Blood flow through a capillary is controlled by a precapillary sphincter, which opens or closes due to the requirements of the cells supplied by the capillary.
A.
True
B.
False
The Correct Answer and Explanation is:
The correct answer is A. True.
Explanation:
Capillaries are the smallest blood vessels in the body, and they play a crucial role in the exchange of nutrients, gases, and waste products between the blood and the tissues. The flow of blood through these capillaries is finely regulated by structures called precapillary sphincters.
Precapillary Sphincters:
Precapillary sphincters are small rings of smooth muscle located at the junction where the arterioles (small arteries) meet the capillaries. These sphincters are crucial in regulating blood flow into the capillary networks. They function by contracting or relaxing in response to various signals, thereby controlling the amount of blood that enters each capillary.
Regulation of Blood Flow:
The primary function of the precapillary sphincters is to adjust blood flow according to the metabolic needs of the tissues. When cells in a particular area are more active and have increased metabolic demands (e.g., during exercise or increased activity), the precapillary sphincters relax, allowing more blood to flow into the capillaries. This increased blood flow ensures that the tissues receive more oxygen and nutrients while facilitating the removal of metabolic waste products.
Conversely, when the metabolic demands of the cells are low (e.g., during rest), the precapillary sphincters constrict, reducing blood flow into the capillaries. This helps to optimize the distribution of blood based on the needs of different tissues and maintains overall circulatory efficiency.
Local and Systemic Factors:
The action of the precapillary sphincters is influenced by both local and systemic factors. Locally, the sphincters respond to changes in tissue conditions such as low oxygen levels or high levels of carbon dioxide. Systemic factors, including hormonal signals and autonomic nervous system activity, can also modulate the function of the precapillary sphincters.
In summary, the precapillary sphincters play a critical role in regulating blood flow through capillaries by adjusting the opening and closing of these vessels based on the metabolic needs of the surrounding cells. Their function is essential for maintaining tissue homeostasis and efficient blood circulation.