- Here we divide the circulatory system into its basic functional segments. These segments can be applied to both the pulmonary and systemic circulations as their basic architecture is highly similar.
|Functional Circulatory Segments|
- The heart generates the tremendous pressures necessary to actuate the flow of blood throughout the entire circulation. Following the heart, blood enters arteries which progressively branch and become narrower. This branching pattern is true of both the systemic and pulmonary circulations.
- The Arteries are designed to rapidly conduct pressurized blood downstream within the circulation without significant loss of blood pressure.
- Arterioles are the final and smallest branches of the arterial system and are the primary regulators of blood flow to downstream capillaries. When arterioles are dilated, the downstream capillary bed can receive large amounts of blood flow
- However, if arterioles are constricted, blood flow through the downstream capillaries can be tremendously limited.
- Capillaries are the primary location in which exchange of nutrients, metabolites, and waste products occurs between the blood and the tissues.
- Capillary converge on one another and form venules which drain the blood from capillary beds and conduct blood to larger veins.
- Veins are designed to conduct blood at low pressures back to the heart for re-pressurization and recirculation. Veins also act as important reservoirs for spare blood volume which can be rapidly called upon to meet physiological demands.