What is the linea alba?

Correct Answer: B

Rationale: The linea alba is a long, midline tendon of collagen fibers where rectus abdominis muscles meet, running from xiphoid to pubis, aiding abdominal wall integrity. It's not a muscle , nor does it connect hip to knee (c that's the iliotibial tract). Tendinous inscriptions are transverse bands within rectus abdominis, not the linea alba. Its tendinous, central role in uniting abdominal muscles makes 'b' the correct definition.

Correct Answer: C

Rationale: Lordosis is an abnormal increase in the lumbar curvature, an exaggerated inward arch (swayback), often from posture, obesity, or pregnancy, altering spinal mechanics. Scoliosis is lateral curvature. Kyphosis affects the thoracic spine outward. Extension is a normal movement, not a condition. Lordosis's focus on lumbar hypercurvature, visible in sagittal views, makes 'c' the correct answer in orthopedic terminology.

Correct Answer: A

Rationale: Parathyroid hormone (PTH), secreted by the parathyroid glands when blood calcium drops, regulates calcium and phosphate balance. In the kidneys, PTH enhances calcium reabsorption in the distal tubules, reducing urinary calcium loss and raising blood levels. Concurrently, it inhibits phosphate reabsorption in the proximal tubules, increasing phosphate excretion and lowering blood phosphate. This dual action maintains mineral homeostasis elevated calcium supports bone and muscle function, while reduced phosphate prevents soft tissue calcification. The kidneys filter 180 liters of plasma daily, and PTH fine-tunes reabsorption to counter hypocalcemia, often triggered by dietary or hormonal shifts. Calcium loss with phosphate retention would worsen hypocalcemia, contradicting PTH's purpose. Losing both minerals isn't selective enough for balance, and retaining both would raise phosphate, risking imbalances. PTH also mobilizes calcium from bone and boosts vitamin D activation, but its renal effect is immediate and precise. Endocrine physiology texts confirm this mechanism, highlighting PTH's critical role in mineral metabolism, distinct from other hormones like calcitonin, which lowers calcium.

Correct Answer: B

Rationale: Epithelial tissue is avascular, lacking blood vessels, and relies on diffusion from underlying connective tissue for nutrients, as seen in the epidermis or gut lining. Vascular or highly vascularized applies to connective tissues like dermis, not epithelium. Nerve endings may penetrate epithelium, but innervation isn't a defining trait avascularity is. This lack of vasculature, ensuring a protective or selective barrier, makes 'b' the correct characteristic.

Correct Answer: B

Rationale: Melanin, produced by melanocytes in the stratum basale, determines skin color, ranging from light to dark, and protects against UV by absorbing it. Hemoglobin colors blood, visible through skin but not primary. Carotene adds yellowish tones, minorly. Keratin is a structural protein, not a pigment. Melanin's dominant role in pigmentation and photoprotection, per dermatology, makes 'b' correct.