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 D
Explanation
Paracrine secretions are chemical signals that affect only nearby cells.
They are released by the sending cell and diffuse through the extracellular space to the target cell, which has a specific receptor for the signal.
Paracrine signaling is a form of local signaling that occurs in multicellular organisms.
Choice A is wrong because autocrine secretions are chemical signals that act on the same cell that produced them.
Autocrine signaling is also a form of local signaling, but it involves cell signaling itself.
Choice B is wrong because endocrine secretions are chemical signals that are secreted into the blood and act at long distances.
Endocrine signaling is a form of long-range signaling that involves ductless glands that secrete hormones.
Choice C is wrong because exocrine secretions are non-hormonal substances that are secreted into ducts to the external environment.
Exocrine signaling is not a form of cell-cell communication, but rather a way of releasing substances such as sweat, saliva, or digestive enzymes.
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.
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