Which of the following illustrates a positive feedback mechanism?
Body temperature control.
Control of blood sugar.
Uterine contractions during childbirth.
Maintaining blood pressure.
The Correct Answer is C
Uterine contractions during childbirth illustrate a positive feedback mechanism.
A positive feedback mechanism is a process in which the end products of an action cause more of that action to occur in a feedback loop.
This amplifies the original action.
For example, when a woman goes into labor, the pressure of the baby’s head on the cervix stimulates nerve impulses that travel to the brain and trigger the release of oxytocin, a hormone that causes the uterus to contract.
The contractions increase the pressure on the cervix, which stimulates more nerve impulses, more oxytocin, and more contractions.
This cycle continues until the baby is delivered.
Choice A is wrong because body temperature control is an example of a negative feedback mechanism, which is when the end results of an action inhibit that action from continuing to occur.
For example, when the body temperature rises above normal, the skin sweats, and blood vessels dilate to release heat.
This lowers the body temperature back to normal and stops sweating and dilation.
Choice B is wrong because control of blood sugar is also an example of a negative feedback mechanism.
For example, when the blood sugar level rises after a meal, the pancreas secretes insulin, a hormone that helps cells take up glucose from the blood.
This lowers the blood sugar level back to normal and stops the insulin secretion.
Choice D is wrong because maintaining blood pressure is another example of a negative feedback mechanism.
For example, when the blood pressure drops due to blood loss or dehydration, the heart beats faster and stronger, and the blood vessels constrict to increase the blood pressure.
This restores the blood pressure back to normal and stops the heart rate and vessel constriction.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is A
Explanation
The lymph nodes of the axillary region receive lymph mainly from the upper limb and mammary gland.
This is because the axillary lymph nodes are located in the armpit area and drain the lymph vessels from the lateral quadrants of the breast and the arm.
Choice B is wrong because the abdominal viscera are drained by the celiac, superior mesenteric, and inferior mesenteric lymph nodes.
Choice C is wrong because the scalp and face are drained by the cervical lymph nodes.
Choice D is wrong because the thoracic viscera are drained by the bronchopulmonary, tracheobronchial, parasternal, and posterior mediastinal lymph nodes.
Correct Answer is C
Explanation
The sinoatrial (SA) node is the natural pacemaker of the heart.
It generates electrical impulses that cause the heart’s chambers to contract, setting the heart rate.
The SA node typically generates 60–100 heartbeats per minute when a person is at rest.
Choice A is wrong because Purkinje fibers are part of the electrical conduction system of the heart that carries impulses to the ventricles.
They are not the primary source of impulses.
Choice B is wrong because the AV bundle (also called bundle of His) is another part of the electrical conduction system of the heart that connects the atria and the ventricles.
It is not the natural pacemaker of the heart.
Choice D is wrong because an atrioventricular node is a relay station between the atria and the ventricles that delays the electrical impulses from the SA node.
It can act as a backup pacemaker if the SA node fails, but it is not the normal pacemaker of the heart.
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