Answer the following question given this paragraph: 

During the systolic phase of the cardiac cycle, the heart is ________. contracting b. relaxing c. contracting and relaxing d. filling with blood 16. How do arteries differ from veins? a. Arteries have thicker wall layers to accommodate the changes in pressure from the heart. Arteries carry blood. Arteries have thinner wall layers and valves and move blood by the action of skeletal muscle. Arteries are thin walled and are used for gas exchange. Most of the hormones produced by the anterior pituitary perform what function? a. regulate growth b. regulate the sleep cycle c. regulate production of other hormones d. regulate blood volume and blood pressure 18. What is the function of the hormone erythropoietin? a.


Q: Arteries have thinner wall layers and valves and move blood by the action of skeletal what?

 Choices:

- marrow

- collagen bands

- hormones

- muscle

A:
muscle
