Blood flow in the veins is much slower because the blood is much farther from the left ventricle. Since the force of this powerful contraction is far "behind" venous flow, blood in veins is more likely to flow backward than in an artery. Because of this, veins have valves to prevent backflow much like the valves in the heart prevent back flow between chambers. The reason the blood flow in deep veins is generally faster than that of superficial veins is because muscle contractions help to move blood along in deep veins. A prime example is the lower legs. Contraction of the gastrocnemius (calf) muscle causes blood to move up through the lesser saphenous vein. 

Arteries are strong elastic vessels that carry blood moving away from the heart. As arteries move away from the heart they become smaller (think of a tree and its branches, the trunk is larger than the branches and as each branch grows out it becomes smaller) and are referred to as arterioles, which connect to capillaries. Capillaries penetrate nearly all tissue; their walls are very thin and allow exchange of materials (oxygen, nutrients) between blood and tissues. Veins are thinner-walled and less muscular. The smallest ones are called venules and connect to capillaries. 

Blood flow through veins is not very efficient. Slow and weak "pushing" by arteries does not contribute much to blood flow, as the hydrostatic pressure in veins is roughly zero. However, contraction of the diaphragm and skeletal muscles, along with the one way valves in veins (these prevent back flow) are important factors. 

Note: Blood clots can occur if blood does not flow properly through veins. This can occur if a person doesn't move enough (for example a long international flight).

Venules are formed from merged capillaries. They progressively merge to form veins. Veins are thin-walled, are under low pressure, and contain the highest proportion of the blood in the cardiovascular system. The largest vein in the body is the vena cava, which returns blood to the heart.

Capillaries have the largest total cross-sectional and surface area. Arterioles are the site of highest resistance in the cardiovascular system. Arteries are thick-walled with extensive elastic tissue and smooth muscle.

The nasal cavity has a rich blood supply that derives from branches of both the internal and external carotid arteries. The maxillary artery, facial artery, and ophthalmic artery also contribute branches to provide blood supply to the nose. This being said, the posterior nose is supplied by the internal and external carotid arteries, the maxillary branch of the external carotid artery, and the sphenopalatine artery, which branches off the maxillary artery.

Veins are the most compliant entity within the circulatory system. The compliance of a systemic vein is 24 times that of its corresponding artery. Veins serve as the major blood reservoir within the human body, and are 8 times as distensible as arteries.

The cephalic vein is a superficial vein of the upper limb. It communicates with the basilic vein via the median cubital vein. It travels along the anterolateral surface of the biceps brachii muscle. The cephalic veins empties into the axillary vein (a continuation of the brachial and basilic veins). The cephalic vein terminates at the lateral margin of the first rib where it becomes the subclavian vein.

Fluid movement into and out of capillaries is mainly dependent on two forces: hydrostatic pressure and osmotic pressure. Hydrostatic pressure is determined by fluid volume and the pressure of the fluid against the capillary walls. Osmotic pressure is determined by osmotic gradient, pulling water in the direction of higher protein concentration. Osmotic pressure is largely directed into the capillary due to the high concentration of albumin in the plasma. The osmotic pressure outside of the capillary remains relatively constant, however, as the capillary moves from the arteriole end to the venule end the hydrostatic pressure drops significantly. Eventually, the osmotic pressure in the interstitium becomes greater than the hydrostatic pressure in the capillary, and fluid returns to the capillaries.

The walls of arteries, arterioles, veins, and venules are all much too thick to allow for the diffusion of substances. However, capillaries only have simple squamous endothelial cells lining their walls, without muscular and/or elastic tissue surrounding them. Their walls are thin enough to allow for diffusion of substances into the interstitium.

Pericytes, sometimes referred to as Rouget cells, are cells that wrap around the endothelial cells of capillaries. These cells play an important role in angiogenesis, the process of formation of new blood vessels. Monocytes are macrophages of the immune system, Purkinje fibers are found in the heart, and allow conductance of electricity to the cardiomyocytes, Schwann cells are glial cells in the peripheral nervous system that myelinate axons.