Pigments Flashcards
What is melanin?
A yellow-brown pigment formed by melanocytes
- Protein -tyrosine complex
- Involves tyrosinase enzyme
- Pigment is excreted out of the cell
- Melanocytes produce variable amounts of granules
What is congenital decreased formation of melanin?
Albinism
What is acquired decreased formation of melanin?
- Melanocyte damage
- Copper deficiency
- Vitiligo
- Hormonal imbalances
What increases formation of melanin?
- UV light - increases the efficiency of the melanocytes
What arises from increased formation of melanin?
- Congenital melanosis
- Moles
- Melanoma
What results from breakdown of haemoglobin?
- Jaundice
- Anaemia
- Bruising
- “red water”
What is Haemaglobin made up of?
- Heme
- Globin
- Iron
What is haemolysis?
The lysing of RBCs
What happens in normal recycling of RBCs?
- Occurs in splenic macrophages
- Extravascular haemolysis
- Hb breaks down into Heme, Iron and globin
Iron -> Haemosiderin
Heme -> bilirubin
Globin- -> AA’s
Describe Extravascular Haemolysis…
Is a normal process where splenic macrophages remove old RBCs
- Can be excessive in some diseases where there is excessive phagocytosis and breakdown
e. g. Malaria and incompatible blood transfusions
Describe Intravascular Haemolysis…
- Always pathological process
- Causes the release of free haemoglobin into the plasma
- May be filtered by the kidneys
- Some is resorbed into tubular epithelial cells
What is Haemoglobinaemia?
Release of free haemoglobin into the plasma
- Pink Serum
What is Haemoglobinuria?
Haemoglobin in the urine
- Pink/ Orange urine
What diseases can cause intravascular haemolysis?
- Complement- mediated immune reactions
- Damage to RBC membranes
- Congenital defects
- Some RBC parasites
- Oxidative damage e.g cat eating garlic and onions
Describe Haemosiderin…
- A breakdown product of Haemoglobin
- Yellow-brown pigment
- Insoluble storage form of iron
- Small amounts are normally found in macrophages of spleens
- Causes the yellow-brown colour seen in old bruises
Describe the staining of Haemosiderin…
Pearls iodine or Prussian blue can be used to stain
Where can local accumulations of haemosiderin found?
- Bruises (local haemorrhage)
- Areas of vascular congestion (heart failure cells)
Where can systemic accumulations of haemosiderin found?
Haemosiderosis
- Systemic
- e.g. Cattle drinking iron rich bore water gives them orange organs
- Excessive haemoglobin breakdown
- Excessive dietary absorption
- Impaired Iron metabolism
Describe Bilirubin…
- Derived from Haemoglobin
- Orange
- Transported to the bloodstream loosely bound to albumin
- Eventually excreted via bile into the faeces
What happens if you have excessive bilirubin in the bloodstream?
Jaundice
- Causes yellow skin, sclera and mucous membranes
- The source of bilirubin may be:
- Pre-hepatic
- Hepatic
- Post Hepatic
Describe Pre-hepatic jaundice…
- Involves RBC breakdown
- Immune- mediated disease
- Incompatible blood transfusion
- RBC parasites
NB: can be Intra or Extravascular
Describe the normal pattern of Bilirubin metabolism?
Heme fragment > Bilirubin > Into Blood > Bound to albumin (carrier) > = Free bilirubin > Liver > Conjugated to glucuronic acid > = Conjugated bilirubin > Excreted in bile > Duodenum > Distal intestine > Oxidised by intestinal bacteria > Urobilinogens > Urobilin (urine) > Stercobilins (faeces)
What does stercobilins do to faeces?
Makes it brown in colour
What are the consequences of haemolytic jaundice?
- Increased levels of free bilirubin in the blood
- This free bilirubin is toxic to developing neurons at high concentrations
- Anaemia
- With or without haemoglobinaemia & haemoglobinuria
