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Showing posts from February, 2012

Gram staining - Procedure, mechanism, explanation

 INTRODUCTION  The Gram stain was developed in 1884 by the Danish bacteriologist Hans Christian Gram. It is one of the most useful staining procedures because it classifies bacteria into two large groups:  1) gram-positive and  2) gram-negative.  PROCEDURE  1) A heat-fixed smear is flooded with a basic purple dye, usually crystal violet. Because the purple stain imparts its color to all cells, it is referred to as a primary stain . 2) After 1 minute, the crystal violet is drained off and washed with distilled water. The smear is then covered with Gram's iodine, a mordant or helper . When the iodine is washed off, both gram-positive and gram-negative bacteria appear dark violet or purple. 3) Next, the slide is washed with alcohol (95% ethanol) or an alcohol-acetone solution. This solution is a decolorizing agent which removes the purple from the cells of some species but not from others. When the procedure is carried out, the slide is held at an angle and 95% ethanol is

Differences between hyperemia and congestion

Hyperemia and congestion both indicate a local increased volume of blood in a particular tissue. Hyperemia is an active process that result from augmented blood flow due to arteriolar dilation (e.g. at sites of inflammation or in skeletal muscle during exercise). The affected tissue is redder than normal because of engorgement with oxygenated blood. Congestion, on the other hand, is a passive process resulting from impaired venous return out of a tissue. It may occur due to systemic causes like cardiac failure or a local cause like isolated venous obstruction. The tissue is cyanosed because the worsening congestion leads to accumulation of deoxygenated hemoglobin in the affected tissues. 

Third degree atrioventricular block / Complete heart block - ECG

Third degree atrioventricular block is also known as complete heart block because there is complete failure of conduction between the atria and the ventricles. As a result of this there is complete independence between atrial and ventricular contractions. It is thus one type of AV dissociation. The classic characteristics of a complete heart block ECG are as follows : 1) P waves are present and the atrial rate is faster than the ventricular rate, 2) QRS complexes are present and are usually much slower than normal,  3) the P waves bear no relation to the QRS complexes and thus the PR intervals are completely variable. Since there is a block in the conduction, a subsidiary pacemaker will take over the function to make the ventricles contract. Depending at the level of block we can have different QRS complex morphologies.  Below is an ECG showing a complete heart block with the block occurring proximal to the His bundle, usually in congenital cases. The QRS complexes