Common test bank questions and answers (85) from Guyton and Hall Textbook of Medical Physiology / 14th edition
Guyton and Hall Textbook of Medical Physiology 14th Edition Test Bank by John E. Hall, Michael E. Hall
Test Bank For Guyton and Hall Textbook of Medical Physiology 14th Edition By John E. Hall; Michael E. Hall All Chapters 1-86 ||Complete A+ Guide
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Medicina
Fisiología Humana
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Los nervios simpáticos y parasimpáticos controlan el ritmo cardíaco y
la conducción de impulsos por los nervios cardíacos
La estimulación parasimpática (vagal) frena el ritmo y la conducción
cardíacos. La estimulación de los nervios parasimpáticos cardíacos
libera el neurotransmisor acetilcolina desde las terminaciones
nerviosas vagales. La acetilcolina causa los siguientes efectos:
La frecuencia de descarga del nódulo sinusal disminuye.
La excitabilidad de las fibras entre el músculo auricular y el nódulo A V
disminuye.
La frecuencia cardíaca disminuye a la mitad de lo normal con una
estimulación vagal leve o moderada, pero una estimulación intensa
podría detener temporalmente el latido cardíaco, dando lugar a la
ausencia de impulsos que atraviesan los ventrículos. En esas
condiciones, las fibras de Purkinje desarrollan su propio ritmo de 15-40
latidos/min.
Este fenómeno se denomina escape ventricular.
Los mecanismos de los efectos vagales en la frecuencia cardíaca son
los siguientes:
l. La acetilcolina aumenta la permeabilidad del nódulo sinusal y las
fibras de la unión AV al potasio, lo que provoca la hiperpolarización de
esos tejidos y los hace menos excitables.
2. El potencial de membrana de las fibras del nódulo sinusal disminuye
de -55 a -60 mY hasta -65 a -75 mV.
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