Questions: Which of the following forces does not help lymph to flow? a. Arterial pulsations squeezing lymphatic vessels b. The thoracic pump c. Rhythmic contractions of lymphatic vessels d. The lymphatic node pump e. The skeletal muscle pump

The answer is (d): The lymphatic node pump.

Explanation for each option:

a. Arterial pulsations squeezing lymphatic vessels: This is correct. Arterial pulsations can help to squeeze the lymphatic vessels, aiding in the movement of lymph.

b. The thoracic pump: This is correct. The thoracic pump, which involves changes in pressure within the thoracic cavity during breathing, helps to move lymph through the lymphatic system.

c. Rhythmic contractions of lymphatic vessels: This is correct. Lymphatic vessels have smooth muscle in their walls that can contract rhythmically to help propel lymph.

d. The lymphatic node pump: This is incorrect. There is no such mechanism as a "lymphatic node pump." Lymph nodes filter lymph but do not actively pump it.

e. The skeletal muscle pump: This is correct. The contraction of skeletal muscles during movement helps to squeeze lymphatic vessels and push lymph through the system.

Summary: The force that does not help lymph to flow is the lymphatic node pump.