Heart. Johannes Hinrich von Borstel
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but what does this have to do with the heart? Well, this mnemonic helps young medics remember where to place their stethoscope when listening to the function of the heart valves.
Having memorised this little sentence, all a doctor has to remember is that the listening points are described from top right to bottom left. The time 22.45 describes the intercostal spaces (between the ribs), and the initial letters of the words in the sentence are the same as those of the names of the valves (Aortic, Pulmonic, Tricuspid, and Mitral). Once you know this, you can listen very precisely to your own heart-valve sounds and any possible murmurs. However, interpreting these sounds is a complicated business and should be left to an experienced cardiologist, since recognising the subtle differences and changes is almost impossible without decades of practice.
There is a six-level scale for grading the loudness of heart sounds, ranging from ‘difficult to hear even by expert listeners’ via ‘readily audible but with no palpable thrill’ (medical word for tremor or vibration) to ‘loudest intensity, audible even with the stethoscope raised above the chest’. In addition, doctors distinguish between different ways the sounds change over time, using criteria like crescendo or decrescendo, i.e. getting louder or getting softer; or diamond-shaped, which means getting louder then softer again; or a constant, unchanging intensity. The heart is an instrument that can play many kinds of music. Doctors use these distinctive features as the basis for diagnosing problems with the valves of the heart, and prescribing the best treatment.
All Physicians Take Money at 22.45 — the stethoscope listening points
The way all the components of the heart work together is complex, but also absolutely fascinating. However, even the greatest, most powerful engine is useless if there are no roads for the vehicle to drive on. Our blood vessels are precisely those ‘roads’, without which our heart, as the central pump, would have no meaning. In the end, the heart’s strength and stamina, as well as its intricate valve construction and conduction system, all serve one single purpose: to send our blood rushing at full throttle along those roads.
The Body’s Highway System
Our blood vessels transport blood and nutrients to the farthest reaches of our body. In fact, there are only a very few areas that are not permeated by them. Those include the corneas of our eyes, the enamel of our teeth, our hair, our fingernails, and the outermost layer of our skin. To transport all that blood, our body needs a proper system of pipes and ducts: our blood vessels. They are also the highway system of our bodies. With the difference, however, that taken together, our arteries, veins, and capillaries (the finest branches of our blood vessels within tissues), are more than ten times longer than Germany’s famous autobahn system — totalling around 150,000 kilometres (over 93,205 miles).
Unlike the pipes that form the sewerage systems beneath our cities, blood vessels are very elastic. This is a good thing, because it allows the body to regulate the diameter of the blood vessels. It’s what enables the body to provide certain organs and structures with a greater or lesser supply of blood according to whether they require more or fewer nutrients and oxygen molecules at any given time. When it comes down to it, this is no different to the engine of a car: the more you step on the accelerator, the more fuel is injected into the motor’s cylinders.
When we are out jogging, our muscles need a better supply of blood to satisfy the increased need for oxygen. At the same time, our skin also receives more blood, so that it can release some of the increased heat into the environment via the cool, sweat-moistened surface of the skin. To make this increase in blood supply happen, our body reduces the amount of blood it provides to other parts of the body — for example, the gut. After all, digestion can always wait till later. A similar thing happens in our lungs: if a section of the lung registers a reduced oxygen supply, the vessels in that section will constrict. There is no point in sending blood to pick up oxygen where there is none to be had.
All this is possible because our arteries and veins have an elastic structure. The two types of blood vessel are similar, but there are certain differences between them. All have walls consisting of three layers, with the innermost layer made up of supporting connective tissue and what doctors call the endothelium. The endothelial cells line the inside of our blood vessels, serving as a barrier to protect the tissue of the vessel wall, and they can play an active part in the regulation of the cardiovascular system. They are the interior decoration and the Anaglypta of our blood vessels, but they are also much more than that. For instance, they can release nitric oxide, which acts as a signal to the vessels surrounding the heart and those of the skeletal muscles to relax, allowing them to dilate. This happens during physical exercise and other times of exertion to supply more oxygen-rich blood to the muscles as they work.
Structure of a blood vessel wall
The middle layer is muscular, or, more accurately, it consists of elastic fibres and smooth muscle cells that encircle the blood vessel. Here, the fibres of the autonomic nervous system — that is, the part of our nervous system that we don’t consciously control — regulate the dilation or constriction of the vessel by tensing or relaxing the smooth muscle cells. Of course, the more dilated a vessel is, the more blood can flow through it.
The outermost layer of blood vessels is made up of connective tissue fibres, which anchor the vein or artery to the surrounding parts of the body. This layer houses those nerves that control the smooth muscles in the middle layer. But blood vessels also need oxygen themselves. This is provided by a network of tiny blood vessels, called the vasa vasorum. These ‘blood vessels of the blood vessels’ are also contained in the outer layer.
The arteries are like the sporty types within our bodies, while the veins are the couch potatoes. Their layered structures are basically the same, but the arteries are considerably more muscular. By the same token, veins have a larger internal diameter. These differences are due to the fact that the pressure inside our arteries is higher and they must be able to resist that pressure to avoid blowing up like wobbly, water-filled balloons.
Arteries can be divided into three types: elastic, muscular, and the smallest branches of the arterial system, the arterioles. The elastic arteries tend to be those closer to the heart, and the best-known artery of this type is the body’s largest: the aorta, our main artery. It’s about as thick as a garden hose. When the heart beats, the aorta dilates to accommodate a rush of extra blood, before contracting again to maintain internal pressure. Medics call this the Windkessel effect,* and it helps significantly in reducing fluctuations in the flow of blood to the peripheral areas of the body.
So, the arteries change their size by tensing or relaxing the muscles of their walls, and this regulates the amount of blood flowing to our muscles and organs. When they have almost reached their destination, the vessels branch out more and more to form arterioles. These get smaller and smaller until their walls are no longer made up of three layers, but just one layer of smooth capillary epithelial cells. At this level and smaller, scientists speak of capillaries. Every part of the body that has a blood supply contains a very extensive interwoven network of these tiny blood vessels, which can be so narrow that blood corpuscles* can only travel down them in single file, one behind the other.
The capillaries form the connection between the high-pressure arterial system and the low-pressure venous system. And since their walls are only one cell thick, oxygen can flow out of them and into the surrounding tissue much more easily than from other blood vessels. In fact, the endothelium is so porous that when tissue is infected and inflamed, white blood cells — which can be quite chubby little chappies — can leave the bloodstream through them. Eventually, the blood removes the carbon dioxide that has accrued in the body’s cells and flows with it through venules and ever-larger veins, back to the heart.
Apart from a few exceptions, there is a clear division of labour between the arteries and the veins. In general, arteries transport oxygenated blood away from the heart, while veins take deoxygenated blood back to it.