Direct effects on the heart are determined largely by:

Correct Answer: C

Rationale: The correct answer is C: Beta1 receptor. Stimulation of Beta1 receptors in the heart leads to increased heart rate, contractility, and conduction velocity. This is crucial for the direct effects on the heart. Alpha1 receptors (choice A) primarily cause vasoconstriction, not direct effects on the heart. Alpha2 receptors (choice B) inhibit norepinephrine release and have minimal effects on the heart. Beta2 receptors (choice D) are mainly found in the lungs and blood vessels, leading to bronchodilation and vasodilation, rather than direct effects on the heart.

Correct Answer: C

Rationale: The correct answer is C because hypnotic drugs are primarily used to induce drowsiness and promote sleep. They help with insomnia and encourage the onset and maintenance of sleep. This is achieved by affecting the brain's neurotransmitters and promoting relaxation. Options A and D are incorrect as hypnotic drugs are not intended to specifically reduce anxiety, exert a calming effect, or prevent mood swings in patients with bipolar affective disorders. Option B is incorrect as hypnotic drugs do not induce an absence of sensation; that would be more characteristic of anesthetics.

Correct Answer: A

Rationale: Sure! Valproate is the correct answer as it is used as an anti-absence drug due to its effectiveness in treating absence seizures. Valproate works by enhancing the activity of a neurotransmitter called gamma-aminobutyric acid (GABA), which helps to calm overactive brain activity that causes absence seizures. Phenobarbital, Carbamazepine, and Phenytoin are not typically used to treat absence seizures, as they are more commonly used to treat other types of seizures such as tonic-clonic seizures or focal seizures.

Correct Answer: B

Rationale: Levodopa is the precursor of dopamine as it is converted into dopamine in the brain. Bromocriptine is a dopamine agonist, not a precursor. Selegiline is a MAO-B inhibitor that helps preserve dopamine, not a precursor. Amantadine is an antiviral drug with unclear mechanisms regarding dopamine production. Therefore, B is the correct answer.

Correct Answer: C

Rationale: The correct answer is C: Meperidine. Meperidine is commonly used in obstetric labor due to its rapid onset of action and short duration, making it suitable for managing acute pain during labor without affecting the fetus adversely. Fentanyl (A) is also a potent opioid analgesic, but its rapid onset and short duration make it more suitable for surgical procedures. Pentazocine (B) is a partial opioid agonist-antagonist and is not commonly used in obstetric labor due to its limited efficacy in managing severe pain. Buprenorphine (D) is a partial agonist with a long duration of action and is typically used for opioid maintenance therapy rather than acute pain management during labor.