Histopathological techniques

Histopathological examination studies tissues under the microscope. During this study, the pathologist looks for abnormal structures in the tissue. Tissues for histopathological examination are obtained by biopsy. Biopsy is a tissue sample from a living person to identify the disease. Biopsy can be either incisional or excisional.

Once the tissue is removed from the patient, it has to be immediately fixed by putting it into adequate amount of 10% Formaldehyde (10% formalin) before sending it to the pathologist.

The purpose of fixation is:

1. to prevent autolysis and bacterial decomposition and putrefaction

2. to coagulate the tissue to prevent loss of easily diffusible substances

3. to fortify the tissue against the deleterious effects of the various stages in the preparation of sections and tissue processing.

 4. to leave the tissues in a condition which facilitates differential staining with dyes and other reagents.

Molecular techniques

Different molecular techniques such as fluorescent in situ hybridization, Southern blot, etc... can be used to detect genetic diseases.

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.

Cholelithiasis (Biliary calculi)
- These are insoluble material found within the biliary tract and are formed of bile constituents (cholesterol, bile pigments and calcium salts). 

Sites: - -Gall bladder, extra hepatic biliary tract.  Rarely, intrahepatic biliary tract. 

Predisposing factors:- 
- Change in the composition of bile. - It is the disturbance of the ratio between cholesterol and lecithin or bile salts which may be due to Hypercholesterolaemia which may be hereditary or the 4 F (Female, Forty, Fatty, Fertile). Drugs as clofibrate and exogenous estrogen. High intake of calories (obesity).
Increased concentration of bilirubin in bile- pigment stones
Hypercalcaemia:- Calcium carbonate stones.

2- Staisis.
3- Infection. 

Pathogenesis   i- Nucleation or initiation of stone formation:- The nidus may be cholesterol “due to supersaturation” Bacteria, parasite
RBCs or mucous.  
ii- Acceleration:- When the stone remains in the gall bladder, other constituents are added to the
nidus to form the stone. 

Complications of gall stones:- 
- Predispose to infection.- Chronic irritation leading to 
a. Ulceration       b. Squamous metaplasia & carcinoma.