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 C
Explanation
The thyroid gland secretes triiodothyronine (T3), which is one of the two main thyroid hormones that affect almost every physiological process in the body.
T3 is the more metabolically active hormone produced from thyroxine (T4), which is the other thyroid hormone.
Choice A is wrong because the adrenal gland secretes hormones such as cortisol, adrenaline, and aldosterone, which are involved in stress response, blood pressure regulation, and metabolism.
Choice B is wrong because the pancreas secretes hormones such as insulin, glucagon, and somatostatin, which are involved in blood glucose regulation and digestion.
Choice D is wrong because the parathyroid gland secretes parathyroid hormone (PTH), which is involved in calcium and phosphate homeostasis.
Normal ranges for T3 levels vary depending on the laboratory and the method of testing, but they are usually between 100 and 200 nanograms per deciliter (ng/dL) for total T3 and between 2.3 and 4.2 picograms per milliliter (pg/mL) for free T.
Correct Answer is D
Explanation
Circadian rhythm is the term for the biological clock that regulates the sleep-wake cycle and other physiological processes in the body.
Melatonin is a hormone that is produced by the pineal gland in the brain in response to darkness.
It helps with the timing of the circadian rhythm and promotes sleep.
Choice A is wrong because metabolic rate is not affected by light exposure, and thyroxine is a hormone that regulates metabolism, not sleep.
Choice B is wrong because the limbic system is a part of the brain that is involved in emotions, memory, and motivation, not sleep.
Thymosin is a hormone that stimulates the development of T cells, which are part of the immune system.
Choice C is wrong because the circulatory system is the system of blood vessels and organs that transport blood throughout the body, not a part of the brain that controls sleep.
Dopamine is a neurotransmitter that is involved in reward, motivation, and movement, not sleep.
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