NEET MDS Lessons
General Pathology
Nonspecific or Innate Immunity
1. Genetic factors
- Species: Guinea pig is very susceptible to tuberculosis.
- Race: Negroes are more susceptible to tuberculosis than whites
- Sickle cells (HbS-a genetic determined Haemoglobinopathy resistant to Malarial parasite.
2. Age Extremes of age are more susceptible.
3. Hormonal status. Low resistance in:
- Diabetes Mellitus.
- Increased corticosteroid levels.
- Hypothyroidism
4. Phagocytosis. Infections can Occur in :
- Qualitative or quantitative defects in neutrophils and monocytes.
- Diseases of mononuclear phagocytic system (Reticuloendothelial cells-RES).
- Overload blockade of RES.
5. Humoral factors
- Lysozyme.
- Opsonins.
- Complement
- Interferon (antiviral agent secreted by cells infected by virus)
Varicose Veins
- are abnormally dilated, tortuous veins produced by prolonged increase in intraluminal pressure and loss of vessel wall support.
- The superficial veins of the leg are typically involved
-venous pressures in these sites can be markedly elevated -> venous stasis and pedal edema (simple orthostatic edema)
-Some 10% to 20% of adult males and 25% to 33% of adult females develop lower extremity varicose veins
RISK FACTORS
-> obesity
-> Female gender
-> pregnancy.
-> familial tendency (premature varicosities results from imperfect venous wall development)
Morphology
- wall thinning
- intimal fibrosis in adjacent segments
- spotty medial calcifications (phlebosclerosis)
- Focal intraluminal thrombosis
- venous valve deformities (rolling and shortening)
COMPLICATIONS
- stasis, congestion, edema, pain, and thrombosis
- chronic varicose ulcers
- embolism is very rare.
Q Fever
An acute disease caused by Coxiella burnetii (Rickettsia burnetii) and
characterized by sudden onset of fever, headache, malaise, and interstitial
pneumonitis.
Symptoms and Signs
The incubation period varies from 9 to 28 days and averages 18 to 21 days. Onset
is abrupt, with fever, severe headache, chills, severe malaise, myalgia, and,
often, chest pains. Fever may rise to 40° C (104° F) and persist for 1 to > 3
wk. Unlike other rickettsial diseases, Q fever is not associated with a
cutaneous exanthem. A nonproductive cough and x-ray evidence of pneumonitis
often develop during the 2nd wk of illness.
In severe cases, lobar consolidation usually occurs, and the gross appearance of
the lungs may resemble that of bacterial pneumonia
About 1/3 of patients with protracted Q fever develop hepatitis, characterized
by fever, malaise, hepatomegaly with right upper abdominal pain, and possibly
jaundice. Liver biopsy specimens show diffuse granulomatous changes, and C.
burnetii may be identified by immunofluorescence.
Infections caused by gonorrhea
1. Acute urethritis. Mostly in males. Generally self-limiting. Dysuria and purulent discharge.
2. Endocervical infection. Purulent vaginal discharge, abnormal menses, pelvic pain. Often co-infection with other STD’s. Some women are asymptomatic.
3. Pelvic Inflammatory Disease (PID). Consequence of ascending endocervical infection. Causes salpingitis, endometriosis, bilateral abdominal pain, discharge, fever. May lead to sterility, chronic pain, and ectopic pregnancy because of loss of fallopian cilia.
4. Anorectal inflammation. Mostly in homosexual men. Pain, itching, discharge from anus.
5. Dermatitis/arthritis. Occurs after bacteremia. Skin will have papules on an erythematous base which develop into necrotic pustules. Asymmetric joint pain. These infections are susceptible to penicillin.
6. Neonatal infections. Ophthalmia neonatorum is a conjunctival infection from going through infected vagina. After one year of age, suspect child abuse.
Sickle Cell Disease
Sickle cell anemia is a autosomal recessive genetic disorder. It affects the BETA GLOBIN gene on the CHROMOSOME 16. In sickle cell anemia, the hemoglobin abnormality consists of a point mutation in the beta chain gene for hemoglobin; the resulting abnormal gene product is denoted HbS. If you are heterozygous for the HbS gene you will have what is called sickle trait, which is asymptomatic .
If you are homozygous for the HbS gene you will get sickle cell disease, which is symptomatic in most patients.
The problem with HbS is that as it releases oxygen, it polymerizes and aggregates with other HbS molecules, making the red cell stiff and distorted. These distorted, sickle-shaped red cells are fragile so the patient can end up with a hemolytic anemia.
This can occur as pure disease (homozygous) or trait (heterozygous) or with other haemoglobinopathies. It is common. in Negroes. It is due to Hb-s which is much less soluble than Hb-A hence deoxygenation insoluble form sickling of RBC.
This causes:
• Removal by RE system.
• Blockage of microvessels causing ischaemia.
Haemolysis due to drugs and chemicals
This can be caused by :
1. Direct toxic action.
-> Naphthalene.
-> Nitrobenzene.
-> Phenacetin.
-> Lead.
Heinz bodies are seen in abundance.
2. Drug action on G-6-PD deficient RBC
3. Immunological mechanism which may be :
-> Drug induced autoantibody haemolysis, Antibodies are directed against RBC.
-> Hapten-cell mechanism where antibodies are directed against which is bound to cell surface e.g. Penicilin.
Str. agalactiae
β-hemolytic, with its capsule being the major virulence factor. Capsule inhibits phagocytosis and complement activation. The CAMP factor (a hemolysin) is another virulence factor.
Group B strep are normally found in GI tracts and vaginas.
Major disease is neonatal sepsis/meningitis after passage through infected birth canal. May lead to meningitis, and CNS damage is high. Mothers colonized with Group B strep should be treated pre-delivery.