What is the major function of the valves found in human veins?

Adigestive system that is a series of tubes beginning at the mouth and ending at the anus is a digestive system.

Which statement describes an endocrine function rather than an exocrine function? a. salivary glands release saliva into the mouth. b. sweat glands release sweat onto the skin c. the pineal gland releases melatonin into the blood. d. esophageal glands release mucus into the esophagus.

Why are some places regularly warmer or cooler than others in a given month