Download Cell Pathology Lecture 4

Cellular Pathology
(VPM 152)
Lecture 4 (web)
Paul Hanna
Jan 2016
IRREVERSIBLE CELL INJURY
1) Necrosis
• describes the range of morphologic changes that follow cell death in living tissue
• the morphologic appearance is due to 2 concurrent processes:
 denaturation of proteins (nonproteolytic alteration 2o or 3o structure)
Raw egg white (albumin protein) is a transparent
(clear) viscous liquid
Adding heat, acid or alkali will denature (misfold) the
proteins which results in a change of the color to white
(opaque) & the texture becomes solid.
 enzymatic digestion
 autolysis* (self digestion) = endogenous enzymes derived from the lysosomes
of the dead cells themselves.
 heterolysis = lysosomes of immigrant leukocytes.
*autolysis also used for changes that occur in all cells after death, ie postmortem autolysis
1) Necrosis
• distinctive morphologic patterns depending on whether enzyme catabolism or
protein denaturation predominates
• morphologic patterns of necrosis include: Coagulation Necrosis
Liquefactive Necrosis
Caseous Necrosis
*Gangrenous Necrosis
*Fat Necrosis
a) Coagulation Necrosis
• most common manifestation of cell death
• characteristic of hypoxic / ischemic death of cells in all tissues (except brain)
• on LM, basic outline of the coagulated cell persists at least a few days
(protein denaturation predominates over enzymatic digestion)
• necrotic cells eventually removed by leukocyte proteolysis & phagocytosis
a) Coagulation Necrosis
Gross Appearance
• architecture resembles normal tissue, but color and texture are different
• lighter in color – denatured cytoplasmic proteins & decreased blood flow
• usually firm
• tissue may be swollen or shrunken
• may see a local vascular / inflammatory reaction to necrotic tissue
Figure 01-18A (McGavin & Zachary). Coagulation
necrosis, infarcts, kidney, cow. A, Note the pale regions
of acute coagulation necrosis surrounded by a red rim of
active hyperemia and inflammation (far left).
Bovine, kidney, renal infarct, cut surface. Note pyramidal
(wedge) shaped area of necrosis with hyperemic border.
Bovine, fetus, liver, IBR (infectious
bovine rhinotracheitis) - multifocal
hepatic necrosis (necrotizing
hepatitis)
Bovine, liver: Multifocal hepatic necrosis (coagulative) due to infection with the bacterium
Fusobacterium necrophorum. The majority of bacterial infections cause liquefactive necrosis due to
the marked infiltration of neutrophils with associated heterolysis; however in this particular bacterial
infection there are toxins which result in coagulative necrosis (at least initially).
Bovine, heart, myocardial necrosis (coagulative);
note irregular area of pallor within myocardium.
a) Coagulation Necrosis
Microscopic Appearance
• original cell shape & tissue architecture is preserved (ie eosinophilic "shadow“)
• cytoplasm:
 increased eosinophilia (H&E stain)
 usually hyalinized (homogeneous / glassy)
 may be mineralized
• nucleus:



karyolysis
pyknosis
karyorrhexis
Figure 01-17B (McGavin & Zachary). Pyknosis and karyolysis, renal cortex, chloroform toxicosis, mouse. Some
epithelial cells exhibit hydropic degeneration, whereas others are necrotic. Some necrotic cells exhibit pyknosis
(arrow), whereas others have lost the nucleus or have a very pale nucleus (karyolysis) (arrowheads)
Figure 01-17C (McGavin & Zachary) Karyorrhexis, lymphocytes, spleen, dog. Spleen of a dog with
parvovirus infection. Lymphocyte nuclei have fragmented because of the infection (arrow). H&E stain.
Skeletal muscle, white muscle disease; note coagulation necrosis of myofibers characterized by
fragmentation and hyalinization; also note extensive mineralization (blue-purple staining)
b) Liquefactive Necrosis
• when enzymatic digestion of necrotic cells predominates
• many bacterial infections; neutrophils contain potent hydrolases
• in hypoxic damage of the CNS
Gross appearance
• affected tissue is liquefied, ie soft to viscous to fluid mass
• in inflammation, the liquid is often mostly dead WBC’s (pus)
Microscopic appearance
• may see degenerate neutrophils and/or amorphous necrotic material
Porcine, abscess in ventral neck /
shoulder area; note escape of
purulent exudate (pus) when the
abscess is lanced.
(ie purulent exudate is an example of
liquefactive necrosis).
Porcine, kidney, pyelonephritis,
note purulent exudate (again an
example of liquefactive
necrosis).
Ovine, pituitary gland abscess,
irregular shaped aggregates of
amorphous acidophilic material
(liquefied cells) with basophilic
granular material (degenerate
neutrophils) at margins
Figure 01-20A (McGavin & Zachary). Liquefactive necrosis. Acute polioencephalomalacia, brain, goat. A
thiamine deficiency has resulted in polioencephalomalacia (ie polio = grey, encephalo = brain and malacia =
necrosis). This is liquefaction necrosis with varying degrees of tissue separation (arrows). Scale bar = 2 cm.
Note: can see this same lesion resulting from either ischemia, lead poisoning or “salt” poisoning.
Also note:
c) Caseous Necrosis
• typical seen with specific bacterial diseases, eg TB, caseous lymphadenitis
• infections in birds, since heterophils lack myeloperoxidase
Gross appearance
• grey-white, dry, friable to pasty (caseous = cheese like)
Microscopic appearance
• dead cells persist as amorphous, coarsely granular, eosinophilic debris
• retain cellular outline (coagulative)  caseous  complete dissolution (liquefactive)
Ovine, submandibular lymph node,
with a disease called “caseous
lymphadenitis” caused by infection
with the bacteria Corynebacterium
pseudotuberculosis;
note the type of necrosis in this
exudate is caseous (not quite
liquefactive, but more broken down
than coagulation necrosis, ie it
would be a thick pasty texture, if
you could cut / feel it)
Equine, lung tissue, pyogranulomatous
pneumonia due to Rhodococcus equi;
note caseous exudate (arrows).
Figure 01-19. Tuberculosis, lymph node,
transverse section, ox. A, The lymph has
been replaced by a caseating granuloma.
Note the caseous necrosis characterized by
a pale yellow, crumbly exudate. B,
Granulomatous inflammation in caseous
necrosis. Cell walls are disrupted and tissue
architecture is lost. Mineralization (not seen
here) is common in this type of necrosis.
H&E stain.
d) Gangrenous Necrosis
• definition = necrosis (usually ischemic) of extremities, eg digits, ear tips
• dry gangrene = coagulation necrosis of an extremity
• wet gangrene = when the coagulative necrosis of dry gangrene is modified
by liquefactive action of saprophytic / putrefactive bacteria
Cat, note, sloughing of ear tips and paws
following dry gangrene due to frostbite.
Bovine, calf, gangrenous necrosis / dry gangrene
with sloughing of distal limbs, ergot poisoning
Calf, gangrenous necrosis of distal limbs due
to ischemia; this ischemia could result from
frostbite or sepsis or a mycotoxin such as
ergot.
Fig 1-21A (McGavin & Zachary), Moist
gangrene, udder, sheep. The surrounding
tissue is well vascularized, which contributes
to the wet and bloody nature of the lesion.
Often saprophytic bacteria and clostridia
contaminate areas of necrosis.
Bovine, mammary gland, wet gangrene;
tissue starting to slough.
Bovine, lung, “gangrenous” pneumonia following aspiration of rumen content. [Although
historically called “gangrenous” pneumonia, it is probably better called necrotizing pneumonia as
a morphologic Dx or aspiration pneumonia as an etiologic Dx]
e) Fat Necrosis
• distinguished by its location within body fat stores
• etiology: inflammation (eg pancreatitis), Vit E deficiency, trauma, idiopathic
Canine, pancreatitis (“recurrent pancreatic necrosis”) with mesenteric fat necrosis
Canine, pancreatitis
(“recurrent pancreatic
necrosis”) with omental fat
necrosis.
Canine, pancreatitis (“recurrent pancreatic necrosis”) with fat necrosis; note necrosis of
fat (larger arrow) and pancreatic tissues (smaller arrow)– some areas of coagulative type
and other areas with significant enzyme degradation (liquefaction) of necrotic tissue.
2) Apoptosis
• Greek = “falling off”
• death of single cells through activation of genetically programmed “suicide” pathways
• apoptosis indicates selective elimination of cells (either physiologic or pathologic),
while necrosis points to widespread tissue injury (severe pathologic stimuli)
• apoptosis → death of single cells / intact membranes / phagocytosed with no inflam.
necrosis → area of dead cells / damaged membranes / enzyme digest. & 2o inflam.
Figure 17-35 (Molecular Biolology of the Cell, 4th ed) Sculpting the digits in the developing mouse paw by apoptosis (A) The
paw in this mouse embryo has been stained with a dye that specifically labels cells that have undergone apoptosis. The apoptotic
cells appear as bright green dots between the developing digits (arrows). (B) This interdigital cell death eliminates the tissue between
the developing digits, as seen one day later, when few, if any, apoptotic cells can be seen.
Incomplete tissue
sculpting (ie incomplete
apoptosis) of the digits
results in syndactyly
(from Greek syn =
"together" + dactyly =
“digits”)
It can be partial, as in
the web toes (above left)
or complete as seen in
the childs hand (above
right) and calves hooves
(below left)
2) Apoptosis
• seen in many physiologic, adaptive and pathologic events:
Physiologic causes:
 Cells undergoing programmed cell death during embryogenesis
 Cells undergoing normal turnover
- hormone-dependent involution
- cell deletion in proliferating population
 Immune System
- deletion of autoreactive T cell in thymus
- immune regulation
2) Apoptosis
Pathologic causes:
 DNA damaged beyond repair – eg radiation, toxins
 Misfolded proteins – ER stress
 Specific infectious agents – esp viruses
 Specific immune responses – via cytotoxic T cells
 Pathologic atrophy of organs after duct obstruction
c) Biochemical Mechanisms
 Signaling pathways that initiate apoptosis (“Death Signals”)
• stimulate targets on cell surface or within the cell
c) Biochemical Mechanisms
 Control and integration
• balance of +ve / -ve regulatory molecules determines outcome of the affected cell
c) Biochemical Mechanisms
 Common execution phase
• actual death program accomplished by endonucleases & proteases (esp caspases)
c) Biochemical Mechanisms
 Removal of dead cells
• apoptotic bodies have ligands for phagocytic cells (efficient / no inflammation)
2) Apoptosis
d) Morphology
• considerable apoptosis may occur in tissues before it is evident on histology
 Cell shrinkage
- cytoplasm has packed organelles
 Chromatin condensation
- dense aggregates of chromatin ± fragmentation
 Formation of cytoplasmic blebs / apoptotic bodies
- with intact membranes (± nuclear fragments)
 Phagocytosis of apoptotic cells / bodies
- usually by macrophages with no inflammation
Figure 1-8 (Robbins) Schematic illustration of morphologic changes in cell injury culminating in necrosis or apoptosis.
Note: with necrosis cells swell, lose membrane integrity and incite an inflammatory response VS apoptosis where cells
shrink (condense), membranes remain intact in forming apoptotic bodies and are removed with minimal inflammation.
SEM showing showing cytoplasmic
blebbing / apoptotic body formation.
Figure 3–23 (Junqueira’s Basic Histology) Late apoptosis-formation of apoptotic bodies. TEM of a cell in
late apoptosis shows that during this process the cell’s shape changes radically and large cytoplasmic vesicles
(blebs) are formed. These detach from the cell and often separate one from another, but remain contained within
plasma membrane so that no cytoplasmic contents are released into the extracellular space.
Figure 01-33 (McGavin & Zachary). Apoptosis, cytoarchitecture of cells, pancreas, rat. Individual acinar
cells are shrunken and their chromatin condensed and fragmented (arrows). Cytoplasmic blebs are found in
adjacent cells. Inflammation is absent. H&E.
(note: blockage of glandular ducts typically results in apoptosis within the gland)
www.skin-science.com
Note, arrows indicate apoptotic epidermal
keratinocytes (“sunburn cells”) due to UVB radiation. These can be induced within
30 minutes of sun exposure.
e) Consequences of “too much” or “too little” apoptosis
 Disorders associated with defective apoptosis (increased cell survival)
• increased survival of abnormal cells with neoplasia
• increased survival of autoreactive lymphocytes causing autoimmune disorder
 Disorders associated with increased apoptosis (excessive cell death)
• increased loss of cells in:
neurodegenerative diseases
ischemic injured cells
viral infected cells