Question

multiple choice question
how does the respiratory pump promote the flow of lymph?

when one inhales, lymph is pushed from the thoracic cavity into the abdominal cavity.
when one exhales, lymph is pushed from the thoracic cavity into the abdominal cavity.
when one exhales, lymph is pushed from abdominal cavity into the thoracic cavity.
when one inhales, lymph is pushed from the abdominal cavity into the thoracic cavity.

Explanation:

To determine how the respiratory pump promotes lymph flow, we analyze the mechanics of inhalation and exhalation on thoracic and abdominal pressure. During inhalation, the thoracic cavity expands, lowering its pressure relative to the abdominal cavity. This pressure gradient pushes lymph from the higher - pressure abdominal cavity into the lower - pressure thoracic cavity.

Let's analyze each option:

• Option 1: Inhalation does not push lymph from thoracic to abdominal (thoracic pressure is lower during inhalation, so lymph would move into thoracic), so this is incorrect.
• Option 2: Exhalation increases thoracic pressure, so lymph would not move from thoracic to abdominal; this is wrong.
• Option 3: Similar to option 2, exhalation increases thoracic pressure, so lymph movement from abdominal to thoracic is not due to exhalation; this is incorrect.
• Option 4: During inhalation, thoracic pressure drops, and abdominal pressure is relatively higher, so lymph is pushed from the abdominal cavity into the thoracic cavity. This is correct.

Answer:

D. When one inhales, lymph is pushed from the abdominal cavity into the thoracic cavity.