Tick the substance which changes the activity of an effector element but doesn’t belong to second messengers:

Correct Answer: C

Rationale: Step-by-step rationale: 1. G-proteins are signaling proteins that transmit signals from cell surface receptors to effector elements. 2. G-proteins do not directly change the activity of effector elements like cAMP and cGMP do. 3. cAMP and cGMP are second messengers that mediate intracellular signaling processes. 4. Calcium ions act as second messengers by regulating various cellular functions. Summary: Choice C (G-protein) is the correct answer as it does not belong to second messengers category and does not directly change the activity of effector elements. Choices A, B, and D are incorrect as they are all second messengers that modulate cellular responses.

Correct Answer: C

Rationale: Physostigmine is the correct answer for treating atropine intoxication due to its ability to cross the blood-brain barrier and inhibit acetylcholinesterase, increasing acetylcholine levels. Neostigmine (A) is primarily used for myasthenia gravis, Carbochol (B) is a non-selective cholinomimetic, and Lobeline (D) is a nicotinic receptor agonist.

Correct Answer: A

Rationale: The correct answer is A: Atracurium. Atracurium is preferred in patients with renal failure because it is metabolized by Hoffman elimination independent of renal or hepatic function. Succinylcholine (B) is not recommended in renal failure due to prolonged paralysis. Pipecuronium (C) and Doxacurium (D) are primarily eliminated by renal excretion, making them unsuitable for patients with renal failure.

Correct Answer: A

Rationale: Norepinephrine is a neurotransmitter that acts on alpha-adrenergic receptors causing vasoconstriction by stimulating smooth muscle contraction in blood vessels. This leads to increased blood pressure. Vasodilatation (B) is incorrect as norepinephrine does not cause blood vessels to dilate. Bronchodilation (C) is incorrect because norepinephrine primarily affects blood vessels, not bronchioles. Decreased potassium concentration in the plasma (D) is incorrect as norepinephrine does not directly impact potassium levels. Therefore, the correct answer is A: Vasoconstriction.

Correct Answer: D

Rationale: The correct answer is D: All of the above. Beta-blocking drugs lower blood pressure by affecting multiple systems. 1. The heart: Beta blockers reduce heart rate and contractility, leading to decreased cardiac output. 2. The blood vessels: Beta blockers cause vasodilation, reducing peripheral resistance. 3. The renin-angiotensin system: Beta blockers can inhibit renin release, decreasing angiotensin II levels and reducing vasoconstriction. Therefore, the effects of beta blockers on the heart, blood vessels, and renin-angiotensin system collectively result in chronically lower blood pressure. Choices A, B, and C are incorrect because beta blockers impact all these systems, not just one.