What is the effect of acetylcholine secretion?
It decreases the heart rate.
It increases the heart rate.
It increases the rate of spontaneous depolarization
It shortens the time for repolarization.
The Correct Answer is A
A. It decreases the heart rate.: Acetylcholine is a neurotransmitter that binds to receptors in the heart, leading to a decrease in heart rate by activating the parasympathetic nervous system.
B. It increases the heart rate.: Acetylcholine does not increase heart rate; that function is primarily associated with norepinephrine, which is part of the sympathetic nervous system.
C. It increases the rate of spontaneous depolarization: Acetylcholine actually decreases the rate of spontaneous depolarization in pacemaker cells of the heart, leading to a slower heart rate.
D. It shortens the time for repolarization.: Acetylcholine does not shorten repolarization; it increases the duration of repolarization due to the hyperpolarizing effects on the heart cells.
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Related Questions
Correct Answer is B
Explanation
A. To increase the effectiveness of drugs and hormones in the blood: Tubular secretion helps in removing drugs and hormones, not increasing their effectiveness.
B. To remove excess quantities of substances from the blood: Tubular secretion is responsible for removing excess ions, waste products, and drugs from the blood and excreting them into the urine.
C. To filter out pathogens from the blood: Filtration primarily occurs at the glomerulus, not tubular secretion, and it does not focus on pathogens.
D. To remove 99% of the water from the blood: This is not the purpose of tubular secretion; water reabsorption primarily happens in the nephron’s other parts.
Correct Answer is A
Explanation
A. Enters the superior or inferior vena cava; exits the pulmonary arteries: Deoxygenated blood from the body enters the heart through the superior or inferior vena cava and flows into the right atrium. It then passes into the right ventricle and exits through the pulmonary arteries to the lungs for oxygenation.
B. Enters the aorta; exits the pulmonary veins: The aorta and pulmonary veins both handle oxygenated blood, not deoxygenated blood, making this incorrect.
C. Enters the superior or inferior vena cava; exits the coronary arteries: The coronary arteries supply the heart muscle itself with oxygenated blood, so this is incorrect for deoxygenated blood.
D. Enters the pulmonary veins; exits the aorta: Both the pulmonary veins and the aorta are part of the oxygenated blood circuit, making this incorrect for deoxygenated blood flow.
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