NEET MDS Lessons
General Pathology
Lymphangitis
is the acute inflammation due to bacterial infections spread into the lymphatics most common are group A β-hemolytic streptococci.
lymphatics are dilated and filled with an exudate of neutrophils and monocytes.
red, painful subcutaneous streaks (the inflamed lymphatics), with painful enlargement of the draining lymph nodes (acute lymphadenitis).
subsequent passage into the venous circulation can result in bacteremia or sepsis.
Autopsy
Autopsy is examination of the dead body to identify the cause of death. This can be for forensic or clinical purposes.
Eczematous Dermatitis
Eczematous dermatitis includes a large category of skin lesions characterized by severe pruritus and distinctive gross and microscopic features.
- type I hypersensitivity is involved with atopic dermatitis in patients who have an allergic history.
- type IV hypersensitivity is involved in contact dermatitis (poison ivy).
- acute eczematous dermatitis is characterized by a weeping, pruritic rash, while a chronic eczematous dermatitis presents with dry, scaly, plaque-like thickening of the skin, a process called lichenification.
CONGESTION
Congestion or hyperaemia means an increase in the content of blood in an organ. It may be :
A. Active - due to increased arterial flow to the organ with dilatation of micro vessels as in
- Inflammation.
- Increased metabolic activity.
- Neurogenic blushing.
B. Passive - due to decreased venous drainage resulting in pooling of blood. There is always an associated element of oedema.
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.
Chemical Mediators In Inflammation
Can be classified as :
A. Neurogenic
Also called the Triple Response of Lewis. It involves neurogenic vasodilatation of arterioles due to antidromic axon reflex arc. The constituents of the response are:
1. arteriolar vasoconstriction followed by
2. arteriolar vasodilatation
3. swelling
B. Chemical
1. Amines: Histamine and 5 hydroxytryptamine. Released from platelets and mast cells.
Actions: Immediate and short lived.
Dilatation of arterioles.
Increased capillary premeability.
Kinins: Bradykinin and kallidin These are present in inactive from and are activated by kinin forming proteases
Actions:
Arteriolar dilatation.
Increased vascular permeability
Pain
Kinin forming proteases Plasmin and Kallikrein. Present as inactive precursors.
Cleavage products of complement C3a und C5a are called anaphylatoxins
Actions:
Histamine release from mast cells
Chemotaxis (also C567 )
Enhance phagocytosis.
Polymorph components
Cationic: proteins which cause
Increased permeability
Histamine release.
Chemotaxis of monocytes
Neutral proteases which:
Cleave C3 and C5 to active form
Convert Kininogen to Kinin
Increase permeability.
Acid proteases which liberate leucokinins
Slow reacting. substance of anaphylaxis: (SRS-A) is a lipid released from mast cell.
Action --Increases vascular permeability
Prostaglandins: E1 + E2 .
Platelets are rich source
Action:
Platelets are a rich source.
Vasodilatation.
Increased permeability.
Pain.
VIII. Miscellaneous: like
Tissue lactic acid.
Bacterial toxins.
Characteristics of Immunoglobulin subclasses
I. Ig G:
(i) Predominant portion (80%) of Ig.
(ii) Molecular weight 150, 000
(iii) Sedimentation coefficient of 7S.
(iv) Crosses placental barrier and to extra cellular fluid.
- (v) Mostly neutralising effect. May be complement fixing.
(vi) Half life of 23 days.
2.IgM :
(i) Pentamer of Ig.
(ii) Molecular weight 900, 000
(iii) 19S.
(iv) More effective complement fixation and cells lysis
(v) Earliest to be produced in infections.
(vi) Does not cross placental barrier.
(vii) Halflife of 5 days.
3. Ig A :
- Secretory antibody. Found in intestinal, respiratory secretions tears, saliva and urine also.
- Secreted usually as a dinner with secretory piece.
- Mol. weight variable (160,000+)
- 7 S to 14 S.
- Half life of 6 days.
4.Ig D :
- Found in traces.
- 7 S.
- Does not cross placenta.
5. Ig E
- Normally not traceable
- 7-8 S (MoL weight 200,000)
- Cytophilic antibody, responsible for some hypersensitivity states,