Fick's Law of Diffusion

Definition

Fick's law of diffusion is a fundamental principle that describes the movement of molecules down a concentration gradient, without the expenditure of cellular energy. It is a key concept in understanding the mechanisms of capillary exchange within the body.

5 Must Know Facts For Your Next Test

1. Fick's law states that the rate of diffusion is proportional to the concentration gradient of the substance.
2. The rate of diffusion is also influenced by the permeability of the membrane and the surface area available for diffusion.
3. Fick's law is essential in understanding the exchange of gases, such as oxygen and carbon dioxide, between the blood and tissues during capillary exchange.
4. The law also applies to the diffusion of nutrients, waste products, and other small molecules across the capillary walls.
5. Alterations in any of the factors that influence diffusion, such as concentration gradient or membrane permeability, can affect the efficiency of capillary exchange.

Review Questions

• Explain how Fick's law of diffusion relates to the exchange of gases in the capillaries.
  • Fick's law of diffusion is crucial in understanding the exchange of gases, such as oxygen and carbon dioxide, between the blood and tissues during capillary exchange. According to Fick's law, the rate of diffusion is directly proportional to the concentration gradient of the gas. In the capillaries, there is a higher concentration of oxygen in the blood compared to the surrounding tissues, and a higher concentration of carbon dioxide in the tissues compared to the blood. This concentration gradient drives the diffusion of oxygen from the blood into the tissues and the diffusion of carbon dioxide from the tissues into the blood, without the expenditure of cellular energy.
• Describe how the permeability of the capillary membrane and the surface area available for diffusion affect the rate of diffusion according to Fick's law.
  • In addition to the concentration gradient, Fick's law states that the rate of diffusion is also influenced by the permeability of the membrane and the surface area available for diffusion. The capillary membrane is highly permeable to small molecules, such as gases and nutrients, allowing for efficient diffusion. The large surface area of the capillary network, with its extensive branching and thin walls, further enhances the rate of diffusion. If the permeability of the capillary membrane is decreased or the surface area available for diffusion is reduced, the rate of diffusion will be impaired, affecting the exchange of substances between the blood and tissues.
• Evaluate how alterations in the factors that influence diffusion can affect the efficiency of capillary exchange.
  • Alterations in any of the factors that influence diffusion, as described by Fick's law, can significantly impact the efficiency of capillary exchange. For example, if the concentration gradient of a substance, such as oxygen, is decreased, the rate of diffusion will be reduced, leading to decreased oxygen delivery to the tissues. Similarly, if the permeability of the capillary membrane is compromised or the surface area available for diffusion is diminished, the exchange of nutrients, waste products, and other small molecules will be impaired. These changes can occur in various pathological conditions, such as lung diseases, cardiovascular disorders, or microvascular dysfunction, and can have serious consequences for the body's ability to maintain homeostasis and meet the metabolic demands of its tissues.

Related terms

Diffusion: The spontaneous movement of molecules or particles from an area of high concentration to an area of low concentration.

Concentration Gradient: The difference in concentration of a substance between two adjacent regions, which drives the diffusion of that substance.

Passive Transport: The movement of molecules across a cell membrane without the expenditure of cellular energy, driven by a concentration gradient.