Special Circulations

The first system we will consider is the cerebral circulation. The brain requires a large amount of oxygen and glucose to meet its high metabolic demand. Therefore, its circulation has structural and functional adaptations to ensure a consistently high blood flow is maintained. Any interruptions to this supply will lead to a loss of consciousness in a few seconds and irreversible damage to neurones after 4 minutes. The brain is just one of many organs to have a specialised circulation. This article will explore the structural and functional adaptations of the brain’s circulation.

The lungs have both a bronchial and a pulmonary circulation. The bronchial circulation to the lungs is the part of the systemic circulation that supplies O2 and nutrients to meet the metabolic requirements of the lungs. However the pulmonary circulation refers to the portion of the cardiovascular system which carries deoxygenated blood away from the heart, towards the alveoli of the lungs to undergo gas exchange, and then returns oxygenated blood back to the heart. In this article we shall consider the functions of both the bronchial and the pulmonary circulation and the special adaptations required to meet these.

The cutaneous circulation is also adapted to serve the skin it perfuses. The skin is not a very metabolically active tissue and has relatively small energy requirements, so its blood supply is different to that of other tissues. Some of the circulating blood volume in the skin will flow through will flow through arteriovenous anastomoses (AVAs) instead of capillaries. AVAs serve a role in temperature regulation. In this article we shall consider the different adaptations of the cutaneous circulation, and its role in body temperature control.

Our next article will consider the vasculature of our muscles. Skeletal muscle is invaluable for our day to day functioning, controlling voluntary action. However, due to the discrepancy in activity and size of skeletal muscle around the body, a highly regulated circulatory system is required. In this article, we will look at the vasculature, metabolic adaptations and other applications of the skeletal muscle circulation.

Cardiac muscle has its own dedicated circulatory system: the coronary blood vessels. It constantly undergoes phases of contraction and relaxation to pump blood around the body from the heart. As myocardial oxygen demand increases, coronary blood flow must also increase to meet requirements. Anything that prevents blood passing through the coronary vessels, for example atherosclerosis, will result in ischaemia and a consequent myocardial infarction.