Agriculture Reference
In-Depth Information
Haematogenous pigments
Haemoglobin (Hb) is a compound protein in red blood
cells (RBCs) which consists of the iron-containing
porphyrin pigment
haem
combined with the protein
globin.
Certain pigments derived from Hb metabolism are
encountered in some abnormal conditions.
Haematin
is a pigment formed by the oxidation of
haem from the ferrous to the ferric state. It occurs as a
dark-brown, black or yellow granular pigment in the
parasitised RBCs and reticuloendothelial cells in the
spleen, liver, lymph nodes and bone marrow in diseases
like babesiosis in which there is widespread destruction
of RBCs. Several trematodes, for example,
Fascioloides
magna
, and some schistosomes also produce haematins
locally in the tissues.
Haemosiderin
, an iron-containing pigment and
store of iron (the other important iron storage pool is
ferritin
), occurs normally in hepatic cells, bone marrow
and spleen (in macrophages). It appears in excess as
yellowish granules in severe cases of RBC haemolysis as
with haematin, in cases of extensive haemorrhage and
chronic passive congestion. Haemosiderin combined
with ferritin is occasionally observed in Angora goats
in which a brownish or blackish pigmentation in
kidneys has the appearance of enamelled jewellery -
cloisonné kidney
.
Figure 9.20
Icterus/jaundice in a lamb carcase.
cum
), ascarids or tapeworms like
Thysanosoma acti-
noides
in the bile ducts; biliary cirrhosis (especially in the
pig but rarely in cattle or sheep); cholangitis (inflamma-
tion of the gall bladder); and pressure from tumours,
abscesses or granulomas. In pigs, the most common
parasite in temperate regions to invade the bile ducts
from the intestine is
Ascaris suum
.
Haemolytic jaundice
denotes the excessive destruction
of RBCs by infective organisms, for example, in babesio-
sis, eperythrozoonosis, anaplasmosis, equine infectious
anaemia and leptospirosis in pigs. The yellow coloura-
tion is less marked in this form than in the obstructive
and toxic types.
Toxic jaundice
is brought about by the action of toxic
substances on liver cells resulting in fatty change, necro-
sis and the liberation of plasma bilirubin.
Poisonous
plants
incriminated are members of the
Senecio
species
(ragwort and groundsel) such as
S. jacobaea
(ragwort,
benweed),
S. vulgaris
(groundsel),
S. burchelli
and
S. cun-
ninghamii
in North America and the latter with
S. quad-
ridentatus and S. lautus
in Australia. These contain
pyrrolizidine alkaloids which are potent hepatic toxins
also found in certain
Crotalaria
,
Gossypium
(cotton
plant) and
Allium
(garlic, onion) species. The mycotox-
ins associated with some
Lupin
spp. also cause hepato-
cyte injury and icterus. Some
inorganic poisons
, especially
copper and selenium, and
organic compounds
such as
phenothiazine can also cause severe jaundice. Excess
copper in the diet of calves may cause icterus due to toxic
hepatitis, cirrhosis and fatty change resulting in carcase
condemnations.
A form of hyperbilirubinaemia which is not obstruc-
tive, haemolytic or toxic occurs in horses on starvation
rations or from anorexia secondary to other diseases,
for example, colic. Most cases are subclinical but some
progress to frank disease.
Bile pigments
Biliverdin
is a green bile pigment formed from porphyrin
by the breakdown of RBCs in the liver and bone marrow.
It is rapidly reduced, mainly in the spleen, to
bilirubin
, an
orange-yellow pigment, and then, bound with albumin,
transported to the liver via the reticuloendothelial
system. Most of the bilirubin passes from the liver to the
gall bladder and eventually to the small intestine where
it is reduced to meso-bilirubinogen and urobilinogen
by bacteria. The latter, in association with stercobilin,
colours the faeces brown.
Icterus
Icterus
(
jaundice, hyperbilirubinaemia
), arising from
haemolytic, obstructive hepatic or toxic causes, occurs
when the balance between bilirubin production and
clearance is disturbed. Bile pigments, mainly bilirubin,
accumulate in the tissues, which are tinged yellow. The
condition is caused by the reabsorption of bile pigment
into the circulatory system and displays three main types
(Fig. 9.20).
Obstructive jaundice
may be due to mechanical
obstruction to the flow of bile by gallstones; parasites
such as liver flukes (especially
Dicrocoelium dendriti-
