NEET MDS Lessons
General Pathology
Congenital heart defect
Congenital heart defects can be broadly categorised into two groups,
o acyanotic heart defects ('pink' babies) :
An acyanotic heart defect is any heart defect of a group of structural congenital heart defects, approximately 75% of all congenital heart defects.
It can be subdivided into two groups depending on whether there is shunting of the blood from the left vasculature to the right (left to right shunt) or no shunting at all.
Left to right shunting heart defects include
- ventricular septal defect or VSD (30% of all congenital heart defects),
- persistent ductus arteriosus or PDA,
- atrial septal defect or ASD,
- atrioventricular septal defect or AVSD.
Acyanotic heart defects without shunting include
- pulmonary stenosis, a narrowing of the pulmonary valve,
- aortic stenosis
- coarctation of the aorta.
cyanotic heart defects ('blue' babies).
obstructive heart defects
cyanotic heart defect is a group-type of congenital heart defect. These defects account for about 25% of all congenital heart defects. The patient appears blue, or cyanotic, due to deoxygenated blood in the systemic circulation. This occurs due to either a right to left or a bidirectional shunt, allowing significant proportions of the blood to bypass the pulmonary vascular bed; or lack of normal shunting, preventing oxygenated blood from exiting the cardiac-pulmonary system (as with transposition of the great arteries).
Defects in this group include
hypoplastic left heart syndrome,
tetralogy of Fallot,
transposition of the great arteries,
tricuspid atresia,
pulmonary atresia,
persistent truncus arteriosus.
Cytopathologic techniques
Cytopathology is the study of cells from various body sites to determine the cause or nature of disease.
Applications of cytopathology:
- Screening for the early detection of asymptomatic cancer
2. Diagnosis of symptomatic cancer
3. Surveillance of patients treated for cancer
Cytopathologic methods
There are different cytopathologic methods including:
1. Fine-needle aspiration cytology (FNAC) -In FNAC, cells are obtained by aspirating the diseased organ using a very thin needle under negative pressure.
Superficial organs (e.g. thyroid, breast, lymph nodes, skin and soft tissues) can be easily aspirated.
Deep organs, such as the lung, mediastinum, liver, pancreas, kidney, adrenal gland, and retroperitoneum are aspirated with guidance by fluoroscopy, ultrasound or CT scan.
- Exfoliative cytology
Refers to the examination of cells that are shed spontaneously into body fluids or secretions. Examples include sputum, cerebrospinal fluid, urine, effusions in body cavities (pleura, pericardium, peritoneum), nipple discharge and vaginal discharge.
- Abrasive cytology
Refers to methods by which cells are dislodged by various tools from body surfaces (skin, mucous membranes, and serous membranes). E.g. preparation of cervical smears with a spatula or a small brush to detect cancer of the uterine cervix at early stages.
Blood-Lymphatic Pathology
Disorders of primary hemostasis
1. General characteristics of disorders of primary hemostasis (due to problems of blood vessels or platelets):
a. Occur early in life.
b. Unlike secondary hemostasis, bleeding occurs in more superficial areas such as skin and mucous membranes rather than in secondary hemostasis.
c. Signs include petechiae.
d. Can be caused by vascular and platelet abnormalities or alterations in the plasma proteins required for adhesion of platelets to vascular subendothelium.
e. Laboratory findings include prolonged bleeding time, as seen in platelet disorders.
2. Vascular abnormalities
Scurvy
(1) Caused by a vitamin C deficiency leading to decreased synthesis of collagen. Note: vitamin C is necessary for the formation of collagen via hydroxylation of lysine and proline.
(2) Symptoms include:
- Delayed wound healing.
- Petechiae and ecchymosis.
- Gingival bleeding, swelling, and ulcerations.
3. Platelet abnormalities
a. Thrombocytopenia
(1) Characterized by a decreased number of platelets.
(2) The most common type of bleeding disorder.
(3) Can be caused by a number of diseases, such as irradiation, acute leukemia, disseminated intravascular coagulation (DIC), or idiopathic thrombocytopenic purpura (ITP).
b. Thrombocytopenic purpura
(1) Idiopathic: An autoimmune disease characterized by the presence of autoantibodies against platelets, resulting in the removal of platelets by splenic macrophages.
(2) May also be drug-induced.
Disorders of secondary hemostasis
1. General characteristics of disorders of secondary hemostasis (due to problems with clotting factors):
a. Symptoms occur later in life.
b. As compared to disorders of primary hemostasis, bleeding occurs in deeper areas and larger vessels (i.e., joint spaces).
c. Laboratory findings include abnormal:
- Partial thromboplastin time (PTT)—measures the intrinsic and common clotting pathway (i.e., tests all coagulation factors except factor 7).
- Prothrombin time (PT)—measures the extrinsic pathway.
- Does not affect the bleeding time.
Hemophilia
a. Caused by a deficiency of particular clotting factor(s).
b. All types of hemophilia affect the intrinsic pathway of the clotting cascade.
c. Signs and symptoms include:
- Prolonged PTT.
- Continuous bleeding from cuts or trauma, which can lead to excessive blood loss.
- Bleeding into joint cavities (hemarthroses) and muscle.
Two types:
(1) Hemophilia A (classic hemophilia)
- Caused by a deficiency of factor 8 (antihemophilic factor).
- Transmission: sex-linked recessive—only occurs in males; however, females can be carriers.
(2) Hemophilia B (Christmas disease)
- Caused by a deficiency of factor 9 (plasma thromboplastin).
- Transmission: sex-linked recessive—only occurs in males; however, females can be carriers.
- Lower incidence rate than hemophilia A.
(3). Vitamin K deficiency
- Causes include malnutrition and malabsorption of fats.
- A decrease in clotting factors 2, 7, 9, and 10 and prothrombin is observed.
- Prolonged PT.
Disorders of both primary and secondary hemostasis
1. von Willebrand’s disease
a. Characterized by a defective von Willebrand’s factor (vWF). Defective vWF affects both primary hemostasis by affecting platelet adhesion to
endothelium, and secondary hemostasis, by a defective factor 8.
b. Genetic transmission: autosomal dominant.
It is the most common hereditary bleeding disorder.
2. Liver disease—disease of the liver results in a decreased production of coagulation factors and therefore can lead to problems with hemostasis.
3. Disseminated intravascular coagulation a condition in which clots form throughout the vasculature. This uses up all available clotting factors and platelets, resulting in problems with bleeding.
German measles (rubella)
- sometimes called "three day measles".
- incubation 14-21 days; infectious 7 days before the rash and 14 days after the onset of the rash.
- in adults, rubella present with fever, headache, and painful postauricular Lymphadenopathy 1 to 2 days prior to the onset of rash, while in children, the rash is usually the first sign.
- rash (vasculitis) consists of tiny red to pink macules (not raised) that begins on the head and spreads downwards and disappears over the ensuing 1-3 days; rash tends to become confluent.
- 1/3rd of young women develop arthritis due to immune-complexes.
- splenomegaly (50%)
Neutrophilia
Causes
-Pyogenic infections.
-Haemorrhage and trauma.
-Malignancies.
-Infarction.
-Myelo proliferative disorders.
STREPTOCOCCAL INFECTIONS
Most streptococci are normal flora of oropharynx
Group A streptococci: Str. pyogenes
Group B streptococci: Str. agalactiae
Str. pneumoniae
Strep viridans group
Group D: Enterococcus (lately Strep. Fecalis and E. fecium), causes urinary tract infections,
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.