Precapillary resistance

Precapillary resistance is a term used in physiology to describe the resistance offered by the arterioles and capillaries in the circulatory system. This resistance is crucial in controlling the distribution of blood flow to different parts of the body.

Overview

Diagram of the human circulatory system. Precapillary resistance occurs in the arterioles and capillaries.

Precapillary resistance is primarily determined by the diameter of the arterioles and capillaries. These small blood vessels have muscular walls that can contract or relax to change their diameter, thereby increasing or decreasing resistance. This mechanism is known as vasoconstriction and vasodilation, respectively.

Role in Blood Pressure Regulation

Precapillary resistance plays a significant role in the regulation of blood pressure. By adjusting the resistance in the arterioles and capillaries, the body can control the distribution of blood flow to meet the metabolic needs of different tissues. For example, during exercise, the arterioles in the muscles dilate to increase blood flow, while those in other parts of the body constrict to maintain blood pressure.

Role in Tissue Perfusion

Precapillary resistance also plays a crucial role in tissue perfusion, which is the passage of blood through the blood vessels of an organ. By adjusting the resistance in the arterioles and capillaries, the body can control the amount of blood that reaches different tissues. This is particularly important in organs such as the brain and heart, which require a constant supply of blood.

Factors Affecting Precapillary Resistance

Several factors can affect precapillary resistance, including:

• Hormones: Certain hormones, such as adrenaline and noradrenaline, can cause vasoconstriction, thereby increasing precapillary resistance.
• Autonomic nervous system: The autonomic nervous system can influence precapillary resistance through the release of neurotransmitters that cause vasoconstriction or vasodilation.
• pH: Changes in the pH of the blood can affect the diameter of the arterioles and capillaries, thereby influencing precapillary resistance.

See Also

• Blood pressure
• Vasoconstriction
• Vasodilation
• Tissue perfusion

References

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