Biological and medical applications

Physics> Biological and Medical Applications

The transport of nutrients, as well as the circulation and purification of the blood, are affected by the movement of fluids.

Learning challenge

• Understand the circulatory system in terms of fluid dynamics.

Key points

• There are many fluids in biology. Understanding their movement helps create effective medicine.
• The heart drives blood through all the tubes in the body.
• Circulation can be enhanced with knowledge of fluid dynamics.
• Diffusion is the dominant mechanism through which nutrients and waste are exchanged between blood and tissue.
• The kidneys use osmosis and dialysis to purify the blood. This is important in medicine, as it helps to cope with kidney dysfunction.

Terms

• Vascular – containing vessels through which fluid is transported.
• Osmosis is the net movement of molecules from a high potential to a lower potential through a partially permeable membrane.
• Dialysis is the separation of molecules or particles of different sizes using differential diffusion through a semipermeable membrane.

Fluids can be static, but there are also cases where the fluid is displaced. For example, smoke rises above a fire or a stream of water erupting from a hose. Why does the rising smoke swirl? How does the nozzle increase the speed of the water? Fluid dynamics help to answer all of this.

Use in the circulatory system

The circulatory system is a connected tube through which fluid flows. The heart is a pump that pumps blood and sets the rhythm. It changes the regional pressure and ensures the movement of blood in a given direction. Heartbeats create a pulsating blood flow that propels fluid into the arteries and venous system.

The main artery is the aorta. It emerges from the left side of the heart and branches into smaller arteries: arterioles and capillaries (carry oxygen). The latter are connected to venules. Further, the blood passes into the right heart.

Through the venous system, the deoxidized blood returns to the right side of the heart, where it passes into the lung and is transformed into oxygen. Then the blood flows to the left side and repeats the whole process. The heart, blood vessels and lungs take an active part.

Liquids and diffusion

Diffusion is the movement of substances due to random thermal molecular motion. This process can be carried out even in solid particles (vapors enter ice cubes). Diffusion is the main mechanism by which the exchange of substances and waste between blood and tissue is ensured. Evolution has increased organisms, resulting in the need for rapid transportation methods that surpass pure diffusion. That is why the circulatory system has developed. Single-celled organisms are still limited by diffusion.

Semi-permeable membrane with tiny pores allowing only small molecules to pass through

Another important form of fluid movement is osmosis. It is the transport of water through a semi-permeable membrane from an area with a high concentration to a low one. The responsibility lies with the imbalance in the concentration of the water. Similarly, dialysis is the transfer of any molecule through a semipermeable membrane due to differences in concentrations. The kidneys use dialysis and osmosis to purify the blood.

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