Biological barriers include all except:

Correct Answer: A

Rationale: The correct answer is A: Renal tubules. Biological barriers are structures that prevent the entry of harmful substances into the body. Renal tubules are not considered a biological barrier as they are involved in the filtration and reabsorption of substances within the body, rather than acting as a physical barrier. Cell membranes, capillary walls, and the placenta are all examples of biological barriers as they selectively control the passage of substances into and out of cells, tissues, and organs to maintain homeostasis. Therefore, the renal tubules do not fit the criteria of a biological barrier, making option A the correct answer.

Correct Answer: C

Rationale: The correct answer is C because cocaine actually causes myocardial stimulation and vasoconstriction, not depression and vasodilatation. Cocaine is a local anesthetic and vasoconstrictor, commonly used in nose and throat procedures (Choice A). Its abuse potential limits its medical use (Choice B). Cocaine causes sympathetically mediated effects such as tachycardia and vasoconstriction (Choice D). Therefore, the incorrect statement is C because cocaine does not cause myocardial depression and peripheral vasodilatation.

Correct Answer: A

Rationale: The correct answer is A: Eye. The parasympathetic nervous system controls functions like pupil constriction in the eye. This effect is mediated by the neurotransmitter acetylcholine. The eye has a unique structure called the iris sphincter muscle, which responds to parasympathetic stimulation by constricting the pupil. Unlike other organs, the effect on the eye is not subject to rapid decline, as the iris sphincter muscle has a high sensitivity to acetylcholine. Therefore, the parasympathetic function in the eye does not decline rapidly compared to other organs. Summary of other choices: B: Heart - Parasympathetic control of heart rate can decline rapidly due to factors like decreased acetylcholine release. C: Smooth muscle organs - Parasympathetic control of smooth muscle organs can also decline rapidly due to factors like receptor desensitization. D: Glands - Parasympathetic control of glands can

Correct Answer: C

Rationale: Rationale: 1. Nondepolarizing blockers compete with depolarizing agents at the neuromuscular junction, reducing their effects. 2. Aminoglycosides can potentiate neuromuscular blockade. 3. Antiarrhythmic drugs can enhance neuromuscular blockade. 4. Local anesthetics can increase neuromuscular blockade. 5. Therefore, only nondepolarizing blockers do not increase the effects of depolarizing agents.

Correct Answer: B

Rationale: The correct answer is B: Dobutamine. In cardiogenic shock, dobutamine is preferred due to its positive inotropic effects, which increase contractility and cardiac output. Epinephrine (A) has potent vasoconstrictive effects that may worsen coronary perfusion. Isoproterenol (C) can lead to tachycardia and worsen myocardial oxygen demand. Methoxamine (D) is a vasoconstrictor and may further decrease cardiac output in cardiogenic shock. In summary, dobutamine is preferred for cardiogenic shock due to its positive inotropic effects without significant vasoconstriction or tachycardia.