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
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Related Questions
Correct Answer is C
Explanation
Basophils usually account for the smallest percentage of leukocytes in a blood sample. Basophils are a type of white blood cell that is involved in allergic reactions and inflammation.
Choice A is wrong because eosinophils are not the least common type of leukocyte.
Eosinophils are another type of white blood cell that is involved in allergic responses and parasitic infections.
They typically make up about 1-6% of the total leukocyte count.
Choice B is wrong because monocytes are not the least common type of leukocyte.
Monocytes are a type of white blood cell that can differentiate into macrophages and dendritic cells, which are important for phagocytosis and antigen presentation.
They typically make up about 2-10% of the total leukocyte count.
Choice D is wrong because neutrophils are not the least common type of leukocyte.
Neutrophils are a type of white blood cell that are the first responders to bacterial infections and tissue damage.
They typically make up about 55-70% of the total leukocyte count.
Correct Answer is B
Explanation
Cardiac output is calculated by multiplying the stroke volume by the heart rate, not by the systolic blood pressure.
Stroke volume is the amount of blood circulated by the heart with each beat. Heart rate is the number of beats per minute.
Systolic blood pressure is the pressure in the arteries when the heart contracts. Choice A is wrong because it confuses systolic blood pressure with heart rate.
Systolic blood pressure is not directly related to cardiac output, although it can be affected by it.
1: Cardiac Output- Definition, Factors Affecting, Cardiac Index - BYJU’S 2: Cardiac Output (Fick’s Formula) - MDCalc 3: Calculating how much blood is pumped by the heart - Cellular respiration and transport - Edexcel - GCSE Biology (Single Science) Revision - Edexcel - BBC Bitesize 4: Cardiac output - Structure and function of the heart - Higher Human Biology Revision - BBC Bitesize : Blood Pressure: What Is Normal? How To Measure Blood Pressure (healthline.com)
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