Circulation

Blood pressure is a measure of how well our cardiovascular system is functioning. We all require a blood pressure high enough to give our organs the blood and nutrients they need, but not so high our blood vessels become damaged. As such, our bodies must maintain control over our blood pressure to keep it at a normal level. In this article, we will consider the short term and long term control of blood pressure, as well as some of the problems when control of blood pressure is lost.

In this next article on capillaries, we will look at the mechanisms of capillary exchange. Exchanging molecules from the bloodstream to tissues forms the basis of life, delivering nutrients and carrying waste products to be disposed of. This occurs in blood vessels known as capillaries. In this article, we shall look at how molecules move between capillaries and tissues as well as related clinical conditions.

The peripheral circulation is extremely important for transporting blood around the body, exchange of nutrients with tissues and storing blood. As the tissues in the body vary their need for blood e.g. during exercise, the peripheral circulation will match the flow to the demand. In this article, we will look at how flow is regulated through the peripheral circulation.

There are two ways in which blood flows within our vessels. In most straight blood vessels, the flow is laminar. Velocity is highest in the centre of the tube and decreases closer to the vessel wall. This decreasing velocity gradient is due to increasing resistance closer to the vessel wall. However, if the blood vessels branch off or become constricted, the flow becomes turbulent. Sometimes turbulent flow can be heard (known as a ‘bruit’) over arteries containing atherosclerotic plaques. This article will consider the physiology of blood flow and its importance in subsequent pathology.

In our final article in this section, we will discuss venous return. The heart is a myogenic pump which means it is responsible for its own stimulation to pump blood out to the rest of the body. However, to do this blood must be efficiently returned to the heart so that it can be pumped around again in the next cycle. Venous return is therefore important in maintaining normal circulation and this article will discuss those factors which influence venous return.