Chapter 15.docx

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21 Apr 2012
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Chapter 15
The Secretory Hypothalamus
Overview of the hypothalamus
The hypothalamus integrates somatic and visceral responses in accordance with the needs of the
brain
Homeostasis
Homeostasis: maintaining the body within a narrow physiological range
Running in the snow: turn blue (blood to extremities), goose bumps (attempt to
raise fur),
Running in tropics: turn red (blood to surface to release heat), sweating
(evaporation of heat)
Structure and connections of HT
Three fnal zones: lateral, medial and periventricular
Periventricular zone: most of these cells lie next to wall of 3d ventricle. The
suprachiasmtic nucleus is involved in circadian rhythms through direct retinal
innervations. Neurosecretory neurons extend axons to pituitary.
Pathways to pituitary
The PT has a posterior (PP) and anterior (AP) portion
Ht control of PP
o The magnocellular neurosecretory cells are the largest neurons cells that extend their axons
down the stalk of the pituitary into the PP. The Scharres theorized that these could directly
release neurohormones into capillaries of PT.
They release two different types of polypeptides (9 AAs).
Oxytocin contracts the uterus to push the baby out during childbirth and also is
involved in lactation. It may be stimulated by tactile (baby suckling), visual (seeing
baby cry) or auditory (baby cry) stimuli. It can be inhibited by anxiety.
Vasopressin, aka antidiuretic hormone (ADH), regulates blood volume and salt
concentration. When we lack water for example, blood volume dec and blood salt
concen increase. As a result, pressure receptors in cardiovascular system and blood-
salt receptors in HT sense this. The kidneys release rennin, which converts a protein
from the liver (angiotensinogen) into (angiotensin I) and then A1 into A2. A2 affects
kidneys and a blood vessel to increase BP. A2 also affects the subfornical organ,
which is outside the BBB. Some of these cells will affect the HT to stimulate release
of ADH, and also cells in the lateral HT to produce thirst.
HT control of AP
o The AP is an actual glad rather than a part of the brain (unlike PP). It affects all other glands
(gonads, adrenal, thyroid, mammary). It’s controlled by the HT.
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