As a result of the allergen-antibody reaction, mast cells release histamine:
False
True
The Correct Answer is B
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.
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.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is B
Explanation
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
Correct Answer is A
Explanation
This is the correct sequence of parts through which blood moves from the vena cava to the lungs.
Choice B is wrong because it reverses the order of the right atrium and right ventricle. Blood flows from the right atrium to the right ventricle, not the other way around.
Choice C is wrong because it switches the positions of the tricuspid valve and the pulmonary valve.
Blood flows from the right atrium through the tricuspid valve to the right ventricle, and then through the pulmonary valve to the pulmonary artery.
Choice D is wrong because it also switches the positions of the tricuspid valve and the pulmonary valve, and reverses the order of the right atrium and right ventricle.
Blood flows from the right atrium through the tricuspid valve to the right ventricle, and then through the pulmonary valve to the pulmonary artery.
The normal range of blood pressure in the vena cava is about 0 to 5 mmHg, while in the pulmonary artery, it is about 15 to 25 mmHg.
The normal range of oxygen saturation in the vena cava is about 60% to 80%, while in the pulmonary vein, it is about 95% to 100%.
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