Before that, support for the elderly wasn't a federal concern - it mostly fell to states, towns and, of course, families. The program is based on contributions that workers make into the system. While you're employed, you pay into Social Security; you receive benefits later on, when it's your turn to retire. Contributions take the form of the Federal Insurance Contributions Act (FICA) taxes that are withheld from most paychecks.
The blood vessels are part of the circulatory system and function to transport blood throughout the body. The most important types, arteries and veins, carry blood away from or towards the heart, respectively. All blood vessels have the same basic structure. The inner lining is the endothelium and is surrounded by subendothelial connective tissue. Around this there is a layer of vascular smooth muscle, which is highly developed in arteries. Finally, there is a further layer of connective tissue known as the adventitia, which contains nerves that supply the muscular layer, as well as nutrient capillaries in the larger blood vessels.
An artery is an elastic blood vessel that transports blood away from the heart. There are two main types of arteries: pulmonary arteries and systemic arteries. Pulmonary arteries carry blood from the heart to the lungs where the blood picks up oxygen. The oxygen-rich blood is then returned to the heart via the pulmonary veins. Systemic arteries deliver blood to the rest of the body. The aorta is the main systemic artery and the largest artery of the body.