In certain cities, too, traditional farms and other forms of urban farming - such as crops grown on rooftops or vacant lots - may only be 60 to 100 miles away, close enough to compete with vertical farms. Vertical-farming projects have sprouted up in several North American cities as well as in the Netherlands, Scandinavia, Germany, Korea, Japan, Abu Dhabi and Singapore among others.
Deoxygenated blood enters the right atrium through three major veins: the superior and inferior vena cava and the coronary sinus. The superior vena cava returns all of the blood to the heart from tissues superior to the heart in the head, neck, arms and upper thorax. Likewise, the inferior vena cava returns blood to the heart from tissues inferior to the heart, including the legs, abdomen and lower thorax.
The circulatory system is made up of the heart and blood vessels. The heart pumps oxygen-rich blood through vessels called arteries. Veins carry blood from various parts of the body back to the heart. Arteries and veins are connected by tiny capillaries (KAP'ih-laireez). The heart's right side receives dark bluish blood from the superior and inferior vena cava. (The superior vena cava is the large vein that brings blood back from the upper part of the body. The inferior vena cava is the vein that brings blood from the lower body.) The heart's right side pumps this blood to the lungs. There, waste gas (carbon dioxide) is removed and oxygen is picked up. The bright red oxygenated blood returns to the heart's left side.