In females, the onset of puberty is first marked by

Correct Answer: B

Rationale: Puberty in females begins with thelarche, the development of breast buds, typically at ages 10-11. Triggered by rising estrogen from ovarian activation via gonadotropins (FSH, LH) from the pituitary, it marks the start of secondary sexual characteristics. Breast budding often appears unilaterally first, reflecting hormonal sensitivity in mammary tissue. Menarche, the first menstrual period, follows 2-3 years later, around 12-13, after significant growth and hormonal maturation, peaking before menstruation starts. Pubarche, pubic hair growth, and adrenarche, adrenal androgen increase, occur later, driven by adrenal and ovarian androgens, not initial puberty onset. Thelarche's precedence reflects the hypothalamic-pituitary-ovarian axis activating earlier than adrenal changes. Puberty spans years, completing by 15-17, with thelarche as the visible starting point, followed by growth spurts and reproductive capability. Pediatric endocrinology data confirm this sequence, distinguishing thelarche from later milestones like menarche, which depends on established ovarian cycles, highlighting its role as puberty's initial physical sign.

Correct Answer: D

Rationale: Hair's primary functions include all listed: UV protection (scalp shielding), sensory reception (via nerve endings at follicles), and insulation (trapping air for warmth), varying by location (e.g., scalp vs. eyebrows). No single role overshadows others universally scalp hair insulates, eyelashes protect, all sense. This multifunctionality, per hair's evolutionary roles, makes 'd' the correct answer.

Correct Answer: A

Rationale: Compact bone, dense and cortical, provides strength and rigidity, forming bones' outer layer (e.g., femur shaft). Spongy bone and cancellous are synonymous, porous for marrow, less strong. Cartilage is flexible, not bone. Compact bone's density, per skeletal structure, makes 'a' correct.

Correct Answer: C

Rationale: The lumbar curve, a secondary curvature, forms when a child walks, shifting weight to an upright posture, enhancing balance. Cervical forms earlier (head lifting). Thoracic and sacral are primary, fetal curves. Lumbar's development, per spinal ontogeny, makes 'c' correct.

Correct Answer: B

Rationale: A herniated disc is a bulging or ruptured intervertebral disc, pressing on spinal nerves, causing pain (e.g., sciatica). It's not a fracture , osteoporosis (c, bone loss), or joint inflammation (d, arthritis). Disc protrusion's effect, per pathology, makes 'b' correct.