Carbohydrates

Question 1

What are the four main types of carbohydrates

Answer 1

Glycogen
Glycoproteins
Glycolipids
Heparin

Question 2

Where is Glycogen found

Answer 2

Storage form of sugar

Found in liver, muscle and cervical epithelium

Question 3

Where is glycoproteins found

Answer 3

Mucin, mucosubstances, glycoconjugates

Secreted by epithelial cells

Question 4

Write about glycoproteins
(5)

Answer 4

Mucins

proteins with attached sugar molecules

Present in normal and pathological conditions

Group of substances with various functions

Important in histology as location and quantity changes in pathological conditions

Question 5

What are the four main functions of glycoproteins

Answer 5

Cell to cell interactions

Structural proteins

Lubrication of epithelial surfaces

Protection from proteolytic enzymes and microorganisms

Question 6

Write about mucins

Answer 6

Classified by histochemical reactions: acid mucins, neutral mucins

Some tissues contain both acid and neutral mucins e.g. salivary glands

Question 7

Write about acid mucins
(4)

Answer 7

Contain sulphated and carboxyl ester groups

Found mainly in GIT

Hyaluronic acid

Non-sulphated mucin in connective tissue, epithelium and neural tissue

Question 8

Write about neutral mucins

Answer 8

GIT
Squamous epithelium e.g. cervix
Bronchus
Prostate

Question 9

Write about neutral mucins

Answer 9

GIT
Squamous epithelium e.g. cervix
Bronchus
Prostate

Question 10

How do we stain for glycogen

Answer 10

Periodic acid schiff

Question 11

What does PAS also stain

Answer 11

Other carbohydrates

Glycogen is diastase-sensitive
- Salivary amylase
- Malt diastase (alpha + beta amylases)
- If no stain after digestion then substrate was glycogen

Question 12

What stain is used for acid mucins

Answer 12

Alcian Blue

Question 13

How does Alcian Blue staining work?
(2)

Answer 13

Selective staining at different pH

Generally pH 2.5 will stain most acid mucins but can be more selective by changing pH and concentration of magnesium chloride in stain

Question 14

Write about sulphated mucins
(4)

Answer 14

Strongly sulphated (low pH levels - pH 0.2 to <1)

Produced by connective tissue

Weakly sulphated (less acid levels - pH 2.5 to 1)

Produced by epithelial cells and seen in goblet cells of large intestine

Question 15

Write about neutral mucins

Answer 15

Positive with PAS

Diastase digestion is needed if tissue rich in glycogen

Do not stain with Alcian Blue

Question 16

What are the two reactions in the PAS reaction

Answer 16

Treat with 1% Periodic acid

Treat with Schiff reagent

Question 17

What does treatment with 1% Periodic acid do

Answer 17

Diglycol groups in hexose molecules are oxidised to dialdehydes

Question 18

What does treatment with Schiff reagent

Answer 18

Dialdehyde bind and recolour basic fuchsin (magenta)

Question 19

What is AB-PAS

Answer 19

Can combine 2 stains

Where component has mix of acid and neutral mucins will see range of blue-purple to violet

Question 20

What are other glycoproteins

Answer 20

Hyaluronic acid in CT, mesothelium and synovium

Sialomucin in prostate

Hyaluronic acid and sialomucin can be digested with enzymes such as hyaluronidase and salidase before Alcian Blue

Heparin

Question 21

What is heparin?

Answer 21

Sulphated glycoprotein secreted by mast cells

Stained with Toluidine blue stain

Question 22

Write about the application of mucin histochemistry
(6)

Answer 22

Investigation of mucin distribution in normal and pathological states e.g. increased mucin production in adenocarcinoma

Barratt’s Oesophagus -> epithelial metaplasia

Alpha-1-antitrypsin deficiency

Hurler Syndrome

Fungal infections

Basement membrane alterations

Question 23

What is Hurler Syndrome

Answer 23

Accumulation of mucopolysaccharides due to enzyme deficiency