Help please Veins have to ensure that blood under low pressure can return to the heart.
The circuit of circulation that goes from the heart to the body cells and back to the heart is called circulation.
he oxygenated and deoxygenated blood are kept separate in the mammalian heart by the .

Based on their location in the atmosphere, the layers are able to have their own special characteristics. for example, most weather occurs in the troposphere. what occurs in each of the other layers? (site 1)

Which of the following is the most likely result of converting forestland to urban development? a.the amount of land available for lumber production decreases. b.fewer trees are needed because cities are made mainly of concrete. c.people discover more efficient ways to grow trees. d. the price of lumber goes down.

Abnormal softening of a gland is known as