Colours of pathology

What are exogenous pigments?

Pigments that are formed outside of the body.

What are endogenous pigments?

Pigments that are formed inside the body.

What are pigments?

Substances that give colour to tissues.

What are some ways exogenous pigments enter the body?

• Inhaled

• Ingested

• Latrogenic (caused by a medical treatment)

What is pneumoconiosis?

Lung disease caused by inhaling dust.

What is silicosis?

A type of pneumoconiosis caused by inhaling silica dust.

What is anthracosis?

A type of pneumoconiosis caused by inhaling carbon particles. This leads to black discolouration of the bronchial mucosa.

What causes yellow fat?

Stored carotenoids from plants which have been ingested.

What happens if tetracycline is given during pregnancy?

The offspring’s teeth are stained brown as tetracycline is deposited in the bone, dentine, enamel and cementum.

What is melanin?

A brown pigment found in skin, hair, retina and iris.

How is melanin formed?

By the oxidation of tyrosine by tyrosinase, in the melanocytes.

Why are albinos so pale?

They have little/no melanin.

What is congenital melanosis?

Brown to black sports found in the lungs, aorta and other tissues. This is an incidental finding with no clinical or pathological significance, common in blackface sheep, cattle and pig breeds.

What is lipofuscin?

A yellow/brown pigment that accumulates with age, in post-mitotic or slowly diving cells. It can only be seen using H&E stain.

What could is oxyhaemoglobin?

Bright red

What colour is unoxygenated heamoglobin?

Blue

What is cyanosis?

Blue mucous membranes due to hypoxia.

How can you identify carboxyhaemoglobin?

It is cherry red and does not clot

What are some derivative pigments of haemoglobin?

• Haemosiderin

• Haematin

• Porphyrin

• Bilirubin

• Haemotoidin

What is haemosiderin?

Golden yellow/brown pigment formed from intracellular aggregates of ferritin. Often found in the spleen.

What causes haemosiderin accumuation?

• Ecchymosis > 12 hours prior

• Left-sided cardiac failure

What is haemotoidin?

A yellow/orange/brown pigment formed following phagocytosis of RBCs in areas of haemorrhage

What is bilirubin?

The remaining product after RBCs are phagocytosed and their iron is removed.

What causes jaundice (icterus)?

Systemic increase of bilirubin due to abnormally high levels of RBC breakdown or liver damage which disrupts the excretion of bilirubin.

What is prehepatic icterus?

Icterus caused by a process occurring before the liver. For example, copper toxicity causing premature breakdown of RBCs.

What is hepatic icterus?

Icterus caused by compromised liver function.

What is post-hepatic icterus?

Icterus caused by the liver being unable to excrete properly. For example, gallbladder tumour.

What happens if porphyrin accumulates?

Brown staining of teeth, bones and skin - leading to photosensitisation and dermatitis.

What is haematin?

A black pigment.

Where does haematin come from?

• It may be excreted by parasites like liver fluke

• It may be caused by tissue fixation with formalin