Heart, vessels and blood — the transport network every other system depends on, and where honest advice looks least like a shopping list.
~13 min read
No living cell in your body is more than a fraction of a millimetre from a capillary. That measurement is the design constraint of the whole system — oxygen and glucose cross the last stretch by diffusion, and diffusion is hopeless over any real distance. The network cannot be pipes running past. It has to be a mesh threaded through everything, at that scale.
Which is why every other system ends here. The respiratory system is only useful because blood waits on the far side of the air sac, digestion ends at a capillary in the intestinal wall, the endocrine system shouts into the bloodstream.
The organs and structures involved
Tap any of these for its own page.
The heart is the size of your closed fist and weighs roughly 300 grams. Four chambers — two thin-walled atria that collect, two thick-walled ventricles that eject — with four one-way valves that shut hard enough to hear through a stethoscope. And it is not one pump but two, sharing a wall and a beat.
The pulmonary circuit — the right pump
Blood returning from the body, low in oxygen, is pushed from the right ventricle to the lungs — a short trip at low pressure. It gives up carbon dioxide, takes on oxygen, returns to the left side.
The systemic circuit — the left pump
Oxygen-rich blood is driven from the left ventricle through the aorta to everything else, to the toes and back. A long trip against gravity, and it takes pressure.
The circuits have incompatible requirements. Lung vessels are thin and fragile; push blood through them at the pressure a leg needs and fluid is forced into the air spaces. One pressure cannot serve both, so the left ventricle wall is around three times the right.
Diagram to come
A figure-of-eight laid on its side, with the heart at the crossing point drawn as two chambers side by side rather than one shape — the right pump visibly thinner-walled than the left. The small left-hand loop runs heart to lungs and back; the large right-hand loop runs heart to body and back, drawn long enough that the difference in scale is obvious at a glance. Deoxygenated blood in one tone, oxygenated in another, switching colour inside the lungs and again inside the body loop, never at the heart. Arrowheads on every segment so direction is unmistakable. A small inset showing the two ventricle walls in cross-section, side by side, for the thickness difference. The reader should be able to tell, without reading a word, that one pump does a short easy job and the other does a long hard one.
The vessels are not pipes of different widths. An artery has a thick elastic wall that stretches as the ventricle ejects and recoils between beats, smoothing a series of violent pushes into steadier flow — that recoil is what you feel at your wrist.
Arterioles are the taps: small arteries ringed with smooth muscle that widens or narrows on instruction, deciding which tissue gets the supply at any moment. Veins are thin-walled, hold around sixty per cent of your blood, and carry one-way valves because the pressure there is low — which is the fact the whole of the next section turns on.
Everything the heart and the great vessels do is logistics. The transaction — oxygen out, carbon dioxide in, glucose out, waste in — happens only in the capillaries, and their construction answers a physics problem. A capillary wall is one cell thick: one flattened endothelial cell wrapped into a tube, half a micrometre through at its thinnest. The tube is five to ten micrometres across; a red blood cell is seven or eight, so it folds into a bullet and squeezes through in single file.
That is not a flaw. Diffusion time rises with the square of distance: double the gap and it takes four times as long. Over a few micrometres it is instant; over a millimetre, useless. So the wall is as thin as a wall can be — and the traffic slows exactly where crossing happens, from forty centimetres per second in the aorta to a third of a millimetre per second in a capillary bed, because all those tiny tubes together are hundreds of times wider.
Fluid movement across the wall is a tug-of-war. Blood pressure pushes water and small dissolved molecules out; plasma proteins — mostly albumin, too big to leave — pull it back in, and that pull wins at the venous end. Most of what leaves returns. The leftover, near a tenth, drains into lymphatic vessels, passes through the lymph nodes and rejoins the blood near the collarbone, which is why your circulation and your immune system are hard to separate.
One more thing this settles. Blood is listed among the organs above, but it is a tissue — the distinction taught in The Body as Systems. A tissue is similar cells together with the material they sit in, and blood is exactly that: red cells, white cells and platelets suspended in plasma, with plasma as the matrix. Cells are about forty-five per cent of the volume, plasma the rest. A red cell is made in bone marrow, lives about 120 days, and discards its nucleus to make room for haemoglobin.
Diagram to come
A single capillary drawn horizontally across the frame, arterial end left, venous end right, with body cells packed around it closely enough to show that none of them is far from the tube. The wall drawn as one flattened cell so the one-cell thickness is visible, with a scale marker for half a micrometre. Red blood cells inside folded into bullet shapes in single file. Two opposing arrow sets: fluid pushed out at the arterial end, pulled back in at the venous end, with a small stream of leftover fluid leaving into a lymphatic vessel below. Small-molecule arrows crossing the wall in both directions. Width markers on both the tube and one red cell, so the reader sees the cell is wider than the space it is passing through.
Elsewhere the supportive practices sit at similar weight. Here they do not.
Diagram to come
A lower leg in cross-section, shown twice side by side: relaxed on the left, calf contracted on the right. A vein runs through the muscle with two one-way valves drawn in it. On the relaxed side the lower valve is open and blood is filling the segment; on the contracted side the muscle is visibly squeezing the vein, the lower valve has shut and the upper has opened, moving blood upward. Arrows show direction. A third, smaller panel shows a leg standing still with no arrows at all, so the reader sees immediately that the pump only runs when the muscle moves.
Say this part plainly
Those five outrank anything in a bottle, and it is not close. This is the system where the evidence for lifestyle is strongest and for products weakest, and a healer who is honest says so. Oils and supplements belong here as what they are: aroma, sensation, ordinary nutrients in a convenient form. They are not the intervention. The walk is.
Tap any of these for its own page.
Each is a cofactor or a building material in something this system already does. Where one is missing the machinery runs badly; where it is sufficient, more does not help.
Omega-3 fatty acids
Long-chain fats the body cannot make in useful quantity, so they come from food — oily fish above all. They are built into cell membranes, including those of heart muscle, and membrane fluidity affects how well anything embedded in one works. In xEO Mega.
Magnesium and potassium
Calcium drives a muscle contraction; magnesium is required for the release, and heart muscle is muscle. Potassium sits mostly inside cells while sodium sits outside, and that difference across the membrane is the charge every electrical signal is spent from — a heartbeat is an electrical event before a mechanical one. The correction is vegetables and fruit, not a capsule.
Coenzyme Q10 sits in the inner mitochondrial membrane and ferries electrons along the chain that produces ATP. Heart muscle carries one of the highest mitochondrial densities in the body, because it never rests. In Alpha CRS+ and Mito2Max.
Iron is the single atom at the centre of each haem group and the thing oxygen binds to — four per haemoglobin molecule. Without it there is no oxygen carriage at all. Folate, B12 and B6 are cofactors in the pathways that build DNA, which matters because bone marrow turns out new red cells continuously. In Microplex VMz.
More than twenty nutrients serve this system; the nutrient library holds each on its own, and Nutrition and the Body Systems maps them across all nine. The range differs by country, so something named here may not be sold where you are.
An oil constituent does not travel to the cardiovascular system. It travels in it. Getting that the right way round changes what you can honestly expect.
Whatever crosses your skin, the lining of your nose or the wall of an air sac arrives in a capillary and is carried everywhere at once, diluted into five litres of blood, passed through the liver and cleared. Ask of any other system how an oil reaches it and the answer is the bloodstream; here the question collapses, because the bloodstream is the organ.
Two things oils genuinely offer. Aroma: odour molecules reach receptors in the roof of the nasal cavity and signal into the olfactory bulb, which connects to the limbic system without a relay. A calmer nervous system asks less of the heart — a nervous-system statement, not a cardiovascular one. And sensation: some terpenes act on temperature-sensing receptors in skin, so a diluted blend feels warm or cool without much changing skin temperature. That is not evidence of anything happening inside a vessel.
So, plainly: no essential oil is a cardiovascular intervention. Nothing in your cupboard substitutes for a walk, a night’s sleep or an appointment. That is not a cautious hedge, it is the accurate description. The Oil Effect describes independent work at Roseman University College of Pharmacy in which whole oils showed activity that could not be reproduced by recombining their purified constituents; that was done on cells in a dish, which is not the same as what happens in a person.
Chosen for aroma and for what they are like under a massage — not for any effect on a vessel.
Cypress — Cupressus sempervirens
Alpha-pinene, delta-3-carene and cedrol — monoterpenes over a sesquiterpene base — give a clean, dry, evergreen character. The traditional leg-massage oil: one to two drops in a teaspoon of carrier, worked from ankle upward. The massage is the act; the oil gives it aroma and slip.
Ylang Ylang — Cananga odorata
Germacrene-D, beta-caryophyllene, benzyl benzoate and linalool layered together, which is why perfumery has leant on it. Very strong: one to two drops in a diffuser is enough, and more brings on a headache.
Frankincense — Boswellia carterii, sacra, papyrifera and frereana
Boswellic acids alongside alpha-pinene, limonene and sesquiterpenes. A base note — slow, dry, resinous, still in a room after the top notes have gone. See Frankincense.
Lemon — Citrus limon
Cold pressed from the peel rather than distilled. 60–75% limonene, effectively a single-constituent oil. Because it is expressed it carries furocoumarins, so if you apply it to skin, keep that skin out of direct sunlight and UV for at least twelve hours. See Lemon.
Marjoram and ginger — Origanum majorana, Zingiber officinale
Marjoram is terpinen-4-ol, gamma-terpinene and sabinene — monoterpenols over monoterpenes, behind its warm, herbal smell — for a massage blend for tired muscles. Ginger is almost entirely sesquiterpenes; diluted on skin it feels distinctly warming.
Balance, the blend this page has always led with, is spruce, ho wood, frankincense, blue tansy, blue chamomile and osmanthus in fractionated coconut oil — gentle enough to apply directly. Two to four drops to the soles of the feet in the morning, or three to four in a diffuser.
Dilute for topical use: one to two drops in a teaspoon of carrier oil, less on delicate skin or on children. Cypress, ylang ylang, marjoram and ginger each carry a possible skin-sensitivity note, so patch a small area first. Several are labelled for internal use in some markets and not in others — only ever take an oil internally if the label on your own bottle says so. Safety covers the rest.
Morning — before anything else, the walk
Two to four drops of Balance to the soles of both feet on the edge of the bed, then shoes on and out. Twenty to forty minutes, most days, at a pace that warms you but still lets you hold a conversation. If the morning will not allow it, walk at lunch or walk home — the time of day is negotiable and the walk is not.
Evening — the legs, after a day standing
Shoes off, ten minutes with your legs up the wall, then the massage: one to two drops of cypress in a teaspoon of fractionated coconut oil, worked ankle to knee in slow upward strokes. Marjoram instead when the muscles feel tired. Ten unhurried minutes, which is exactly the claim made for it.
Night — the part most people skip
One to two drops of ylang ylang or frankincense in the diffuser an hour before bed, screens down, room cool and dark. Then the sleep itself — second on the ranking, and the first thing most of us give away. See How to Use Oils.
This part is not negotiable
Chest pain, tightness or pressure. Breathlessness that is new, or out of all proportion to what you are doing. A heart that races, thuds or skips in a way that frightens you. Sudden swelling in a leg, an arm or the face. Fainting, or nearly fainting. Pain spreading into the jaw, neck, back or an arm. Any of these means professional medical care now — today, or an emergency number, not in the morning and not after you have tried something first. Not a diffuser. Not a roll-on. Not a walk, not a herbal tea, not waiting to see. Put the bottle down and make the call. There is no version of this in which an essential oil is the right response to those signs, and the cost of being slow is higher here than anywhere else.
Below that line sit the things that deserve an appointment rather than an emergency number, and should not be quietly absorbed into normal: breathlessness on stairs you used to manage without thinking, swelling that appears reliably by evening, a pulse you cannot account for, a tiredness a good week of sleep does not touch. Book the appointment — describing a change early gives a practitioner something to work with, describing it a year late gives them much less. And have your blood pressure and routine bloods checked at whatever interval your practitioner suggests, precisely because this system is quiet.
Reading Your Own Body is about telling the difference between a sensation to note and one to act on. For every other system that threshold sits fairly high — you watch, you track, you give it a week. Here it is deliberately low, and it should be. One boundary, stated plainly: this is education about how a body is built and how it works. It is different from professional medical care and does not replace it, and nothing here is a reason to delay an appointment or stop a medication.
Keep oils away from eyes and inner ears, and out of reach of children. If you are pregnant, nursing, under medical care or taking medication, speak to your healthcare practitioner before use. Nothing here is intended to diagnose, treat, cure or prevent any disease.
Lesson 8 of 11 · Body Systems