NEET MDS Lessons
General Pathology
INFARCTION
An infarct is an area of ischemic necrosis caused by occlusion of either the arterial supply or the venous drainage in a particular tissue
Nearly 99% of all infarcts result from thrombotic or embolic events
other mechanisms include: local vasospasm, expansion of an atheroma, extrinsic compression of a vessel (e.g., by tumor); vessel twisting (e.g., in testicular torsion or bowel volvulus; and traumatic vessel rupture
MORPHOLOGY OF INFARCTS
infarcts may be either red (hemorrhagic) or white (anemic) and may be either septic or aseptic
All infarcts tend to be wedge-shaped, with the occluded vessel at the apex and the periphery of the organ forming the base
The margins of both types of infarcts tend to become better defined with time
The dominant histological characteristic of infarction is ischemic coagulative necrosis
most infarcts are ultimately replaced by scar. The brain is an exception, it results in liquefactive necrosis
RED INFARCTS:
occur in
(1) venous occlusions (such as in ovarian torsion)
(2) loose tissues (like lung) that allow blood to collect in the infarcted zone
(3) tissues with dual circulations (lung and small intestine)
(4) previously congested tissues because of sluggish venous outflow
(5) when flow is re-established to a site of previous arterial occlusion and necrosis
WHITE INFARCTS
occur with:
1) arterial occlusions
2) solid organs (such as heart, spleen, and kidney).
Septic infarctions - occur when bacterial vegetations from a heart valve embolize or when microbes seed an area of necrotic tissue. - the infarct is converted into an abscess, with a correspondingly greater inflammatory response
FACTORS THAT INFLUENCE DEVELOPMENT OF AN INFARCT
- nature of the vascular supply
- rate of development of the occlusion (collateral circulation )
- vulnerability to hypoxia - Neurons undergo irreversible damage
- 3 to 4 minutes of ischemia. - Myocardial cells die after only 20 to 30 minutes of ischemia
- the oxygen content of blood
Emphysema
Emphysema is a chronic lung disease. It is often caused by exposure to toxic chemicals or long-term exposure to tobacco smoke.
Signs and symptoms
loss of elasticity of the lung tissue
destruction of structures supporting the alveoli
destruction of capillaries feeding the alveoli
The result is that the small airways collapse during expiration, leading to an obstructive form of lung disease
Features are: shortness of breath on exertion
hyperventilation and an expanded chest.
As emphysema progresses, clubbing of the fingers may be observed, a feature of longstanding hypoxia.
Emphysema patients are sometimes referred to as "pink puffers". This is because emphysema sufferers may hyperventilate to maintain adequate blood oxygen levels. Hyperventilation explains why emphysema patients do not appear cyanotic as chronic bronchitis (another COPD disorder) sufferers often do; hence they are "pink" puffers (adequate oxygen levels in the blood) and not "blue" bloaters (cyanosis; inadequate oxygen in the blood).
Diagnosis
spirometry (lung function testing), including diffusion testing
X-rays, high resolution spiral chest CT-scan,
Bronchoscopy, blood tests, pulse oximetry and arterial blood gas sampling.
Pathophysiology :
Permanent destructive enlargement of the airspaces distal to the terminal bronchioles without obvious fibrosis
Oxygen is inhaled in normal breathing
When toxins such as smoke are breathed into the lungs, the particles are trapped by the hairs and cannot be exhaled, leading to a localised inflammatory response. Chemicals released during the inflammatory response (trypsin, elastase, etc.) are released and begin breaking down the walls of alveoli. This leads to fewer but larger alveoli, with a decreased surface area and a decreased ability to take up oxygen and loose carbon dioxide. The activity of another molecule called alpha 1-antitrypsin normally neutralizes the destructive action of one of these damaging molecules.
After a prolonged period, hyperventilation becomes inadequate to maintain high enough oxygen levels in the blood, and the body compensates by vasoconstricting appropriate vessels. This leads to pulmonary hypertension. This leads to enlargement and increased strain on the right side of the heart, which in turn leads to peripheral edema (swelling of the peripherals) as blood gets backed up in the systemic circulation, causing fluid to leave the circulatory system and accumulate in the tissues.
Emphysema occurs in a higher proportion in patient with decreased alpha 1-antitrypsin (A1AT) levels
Prognosis and treatment
Emphysema is an irreversible degenerative condition
Supportive treatmentis by supporting the breathing with anticholinergics, bronchodilators and (inhaled or oral) steroid medication, and supplemental oxygen as required
Lung volume reduction surgery (LVRS) can improve the quality of life for only selected patients.
Roseola
- alias exanthem subitum; caused by Herpes virus type 6.
- children 6 months to 2 years old; spring and fall; incubation 10-15 days.
- sudden onset of a high fever with absence of physical findings; febrile convulsions are particularly common.
- fever falls by crisis on the 3rd or 4th day → 48 hours after temperature returns to normal macular or maculopapular rash starting on the trunk and spreading centrifugally.
Infectious Mononucleosis
It is an Epstein Barr virus infection in children and young adults.
Features
-Constitutional symptoms.
-Sore throat.
-Lymphnode enlargement.
-Skin rashes
-Jaundice.
-Rarely pneumonia, meningitis and encephalitis.
Blood Picture
- Total count of I0,000. 20,000 /cu.mm.
- Lymphocytosis (50-90%) with atypical forms. They are larger with more cytoplasm which may be vacuolated or basophilic. Nucleus may be indented. with nucleoli (Downy type I to III).
- Platelets may be reduced.
- Paul Bunell test (for heterophil antibody against sheep RBC) is positive
Leukaemias
Uncontrolled proliferation of leukocyte precursors (may be with associated red cell and platelet series proliferation).
Factors which may playa causal role are.
- Viral
- Radiation.
- Genetic.
Classification
1. Acule leukaemia:
a. Lymphocytic (lymphoblastic).
b. Myelocytic and promyelocytic (myeloblastic).
c. Monocytic.
d. Myelomonocytic.
e. Undifferentiated (Stem cell).
2. Chronic leukaemia:
a. Lymphocytic
b. Myelocytic
3. Miscellaneous:
a. Erythroleukaemia (De Guglielmo's disease).
b. Eosinophilic leukaemia.
c. Megakaryocytic leukaemia.
Nephrolithiasis, urolithiasis
Formation of calculi (calcium stones) in the kidney (nephrolithiasis) or urinary tract (urolithiasis).
Commonly associated with hyperparathyroidism.
Signs and symptoms
urinary tract obstruction, severe pain, and pyelonephritis.
Note: an enlarged prostate can also cause urinary tract obstruction in males.
Eosinophilia:
Causes
-Allergic disorders.
-Parasitic infection.
-Skin diseases.
-Pulmonary eosinophilia.
-Myeloproliferative lesions and Hodgkin's disease.