Question

Why are hormones released into venous blood and not to arteial blood?

Answer 1

Hormones are released by a secretory gland to the blood to act on a distant target. Arteial blood, is the blood that come towards the organ from the heart. So, if the hormone is secreted onto the arteial blood, it will come back to the gland which secreted it, which is of no use. The hormones has to be secreted into venous blood, which is the part of blood that moves towards heart from the gland, so that the hormones will be taken to heart. The heart will then pumps the hormone containing blood to the distant parts of the body for initiating the hormonal action.

Thus the glands pour their hormonal secretions to venous blood.