Cumulus clouds are large, puffy, mid-altitude clouds with a flat base and a rounded top. These clouds grow upward and can develop into a cumulonimbus or thunderstorm cloud.

If the ovum fails to become fertilized, the lining of the uterus sloughs off during menstruation. From puberty to menopause, this cycle of menstruation repeats monthly (except during pregnancy).

Rising into the atmosphere, the water condenses into clouds. When the clouds become too saturated with water, the water is released as snow or ice precipitation which may warm as it falls to reach Earth as rain.

Clouds are categorized based on their shape, size, and altitude. Stratus clouds are low-altitude clouds characterized by horizontal layering with a broad flat base. When stratus clouds occur on the ground the result is fog.

Veins carry blood back to the heart from the body. While arteries are thick-walled because they carry oxygenated blood at high pressure, veins are comparatively thin-walled as they carry low-pressure deoxygenated blood. Like the heart, veins contain valves to prevent blood backflow.