Following drugs directly activate the respiratory center EXCEPT:

Correct Answer: D

Rationale: The correct answer is D: Cytiton. The respiratory center is primarily stimulated by drugs that act on the central nervous system. Cytiton is not known to directly activate the respiratory center. Bemegride, caffeine, and aethymizole are central nervous system stimulants that can directly activate the respiratory center. Caffeine, for example, is a respiratory stimulant and can increase respiratory rate. Aethymizole is used to treat respiratory depression caused by opioid overdose. Bemegride is a respiratory stimulant used to treat respiratory depression. Therefore, D is the correct answer as it is not a drug known to directly activate the respiratory center.

Correct Answer: A

Rationale: The correct answer is A: Digoxin. Foxglove (Digitalis) is a plant known for containing cardiac glycosides, specifically digoxin. Digoxin is derived from the leaves of the Foxglove plant and is commonly used to treat heart conditions such as heart failure and atrial fibrillation. Strophantin K is a cardiac glycoside derived from the Strophanthus plant. Dobutamine is a synthetic catecholamine used as a cardiac stimulant. Amrinone is a phosphodiesterase inhibitor used for treating heart failure. These choices are incorrect as they are not derivatives of the plant Foxglove.

Correct Answer: C

Rationale: The correct answer is C: Amyl nitrite, inhalant. Amyl nitrite is a short-acting drug used for the treatment of angina pectoris and cyanide poisoning. It works quickly to dilate blood vessels and relieve chest pain. Nitroglycerin ointment and sustained-release tablets have longer durations of action, making them not short-acting. Sustac is not a nitrate or nitrite drug, so it is an incorrect choice. Overall, the rapid onset and short duration of action of amyl nitrite make it the correct choice for a short-acting nitrate/nitrite drug.

Correct Answer: C

Rationale: The correct answer is C: Phenylephrine. Phenylephrine is a synthetic vasoconstrictor that acts by stimulating adrenergic receptors, specifically alpha-adrenergic receptors, leading to vasoconstriction. Noradrenaline (A) and adrenaline (B) are endogenous catecholamines that also have vasoconstrictive effects but are not synthetic. Angiotensinamide (D) is not a synthetic vasoconstrictor and acts through a different mechanism involving the renin-angiotensin system. In summary, Phenylephrine is the correct choice as it is a synthetic vasoconstrictor with adrenomimetic effects, while the other options do not fit this description.

Correct Answer: D

Rationale: Thyroid stimulating hormone (TSH) regulates all the mentioned functions. 1. A: TSH stimulates iodine uptake by thyroid follicular cells for thyroid hormone synthesis. 2. B: TSH promotes the biosynthesis of iodothyroglobulin, a precursor of thyroid hormones. 3. C: TSH triggers the release of thyroid hormones into the bloodstream. Therefore, the correct answer is D as TSH regulates all these processes essential for thyroid hormone production and release. Other choices are incorrect as they do not encompass all the functions regulated by TSH.