The most widely used inhalation system is

Correct Answer: A

Rationale: Inhalation anesthesia systems vary by gas flow and rebreathing. 'Semiclosed system,' is correct as the most widely used, balancing efficiency and safety with partial rebreathing (e.g., circle system), per Miller's Anesthesia. 'Closed system,' fully recycles gases, less common due to complexity. 'Semiopen system,' is a misnomer; it's not standard. 'Open system,' (e.g., mask without rebreathing) is rare today. Semiclosed systems' prevalence in modern operating rooms, optimizing gas use and monitoring, makes A the precise answer.

Correct Answer: A

Rationale: Thoracic vertebrae (T1-T12) lack transverse foramina, present in cervical vertebrae for arteries. 'Transverse foramina,' is correct, per anatomy texts (e.g., Moore's Clinically Oriented Anatomy). 'Transverse processes,' articulate ribs. 'Pedicle,' and 'Spinous processes,' are standard features. The absence of transverse foramina in thoracic vertebrae makes A the accurate answer.

Correct Answer: B

Rationale: The SA node's pacemaker potential results from calcium influx via T-type channels, depolarizing cells. 'Calcium,' is correct, per cardiac physiology (e.g., Opie). 'Sodium,' contributes later in action potentials. 'Potassium,' hyperpolarizes. 'Magnesium,' is minor. Calcium's role in phase 4 depolarization makes B the precise answer.

Correct Answer: C

Rationale: Parathyroid hormone (PTH) increases plasma calcium by mobilizing bone calcium and renal reabsorption when levels drop. 'Parathyroid hormone,' is correct, per endocrinology texts like Williams, countering hypocalcemia. 'Calcitonin,' lowers calcium, opposing PTH. 'Aldosterone,' regulates sodium, not calcium directly. 'Adrenaline,' affects metabolism, not calcium. PTH's specific response to low calcium, restoring balance, makes C the precise answer, rooted in calcium homeostasis.

Correct Answer: B

Rationale: Oogenesis is the formation of ova (eggs) in the ovaries, from oogonia to mature oocytes. 'Oogenesis,' is correct, per reproductive physiology (e.g., Tortora). 'Spermatogenesis,' is sperm formation. 'Ovulation,' is egg release. 'Fertilization,' is conception. Oogenesis' full developmental process makes B the accurate answer, specific to female gametes.