The location of a muscle's insertion and origin can determine

Correct Answer: A

Rationale: A muscle's origin (fixed point) and insertion (movable point) dictate its action e.g., biceps brachii originates on the scapula and inserts on the radius, flexing the elbow. Force of contraction depends on fiber type and size, not just attachments. Muscle name may reflect location (e.g., temporalis) but isn't determined solely by it action or shape also factor in. Load capacity relates to cross-sectional area, not just origin/insertion. Action's dependence on attachment points' leverage and pull direction makes 'a' the correct answer.

Correct Answer: D

Rationale: A fossa is a depression or indentation in a bone, such as the mandibular fossa of the temporal bone where the mandible articulates, serving as a surface for muscle attachment or joint articulation. An air-filled cavity describes sinuses (e.g., frontal sinus), not all fossae. A hollow passage suggests a canal or foramen (e.g., carotid canal), not a fossa's shallow nature. Fused cartilage refers to structures like synchondroses, unrelated to fossae. The term 'fossa' (Latin for ditch) denotes a sunken area, making 'd' the precise anatomical 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.