Which phase of pharmacokinetics is affected by the first pass effect?
Excretion
Metabolism
Distribution
Absorption
The Correct Answer is D
Choice A: Excretion
Excretion is the process by which drugs and their metabolites are eliminated from the body, primarily through the kidneys (urine), but also via bile, sweat, saliva, and other routes. While excretion is a crucial phase of pharmacokinetics, it is not directly impacted by the first pass effect. The first pass effect primarily involves the metabolism of a drug before it reaches systemic circulation, which occurs prior to the excretion phase.
Choice B: Metabolism
The first pass effect, also known as first-pass metabolism or presystemic metabolism, significantly impacts the metabolism phase of pharmacokinetics. This phenomenon occurs when a drug is metabolized at a specific location in the body, such as the liver or gut wall, before it reaches systemic circulation. As a result, the concentration of the active drug is reduced, affecting its bioavailability. The liver is the primary site for this metabolic process, where enzymes break down the drug, potentially leading to a significant reduction in its therapeutic effect.
Choice C: Distribution
Distribution refers to the process by which a drug is transported from the bloodstream to various tissues and organs in the body. This phase is influenced by factors such as blood flow, tissue permeability, and binding to plasma proteins. However, the first pass effect does not directly alter the distribution phase. Instead, it affects the amount of drug that enters systemic circulation, which in turn can influence the extent of distribution.
Choice D: Absorption
Absorption is the process by which a drug enters the bloodstream from its site of administration. This phase is crucial for determining the onset of a drug’s action. While the first pass effect occurs after absorption, it does not directly change the absorption phase itself. Instead, it affects the drug’s concentration after it has been absorbed and before it reaches systemic circulation.
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Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is A
Explanation
Choice A Reason:
Norepinephrine is a key neurotransmitter released by the sympathetic nervous system during the “fight-or-flight” response. It plays a crucial role in preparing the body to respond to stress by increasing heart rate, blood pressure, and blood flow to muscles, as well as dilating the airways. These physiological changes are essential for coping with acute stress.
Choice B Reason:
Cortisol is a hormone released by the adrenal glands in response to stress, but it is primarily associated with the hypothalamic-pituitary-adrenal (HPA) axis rather than the sympathetic nervous system. While cortisol contributes to the body’s overall stress response by increasing blood sugar levels and suppressing the immune system, it is not the primary mediator of the acute “fight-or-flight” response.
Choice C Reason:
ACTH (adrenocorticotropic hormone) is a hormone produced by the pituitary gland that stimulates the adrenal glands to release cortisol. It is part of the HPA axis and plays a role in the body’s long-term stress response, but it is not directly involved in the immediate activation of the sympathetic nervous system.
Choice D Reason:
Glucagon is a hormone produced by the pancreas that raises blood glucose levels by promoting the breakdown of glycogen to glucose in the liver. While it can be involved in the body’s response to stress by ensuring an adequate supply of glucose, it is not a primary mediator of the acute stress response mediated by the sympathetic nervous system.
Correct Answer is B
Explanation
Choice A Reason:
Biotransformation, also known as drug metabolism, is the process by which the body chemically alters a drug. This typically occurs in the liver and results in the conversion of the drug into metabolites, which can be more easily excreted from the body. Biotransformation is crucial for drug elimination but is not the process by which a drug is transported to receptor sites.
Choice B Reason:
Distribution is the correct answer. This process involves the dispersion of a drug throughout the body via the bloodstream after it has been absorbed. The drug is transported to various tissues and organs, including the target receptor sites where it exerts its therapeutic effects. Distribution is influenced by factors such as blood flow, tissue permeability, and the binding of the drug to plasma proteins.
Choice C Reason:
Osmosis is the movement of water molecules across a semipermeable membrane from an area of lower solute concentration to an area of higher solute concentration. While osmosis is a fundamental biological process, it is not involved in the transport of drugs to receptor sites.
Choice D Reason:
Absorption is the process by which a drug enters the bloodstream from its site of administration. This can occur through various routes, such as oral, intravenous, or transdermal. Absorption is the initial step in drug delivery, but it is not the process by which the drug is transported to receptor sites.
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