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Course: Clinical Analysis
Lecturer: Dr. Weam Saad
Lecture: Principles of Pathological Clinical Analyses
Principles of Pathological Clinical Analyses
Terms and Definitions:
Pathology, branch of Biology, refers to the study of diseases and the
abnormalities or
alterations induced by an infection either in structure or in
function causing the clinical
manifestations to appear.
Pathogenesis, the events of disease development producing the pathology.
Pathogenic microorganism is a microbe that can cause pathology.
Disease refers to the existence of pathology, either infectious (resultant
from a pathogenic infection like Cholera), or non-infectious disease
(resultant from physiological defect like Diabetes).
Infectious disease is a disease caused by a microorganism due to its
virulence factors.
Virulence is a term referring to the abilities of a microbe to produce
disease in a host, like presence of capsule or production of toxins and
enzymes.
Immunity refers to the degree of resistance of the host for the invading
microbe.
Etiology refers to the study of disease occurrence, causes, development,
modes of transmission
and prevention.
The host-parasite interaction, the dynamic process of infectious diseases
occurrence when the parasite tries to multiply and the host defenses try to
control.
Epidemiology is the study of diseases and public health conditions in a
defined population and usually needs statistical analysis.
Steps of infectious Diseases:
1. Infection.
2. Inflammation and Tissues Damage.
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3. Immune System Response.
4. Recovery and Cure (repairing damage).
Cells Damage due to infection:
Infections can lead to individual cell damage; cell membrane and DNA are
the most important cellular component that may be affected by infection, then
cellular proteins and fats, and that can cause lose the function of cell. If damage
or injury cannot be repaired, cell may die by apoptosis
process (programmed cell
death).
Tissues Damage due to infection:
1. Atrophy:
the partial or complete loss of tissue (breakdown of tissues) due
to an increase in apoptotic cells.
2.
Hypertrophy: the
increase in the volume of an organ or tissue due to the
enlargement of its cells
(cells size increase and the number stay fixed not
like hyperplasia).
3.
Hyperplasia:
the increase in cells number (proliferation of cells) and
sometimes called benign neoplasia or benign tumor. The cells under
microscope look normal but increased in number. This change in tissues
differ from neoplasia (cancer) because cells still under regulation control
mechanisms and the proliferation of them is genetically normal, also the
cells able to response to normal stimulations.
4.
Hypoplasia:
the incomplete development of a tissue or organ, cells number
below normal due to congenital medical condition, e.g. hypothyroidism
during gestation cause hypoplasia in the Mandible of fetus.
5.
Metaplasia:
the change of differentiated cells to another cell type, lead to
suppress function of organ, but it is reversible and tissue can return back as
it was.
6. Odema: the accumulation of liquids in tissues due to imbalance in osmotic
pressure of vessels in that organ or tissue due to infections and inflammation
process.
7. Necrosis: death of living premature cells in tissues
due to unregulated
digestion of cells components (autolysis), this type of tissue damage is
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irreversible injury and can be
fatal for whole human body when occurs in
important organs like lung or liver.
Necrosis starts by the loss of cell membrane integrity and an
uncontrolled release of products of cell death into the intracellular space
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This initiates an inflammatory response in the surrounding tissue;
phagocytes are prevented from locating and engulfing the dead cells. The
result is dead tissue and cell debris at, or near, the site of the cell death and
it is necessary to remove necrotic tissue surgically,
the classic example is
gangrene.
Even after healing, the necrotic tissue will remain in the body.
The
standard therapy for necrosis is removal of the dead tissue (debridement)
either by surgical or non-surgical means. Depending on the severity of the
necrosis, the affected limbs or organs may be whole removed to save patient
life. In some cases, special maggot therapy using Lucilia sericata larvae has
been employed to remove necrotic tissue and infection.
Types of Necrosis:
Coagulative necrosis can be observed by light microscopy. Coagulation
occurs as a result of protein denaturation, mainly the albumin forming gel
like substance, e.g. occurs in tissues such the kidney, heart and adrenal
glands.
Liquefactive necrosis occurs due to digestion of dead cells to form a
viscous liquid mass. This is typical in bacterial, or sometimes fungal,
infections because of their ability to stimulate an inflammatory response.
The necrotic liquid mass is frequently creamy yellow due to the presence of
dead leukocytes and is commonly known as pus.
Caseous necrosis can be considered a combination of coagulative and
liquefactive necroses, caused by mycobacteria (e.g. tuberculosis), fungi and
some foreign substances. The necrotic tissue appears as white and like
clumped cheese. Dead cells disintegrate but are not completely digested,
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leaving granular particles. Microscopic examination shows amorphous
granular debris enclosed within an inflammatory border, e.g. Granuloma.
Fat necrosis is specialized necrosis of fat tissue resulting from the action of
activated lipases on fatty tissues such as the pancreas.
Fibrinoid necrosis is a special form of necrosis usually caused by immune-
mediated vascular damage. It is marked by complexes of antigen and
antibodies, sometimes referred to as “immune complexes” deposited
together with fibrin.
Note: the recycling of cellular materials process cannot occurs after necrotic
cell death due to the apoptotic pathway non-activation.