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Showing posts from June, 2011

ECG waves, their meaning and normal duration.

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

Cardiac action potential

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 muscles properties - morphology

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

Conducting system of the heart - SAN, AVN, Bundle of His, Purkinje fibres

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

Pleura - parietal, visceral and mediastinum

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 - PCR

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.

Beta thalassemia - target cells

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.

Hunt-Hess scale - Subarachnoid hemorrhage

This scale is used to classify the severity of non-traumatic subarachnoid hemorrhage. It includes : 1- Asymptomatic, mild headache, slight or no neck rigidity. 2- Moderate to severe headache, neck rigidity, no neurologic deficit other than cranial nerve palsy. 3- Drowsiness, confusion, mild focal neurologic deficit. 4- Stupor, moderate to severe deficit, hemiparesis. 5- Coma, decerebrate posturing.

Xanthomas in tendon and xanthelasmata

Above is a picture of xanthomas in the tendon and below it xathelasmata in a middle aged woman. Both are clinical features of familial hypercholesterolemia. The latter is an autosomal dominant condition and is associated with marked atherosclerosis that results in ischaemic heart disease, stroke and peripheral vascular disorders. Other clinical features that may be there include: 1) Skin xanthomas and 2) Arcus senilis which sets in at a younger age.

Iron deficiency anemia - Microcytic hypochromic cells

It is a typical peripheral blood smear for an iron deficiency anemia patient showing microcytic hypochromic red blood cells at magnification 50X. In normal conditions, the size (diameter) of an RBC should roughly correspond to that of the nucleus of a lymphocyte. In this slide, it is smaller. The numerous small dots refer to platelets and they are found in a larger number (thrombocytosis), a finding commonly seen in iron deficiency anemia. Differential diagnosis includes: 1) anemia of chronic disorders, 2) thalassemia, 3) sideroblastic anemia.

Abnormal Uterine Bleeding (AUB) - PALM-COEIN classification

This is a new classification for abnormal bleeding in a non pregnant woman of reproductive age group. It stands for : P - Polyp A- Adenomyosis L- Leiomyoma M- Malignancy/ Hyperplasia C- Coagulopathy O- Ovulatory dysfunction E- Endometrial causes I- Iatrogenic N- Not classified causes. The classification is as such since the first 4 ones i.e. PALM can be diagnosed and measured directly by inspection or imaging techniques. The other ones need investigations other than imaging in most cases to reach a diagnosis.

Vitamin D - recommended level in blood, value for deficiency

The minimum recommended vitamin D level is 30 ng/mL but a range of 40-60 ng/mL has been put to guarantee sufficiency. The vitamin D level actually refers to the level of 25-Hyhroxy-cholecalciferol i.e. 25[OH]D and not that of 1,25-Dihydroxy-cholecalciferol. 25[OH]D is the major storage form of vitamin D. Around 88% of it circulates bound to vitamin D-binding protein, 0.03% is free and rest circulates bound to albumin. It has a half life of around 2-3 weeks. If this level is less than 20 ng/mL, it is considered as vitamin D deficiency.

Differential cyanosis

It is a condition whereby the patient will have well perfused pink upper extremities evident by the pink finger nails while the lower extremities will both have cyanosis and clubbing in the toes, as shown in the picture above. In adults, it is commonly seen in patients of Patent Ductus Arteriosus (PDA) who have Pulmonary Hypertension at the same time. This occurs because venous blood shunts through the ductus and enters the aorta distal to the subclavian arteries.  In newborns, it can also occur in pre-ductal coarctation of aorta along with PDA. 

New York Heart Association (NYHA) Functional Classification

Class New York Heart Association (NYHA) Functional Classification I Patients with cardiac disease but without resulting limitations of physical activity. Ordinary physical activity does not cause undue fatigue, palpitation, dyspnea, or anginal pain. II Patients with cardiac disease resulting in slight limitation of physical activity. They are comfortable at rest. Ordinary physical activity results in fatigue, palpitation, dyspnea, or anginal pain. III Patients with cardiac disease resulting in marked limitation of physical activity. They are comfortable at rest. Less than ordinary physical activity causes fatigue, palpitation, dyspnea, or anginal pain. IV Patients with cardiac disease resulting in inability to carry on any physical activity without discomfort. Symptoms of cardiac insufficiency or of the anginal syndrome may be present even at rest. If any physical activity is undertaken, discomfort is increas

Vertebra - diagram of a typical vertebra

The function of the vertebral body is mostly weight bearing. As we go caudally, the size of the body increases. Other structures are well illustrated in the diagrams above. 


The mediastinum is divided into superior and inferior, the plane of division being a line from the manubriosternal joint to the lower surface of the fourth thoracic vertebra. The inferior mediastinum is further divided into anterior, middle and posterior mediastinum. Anterior boundary includes the sternum, posterior one being the thoracic vertebral column. Superiorly it starts at the thoracic inlet and ends at the diaphragm.

Hyperkalemia - ECG changes

Hyperkalemia is a very dangerous and potentially lethal condition because it will eventually affect the heart. With mild increase in plasma K + level, the first change in the ECG is the appearance of tall peaked T waves, which is a manifestation of altered repolarization. As plasma K + levels rise further, there is the paralysis of the atria and QRS complexes are prolonged and slurred.  Ventricular arrhythmias may develop. The resting membrane potential of the muscle fibers decreases as the extracellular K + concentration increases. The fibers eventually become unexcitable, and the heart stops in diastole.

Differences between Type I and Type II Diabetes Mellitus

                                                                Type 1                                                Type 2 Ketosis prone                                            Yes                                                Uncommon Insulin requirement                            Yes (absolute insulin deficiency)            Often later in disease (insulin                                                                                                                                                                                                                                                                                resistance ± deficiency)     Onset of symptoms                                     Acute                                             Often insidious Obesity                                                     Uncommon                                     Common Age at onset (yr)                                       Usually <30