CHAPTER 18
Hypothalamic Regulation of Hormonal Functions 275vessels
form a direct vascular link between the hypothalamus
and the anterior pituitary. Arterial twigs from the carotid arter-
ies and circle of Willis form a network of fenestrated capillaries
called the
primary plexus
on the ventral surface of the hypo-
thalamus (Figure 18–1). Capillary loops also penetrate the me-
dian eminence. The capillaries drain into the sinusoidal portal
hypophysial vessels that carry blood down the pituitary stalk to
the capillaries of the anterior pituitary. This system begins and
ends in capillaries without going through the heart and is there-
fore a true portal system. In birds and some mammals, includ-
ing humans, there is no other anterior hypophysial arterial
supply except capsular vessels and anastomotic connections
from the capillaries of the posterior pituitary. The
median emi-
nence
is generally defined as the portion of the ventral hypo-
thalamus from which the portal vessels arise. This region is
outside the blood–brain barrier (see Chapter 34).
HYPOTHALAMIC FUNCTION
The major functions of the hypothalamus are summarized in Ta-
ble 18–1. Some are fairly clear-cut visceral reflexes, and others in-
clude complex behavioral and emotional reactions; however, all
involve a particular response to a particular stimulus. It is impor-
tant to keep this in mind in considering hypothalamic function.RELATION TO AUTONOMIC FUNCTION
Many years ago, Sherrington called the hypothalamus “the head
ganglion of the autonomic system.” Stimulation of the hypothal-
amus produces autonomic responses, but the hypothalamus does
not seem to be concerned with the regulation of visceral func-
tion per se. Rather, the autonomic responses triggered in theTABLE 18–1
Summary of principal hypothalamic regulatory mechanisms.
Function Afferents from Integrating Areas
Temperature regulation Temperature receptors in the skin, deep tissues, spinal
cord, hypothalamus, and other parts of the brainAnterior hypothalamus, response to heat;
posterior hypothalamus, response to cold
Neuroendocrine control of:
Catecholamines Limbic areas concerned with emotion Dorsal and posterior hypothalamus
Vasopressin Osmoreceptors, “volume receptors,” others Supraoptic and paraventricular nuclei
Oxytocin Touch receptors in breast, uterus, genitalia Supraoptic and paraventricular nuclei
Thyroid-stimulating hormone (thyrotropin,
TSH) via TRHTemperature receptors in infants, perhaps others Paraventricular nuclei and neighboring
areas
Adrenocorticotropic hormone (ACTH) and
β
-lipotropin (
β
-LPH) via CRHLimbic system (emotional stimuli); reticular formation
(“systemic” stimuli); hypothalamic and anterior pituitary
cells sensitive to circulating blood cortisol level; suprachi-
asmatic nuclei (diurnal rhythm)Paraventricular nucleiFollicle-stimulating hormone (FSH) and lu-
teinizing hormone (LH) via GnRHHypothalamic cells sensitive to estrogens, eyes, touch re-
ceptors in skin and genitalia of reflex ovulating speciesPreoptic area; other areasProlactin via PIH and PRH Touch receptors in breasts, other unknown receptors Arcuate nucleus; other areas (hypothala-
mus inhibits secretion)
Growth hormone via somatostatin and GRH Unknown receptors Periventricular nucleus, arcuate nucleus
“Appetitive” behavior
Thirst Osmoreceptors, probably located in the organum vasculo-
sum of the lamina terminalis; angiotensin II uptake in the
subfornical organLateral superior hypothalamusHunger Glucostat cells sensitive to rate of glucose utilization; leptin
receptors; receptors for other polypeptidesVentromedial, arcuate, and paraventricu-
lar nuclei; lateral hypothalamus
Sexual behavior Cells sensitive to circulating estrogen and androgen, others Anterior ventral hypothalamus plus, in
the male, piriform cortex
Defensive reactions (fear, rage)
Sense organs and neocortex, paths unknown Diffuse, in limbic system and hypothala-
mus
Control of body rhythms
Retina via retinohypothalamic fibers Suprachiasmatic nuclei