In an ECG pattern, the P wave is caused by:
Repolarization of atrial muscle fibers.
Depolarization of atrial muscle fibers.
Depolarization of ventricular muscle fibers.
Repolarization of ventricular muscle fibers.
The Correct Answer is B
This means that the electrical activity that causes the atria to contract starts from the sinoatrial node and spreads across the atria.
The P wave on the ECG reflects this atrial depolarization.
Choice A is wrong because repolarization of atrial muscle fibers is not visible on the ECG, as it occurs during the QRS complex when the ventricular depolarization masks it.
Choice C is wrong because the depolarization of ventricular muscle fibers is represented by the QRS complex on the ECG, not the P wave.
Choice D is wrong because the repolarization of ventricular muscle fibers is represented by the T wave on the ECG, not the P wave.
Normal ranges for the P wave are:
Duration: less than 0.12 seconds (less than 3 small squares)
Amplitude: less than 2.5 mm (0.25 mV) in the limb leads, less than 1.5 mm (0.15 mV) in the precordial leads
Axis: between 0° and +75°12
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is B
Explanation
This is because erythroblastosis fetalis, also known as hemolytic disease of the newborn, is caused by Rh incompatibility between the mother and the fetus.
Rh incompatibility occurs when a Rh-negative mother is impregnated by a Rh-positive father, resulting in a Rh-positive fetus.
The mother’s immune system can detect the Rh factor on the fetus’s red blood cells as foreign and produce antibodies against them.
These antibodies can cross the placenta and destroy the fetus’s red blood cells, causing anemia, jaundice, edema, and other complications.
Choice A is wrong because a second Rh-negative fetus developing in an Rh-negative woman will not cause erythroblastosis fetalis.
The mother and the fetus have the same Rh factor, so there is no immune reaction.
Choice C is wrong because a first Rh-positive fetus developing in an Rh-negative woman will not cause erythroblastosis fetalis.
The mother’s immune system will not produce antibodies against the Rh factor until after the first exposure to it, which usually happens during delivery.
Therefore, the first pregnancy is usually unaffected.
Choice D is wrong because a first Rh-negative fetus developing in an Rh-negative woman will not cause erythroblastosis fetalis.
The mother and the fetus have the same Rh factor, so there is no immune reaction.
The normal range of red blood cell count for newborns is 4.1 to 6.1 million cells per microliter of blood.
The normal range of bilirubin level for newborns is 0.3 to 1.9 milligrams per deciliter of blood.
Correct Answer is B
Explanation
The correct answer is choice B. True.
As a result of the allergen-antibody reaction, mast cells release histamine.
This is because when mast cells are exposed to an allergen that binds to IgE antibodies attached to their FcɛRI receptors, they release histamine and other inflammatory mediators.
Histamine causes vasodilation, increased capillary permeability, mucus secretion, and smooth muscle contraction, which result in allergic symptoms such as itching, swelling, sneezing, and wheezing.
Choice A is wrong because it is the opposite of the correct answer.
Mast cells do release histamine in response to allergen-antibody reactions. Some additional sentences are:
Normal ranges of histamine levels vary depending on the tissue and the method of measurement, but they are usually low in healthy individuals and elevated in allergic conditions.
Histamine can be degraded by enzymes such as diamine oxidase and histamine N-methyltransferase, or inhibited by drugs such as antihistamines.
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