Diaphragm and rib cage movements in inhalation

Steps:

• Air flows into lungs during inhalation when thoracic volume increases, lowering internal pressure below atmospheric pressure.
• Diaphragm contracts, changing from dome-shaped to flattened while descending to enlarge vertical dimension.
• External intercostal muscles contract, elevating ribs up and outwards to expand lateral and anterior-posterior dimensions.
• Combined actions create pressure gradient drawing air in.

Why D is correct:

• Flattened up and outwards matches diaphragm flattening with rib cage elevation, per Boyle's law where volume increase reduces pressure for inflow.

Why the others are wrong:

• A: Dome-shaped down and inwards describes exhalation, where diaphragm relaxes and rises, decreasing volume.
• B: Dome-shaped up and outwards is incorrect; diaphragm is dome-shaped at rest, not during active inhalation movement.
• C: Flattened down and inwards wrongly implies inward collapse, reducing volume instead of expanding it.

Final answer: D