amylase, and lipase.
    • Specific receptors for cholecystokinin.
• Centroacinar cells:
  
  • Form a truncated cuboidal epithelium within the lumen of acini.
  • Continuous with the epithelium of the intercalated duct.
  • Unique to pancreas.
• No striated ducts.
• No myoepithelial cells.
• Release of digestive enzymes from serous acinar cells is stimulated by CCK.
• Bicarbonate-rich, alkaline fluid is released by ductal epithelial cells in response to secretin.

Question 44

What are cadherins?

Answer 44

Cadherins are major components in calcium-mediated adherens junctions. They typically for cis- and trans-homophilic dimers.

• Classical cadherins:
  
  • E-cadherins: Found in epitheleal tissues
  • N-cadherins: Found in nerve cells
  • P-cadherins: Found in placenta
• Nonclassical cadherins:
  
  • Include desmocollins and desmogleins
  • Found in desmosomes (macula adherens)

Question 45

Describe the intrinsic pathway.

Answer 45

Intrinsic Pathway

• Injury to endothelium of blood vessel exposing collagen fibers leads to the activation of Factor XII (Hageman factor):
  
  • Activated Factor XII activates Factor XI.
    
    • Note also that activated factor XII also converts prekallikrein to kallikrein.
    • Kallikrein is involved in the formation of bradykinin (increases vascular permeability) in the kinin cascade and in the conversion of plasminogen to plasmin in the fibrinolytic system.
    • Kalikrein can also feedback and activate more Hageman factor.
  • Activated factor XI activates factor IX.
    
    • **Note that thrombin is also involved in the activation of factor XI and factor VIII.
  • Activated factor IX combines with activated factor VIII and calcium to activate factor X.
    
    • **Note that factor VIII is activated by thrombin.

Question 46

Describe the extrinsic pathway.

Answer 46

Blood Clotting - Extrinsic Pathway

• Damaged cell membranes from injured tissues release thromboplastin into the blood:
  
  • Thromboplastin leads to the activation of factor VII.
  • Activated factor VII and calcium activate factor X.