Fluids in Living Things and Machines

Your body's plumbing

Right now your heart is pushing blood through a huge network of tubes that reaches every part of your body. An adult's heart pumps about 5 litres of blood every minute, even at rest. Meanwhile, in your basement, a sump pump might be waiting to switch on when rain fills the pit.

Living things and machines face the same problems: how to move a fluid, and how to control its flow. Let's compare their solutions.

Moving fluids: pumps

Remember: fluids flow from high pressure to low pressure. Something has to create that pressure difference.

• In your body: the heart is a muscular pump. When it squeezes, the pressure of the blood inside rises and pushes the blood out into the arteries. Your heart is really two pumps side by side: the right side pumps blood to the lungs, the left side pumps it to the rest of the body.
• In your lungs: when the diaphragm muscle under your lungs tightens and moves down, the space in your chest gets bigger, so the air pressure inside your lungs drops. Outside air, at higher pressure, flows in. (That's the pressure-volume relationship from the lesson Pressure, Volume and Temperature.)
• In plants: water evaporates from leaves. This pulls water up through thin tubes called xylem, all the way from the roots, a bit like sipping through a very long straw.
• In machines: pumps push water through city pipes, a sump pump lifts water out of a basement, and a fuel pump moves gasoline to a car's engine.

Controlling flow: valves and tube width

• One-way valves. Your heart has four valves, and many veins have valves too. They are flaps that open to let blood through, then snap shut to stop it flowing backward. Machines use check valves that work the same way: a sump pump's outlet pipe has one so the water it pumped out can't flow back into the pit.
• Changing tube width. Your blood vessels can narrow or widen to send more blood where it's needed. When you're cold, vessels in your skin narrow, so less warm blood flows near the surface. In machines, a tap or valve opens wider or narrower to change the flow.
• Changing pump speed. When you exercise, your heart beats faster to pump more blood to your muscles. A machine's pump can also be run faster or slower.
• Openings that open and close. Plants control water loss through stomata, tiny openings in the leaves that close on hot, dry days to save water.

When flow goes wrong

The factors that affect flow (from the lesson What Affects How Fluids Flow?) matter in health too. If fatty deposits called plaque build up inside an artery, the artery becomes narrower. Like a clogged pipe, it lets less blood through, and the heart has to work harder. That's one reason doctors measure blood pressure (often written like 120/80) and encourage exercise and healthy eating.

In machines, a clogged filter, a kinked hose or a stuck valve causes the same kinds of problems.

Automating fluid systems with code

Many fluid systems now run automatically, controlled by a small computer following code. A sump pump, for example, can use a sensor to measure the water level in the pit and turn itself on and off.

Here is an algorithm in pseudocode (plain-language code). Read it like a computer would, one line at a time.

Emerging technologies

Coding and new technologies are changing how we manage fluids:

• Smart water sensors in homes can detect a leak or a burst pipe and send an alert to a phone, or even shut off the water automatically.
• Some cities collect data from sensors in water mains and use computer programs, including artificial intelligence systems, to help spot leaks early.
• Some people with diabetes use insulin pumps that can adjust how much insulin they deliver, using readings from a glucose sensor.
• Farms use automated irrigation that waters crops only when soil sensors say the soil is dry, saving water.

These tools also raise questions: who owns the data, what happens if the software fails, and how do workers such as plumbers and technicians keep their skills up to date?