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.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is B
Explanation
Choice A: Convert Amino Acid to Glucose
The process of converting amino acids to glucose is known as gluconeogenesis. This metabolic pathway allows the body to produce glucose from non-carbohydrate sources, such as amino acids, during periods of fasting or intense exercise. While this process is crucial for maintaining blood glucose levels, it is not the definition of glycogenolysis.
Choice B: Break Down Glycogen to Glucose
Glycogenolysis is the biochemical process of breaking down glycogen into glucose. Glycogen, a stored form of glucose in the liver and muscle cells, is broken down to provide immediate energy and to maintain blood glucose levels during fasting or intense physical activity. This process is regulated by hormones such as glucagon and epinephrine, which activate enzymes that catalyze the breakdown of glycogen into glucose-1-phosphate and then into glucose-6-phosphate3. The glucose-6-phosphate can then be used in glycolysis to produce energy or released into the bloodstream to maintain blood glucose levels.
Choice C: Convert Glucose to Amino Acid
The conversion of glucose to amino acids is not a typical metabolic pathway. Instead, glucose is primarily used for energy production through glycolysis and the citric acid cycle. Amino acids are synthesized from intermediates of these pathways and other metabolic processes, but glucose itself is not directly converted into amino acids.
Choice D: Convert Fat to Amino Acid
The conversion of fats to amino acids is not a standard metabolic process. Fats are broken down into fatty acids and glycerol through lipolysis. Fatty acids can be further oxidized to produce energy, while glycerol can enter gluconeogenesis to produce glucose. Amino acids, on the other hand, are derived from dietary proteins or synthesized from other amino acids and metabolic intermediates.
Correct Answer is D
Explanation
Choice A: Minimal Effect on Vessels
A reduction in blood pH, which indicates acidosis, does not have a minimal effect on blood vessels. Acidosis can significantly impact vascular tone and function. Therefore, this choice is incorrect as it underestimates the physiological changes that occur in response to a decrease in pH.
Choice B: No Effect on Vessels
Similarly, stating that a reduction in blood pH has no effect on vessels is inaccurate. Blood pH is tightly regulated, and deviations from the normal range (7.35-7.45) can lead to significant physiological responses. Acidosis can alter vascular tone, making this choice incorrect.
Choice C: Vasodilation
While vasodilation can occur in response to certain conditions, a reduction in blood pH typically leads to vasoconstriction rather than vasodilation. Vasodilation is more commonly associated with an increase in blood pH (alkalosis) or other factors such as increased levels of nitric oxide or prostaglandins.
Choice D: Vasoconstriction
When the pH of blood reduces, indicating acidosis, it often leads to vasoconstriction. This response is mediated by chemoreceptors that detect changes in pH and stimulate the vasomotor center to increase vascular tone. Vasoconstriction helps to maintain blood pressure and ensure adequate perfusion of vital organs during acidosis. Therefore, this is the correct answer.
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