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Transcript
Key Issues part one:
• Almost every subdivision of the CNS
communicates with the Hypothalamus.
• The hypothalamus communicates with
virtually all peripheral organs.
• The hypothalamus responds to input from
the peripheral organs that it regulates.
• The median eminence (at the floor of the
third ventricle) is the gateway through
which the hypothalamus exerts control.
Key Issues:part 2
• Most hypothalamic neurons exert regulatory control by
releasing peptides and DA into the vasculature running
through the infundibular stalk.
• Axons of the hypothalamic neurons can also pass
through this stalk to the vascular beds of the posterior
pituitary. The vascular beds there can transport peptides
to the anterior pituitary.
• These peptides can be made within the PVH and
arcuate nuclei and released into the anterior pituitary.
• So, neural signals coming into the hypothalamus can be
integrated, translated into a “humoral” signal, and directly
affect peripheral endocrine systems.
Key Issues:Part 3
• Neurons in the PVN and supraoptic nuclei
project give rise to axons that run through
the median eminence and the stalk and
synapse in the posterior pituitary. This
provides a direct neural connection
between the hypothalamus and the
pituitary.
Development of the
Hypophysial-portal system:
The Transition between the
Hypothalamus and the Pituitary:
Alternative labels for the same
system:
Relevant Cell Types:
Adenohypophesis or Anterior
Pituitary
Acidophils
Cells that contain the glycoprotein hormones:
•Somatotropes which produce growth hormone
•Lactotropes which produce prolactin
Basophils
Cells that contain the glycoprotein hormones:
•Thyrotropes which produce thyroid stimulating hormone
•Gonadotropes which produce luteinizing hormone or follicle-stimulating
hormone
•Corticotropes which produce adrenocorticotrophic hormone
Due the high carbohydrate content of the hormones within acidophils, they
also stain bright purple with PAS stains.
chromophobes
These are cells that have minimal or no hormonal content. Many of
the chromophobes may be acidophils or basophils that have
degranulated and thereby are depleted of hormone. Some
chromophobes may also represent stem cells that have not yet
differentiated into hormone-producing cells.
The Neurohypophysis has herring bodies that contain neurosecratory
granules that produce oxytocin and antidiuretic hormone.
FIGURE 2 Depiction of a coronal section through the median eminence cell showing its three major
zones and the typical projections of neuroendocrine cells to the external zone containing the portal
capillaries leading to the anterior pituitary gland. iii, third ventricle; E, ependymal zone; ZI, internal
zone; ZE, external zone.
Anter
ior
Pituit
ary
Poste
rior
Pituit
ary
Growth hormone
Liver, adipose
tissue
Promotes growth (indirectly), control of protein, lipid and
carbohydrate metabolism
Thyroid-stimulating
hormone
Thyroid gland
Stimulates secretion of thyroid hormones
Adrenocorticotropic
hormone
Adrenal gland
(cortex)
Stimulates secretion of glucocorticoids
Prolactin
Mammary
gland
Milk production
Luteinizing hormone
Ovary and
testis
Control of reproductive function
Follicle-stimulating
hormone
Ovary and
testis
Control of reproductive function
Antidiuretic
hormone
Kidney
Conservation of body water
Oxytocin
Ovary and
testis
Stimulates milk ejection and uterine contractions
Key Issues part one:
• Almost every subdivision of the CNS
communicates with the Hypothalamus.
• The hypothalamus communicates with
virtually all peripheral organs.
• The hypothalamus responds to input from
the peripheral organs that it regulates.
• The median eminence is the gateway
through which the hypothalamus exerts
control.
Key Issues:part 2
• Most hypothalamic neurons exert regulatory control by
releasing peptides and DA into the vasculature running
through the infundibular stalk.
• Axons of the hypothalamic neurons can also pass
through this stalk to the vascular beds of the posterior
pituitary. The vascular beds there can transport peptides
to the anterior pituitary.
• These peptides can be made within the PVH and
arcuate nuclei and released into the anterior pituitary.
• So, neural signals coming into the hypothalamus can be
integrated, translated into a “humoral” signal, and directly
affect peripheral endocrine systems.
Key Issues:Part 3
• Neurons in the PVN and supraoptic nuclei
project give rise to axons that run through
the median eminence and the stalk and
synapse in the posterior pituitary. This
provides a direct neural connection
between the hypothalamus and the
pituitary.
Structures that directly influence
the hypothalamus…
- nucleus of the solitary tract - this nucleus collects all of the visceral
sensory information from the vagus and relays it to the hypothalamus
and other targets. Information includes blood pressure and gut
distension.
- reticular formation - this catchall nucleus in the brainstem receives a
variety of inputs from the spinal cord. Among them is information
about skin temperature, which is relayed to the hypothalamus.
- retina - some fibers from the optic nerve go directly to a small
nucleus within the hypothalamus called the suprachiasmatic nucleus.
This nucleus regulates circadian rhythms, and couples the rhythms to
the light/dark cycles.
(MORE) Structures that directly
influence the hypothalamus
- circumventricular organs - these nuclei are located along the
ventricles, and are unique in the brain in that they lack a blood-brain
barrier. This allows them to monitor substances in the blood that
would normally be shielded from neural tissue. Examples are the
OVLT, which is sensitive to changes in osmolarity, and the area
postrema, which is sensitive to toxins in the blood and can induce
vomiting. Both of these project to the hypothalamus.
- limbic and olfactory systems - structures such as the amygdala, the
hippocampus, and the olfactory cortex project to the hypothalamus,
and probably help to regulate behaviors such as eating and
reproduction.
How does the hypothalamus
maintain a particular set point??
In addition to the feed-back loops, the hypothalamus also has some
intrinsic receptors, including thermoreceptors and osmoreceptors to
monitor temperature and ionic balance, respectively.
Once the hypothalamus is “aware” of a problem, how does it fix it?
Essentially, there are two main outputs:
1. Neural signals to the autonomic system - the (lateral) hypothalamus
projects to the (lateral) medulla, where the cells that drive the
autonomic systems are located. These include the parasympathetic
vagal nuclei and a group of cells that descend to the sympathetic
system in the spinal cord. With access to these systems, the
hypothalamus can control heart rate, vasoconstriction, digestion,
sweating, etc.
2. Endocrine signals are sent to/through the pituitary (recall that an
endocrine signal is a chemical signal sent via the bloodstream).
Ultimately the hypothalamus can control every endocrine gland in
the body, and alter blood pressure (through vasopressin, etc.),
body temperature, metabolism (through TSH), and adrenaline
levels (through ACTH).
COMING NEXT – IS IT ALWAYS
FUNCTIONAL TO MAINTAIN A
SET POINT???