The hypophyseal portal system is a direct vascular route consisting of a primary capillary plexus in the infundibulum, hypophyseal portal veins, and a secondary capillary plexus in the anterior lobe. Because these portal veins connect the two capillary beds directly, the releasing and inhibiting hormones travel from the hypothalamus to the anterior pituitary without entering the systemic circulation. This ensures that even minute quantities of hormones reach their target rapidly and without being diluted.

Key points

The portal system is a capillary bed that drains into veins, which then feed into a second capillary bed.
Hypothalamic releasing and inhibiting hormones are secreted into the primary capillary plexus in the infundibulum.
From there, the hormones travel through the hypophyseal portal veins to the secondary capillary plexus in the anterior pituitary.
Bypassing the systemic circulation prevents dilution of the small hormone amounts.
This direct vascular connection allows rapid delivery and regulation of anterior pituitary hormone secretion.

How does the hypophyseal portal system ensure that releasing and inhibiting hormones from the hypothalamus reach the anterior pituitary rapidly and without dilution?

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