Medicine Hack

1) P wave - atrial depolarisation, < 120 ms 2) PR segment - end of P wave till beginning of QRS complex i.e. time taken between atrial and ventricular activation. 3) PR interval - onset of P wave till onset of QRS complex, 120-200 ms 4) QRS complex - ventricular depolarisation, <110 ms 5) T wave - ventricular repolarisation 6) U wave - repolarisation of Purkinje fibres 7) QT interval - beginning of QRS complex till end of T wave

The action potential of a cardiac muscle fiber can be broken down into several phases: 0- depolarization, 1- initial rapid repolarization, 2- plateau phase, 3- late rapid repolarization, 4- baseline. Many persons find it hard to understand why the curve is as such. I'll try to give a simple explanation in phases. The diagram shows the action potential and below it is what happens to the different ions. By convention, influx is shown by downward deflection while efflux by upward deflection. If positive ions get inside the curve will show an increase and it will show a decrease if ions get out. Phase 0 Unlike in skeletal muscles where there is only the fast sodium channels, in cardiac muscles there are both fast sodium channels and slow calcium-sodium channels. Both open simultaneously. Phase 0 is due to the rapid opening of the voltage gated sodium channels that leads to a massive influx of sodium ions that cause the initial rapid depolarisation. The slower calcium-sodiu

Cardiac muscle is striated same as a typical skeletal muscle. The muscle fibrils are surrounded by numerous and elongated mitochondria since the heart needs energy supply continously. The muscle fibres branch and interdigitate. They lie parallel to one another but at the end of each muscle fibres there are extensive folds of the cell membrane that are called as intercalated disks/discs . The intercalated discs act as gap junctions that is very permeable and allow almost free diffusion of ions. They always occur at the Z lines i.e. the dark middle section of the light (I) band of the muscle. They provide a strong union between fibers, maintaining cell-to-cell cohesion, so that the pull of one contractile cell can be transmitted along its axis to the next. The heart muscle thus acts as a syncytium. i.e. a multinucleated mass. Therefore when one of the cells is excited, the action potential spreads from cell to cell through the latticework interconnections fast and the syncytium as

The conducting system of the heart consists of: 1) Sino-Atrial Node (SAN), 2) Internodal tract, 3) Atrio-Ventricular Node (AVN), 4) Bundle of His or A-V Bundle, 5) Right and left Bundle branches, 6) Fascicles and  7) Purkinje fibres. In the human heart, the SA node is located at the junction of the superior vena cava with the right atrium.  The AV node is located in the right posterior portion of the interatrial septum.  There are three bundles of atrial fibers that contain Purkinje-type fibers and connect the SA node to the AV node:  a) the anterior internodal tract of Bachman,  b) the middle internodal tract of Wenckebach, and  c) the posterior internodal tract of Thorel.  Conduction also occurs through atrial myocytes, but it is more rapid in these bundles.  The AV node is continuous with the bundle of His, which gives off a left bundle branch at the top of the interventricular septum and continues as the right bundle branch.  The

Each pleural cavity is completely lined by a mesothelial membrane called the pleura. The latter is a serous membrane arranged as a closed invaginated surface. During development, the lungs grow out of the mediastinum, becoming surrounded by the pleural cavities. As a result, the outer surface of each organ is covered by pleura. The pleura lining the walls of the cavity is the parietal pleura, whereas that reflected from the mediastinum at the roots and onto the surfaces of the lungs and interlobar fissures is the visceral pleura or pulmonary pleura. The space formed between the two is called pleural cavity. The parietal and visceral layer are continuous at the hilar structures. The lung does not completely fill the potential space of the pleural cavity, resulting in recesses, which do not contain lung and are important for accommodating changes in lung volume during breathing. The costodiaphragmatic recess, which is the largest and clinically most important recess, lies

Polymerase chain reaction is a test tube method to amplify a selected DNA sequence. The advantage is that millions of copies can be made within hours. The steps in one cycle of synthesis include: 1) Primer construction 2) Denaturation of DNA 3) Annealing of primers to single stranded DNA 4) Extension of the chain. This technique can be used for: 1) forensic analysis of DNA even from a single strand of hair, single drop of blood/semen. 2) detection of viral DNA sequence e.g. of HIV even at very early stage of infection when only a small number of cells are harbouring the virus. 3) prenatal diagnosis and detection of cystic fibrosis. Most recently, it has been found to be very useful in the screening of CMV in neonates. PCR assays of both liquid and dried saliva are highly sensitive and specific to detect cytomegalovirus in neonates.

This is a slide at 50X magnification of a beta thalassemia patient. This is also a type of microcytic hypochromic  anemia as shown in the slide. The red blood cells have a diameter smaller than that of the nucleus of the lymphocyte. They are also bizarre shaped. Target cells aka codocytes or mexican hat cells are predominantly seen. They are characterised by a dark centre followed by a white ring and then a second rim of dark region.