334 Chapter 11
rather than neural regulation. Releasing and inhibiting hor-
mones, produced by neurons in the hypothalamus, are trans-
ported to axon endings in the basal portion of the hypothalamus.
This region, known as the median eminence ( fig. 11.15 ), con-
tains blood capillaries that are drained by venules in the stalk of
the pituitary.
The venules that drain the median eminence deliver blood
to a second capillary bed in the anterior pituitary. This sec-
ond capillary bed is downstream from the capillary bed in the
median eminence and receives venous blood from it, so the vas-
cular link between the median eminence and the anterior pitu-
itary forms a portal system. (This is analogous to the hepatic
portal system that delivers venous blood from the intestine togonadotropic hormones (FSH and LH) stimulate the adrenal
cortex, thyroid, and gonads, respectively, to secrete their hor-
mones. The anterior pituitary hormones also have a “trophic”
effect on their target glands, in that the health of these glands
depends on adequate stimulation by anterior pituitary hor-
mones. The anterior pituitary, however, is not really the master
gland because secretion of its hormones is controlled by hor-
mones secreted by the hypothalamus.
Releasing and Inhibiting Hormones
Because axons do not enter the anterior pituitary, hypothalamic
control of the anterior pituitary is achieved through hormonal
Figure 11.14 Hormones secreted by the anterior pituitary and their target organs. Notice that the anterior pituitary
controls some (but by no means all) of the other endocrine glands.
Paraventricular nucleusSupraoptic nucleusMedian eminenceAnterior pituitaryHypothalamusPortal system
InfundibulumPosterior pituitaryThyroidTSHProlactinMammary glandAdrenal cortexACTHGrowth
hormoneBone MuscleAdipose
tissueGonadotropinsFSHLHOvary Testis