Heart. Johannes Hinrich von Borstel
Читать онлайн книгу.
via the heart — for instance, the portal venous system of the liver. This is the system that transports blood from the gut straight to the liver before it continues on to the heart. And that’s practical, because some of the toxins we ingest along with our food are broken down in the liver before they can cause any damage in the rest of the body.
As we have seen, the pulmonary vein and artery are also exceptions to the general rule. The pulmonary artery, like all its fellow arteries, leads away from the heart. However, it does not transport oxygenated blood, but rather blood that is on its way to the lungs to be enriched with oxygen. This blood then flows, packed full of oxygen, from the lungs, along the pulmonary vein, to the left atrium of the heart, where it is finally thrust out into the rest of our body via the left ventricle and the aorta, our main artery. This thrust is what we feel as our pulse.
The fact that our arteries are rarely to be found close to the surface of our bodies is a clever trick on the part of evolution, since a damaged artery bleeds heavily. Imagine the mess when you cut your finger while chopping carrots — and the risk of bleeding to death if you’re unlucky. However, since our arteries are buried deep in our tissues, it takes more than a scratch to damage them.
Having survived a cut finger without bleeding to death, we need to ask how our blood gets from the tips of our fingers back to the heart. After all, it needs to return to the lungs to be recharged with oxygen. Before reaching the right atrium, it gathers in two large blood vessels, the superior and inferior vena cava. The superior vena cava receives blood from the upper body, the arms, and the head, while its ‘inferior’ counterpart gathers blood from the abdominal organs, the legs, and the torso.
But how does the blood in the veins of our lower legs manage the 130-or-so centimetre climb to the heart? This is only possible because our veins are equipped with small valves, positioned every few centimetres, that open for blood flowing towards the head but not the other way. Like the valves of the heart, they stop blood flowing back in the undesired direction. In addition, when we move, the muscles surrounding the veins do the rest of the work, pressing blood up towards the heart. This effect is appropriately known as the skeletal-muscle pump.
As we get older, more and more of our venous valves may stop working properly. When one valve gives up the ghost, the pressure is increased on the still-intact valve immediately below it, and the section of vein between them swells up. One unsightly result of this can be varicose veins, although they can also be caused by a general weakness of the connective tissue. This is often also the cause of another unpleasant vascular problem: haemorrhoids, which occur when the veins and arteries of the rectum swell and cause bleeding and itching round the back door.
However, it’s not only the venous valves and the skeletal-muscle pump that are important in transporting blood back to the heart; this process is also aided by the body’s respiratory pump. When blood has eventually made it back to the chest area, our breathing muscles help to transport it into the right atrium. This works because, during abdominal breathing, the pressure in the chest sinks as we suck air into our lungs, and that allows the inferior vena cava to take in blood more easily from the lower body. When we then exhale, the pressure on those vessels rises again, and the blood is literally squeezed into the right atrium of the heart.
As long as all these systems are working properly and all parts of the body are well supplied with blood, there’s usually nothing to worry about. Our cells get what they need and we carry on merrily with our lives. But it would be too good to be true if those systems were not prone to error. And, indeed, just like actual highway systems, the cardiovascular system is susceptible to congestion and, when push comes to shove, even gridlock.
*The word ‘cardiogenic’ comes from the Ancient Greek words kardia, meaning ‘heart’, and genesis, meaning ‘origin’ or ‘creation’.
*Pulmo is Latin for ‘lung’.
†See also, ‘The Holey Heart’, p. 270.
*See p. 34 for more on the portal venous system.
†Meaning ‘two-tipped’.
*Meaning ‘crescent-shaped’.
*Also called ‘mitral insufficiency’, i.e. a failure of the mitral valve to close properly.
†Ventricular dilatation.
*From the German for ‘air chamber’, part of a water-pumping system.
*Blood cells.
Cardiac Congestion
Heart attacks and how they happen
The First Time
It’s a grey Saturday in autumn. The wind whips across the fields, and the rain pelts the tarmac in sheets. The streets are deserted except for the occasional car passing by. It has been more than a year since my work experience in the emergency department at the hospital. I’m 16 years old. Having completed the theoretical part of my training as a paramedic during weekends, I’m now ready for a three-week work-experience placement where I’ll begin my practical training in an actual ambulance team.* I’m walking to the ambulance station to begin my first shift. The terrible weather does nothing to dampen my great expectations, nor does the fact that, in my excitement, I have not only forgotten to pick up my umbrella and put on my waterproof shoes, I’ve also left my packed breakfast at home. Luckily, it isn’t a long walk.
Full of anticipation, I’m excited about my first ambulance call-out. What will it feel like? To be constantly on the go, flashing lights and blaring sirens, with total focus on the emergency at hand — illnesses, accidents, battles against the sheer forces of nature? I am ready to face any challenge! What I do not yet realise is that this is the day that will not only try my self-confidence to the limit, but also severely test my resolve to enter the medical profession at all.
After a few brief introductions in the station, I’m handed my uniform. It fits like a glove, and my chest swells with pride as I put it on. I am also given a handy little pager that will inform me of an emergency by beeping at me. Then I receive a tour of all the different machines and equipment in the ambulances.
As I’m chatting with my new colleague in the vehicle depot, the shift supervisor enters, with a slightly grumpy look on his face. ‘Hello, Mr von Borstel, nice to see you here. I see you’ve been introduced to all the equipment and made some friends,’ he remarks coolly.
‘Yeah, yes, I have,’ I stammer in reply. ‘I’m very grateful for the opportunity to be here!’
He looks me calmly up and down, and a smile slowly spreads across his face. He tells me he has an important and highly responsible job for me. Ten minutes later, I find myself battling manfully against the sheer forces of nature for the first time. With a broom. In the driveway.
Is it a test? Some kind of initiation rite? Whatever: I don’t care. Proudly sporting my safety vest. I do my leaf-sweeping duty in the rain. After an hour or so, I finish my fight against wind and weather, and withdraw to the staff room inside the station. In the staff room, there are couches, a TV, a small kitchen, and a bookshelf, from which I promptly choose some reading matter. Time passes, but there is not the slightest peep from my pager. My colleagues sit calmly with their pagers clipped to their belts, but I can’t resist checking the battery level on mine every few minutes. Where are the emergencies? At lunchtime, we warm up some soup. I wash the dishes. And nothing else happens.
It is unusual for absolutely nothing to happen during a 12-hour shift. Yet with two hours to go, it seems like we’re heading for a shift without a single call-out.
Somewhat frustrated, I move downstairs to the vehicle depot and open the side door of an ambulance. I check the contents of every single drawer once more and try to commit to memory the way the emergency backpacks are organised.
And then, just as everyone has given