The next structure that’s a part of the diencephalon that I want you to understand
is the hypothalamus. Like the thalamus, the hypothalamus is a collection of various nuclei.
You can see all kinds of nuclei identified here. So, what we will do next is I will guide
you through each one of these hypothalamic nuclear structures. First would be
paraventricular and supraoptic nuclei. You can see them identified in the image.
They are highlighted. Here’s your paraventricular nucleus and here’s your supraoptic nucleus.
Collectively, they are involved in the release of antidiuretic hormone, ADH as well as oxytocin.
ADH is involved in the regulation of fluid balance, so it helps to conserve water. Less water
is then eliminated in the urine as a result of its influence. If there’s a lesion that diminishes
ADH concentration, then the individual is no longer able to reabsorb water through the
tubular duct structures of the kidney and more water then is voided in the urine. This increased
urine production then results in diabetes insipidus. Oxytocin is involved in lactation in
women as well as labor or parturition. Oxytocin is a substance that causes uterine contractions.
Next is the preoptic area. The preoptic area is shown here in the shaded area. This is a very
important area for the regulation of body temperature, also sexual behavior and this helps
to define sexual dimorphism. That is the differences in function between men and women.
Lesions of the preoptic area would result in loss of control of sexual behavior. Amenorrhea
would be another symptom. Then impotence can also be a symptom with a lesion of this area.
The anterior hypothalamic nucleus is shown here in red. This too is involved in thermoregulation
but it’s going to help cool the body and it helps to regulate sleep. Lesion of this particular
nucleus would inhibit our ability to cool our body down. So we would have an increase
then in body temperature or hyperthermia that would result. Next, I want you to understand
the suprachiasmatic nucleus. This is shaded here in a light green color. It’s involved
in regulating circadian rhythms. This is a result of direct input from the retina. A lesion of this
nucleus would eliminate or disturb our circadian rhythms, our sleep-wake cycle. Next is the
dorsomedial nucleus. First is its function. It helps to regulate behaviors that are associated
with physiologic circadian rhythms. Those would include eating, drinking, and energy consumption.
It also regulates ingestive behavior as well as our cardiovascular responses to stress.
A lesion of this area would cause overeating or hyperphagia. If food intake is restricted, rage
outbursts may be provoked. So that ties back into the function of ingestive behavior. Another
nucleus of the hypothalamus is the ventromedial nucleus. It is highlighted right in through here.
It helps to regulate appetite, satiety, regulates our energy consumption, involved in fear
as an emotion, and also helps to regulate body temperature. A lesion of this nucleus can
result in hyperphagia as well as obesity syndrome. The posterior nucleus of the hypothalamus
is shown here. This is another area of the hypothalamus that’s involved in thermoregulation.
This helps to increase or heat our body. If there’s a lesion of this area, we have
a diminished ability to heat our body. So our body temperature becomes cooler than normal.
So we would have hypothermia as a result. Next, we have mammillary bodies.
Mammillary bodies, one of them is shown right in through here. Mammillary bodies collectively
control or modulate emotions. In addition, they help to regulate recollective memory.
If there is a lesion of this hypothalamic component, memory deficits can result. It’s also
involved in the pathogenesis of Wernicke's Encephalopathy. Here, we’re looking at the lateral
area of the hypothalamus. This area is involved in regulating appetite and satiety.
Pain perception is also a function of this hypothalamic nucleus as is thermoregulation,
digestive, and the control of blood pressure. Lesions can result in narcolepsy, motility
disorders or functional gastrointestinal disorders. Eating disorders can be associated
with lesions of the lateral area to include starvation and weight loss. Here, we’re looking
at an inferiorly located hypothalamic nucleus, the arcuate nucleus right in here in red.
This nucleus helps to control the anterior pituitary gland with respect to releasing and
inhibitory hormones. It helps to regulate hormone secretion, prolactin of the pituitary gland
via mainly dopamine and growth hormone-releasing hormone, helps to regulate appetite
and body weight via Neuropeptide Y. A lesion in this area can result in galactorrhea,
hyperphagia, and obesity syndrome. At this point, I want you to understand how
the hypothalamus influences the pituitary gland. The pituitary gland is made up of
adenohypophysis. Adenohypophysis is the area that we see in through here
as well as a neurohypophysis which is the area that we see here in the illustration.
The adenohypophysis is the true glandular component of the pituitary gland.
As mentioned in a previous slide, the arcuate nucleus is involved in releasing
hormones that have a positive or inhibitory influence on secretions of hormone-secreting
cells in the adenohypophysis. That is mediated through a portal system from the hypothalamus
to the adenohypophysis. We see that portal system right in through here. This is the
hypothalamic-hypophyseal portal system. Many of the hormones released from the hypothalamus
have a positive influence on the secretory cells in the adenohypophysis. They would be released
into this circulation and then would be delivered to the hormone-secreting cells in the
adenohypophysis to promote their release. The neurohypophysis is not a true glandular
structure but thus store ADH and oxytocin. As mentioned before, supraoptic and paraventricular
nuclei collectively synthesize these hormones. The neurons coming from those bodies travel
through the connection that exists here, the infundibulum down into the neurohypophysis.
Then these axons will store ADH and oxytocin within the neurohypophysis
until the appropriate stimulus promotes their release.