Which of the following drugs selectively stimulates $ß2$ adrenoceptors:

Correct Answer: D

Rationale: In this question, the correct answer is D) Salbutamol. Salbutamol is a selective $ß2$ adrenoceptor agonist. This means that it specifically targets and activates $ß2$ adrenoceptors in the body. These receptors are predominantly found in the smooth muscle of the bronchioles in the lungs. By stimulating $ß2$ adrenoceptors, Salbutamol causes bronchodilation, making it a commonly used drug in conditions like asthma and chronic obstructive pulmonary disease (COPD). Now, let's analyze why the other options are incorrect: A) Adrenaline: Adrenaline (epinephrine) is a non-selective adrenergic agonist, meaning it acts on both $ß1$ and $ß2$ adrenoceptors as well as $α$ adrenoceptors. It is not selective for $ß2$ adrenoceptors. B) Noradrenaline: Noradrenaline (norepinephrine) is also a non-selective adrenergic agonist, acting on $ß1$, $ß2$, and $α$ adrenoceptors. It is not selective for $ß2$ adrenoceptors. C) Isoprenaline: Isoprenaline is a non-selective $ß$ adrenoceptor agonist, stimulating both $ß1$ and $ß2$ adrenoceptors. It is not selective for $ß2$ adrenoceptors like Salbutamol. Educationally, understanding the selectivity of drugs targeting specific receptors is crucial in pharmacology. Knowing which receptors a drug acts on helps healthcare professionals make informed decisions when prescribing medications, ensuring the most effective treatment with minimal side effects. This knowledge is particularly important in conditions like asthma, where selecting the right bronchodilator can significantly impact patient outcomes.

Correct Answer: D

Rationale: In this question, the correct answer is D) Hydrolysis by cholinesterase enzyme. Acetylcholine is a neurotransmitter in the peripheral nervous system that is responsible for transmitting nerve impulses. Its action is terminated quickly to prevent continuous stimulation of the postsynaptic receptor. Acetylcholinesterase is the enzyme responsible for rapidly breaking down acetylcholine into choline and acetate at the synaptic cleft, terminating its action. Option A) Rapid hepatic metabolism is incorrect because acetylcholine is primarily broken down at the neuromuscular junction, not in the liver. Option B) Reuptake by nerve endings is incorrect as acetylcholine is not reuptaken intact by nerve endings; it is broken down by cholinesterase. Option C) Binding to plasma proteins is incorrect because acetylcholine does not bind to plasma proteins but acts at the synaptic cleft. Educationally, understanding the mechanism of action and termination of acetylcholine's effects is crucial in pharmacology, especially when studying drugs that target the peripheral nervous system. Knowing how acetylcholine is quickly broken down helps in comprehending the effects of drugs that inhibit cholinesterase, leading to prolonged acetylcholine action, which can be beneficial in certain clinical conditions.

Correct Answer: D

Rationale: Atropine is a medication commonly used to treat certain medical conditions by blocking the action of the parasympathetic nervous system. The correct answer, option D) Diarrhea, is the exception among the side effects of atropine. Atropine works by inhibiting the activity of acetylcholine in the body, leading to certain physiological responses. Dry mouth (option A) is a common side effect due to decreased salivary gland secretions. Tachycardia (option B) occurs because atropine blocks the inhibitory effects of the parasympathetic nervous system on the heart, leading to an increased heart rate. Blurred vision (option C) is another side effect as atropine affects the muscles in the eye, leading to pupil dilation and difficulty focusing. In an educational context, understanding the side effects of medications like atropine is crucial for healthcare professionals to anticipate, recognize, and manage potential adverse reactions in patients. By knowing the expected side effects, healthcare providers can provide better care and improve patient outcomes. This knowledge also underscores the importance of proper medication administration and monitoring to ensure patient safety.

Correct Answer: D

Rationale: Physostigmine is a drug primarily used in the treatment of glaucoma. This is the correct answer (Option D) because physostigmine is a cholinesterase inhibitor that works by increasing the concentration of acetylcholine, thereby improving the communication between nerves and muscles in the eye. This action helps to reduce intraocular pressure in glaucoma patients. Option A is incorrect because physostigmine is a synthetic, tertiary amine compound, not a natural quaternary ammonium compound. Option B is also incorrect because physostigmine does have central nervous system (CNS) actions, including the potential to cross the blood-brain barrier and affect brain function. Option C is incorrect as well because physostigmine is a reversible anti-cholinesterase, not irreversible. This distinction is important in understanding its pharmacological properties and potential side effects. In an educational context, it is crucial for students to understand the specific actions, uses, and pharmacological properties of drugs targeting the peripheral nervous system. Understanding the correct use of physostigmine in glaucoma treatment highlights the importance of knowing drug mechanisms of action and indications to ensure safe and effective patient care.

Correct Answer: D

Rationale: In this question, the correct answer is D) Increase of salivary secretion. Hyoscine, also known as scopolamine, is an anticholinergic medication that acts by blocking the action of acetylcholine in the peripheral and central nervous systems. It is commonly used to treat motion sickness and nausea due to its antiemetic properties. Explanation of why other options are incorrect: A) Sedation: Hyoscine can cause sedation by crossing the blood-brain barrier and acting on central nervous system receptors. B) Antiemetic action: Hyoscine is a potent antiemetic agent commonly used to prevent motion sickness and nausea. C) Stimulation of the respiratory center: Hyoscine actually depresses the respiratory center, leading to respiratory depression in high doses. Educational context: Understanding the pharmacological actions of drugs for the peripheral nervous system is crucial for healthcare professionals to make informed decisions when prescribing medications. Knowing the specific effects of medications like hyoscine helps ensure safe and effective patient care. It is important to differentiate between the various actions of drugs to optimize treatment outcomes and prevent adverse effects.