The systems of the body

Seventeen pages describing not parts but workings: what commands, what carries, what transforms, what protects. None has a 3D scene, and each says why.

A structure occupies a place; a system performs a function. Pectoralis major can be located, felt and shown. The nervous system sits nowhere in particular: it runs through everything.

These seventeen pages describe workings rather than parts. They were written by the same rule as the rest of the corpus — each because a word kept appearing without ever being described — and they share a constraint the Body pillar displays rather than works around: none has a 3D scene.

What commands

The nervous system and what it produces. These eight pages read in order, from general to particular, and the from an intention to a movement pathway strings them together.

The nervous system — central and peripheral, and the part that works without the will.
The neuron — a signal that never varies in size, only in rate.
The neuromuscular junction — where the command becomes contraction, and why relaxing costs energy.
The brain — its map, its real neuron count, and where they actually are.
Motor control — why a fast movement is launched rather than steered.
Proprioception — the sense that knows where the body is without looking.
Balance — three independent pieces of information the brain must reconcile.
Pain — the difference between the signal sent and the experience lived.

What carries

Five pages on what circulates, and on the two networks that handle it.

The heart — two circuits in series, and what training actually improves.
Blood and circulation — everything happens in the capillaries; the rest is plumbing.
The lungs — an exchange costing no energy, and the fact that breath is not what limits.
The lymphatic system — the return network, with no pump.
The kidneys — a regulator, not a waste filter.

What transforms

The digestive system — a tube whose inside is, technically, outside the body.
The endocrine system — a slow, diffuse network with no designated recipient.

What protects

The skin — barrier, sensor, and above all radiator.
The immune system — a defence that recognises before it fights.

Why none of these pages has a scene

Limit

Three reasons, and each page says which

Body Lab's scenes derive from four anatomical sources: the skeleton, the muscles, the joints and the regions of the body. None of these systems appears among them — but not for the same reason, and running the three together would give a blanket excuse where the project owes an account.

The source does not contain the tissue: nerves, vessels, lungs, heart, glands, skin.

The scale is beyond a mesh's reach: neuron, neuromuscular junction, proprioceptive receptors, capillaries, alveoli.

The data exists, but under a non-commercial licence: the digestive system and the kidneys belong to the visceral system of the atlas used, which the project cannot take up.

The Body hub announced at launch that these systems would not be covered. The position has changed on one point: being unable to show does not require saying nothing, provided the absence is declared.

Where to start

The from an intention to a movement pathway follows a single movement, from the decision through to recovery, crossing nine of these pages in order. It is the most continuous read.

Otherwise the nervous system is the widest door: it links all the others.

Put it into practice in Shapier

Follow the Energy and Recovery pathway

Putting these workings to use for training and recovery happens in Shapier; Body Lab only describes how these systems work.

Follow the Energy and Recovery pathway

Body Lab explains; Shapier lets you act and track.

The seventeen systems

The nervous system
The network that gathers, decides and commands. It works in two directions at once, and a whole part of it escapes the will — otherwise you would have to think about every heartbeat.
Described without a scene
The neuron and the nerve signal
A cell that always sends the same signal, no stronger and no weaker. So it is not the size of the message that codes the intensity of an effort, but its rate.
Described without a scene
The neuromuscular junction
The place where a nerve command becomes a contraction. This corpus described both sides of that crossing without ever describing the crossing itself — and it holds a surprise: relaxing costs energy.
Described without a scene
The brain
The most cited and worst described organ. The number everybody repeats is wrong, and most of its neurons are not where you would imagine.
Described without a scene
Motor control
How an intention becomes a movement. Feedback arrives too late to correct a fast movement, so the nervous system is forced to predict — and a quick movement is launched rather than steered.
Described without a scene
Proprioception
The sense that continuously reports the position and tension of the body without your having to look at it. It is what makes walking in the dark possible — and it is not equally reliable for everything it measures.
Described without a scene
Balance
Three independent sources of information the brain has to reconcile. Standing still is not a stable state: it is a permanent correction, and closing your eyes is enough to make that visible.
Described without a scene
Pain
Forty-six pages of this corpus use the word as a boundary, none made it a subject. The essential distinction is between the signal sent and the experience lived: they are not the same thing.
Described without a scene
The heart
A muscle that obeys nobody and never stops. What training improves is not its top speed — that barely moves — but how much it shifts with every beat.
Described without a scene
Blood and circulation
Thirty-two pages of this corpus mention blood without any of them saying what it carries or how it travels. Everything that matters happens in the smallest vessels, and the return journey poses a problem the outward one does not.
Described without a scene
The lungs and gas exchange
The exchange itself takes no energy: the gases cross on their own. And in a healthy person, what limits an endurance effort is not the lung — which contradicts the sensation.
Described without a scene
The lymphatic system
A return network, with no pump, collecting the fluid that escapes the capillaries. Three pages of this corpus already invoke it: it is the route dietary fat takes and the highway of the defence cells.
Described without a scene
The kidneys and water balance
They are described as waste filters. It is the other way round: they filter almost all the blood and then reclaim almost all of it, and the body's water balance is decided in what they choose to keep.
Described without a scene
The digestive system
A tube several metres long whose inside is, technically, outside the body. Three pages of this corpus describe what becomes of nutrients without any of them describing the route they take.
Described without a scene
The endocrine system
The body's second communication network: slow, diffuse, and addressed to nobody in particular. The hormonal surge following a session does not drive muscle growth, contrary to what common accounts claim.
Described without a scene
The skin
The largest organ of the body, and the only one you see in full. It closes the organism, informs it, and above all it sheds a heat that without it would make any prolonged effort impossible.
Described without a scene
The immune system
A defence that recognises before it fights, and whose main tool — inflammation — is not a malfunction. Two pages of this corpus invoke it without any of them describing it.
Described without a scene

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Trust and method

Author

equipe-editoriale-shapier

Editorial review

Thanh Chau

Scientific review

Pending

Published on

August 2, 2026

Reviewed on August 2, 2026

Next review due August 2, 2027

Limits of this page

This index page describes how a set is organised; the descriptions, their sources and their limits sit on the pages themselves.
None of these pages assesses an individual situation. A sudden disturbance of speech, vision, strength or balance is a medical emergency.

Educational content. Body Lab does not diagnose and does not replace professional advice.

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