Difference between revisions of "Hypothalamus Differences in the Male and Female - Anatomy & Physiology"
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== Defeminizing the Hypothalamus in the Male == | == Defeminizing the Hypothalamus in the Male == | ||
| − | * Testosterone crosses the [[ | + | * Testosterone crosses the [[Blood Brain Barrier - Anatomy & Physiology|blood-brain barrier]] and is converted into oestradiol. |
* In the brain, oestradiol 'defeminizes' the [[Hypothalamus_-_Anatomy_%26_Physiology|hypothalamus]]. | * In the brain, oestradiol 'defeminizes' the [[Hypothalamus_-_Anatomy_%26_Physiology|hypothalamus]]. | ||
* Surge centre function is minimized. | * Surge centre function is minimized. | ||
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* Foetal ovaries produce oestradiol, but this does NOT defeminize the [[Hypothalamus_-_Anatomy_%26_Physiology|Hypothalamus]]. | * Foetal ovaries produce oestradiol, but this does NOT defeminize the [[Hypothalamus_-_Anatomy_%26_Physiology|Hypothalamus]]. | ||
| − | * A protein called alpha-fetoprotein binds oestradiol to prevent it from crossing the [[ | + | * A protein called alpha-fetoprotein binds oestradiol to prevent it from crossing the [[Blood Brain Barrier - Anatomy & Physiology|blood brain barrier]], therefore oestradiol cannot effect the [[Hypothalamus_-_Anatomy_%26_Physiology|Hypothalamus]]. |
* Alpha-fetoprotein is synthesized firstly by the embryonic yolk sac and then by the foetal liver. | * Alpha-fetoprotein is synthesized firstly by the embryonic yolk sac and then by the foetal liver. | ||
* Alpha fetoprotein functions as: | * Alpha fetoprotein functions as: | ||
Revision as of 14:57, 16 August 2009
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Introduction
- The hypothalamus is inherently female.
- Testosterone 'defeminizes' the brain during embryogenesis and eliminates the GnRH surge centre in males.
- The female foetus has no testes to produce testosterone, thus developes a hypothalamic GnRH surge centre.
Defeminizing the Hypothalamus in the Male
- Testosterone crosses the blood-brain barrier and is converted into oestradiol.
- In the brain, oestradiol 'defeminizes' the hypothalamus.
- Surge centre function is minimized.
- Complete 'defeminization' of the brain requires postnatal exposure to androgens.
- Continued exposure to androgens is required to render the surge centre inoperative.
- As a result, LH does not surge, it maintains a relatively consistent episodic pattern of secretion every day.
- Episodes occur every 2-6 hours in the postpubertal male.
- Steady, pulsatile GnRH and LH release results in a steady, pulsatile release of testosterone.
The Female Hypothalamus
- Foetal ovaries produce oestradiol, but this does NOT defeminize the Hypothalamus.
- A protein called alpha-fetoprotein binds oestradiol to prevent it from crossing the blood brain barrier, therefore oestradiol cannot effect the Hypothalamus.
- Alpha-fetoprotein is synthesized firstly by the embryonic yolk sac and then by the foetal liver.
- Alpha fetoprotein functions as:
- Foetal blood osmotic regulator
- Carrier of fatty acids
- As GnRH surges, LH and Oestradiol surge about every 20 days in the female.
- Surge frequency varies between species, dependent on the length of their oestrous cycles.
- Between surges, there are low amplitude LH pulses.