Let’s take a journey through our vascular system and appreciating its ingenious design as we go along.
The vascular system consists of two interacting systems. The transportation of blood to the cells from the heart, via the arterial system and the transportation of blood back to the heart from the cells via the venous system. The movement of blood is created by the heart which is essentially a pump. When it contracts its pushes a significant volume of blood into the arterial system. Here we encounter our first problem, turbulent flow.
Blood is being pushed from the expansive chamber of the heart into a relatively narrow blood vessel (the artery). imagine an emergency evacuation of a crowded area through a door, its chaos or in this case turbulent flow. Thus, unless something is done, it will crash and bang its way down the artery. This is undesirable for two reasons:
- It is not energy efficient as each bang against the side will waste energy [think the extra force required to hit a squash ball to the main wall via 2 walls as opposed to directly]. This means it will not travel very far before it loses its forward momentum and stops flowing foward. Obviously, not the best situation for the cells further away from the heart.
- The trauma from the high energy multi-directional fluid hitting the artery wall will lead to dents and erosion of the inner lining. This can cause a range of problems later in life and it is one of the causes of hypertension. Therefore, the body wants to minimise the effect of this as much as possible.
The body thus this by simply making the artery walls slightly elastic and thus expandable. As the high energy turbulent fluid enters the artery, it’s walls expand just enough to absorb some energy. This calms fluid movement down reducing the multiple directional movement to a more singular direction, termed laminar flow. Therefore, the banging against the inner lining is significantly reduced and also its damage.
The laminar flow of blood travelling in the artery will soon come across a number of branches or tributaries. The best visualisation of the arterial system is to think of our water-ways bring the water from our coasts to the depths of inner lands. As the water flows inwards, the tributaries get narrower and narrower. The same is true of our arterial system. The question is why? The answer is the same for both our water-ways and arterial system. As fluid moves further away from its source, it loses energy and therefore slows down. If we pass that same volume of fluid through an ever decreasing diameter vessel, we can off-set this speed reduction and make it travel further thus ensuring it reaches its destination, the cell.
So to recap, the elastic nature of the arteries and the ever decreasing diameter of the blood vessels ensures the blood can travel as far as possible in order to reach the furthest cells. Now, the next problem is the demanding nature of the cells. They are fussy. Sometimes they are working hard and what more blood, other times they are recuperating and what little blood. Unfortunately, they are not accommodating, if they do not get the right quantities immediately they complain and we the organise suffer. So the arterial system has to be alert and responsive to their demands.
To meet these demands, the arterial system must have control of the vessel diameters because we know the diameter of the vessel controls the rate of flow of blood. Now the arteries role has already been assigned, as they are given elastic walls to absorb energy and create a steady blood flow. The arterioles (note the difference in spelling) are given this role. Their outer walls are composed primarily of muscle. The contraction of these muscles reduces the diameter of the arterioles and thus increases the flow. The control of these muscles involves a complex interaction of the nervous system, hormonal (endocrine) system and local signalling molecules within the arterial system. All of which monitor and communicate with the cells and help ensure their health.