Transcript Pathologic Basis

Definition
• PATHOLOGY IS THE STUDY OF THE
CAUSES, MECHANISMS,PATTERNS
AND EFFECTS OF ILLNESS(DISEASE)
definition
• study (logos) of suffering (pathos).
• it is a bridging discipline involving both basic science and
clinical practice and is devoted to the study of the
structural and functional changes in cells, tissues, and
organs that underlie disease.
• By the use of molecular, microbiologic, immunologic, and
morphologic techniques, pathology attempts to explain
the whys and wherefores of the signs and symptoms
manifested by patients while
• Provides a sound foundation for rational clinical care and
therapy.
vital component
• medical education for all
– doctors,
– nurses and
– other health-care practitioners.
Necessary
• to interpret the complaints of a patient (the
symptoms of disease) understand the
abnormalities found on examination the
signs of disease,
important
• be familiar with the range of abnormalities
possible in an organ or tissue.
Pathology is the bedrock of
clinical medicine, and its study
continues throughout clinical
practice.
Clinical symptoms
• A man complains to his doctor of the sudden
onset of severe, crushing, continuous central
chest pain, radiating into the left side of the neck
and down the left arm.
• he had previously experienced similar, less
severe, pain in his chest on physical exertion,
but that the pain used to go away on resting.
• The latest episode is associated with severe
breathlessness, and the patient feels very
unwell.
signs
• He has cold clammy skin and low blood
pressure.
Goal
• To build up a picture of the most likely
pathological processes at work,
• and to work out what mechanisms are
operating
• and what are the causative factors
• and what are the likely effects
• To institute possibly life-saving, treatment
Deduction
• a knowledge of the range of diseases that can
affect the heart, and their causes,
• the doctor deduces that the patient probably
has severe disease affecting his coronary
arteries, which have become partially blocked by
a disease process called atheroma
• and that this partial blockage has resulted in the
heart muscle occasionally being short of
oxygenated arterial blood in periods of
strenuous physical activity, leading to heart
muscle pain (angina) in the past.
The conclusion
• most recent episode may have resulted from
complete blockage of the artery, which has been
made total by development of a blood clot
(thrombus).
• this has caused complete cessation of arterial
blood supply to part of the muscular wall of the
heart, and consequent death of the heart muscle
cells due to loss of oxygen supply.
• The doctor will make a working diagnosis of
myocardial infarction.
•
Planning
• Knowing the likely aetiology of a disease
allows rational planning of investigations to
confirm the clinical diagnosis.
• In this instance an electrocardiogram
(ECG) will show diagnostic changes,
• and levels of enzymes liberated from dead
heart muscle will be elevated in the blood.
Institution
• knowledge of the mechanisms involved
(pathogenesis) also allows implementation
of treatment;
• in this instance administration of an agent
to promote lysis of thrombus allows reperfusion of heart muscle and may limit
the extent of damage.
The history of chest pain which
improved on rest must
• mean that the coronary arteries are severely
narrowed by atheroma, causing partial blockage
of the lumen.
• Reduction in blood supply to the heart muscle
will have produced symptoms of chest pain only
on exertion, when the heart is working hard and
has high blood and oxygen requirements. It is
characteristic that this type of pain (angina of
effort) disappears on resting.
The constant chest pain
• must mean that the patient now has a true
myocardial infarct, and that the coronary
artery is completely blocked, perhaps by
thrombus.
the patient's life is at risk.
• There will now be an area of dead heart
muscle in the wall of the left ventricle, and
• One must look out for symptoms and
signs of the immediate complications of
myocardial infarction.
• It will take about 8 weeks for the infarcted
heart muscle to heal by scarring; until then
he is at risk.
complications
• This patient's immediate complications are
failure of the left ventricle, leading to reduced
cardiac output (responsible for his cold, clammy
skin and his low blood pressure).
• Also, his damaged left ventricle is unable to
empty completely at systole, so there will be
increased back pressure in the left atrium and
pulmonary veins and capillaries.
• Water will pass from the pulmonary capillary
blood into his alveoli, making him very
breathless (pulmonary oedema).
Treatment
• The breathlessness and shock must mean
that the patient has a failing left ventricle.
• One had better begin treatment
immediately to improve the output and
strength of the damaged left ventricular
muscle.
Pathology encompasses all
aspects of disease
• Special terms are used to refer to patterns,
causes, mechanisms and effects of
disease
• Diseases can result from primary
abnormalities at three levels:
• Genetic function.
• Physiological/biochemical function.
• Gross structural arrangement of cells,
tissues and organs.
A limited number of tissue
responses underlie all diseases
• Cells and tissues respond to disease processes
in a limited number of ways,
• basic pathological responses.
– Adaptation of cells to changes in their environment (
– What happens to cells when they cannot adapt, and
how cells die
– Disorders due to abnormal cell growth, for example
cancer (
– Tissue responses to injury, and how tissues heal
• Genetic and immune factors in disease
• Adverse environmental factors that cause
disease
First manifestations
• Frequently, the first manifestation of a
disease process is not at its primary site,
but takes the form of secondary effects.
• To confirm or screen for disease the
physician or surgeon sends samples from
the patient to the pathology laboratory and
asks for an appropriate analysis.
diagnostic pathology laboratory
medicine.
• For example, in diabetes mellitus,
although there is a primary abnormality in
the pancreas, the diagnosis can be made
by analysis of blood and urine glucose
levels.
• Detection and analysis of similar
secondary effects are of immense value in
deducing the nature and site of underlying
disease processes.
Diagnostic pathology/laboratory
medicine
• A 63-year-old man complains of increasing
weakness and lethargy.
• On examination he appears very pale,
suggesting that he is anaemic.
• The physician takes a blood sample for
haematological analysis,
•laboratory finding implies either inadequate iron intake, or excess
blood loss.
On further questioning
• patient admits that he occasionally
passes very dark faeces. A faecal sample
is sent to the Chemical Pathology
laboratory for analysis.
• The patient is bleeding into his bowel, but
where?
Radiological examination
• by barium enema suggests an abnormality
in the caecum.
colonoscope,
• the surgeon examines the full length of the
colon and finds an ulcer with raised edges
at the site of radiological abnormality in the
caecum.
samples of tissue are taken
• the edges and floor of the ulcer, and sent
to the Histopathology laboratory for
histological examination.