Author Archives: Alila Medical Media

Baroreflex Regulation of Blood Pressure, with Animation.

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Baroreflex, or baroreceptor reflex, is one of the mechanisms the body uses to maintain stable blood pressure levels or homeostasis. Baroreflex is a rapid negative feedback loop in which an elevated blood pressure causes heart rate and blood pressure to decrease. Reversely, a decrease in blood pressure leads to an increased heart rate, returning blood pressure to normal levels.

The reflex starts with specialized neurons called baroreceptors. These are stretch receptors located in the wall of the aortic arch and carotid sinus. Increased blood pressure stretches the wall of the aorta and carotid arteries causing baroreceptors to fire action potentials at a higher than normal rate. These increased activities are sent via the vagus and glossopharyngeal nerves to the nucleus of the tractus solitarius – the NTS – in the brainstem. In response to increased baroreceptor impulses, the NTS activates the parasympathetic system – the PSNS – and inhibits the sympathetic system – the SNS.

As the PSNS and SNS have opposing effects on blood pressures, PSNS activation and SNS inhibition work together in the same direction to maximize blood pressure reduction. Parasympathetic stimulation decreases heart rate by releasing acetylcholine which acts on the pacemaker cells of the SA node. Inhibition of the sympathetic division decreases heart rate, stroke volume and at the same time causes vasodilation of blood vessels. Together, these events rapidly bring DOWN blood pressure levels back to normal.

When a person has a sudden drop in blood pressure, for example when standing up, the decreased blood pressure is sensed by baroreceptors as a decrease in tension. Baroreceptors fire at a lower than normal rate and the information is again transmitted to the NTS. The NTS reacts by inhibiting parasympathetic and activating sympathetic activities. The sympathetic system releases norepinephrine which acts on the SA node to increase heart rate; on cardiac myocytes to increase stroke volume and on smooth muscle cells of blood vessels to cause vasoconstriction. Together, these events rapidly bring UP blood pressure levels back to normal.

Baroreceptor reset : Baroreflex is a short-term response to sudden changes of blood pressure resulted from everyday activities and emotional states. If hypertension or hypotension persists for a long period of time, the baroreceptors will reset to the “new normal” levels. In hypertensive patients for example, baroreflex mechanism is adjusted to a higher “normal” pressure and therefore MAINTAINS hypertension rather than suppresses it.

Sinusite, com Animação.

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Sinusite, também conhecida como rinossinusite, é uma condição muito comum onde os seios paranasais estão inflamados, causando congestão nasal, dor de cabeça e dor facial.

Os seios paranasais são cavidades dos ossos do crânio. Existem quatro pares de cavidades localizadas em ambos os lados da cabeça. Eles são os seios maxilar, frontal, etmoidal e esfenoidal.

Os seios são revestidos por epitélio respiratório que produz muco. A drenagem do muco para a cavidade nasal ocorre através de pequenas aberturas. A drenagem prejudicada tem sido associada com a inflamação dos seios. Quando um seio é bloqueado, o fluido se acumula, tornando esse ambiente favorável para o crescimento de bactérias ou vírus, podendo causar infecção.

Um sintoma típico da sinusite é descrito como uma dor ou pressão constante, geralmente, localizada no seio afetado. A dor pode piorar quando a pessoa se inclina ou enquanto está deitada. Os sintomas geralmente começam em um lado da cabeça e se espalham para o outro lado. A sinusite aguda pode também ser acompanhada de secreção nasal espessa de cor amarelo esverdeado.

A sinusite pode ter diferentes causas, que incluem:

– Alergia (rinite alérgica): alérgenos, como o pólen, pelos de animais … pode desencadear uma resposta inflamatória na mucosa do nariz e seios paranasais, resultando na produção excessiva de muco, congestão nasal, espirros e coceira.

– Infecção: geralmente ocorre como uma complicação de um resfriado comum. A drenagem do seio prejudicada, devido à inflamação da mucosa nasal durante um resfriado, muitas vezes leva à infecção do próprio seio. Sintomas gripais, além de dor de cabeça e dor ou pressão facial são queixas comuns.

– Outras condições que causam bloqueio de drenagem do seio incluem: anormalidades estruturais, tais como desvio de septo nasal; formação de pólipos nasais.

Os tratamentos variam de acordo com a causa da sinusite:

– Para alergia: corticosteróides intranasais são comumente usados.

– Para infecção viral: medicamentos para alívio de sintomas, tais como spray nasal para irrigação e descongestionante; outros tratamentos para resfriado comum, como repouso e beber bastante líquido.

– Para infecção bacteriana: antibióticos podem ser prescritos.

– Para sinusite recorrente ou crônica devido a anormalidades estruturais ou pólipos nasais, a cirurgia nasal pode ser recomendada para desobstruir o canal de drenagem.

Ciclo de Puentes Cruzados – Contracción muscular, con Animación.

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La contracción muscular es la base de todos los movimientos esqueléticos. Los músculos esqueléticos se componen de fibras musculares, que a su vez están hechas de unidades funcionales repetitivas llamadas sarcómeros. Cada sarcómero contiene muchos filamentos paralelos y superpuestos delgados (actina) y gruesos (miosina). El músculo se contrae cuando estos filamentos se deslizan uno sobre el otro, resultando en un acortamiento del sarcómero y por lo tanto del músculo. Esto se conoce como la teoría de los filamentos deslizantes. El ciclo de puentes cruzados forma la base molecular para este movimiento de deslizamiento.

La contracción muscular inicia cuando las fibras musculares son estimuladas por un impulso nervioso y los iones de calcio son liberados.
Las unidades de troponina en los miofilamentos de actina son enlazadas a los iones de calcio. La unión desplaza la tropomiosina a lo largo de los miofilamentos y expone los sitios de unión a la miosina.
En esta etapa, cada cabeza de miosina está unida a un ADP y a una molécula de fosfato remanente del ciclo anterior.
Las cabezas de miosina se unen a los sitios de unión recién expuestos en los miofilamentos de actina para formar puentes cruzados y la molécula de fosfato es liberada.
Los dos miofilamentos se deslizan uno sobre el otro, impulsados por la energía química almacenada en las cabezas de miosina. A medida que avanzan, las moléculas de ADP son liberadas.
Los enlaces entre los miofilamentos de actina y las cabezas de miosina se rompen cuando las moléculas de ATP se unen a las cabezas de miosina.
Las moléculas de ATP son descompuestas en ADP y fosfato – la energía liberada por esta reacción es almacenada en las cabezas de miosina, lista para ser usada en el siguiente ciclo de movimiento.
Las cabezas de miosina reanudan sus posiciones de partida, y ahora pueden empezar una nueva secuencia de unión a la actina.
La presencia de más iones de calcio desencadenará un nuevo ciclo.

Understanding the 12-Lead ECG System, with Animation.

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Electrical activities of the heart can be picked up on the skin via electrodes. An ECG machine records these activities and displays them graphically. The graphs show the heart’s OVERALL electrical potential, or voltage, as it changes over time during a cardiac cycle.
The 12 leads of the ECG represent 12 electrical views of the heart from 12 different angles. The conventional 12-lead procedure involves attaching 10 electrodes to the body: one to each limb and six across the chest.
There are 6 limb leads and 6 chest leads.
The 6 limb leads look at the heart in a vertical plane and are obtained from three electrodes attached to the right arm, left arm, and left leg. The electrode on the right leg is an earth electrode.
The measurement of a voltage requires 2 poles: negative and positive. The ECG machine uses the negative pole as zero reference. Thus, the position of the positive pole is the “point of view”, and the line connecting the 2 poles is the “line of sight”.
Leads I, II, and III are BI-polar – they measure electrical potential between 2 of the 3 limb electrodes: Lead I represents the voltage between the right arm – negative pole – and the left arm – positive pole, and thus looks at the heart from the left. Lead II sees signal movements between the right arm – negative – and the left leg –positive – forming the INFERIOR LEFT view. Similarly, lead III measures electrical potential between the left arm – negative – and the left leg –positive, looking at the heart from an INFERIOR RIGHT angle.
Leads aVR, aVL, and aVF, or “augmented limb leads”, are UNIpolar. They use ONE limb electrode as the positive pole, and take the average of inputs from the OTHER two as the zero reference. Hence, aVR looks at the UPPER RIGHT side of the heart; aVL looks at the UPPER LEFT side of the heart; and aVF looks at the INFERIOR wall of the heart.
The chest leads, or precordial leads, view the heart in a HORIZONTAL plane. These are unipolar leads. The corresponding chest electrodes serve as the positive poles. The reference negative value is the same for all chest leads and is calculated as the average of inputs from the three limb electrodes.
DE-polarization TOWARD a lead produces a POSITIVE deflection; DE-polarization AWAY from a lead gives a NEGATIVE deflection. The REVERSE is true for RE-polarization. Thus, leads that look at the heart from different angles may have waves pointing in different directions.

LASIK ou PRK? O que é mais adequado para mim?

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LASIK, ou “ceratomileuse assistida por excimer laser in situ”, é a cirurgia de olho com laser mais comumente realizada para tratar a miopia, hipermetropia e astigmatismo. O objetivo do tratamento é remodelar a córnea para corrigir o erro refrativo do olho.
A córnea é uma estrutura transparente e possui formato semiesférico, localizada na parte frontal do olho. A córnea refrata a luz e é responsável por cerca de dois terços da potência óptica total do olho. A alteração da curvatura da córnea altera a forma como os raios de luz entram no olho. Como resultado, os raios de luz podem ser adequadamente focados na retina para uma visão mais clara. Para as pessoas com miopia, o laser é usado para tornar a córnea mais plana. Para as pessoas com hipermetropia, deixa-se a córnea mais inclinada. Para os pacientes com astigmatismo, o laser é usado para deixar a forma irregular da córnea mais regular.
A camada exterior da córnea – o epitélio – é capaz de substituir-se dentro de alguns dias depois de ser danificado ou retirado. A camada mais profunda da córnea – o estroma, ao contrário, é um tecido permanente com capacidade de regeneração muito limitada. O estroma, se alterado por um laser, permanecerá assim permanentemente.
Nesse procedimento, um “FLAP” fino e circular é feito na superfície da córnea para ter acesso ao tecido da córnea permanente. Isso pode ser feito com um instrumento de corte mecânico chamado de microquerotomia, OU, sem uso de lâmina, por um laser femtosegundo. Um excimer Laser é então empregado para remover parte do tecido corneano, remodelando a córnea. Excimer laser utiliza raios frios de luz ultravioleta para vaporizar quantidade microscópica do tecido, de forma exata para remodelar a córnea com precisão. O Excimer laser é controlado por computador e está programado com base no erro refrativo do paciente. O “FLAP” é então colocado de volta no lugar para que haja a cicatrização.
A cirurgia ocular LASIK é geralmente indolor e pode ser concluída em poucos minutos. Pode se perceber a melhora da visão de um dia para o outro.

PRK, ou Ceratectomia fotorrefrativa, foi o primeiro tipo de cirurgia ocular a laser para correção da visão e é o precursor do procedimento popular LASIK. No PRK, NÃO é feito o “FLAP”. Em vez disso, as células epiteliais sobre a superfície do olho são simplesmente removidas. Um excimer laser é então usado para remodelar a córnea, assim como é feito no LASIK.
Os resultados da correção da visão com a cirurgia PRK são comparáveis aos do LASIK, mas o período de recuperação é mais longo. Isto porque o epitélio é completamente removido no PRK e leva alguns dias para se regenerar. Os pacientes de PRK também têm mais desconforto e a visão borrada nos primeiros dias após a cirurgia. A melhora da visão também leva mais tempo para ser alcançada.
PRK, no entanto, oferece certas vantagens. O PRK não envolve a criação do “FLAP”, que contém tanto tecido epitelial quanto o tecido estromal, que é o mais profundo, com isso, todo o estroma está disponível para o tratamento. Portanto, o alcance do tratamento é maior. Isto é particularmente útil para pacientes com níveis elevados de miopia ou para aqueles cuja córnea é muito fina para LASIK. PRK também é livre de riscos de complicações relacionadas com o “FLAP”.

Embolización Endovascular para Aneurismas Cerebrales, con Animación.

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La embolización endovascular o espiral endovascular es una técnica mínimamente invasiva que se realiza para tratar los aneurismas cerebrales. El objetivo del tratamiento es bloquear el flujo de sangre hacia el aneurisma y por lo tanto reducir el riesgo de ruptura del aneurisma.

En este procedimiento, un catéter guiado por un cable es insertado a través de la arteria femoral en la ingle y es dirigido todo el camino hacia la arteria cerebral afectada. El cable guía es retirado. Un micro-catéter que lleva una espiral de platino suave se introduce dentro del catéter inicial y es conducido hasta la abertura del aneurisma. La espiral se despliega en el saco aneurismático. Una pequeña corriente eléctrica se pasa para separar la espiral del catéter. Puede tomar varias espirales para rellenar el aneurisma. Las espirales inducen la coagulación sanguínea dentro del aneurisma y lo aíslan de la arteria.

En algunos casos, cuando el cuello del aneurisma es muy amplio, una endoprótesis puede ser usada para mantener las espirales dentro del saco aneurismático. La embolización asistida con endoprótesis consiste en colocar permanentemente una endoprótesis en la arteria antes del bobinado. La endoprótesis actúa como un andamio dentro de la arteria para ayudar a mantener las espirales en su lugar.

Bundle Branch Blocks, Understanding ECG, with Animation.

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Bundle branch blocks happen when there is an obstruction in one of the bundle branches. The names “left bundle branch block” and “right bundle branch block” indicate the side that is affected.

In a normal heart, the two ventricles are depolarized simultaneously by the two bundles and contract at the same time. In bundle branch blocks, the UN-affected ventricle depolarizes first. The electrical impulses THEN move through the myocardium to the other side. This results in a DELAYED and SLOWED depolarization of the affected ventricle, hence a broader QRS complex – typically longer than 120 milliseconds; and a loss in ventricular synchrony.

Left and right bundle branch blocks are diagnosed and differentiated by looking at ECG recordings obtained from the CHEST leads, which register signal movements in a horizontal plane. Of these, the most useful are leads V1 and V6 as they are best located to detect impulses moving between the left and right ventricles.

Activation of the ventricles starts with the interventricular septum. In normal conduction, depolarization of the septum is initiated from the left bundle going to the right, TOWARD V1 and AWAY from V6. This results in a small positive deflection in V1 and a negative deflection in V6. The signals then move both directions to the two ventricles, but as the left ventricle is usually much larger, the NET movement is to the left, AWAY from V1, TOWARD V6. This corresponds to a negative wave in V1 and a positive wave in V6.

In RIGHT bundle branch block the initial septal activation is unchanged. The left ventricle depolarizes NORMALLY toward V6, away from V1, producing a positive deflection in V6, negative in V1. The impulses then REVERSE the direction spreading to the right ventricle, hence a subsequent negative wave in V6, positive in V1. Lead V1 gives a characteristic M shape with a terminal R wave, while V6 sees a broader S wave.

In LEFT bundle branch block septal depolarization is REVERSED, from right to left, giving a negative wave in V1. The right ventricle activates first, with the signals moving to the right, generating a small upward deflection. Depolarization then spreads to the larger left ventricle, resulting in a large downward deflection. Lead V6 sees the opposite, producing a wide, characteristic “bunny ears” QRS complex with two R waves. In some cases, right ventricular depolarization may not be visible.

Some people with bundle branch blocks are born with this condition. They usually do not have any symptoms and do not require treatments. Others acquire it as a consequence of another heart disease. These patients need monitoring, and in severe cases, a pacemaker may be required to restore ventricular synchrony.

Urinary Tract Infections, with Animation.

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A urinary tract infection, or UTI, is an infection in any part of the urinary system — the kidneys, ureters, bladder and urethra.

Symtomps:

An infection of the urethra, or urethritis, may cause burning sensation when urinating and cloudy discharge. A bladder infection, or cystitis, may result in pelvic pain, frequent, painful urination, and blood in urine. A kidney infection, or acute pyelonephritis, may cause back pain (possibly only on one side), high fever, chills and nausea.

Causes and Risk Factors:

UTIs typically occur when bacteria enter the urinary tract through the urethra and multiply in the bladder. Most commonly, these bacteria come from the digestive tract through fecal matter. UTIs are more common in women because of their anatomy. Specifically, the short distance from the anus to the opening of the urethra and bladder makes it easier for the bacteria from the digestive tract to reach the urinary system. This is why the most common UTIs occur mainly in women and affect the bladder and urethra.
Other bacteria may be brought over with sexual contact. Women who use certain types of birth control such as diaphragms or spermicidal agents are more at risk. Hormonal deficiency during menopause also makes women more vulnerable to infection.

Treatment and Complications:

Infection limited to the bladder can be easily treated with antibiotics. However, if left untreated, a lower urinary tract infection may spread up to the kidneys where it becomes more dangerous. A kidney infection may result in permanent kidney damage. In rare cases, an infection may also spread to the bloodstream and can be life threatening.

Prevention:

Urinary tract infections can be prevented following these steps:
– Drink plenty of fluids – to flush out bacteria more frequently.
– Wipe from front to back after a bowel movement – this helps prevent bacteria in stools from spreading to the urethra.
– Empty the bladder soon after intercourse to flush bacteria.
– Avoid feminine products such as douches and powders, which could irritate the urethra.
– Avoid diaphragms and spermicides as birth control methods

Muscle Contraction – The Cross Bridge Cycle, with Animation.

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Muscle contraction is at the basis of all skeletal movements. Skeletal muscles are composed of muscles fibers which in turn are made of repetitive functional units called sarcomeres. Each sarcomere contains many parallel, overlapping thin (actin) and thick (myosin) filaments. The muscle contracts when these filaments slide past each other, resulting in a shortening of the sarcomere and thus the muscle. This is known as the sliding filament theory. Cross-bridge cycling forms the molecular basis for this sliding movement.
– Muscle contraction is initiated when muscle fibers are stimulated by a nerve impulse and calcium ions are released.
– To trigger muscular contraction, the troponin units on the actin myofilaments are bound by calcium ions. The binding displaces tropomyosin along the myofilaments, which in turn (and) exposes the myosin binding sites.
– At this stage, the head of each myosin unit is bound to an ADP and a phosphate molecule remaining from the previous muscular contraction.
– Now, the myosin heads release these phosphates and bind to the actin myofilaments via the newly exposed myosin binding sites.
– In this way, the actin and myosin myofilaments are cross-linked.
– The two myofilaments glide past one another, propelled by a head-first movement of the myosin units powered by the chemical energy stored in their heads. As the units move, they release the ADP molecules bound to their heads.
– The gliding motion is halted when ATP molecules bind to the myosin heads, thus severing the bonds between myosin and actin.
– The ATP molecules bound to myosin are now decomposed into ADP and phosphate, with the energy released by this reaction stored in the myosin heads, ready to be used in the next cycle of movement.
– Having been unbound from actin, the myosin heads resume their starting positions along the actin myofilament, and can now begin a new sequence of actin binding.
– Thus, the presence of further calcium ions will trigger a new contraction cycle

Zika Virus Outbreak Review and May-2016 Updates (with Video)

Feb 2016, WHO has declared the Zika virus a global public health emergency. What you should know?
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Zika virus is a member of the Flavivirus genus which also includes viruses that cause dengue fever, yellow fever and Japanese encephalitis. The name Zika came from the Zika forest of Uganda, where the virus was first isolated in 1947.

Transmission

The virus is mainly spread through daytime active Aedes mosquitoes, but can also be transmitted by blood transfusion, via sexual contact, and from an infected mother to the fetus during pregnancy.

Zika Fever – Symptoms

Infection with Zika virus is known as Zika fever. Most infected people, however, do not develop any symptoms. In those who do, the symptoms are usually mild and may include: fever, rash, conjunctivitis, joint pain and headache. The disease commonly clears up on its own after a week and does not require any treatment other than rest.

So why the big fuss?

Originally considered a mild disease, Zika fever has been getting a lot of attention lately due to reported connection between the virus and incidents of microcephaly in infants born from infected mothers.

Microcephaly is a serious birth defect where the brain of the newborn is underdeveloped and so smaller than usual. Depending on the extent of the defect, microcephaly may result in a number of neurological disorders, including: seizures, developmental delay, intellectual disabilities, vision and hearing loss. The problems are usually life-long and may also be life-threatening.

Several studies newly published in May 2016 showed that Zika virus in infected pregnant mice can cross the placenta to the fetuses, where it destroys neural progenitor cells. Because neural progenitors cells are fast-replicating and give rise to a large number of brain cells, even a small loss of these cells would result in missing parts of the brain.

The number of infants born with microcephaly has surged 20 folds in the affected areas of the Brazil outbreak, which started in May 2015. While the link between Zika and microcephaly has not been fully proven, the evidence has become overwhelming.

Infection in adults has also been linked to Guillain–Barré Syndrome, a rare condition characterized by a rapid onset of muscle weakness.

Where is ZIKA now?

Since the start of its outbreak in Brazil, Zika has spread rapidly to other surrounding countries. The World Health Organization warned that the virus is likely to spread to nearly all countries of the Americas, except perhaps Canada and continental Chile, where it is too cold for Aedes mosquitoes to survive. Large outbreaks may also be expected in Asia.

More than a hundred of pregnant women in the US has been tested positive for Zika (May 2016)

The Asian strain that causes Brazil outbreak is now found in Africa

Prevention

There is currently no vaccine for Zika; the best way to prevent the disease is to avoid mosquitoes. Pregnant women are advised not to travel to affected areas and women living in affected countries to delay getting pregnant.

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