Why Curvy Blood Vessels Are More Efficient

red, blue, white, and pink graphic image of the circulatory system

Biological Strategy

Animals

Sam Stier & AskNature Team

Image: Ustas7777777 / Shutterstock / Public Domain - No restrictions

Distribute Liquids

Liquids include water, as well as body fluids such as blood, gastric juices, nutrient-laden liquids, and more. To survive, many living systems must move such liquids within themselves or between locations. Because of their properties, liquids tend to disperse unless they are confined in some way. To address this, living systems have strategies to confine fluids for transport, and to overcome barriers such as gravity, friction, and other forces. Some of these same barriers also provide opportunities. Trees and giraffes face the same challenge: how to move fluids (water and blood, respectively) upward against gravity. But their strategies are quite different. The tree moves water using capillary action and evaporation, possibly due to water’s properties of polarity and adhesion. The giraffe’s tight skin provides pressure to assist in blood circulation. and keep blood from pooling in the legs.

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Distribute Gases

Gases of particular importance to living systems are oxygen, carbon dioxide, and nitrogen. Oxygen and carbon dioxide are involved in respiration, so distributing these gases efficiently and effectively is important for a living system’s survival. However, gases are difficult to contain because they disperse easily. To accommodate this, living systems have strategies for confining gases and using gases’ properties to their advantage. For example, prairie dogs and mound-building termites build systems of tunnels and mounds that take advantage of wind to ventilate their underground homes.

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Animals

Kingdom Animalia (“having breath or soul”): Mammals, reptiles, sponges, corals, insects, birds

This kingdom captures a staggering variety of life—from the smallest coral polyp to the largest elephant. Although animal body shapes and life histories vary, there are a few defining characteristics. Animals are heterotrophs, meaning they gain energy from eating other organisms, and have developed from single-celled ancestors to highly diversified and coordinated multicellular forms. Unlike plant and fungi cells that have rigid cell walls, animal cells are bound by more flexible combinations of proteins. Most animals have cells organized into tissues and are able to move within their environment.

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This book introduces youth educators to biomimicry and guides them in how to engage students in the topic in ways that will transform their outlook on the world and their own creativity.

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Arteries of humans enhance transport of molecules between blood and the wall by having a helical structure.

Introduction

We may imagine ourselves having essentially solid bodies, but the vascular system that carries oxygen throughout our bodies, makes us less like a mountain of muscle and more like a walking river of fluid. That’s why damage to our veins and arteries can be so devastating, and why cardiovascular disease is a leading cause of death for humans worldwide.

Much of the problem stems from the build-up over time of hardening agents in the walls of arteries. Healthy arterial walls require a constant supply of oxygen––artery walls receiving less oxygen are more likely to harden. Fortunately, our arteries have surprising and subtle adaptations to help us remain healthy throughout our lifetimes.

The Strategy

As our arteries carry oxygen-enriched blood from our lungs to the rest of our bodies, they often curve and twist in three-dimensional space like a corkscrew. Why don’t they just travel in seemingly efficient straight lines?

It turns out that those twists create helical flow patterns within vessels that better mix oxygen in the bloodstream. They also cause our flowing blood to exert more force against the artery walls. This force, called wall shear stress, directly affects the amount of oxygen absorbed by the walls. It’s similar to eating a tasty candy: if you roll it around in your mouth, your taste buds have a chance to experience the flavor, but if you swallow it straight down, you hardly taste a thing,

Similarly, straighter arteries have less opportunity to interact with the oxygen flowing through them. That puts them at greater risk of hardening than helical ones. Thus, the seemingly inefficient twists in our veins and arteries are ultimately critical for maintaining the health and functioning of the system as a whole.

The Potential

The natural helical geometries of our vascular system can serve as an inspiration in the design of grafts, shunts, and stents used in procedures such as dialysis and bypass surgery. Helical stents modeled on the geometry of human arteries, for example, have already been shown to better maintain the health of associated vessels than straight stents.

More broadly, mimicking the twisting path of arteries could improve the absorption in other flowing systems, either for distributing materials into the surroundings, or filtering them out of the flowing liquid.