Flow can be categorized into two types: laminar and turbulent.
In laminar flow the direction of the flow is parallel to the vessel wall and is basically straight. This type of flow is silent: it does not produce an audible noise of any kind. In turbulent flow the direction of the flow is not parallel to the vessel wall and blood flows in different directions. Turbulent flow can often cause small whirlpools to form in the blood, much like the ones seen in rivers at points of obstruction. This type of flow makes an audible noise which can be heard by a stethoscope. Obviously, flow which is turbulent causes much more resistance in the blood vessel than those laminar flow therefore laminar flow allows for better and easier delivery of blood.
There is a considerable turbulence of flow at the branches of large arteries. Also during the rapid phase of ejection by the ventricles turbulent flow occurs at the proximal portions of the aorta and pulmonary artery. However in small vessels blood flow is predominantly laminar.
