General Pathology
(PATH 303)
Lecture # 6
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INTRACELLULAR ACCUMULATIONS
 Steatosis (fatty change, lipidosis); it is abnormal
accumulation of neutral fats
(triglycerides)
within parenchymal cells. More severe than hydropic
degeneration.
 Most common in liver, heart, kidney, and skeletal
muscles.
 Causes:
 1. hypoxia (Anoxic anoxia)
 2. Hepatoxins-bacterial, plant –chemical poisons.
 3. Metabolic diseases e.g. diabetes, ketosis
 4. Deficiency of lipotropic substances e.g. choline.
 5. Miscellaneous – starvation, obesity.
 Pathogenesis:
 Several mechanisms e.g.
 Excessive mobilization of fat and entry into the cell.
 Decreased fatty acid oxidation as in hypoxia.
 Decreased synthesis of apoprotiens.
 Impaired lipoprotien secretion from liver
 Gross appearance:
 Severe form: increase in size, friable and rupture of
organs.
 Change in color, cats-white, cattle- yellow, horsesorange.
 Cut surface buldges and capsule retracts.
 Heart muscle has thrush breast appearance.
 Microscopic appearance:
 Early, mild condition- small membrane bound
inclusions (liposomes) near ER.
 Appear as clear vacuoles which fuse & become large
and displace the nucleus towards periphery.
 Special stains Oil red-O and Sudan IV
 Significance:
 Reversible change
 If injury persist, may cause death of cell
Obesity: excessive accumulation of adipose tissue in
the fat depots. Excessive intake of fat and
Carbohydrates.May cause sterility, diabetes and
atherosclerosis
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Glycogen:
Abnormal accumulation occurs in liver, muscles
and kidney in case of:
Diabetes mellitus ( hyperglycemia)
Corticosteroid therapy
Hereditary glycogen storage diseases.
Neutrophil leukocytes in inflammatory
conditions.
Certain neoplasms
 Gross and microscopic appearance:
 Affected organ becomes enlarged and pale.
 Glycogen appears as clear vacuoles in smooth
endoplasmic reticulum.
 Special stain - iodine gives reddish brown color
and Best’s carmine stains it red.
 Tissues should be fixed in absolute alcohol.
 Protein inclusions:
 Protein inclusions or inclusion bodies have different size,
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shape, staining reaction and location in the cell.
Identification of inclusions used in diagnosis of several
diseases.
Location: may be intracytoplasmic or intranuclear or
both.
Shape; may be spherical, globular or homogenous.
Staining affinity: may be eosinophilic or basophilic.
Mechanism of inclusion formation: viral infection,
toxic injury, absorption of external proteins and secretory
stasis.
 Absorption inclusions:
 Seen in renal epithelial cells in albumen- uria--
endocytic uptake- seen in proximal convoluted
tubules. Protein sequestered in phagolysosomes.
 Appear as hyaline droplets
 Secretory inclusion:
 Secretory synthesis exceeds the capacity for
excretion from the cell.
 Commonly seen in liver- composed of albumen and
fibrinogen.
 Plasma cells develop cytoplasmic condensed globular
inclusions.
 Pigment disorders:
 Pigments are colored substances, synthesized within
the body (endogenous) or coming from outside
(exogenous).
 Endogenous pigments: include melanin,
lipofuscin and derivatives of hemoglobin
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Melanin: A brownish black pigment formed by oxidation of
tyrosine to dihydroxyphenylalanine by enzyme tyrosinase
Melanocytes , the cells which produce melanin are of
neuroectodermal origin, present in the basal layer of epidermis.
Black, brown, red color of skin due to amount and distribution of
melanin.
Protects against UV rays in sunlight.
Microscopic appearance: melanin granules are small, uniform,
dirty brown, round granules.
Foci of melanocytes may be located in intestine, heart, kidney etc
called melanosis – usually harmless.
 Hormonal disturbances may cause
hyperpigmentation – acanthosis nigricans –
observed in dogs due to lesions in adrenal.
 Pathological amounts – associated with tumors of
melanocytes, melanomas and melanocarcinomas
– common in gray horses.
 Nevus is a small accumulation of melanocytes in
the skin.
 Albinism: absence of melanin. Such individuals
have melanocytes but are unable to synthesize
melanin due to lack of tyrosinase. These patients are
vulnerable to cancer.
 Leukoderma is local loss of pigment observed in
areas with rubbing injuries from collar, saddle,
harness etc.
 Lipofuscin : it an insoluble brownish yellow
pigment also called lipochrome, wear and tear
pigment or ageing pigment.
 It contains complexes of lipid and protein derived
from peroxidation of lipids by free radicals.
 It represents indigestible residues of autophagic
vacuoles . It gives brown discolorations to tissues
but is not injurious to the cell.
 Derivatives of hemoglobin:
 Destruction of old ( senescent) erythrocytes occurs
within mononuclear phagocytic cells of spleen,
liver and bone marrow and Hb is released.
 Break down of Hb gives rise to globin (protein) and
pigment complex heme.
 Globin is soluble and is removed by blood and
lymph.
 Oxidation of heme by heme oxygenase gives rise to
biliverdin, carbon monoxide and iron.
 Body iron occurs in two forms – functional (80%)
in Hb, myoglobin and iron containing enzymes
catalase and cytochrome.The storage pool includes
15-20% of total body iron in the form of ferritin
and hemosiderin.
 Ferritin: it is a protein – iron complex found in
liver, spleen, bone marrow and skeletal muscles.
When there is excess of iron , ferritin forms
hemosiderin.
A. hemosiderin : it is a golden- yellow, granular pigment
which is a storage form of iron. Occurs in localized or
systemic accumulations.
1. localized haemosiderosis : This occurs in local injuries,
haemorrhages, bruises, hematomas etc.
 Grossly the bruise goes through different changes
indicating formation of different pigments as below:
 1-Red blue – Hb 2. Greenish blue ( biliverdin green )
3.
Pinkish blue ( bile pigment ) and 4. Golden yellow –
hemosiderin, observed in scars.
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Systemic hemosiderosis:
In this case
hemosiderin is deposited in many organs and
tissues, especially in the liver, spleen, lymph node,
bone marrow etc.
It is caused by increased dietary iron, impaired
utilization, hemolytic anemia and transfusion
 Gross appearance of hemosiderin:
 Hemosiderin appear as golden yellow, granular
pigment in the cytoplasm of macrophages.
 It is seen in renal epithelial cells in intravascular
hemolysis in equine infectious anemia.
 In the lungs hemosiderin occurs in chronic passive
congestion.
 RBC’s released in the lung alveoli are engulfed by
alveolar macrophages.
 Hemosiderin laden macrophages are known as
heart failure cells and the condition is cell brown
induration of lung.
 Prussian blue reaction is used for identification of
haemosiderin. Potassium Ferrocyanide reacts with
ferric iron and converts it into insoluble blue black
ferric ferrocyanide.
B. Bilirubin :
Bilirubin is the major pigment of bile.
Accumulation of bilirubin in blood (hyperbilirubinemia) causes
its deposition in the tissues and the clinical condition is
called jaundice.
 Formation of bilirubin:
 There are different types of bilirubin and its formation goes through
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following stages
1. Hemobilirubin formation 2. Transport to blood. 3. Uptake and
intracellular transport 4. Glucuronidation 5. Secretion into the bile
canaliculi.
Oxidation of heme by heme oxygenase produces biliverdin (green
pigment) CO and iron. Iron is sequestered in ferritin and hemosiderin.
Biliverdin is reduced by biliverdin reductase into yellow pigment
bilirubin inside the macrophages.
Bilirubin is bound with albumen and transported to blood where it
circulates as hemobilirubin or unconjugated bilirubin. It is insoluble in
water and does not pass through the renal filter.
 Hemobilirubin is taken up by the hepatocytes and transported to ER
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where it is conjugated to glucuronide as conjugated bilirubin.
Conjugated bilirubin ( bilirubin diglucuronide ) is soluble in water and
is not toxic, excreted into canaliculi.
Conjugated bilirubin reaches intestine where glucuronide is separated
and bilirubin is converted into urobilinogen by bacteria.
Most of urobilinogen is excreted into feces and about 20% is
reabsorbed and returned to liver for re-excretion into bile.
A small amount reaches kidneys and is excreted into urine.
Jaundice
IT IS THE INCREASE OF BILIRUBIN
IN THE BLOOD AND ITS DEPOSITION
IN THE TISSUES LIKE SKIN AND
SCLERA GIVING THEM YELLOW
DISCLOURATION. ACCORDING TO
THE TYPE OF BILIRUBIN AND ITS
DISTRIBUTION JAUNDICE MAY BE
HEMOLYTIC (PREHEPATIC), TOXIC
(INTRAHEPATIC) OR OBSTRUCTIVE
(POSTHEPATIC) TYPES
1-hemolytic(prehepatic jaundice)
More than 80% serum bilirubin is unconjugated
(hemolytic bilirubin). There are three mechanisms
A. overproduction of hemobilirubin due to intravascular
hemolysis as in
1. protozoan diseases e.g. babesiosis, anaplasmosis,
trypnosomosis,etc
2. Viral infections like equine infectious anemia
3. Bacterial infections due to Clostridium hemolyticum and
leptospirosis
4. Isoimmune hemolytic anemia in newborn foals and
piglets.
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B- Reduced hepatic uptake of bilirubin
 This has been observed in humnan after
administration of certain drugs like rifampin, an
antitubercular drug
C-impaired conjugation of bilirubin
 Due to the aquired or hereditary deficiency of
gllucuronosyl transferase(GT)
 Activity of GT is low at birth and normal levels are
attained at about 2 weeks.
 Therefore every newborn develops a mild,transient
jaundice –called neonatal or physiological jaundice
2-Toxic or intrahepatic jaundice
 Injury to hepatiytes and bile canalculi by infectious
and non infectious agents eg.
 Bacteria (salmonella) ---------(infectious canine
hepatitis), plant and chemical toxins eg
phosphorus, CCl4
 Both conjugated and unonjugated bilirubin
accumulate in the blood
 Swelling and disorganization of hepatocytes may
compress and block canalculi
3- Obstructive (post hepatic) jaundice
There is obstruction to the excretion of conjugated
bilirubinin the extrahepatic bile dut system (cholestasis)
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Obstruction may be caused by
1.
Parasites eg cattle and sheep- fasciola hepatica and F.
gigantica
Pigs- Ascaris lumbricoides
Sheep- tapeworms
2. Gallstones
3.Inflammation of bile duct-cholangitis
4.tumours
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Obstructive (post hepatic) jaundice
 In case of complete obstruction bile disappears
from feces
 The feces are of grey colour like wet cement but
urine is normal in colour
 Bile is necessary for absorption of fats from
intestine
 Malabsorption of vitamin K predisposes the
animals to haemorrhage
 Accumulation of bile pigments in the skin causes
itching(pruritis)
Icterus index
 Test for diagnosis of icterus bycomparison of colour
of plasma or serum with a standard solution of
potassium dichromate
 For accuracy, standard should be prepared for each
species and breed of animals
Van den Bergh reaction
 Ehrlich’ reagent (diazotized sulphanilic acid) is mixed with
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plasma or serum
The developing coloured compound (azobilirubin)
determines the type of bilirubin involved
Three interpretations are
Direct reaction: pink or purple colour develops immediately
and reaches maximum density with 1-2 minutes
Indirect or delayed reaction: no colour change in first two
minutes. A golden colour develops within 10
minutes.indicates uncojugated bilirubin i.e. hemolytic
jaundice
Biphasic reaction: a brownish red colour indicates both
Comparison of three types of jaundice
Ceroid
 It is acid fast, autoflourescent pigment consisting of
partially oxidized and polymerized unsaturated fatty
acids. It is an early form of lipofuscin
 Ceroid is associated with Vit. E deficiency. It does
not stain for iron.
A. Hepatic ceroidosis
 Found in salmon and catfish fed rancid diets.
 Hepatocytes contain acid fast, autoflourescent
pigment and liver has brown- orange discoloration.
B. Ceroid- lipofuscinosis disease
 There are a group of diseases in sheep, cattle, goat
and dogs characterized by accumulation of
fluorescent lipopigments in neuron and other cells
Exogenous pigments
 Most of these are dust particles in the inhaled air,
deposited in the lungs and associated lymph nodes.
 The dust particles act as mild irritants and induce
proliferation of fibrous connective tissue( FCT)(fibrosis) and collection of macrophages.
 The condition is called pneumoconiosis or
occupational hazards
 Particles between 1-5 micrometer diameter are
most dangerous
 Pathogenicity depends upon size, solubility,
cytotoxicity and the amount in the inhaled air
 Phagocytosis of dust particles by alveolar
macrophages provides protection
1- Anthracosis
 It is deposition of carbon or coal dust in the lungs in
horses and mules used in coal mines and dogs living
in the smoky areas. Tattooing is a localized
anthracosis
 Carbon dust is mildly irritating and causes a slight
fibrosis.
 It is insoluble and persists in the tissues for life
2-
Silicosis
 It is perhaps most prevalent chronic occupational
disease associated with silicon industries like glass
etc
 It is a slowly progressive, nodular, fibrosing
pneumoconiosis
 Silica is a powerful irritant and causes extreme
fibrosis, predisposing to diseases like tuberculosis
3-Asbestosis
 The condition is associated with asbestos industries
and it is one of the most dangerous pneumoconioses
 Asbestos particles cause severe irritation and fibrosis
 Asbestos is carcinogenic
4-Plumbism
 It is pigmentation in the tissues resulting from the
presence of lead and hydrogen sulphide.
 Lead poisoning may occur from licking of paints or
from water in lead pipes
 Microscopically lead is deposited in the tissues in
combination with hydrogen sulphide as a black
pigment
Photosensitization and photodynamic
pigments
 Photodynamic pigments or agents that make the
tissues more sensitive to light. Absorption of certain
wavelengths in the sunlight e.g., U.V. light activates
these substances and they produce necrosis and
edema of these tissues.
Continued…..
 Skin lesions are restricted to hairless and non-
pigmented or lightly pigmented areas like teats,
udder, ears, eyelids in cows and ears, eyelids, lips
and coronets in sheep
classification
Photosensitization is classified into three types
according to the origin and mechanism of
photodynamic agent
1. Primary photosensitization
Due to the ingestion of pre-formed photodynamic
agents in different plants (fagopyrine) and
certain drugs like phenothiazine, tetracycline,
sulphonamide etc. The agent is deposited in the
tissues following absorption in the blood. When
such animals are exposed to sunlight,
photosensitization occurs.
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2-Due to abnormal porphyrin
metabolism
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Congenital porphyria is a hereditary metabolic
disorder in cattle and cats with excessive
production of two porphyrins (derivatives of
hemoglobin):
1-Uroporphyrin and
2-Coproporphyrin
Uroporphyrin is deposited in the bones and teeth
causing discoloration (pink tooth)
3-Hepatogenous (hepatotoxic)
photosensitization
 This occurs in liver diseases in which injured
hepatocytes fail to excrete phylloerythrin.
 Phylloerythrin is normal end product of chlorophyll
metabolism and is photodynamic.
 This condition is more common in the animals
grazing on green pastures