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Which hormone is primarily responsible for stimulating the release of LH and FSH from the pituitary gland?
The pituitary gland is known as the 'master endocrine gland' because it regulates only reproductive functions.
False
What role do feedback effects play in the hypothalamo-pituitary-gonadal axis?
They regulate hormone secretion and maintain homeostasis.
The hypothalamus releases _______ to stimulate the pituitary gland.
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Match the following hormones with their primary functions:
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What triggers the LH surge in the human reproductive cycle?
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Neonatal androgen exposure has no effect on the masculinization of the hypothalamus.
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What hormone is secreted by lactotrophs of the anterior pituitary gland?
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The _____ gland secretes GnRH, which stimulates the release of LH and FSH from the anterior pituitary.
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Match the following hormones with their functions:
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What is the main hormone secreted by magnocellular neurons in the hypothalamus?
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The anterior pituitary is derived from neural ectoderm.
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What effect does oxytocin have during labor?
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The hypothalamo-pituitary axis refers to the interaction between the __________ and the __________.
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Match the following hormones with their corresponding pituitary functions:
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Which nuclei are involved in producing gonadotrophin-releasing hormone (GnRH)?
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Testosterone can be converted to estrogens by the enzyme aromatase.
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What physiological role does the suprachiasmatic nucleus play?
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The posterior pituitary releases two main hormones: __________ and __________.
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What happens to GnRH receptors with continuous GnRH administration?
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The hypothalamo-pituitary portal vessels connect the hypothalamus directly to the posterior pituitary.
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What is the primary function of the intermediate lobe of the pituitary gland?
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The __________ nucleus is responsible for regulating drinking behavior and water balance.
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Which hormone is primarily regulated by GnRH pulses?
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In the hypothalamo-pituitary axis, what signals the anterior pituitary to release LH and FSH?
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Study Notes
Hypothalamus-Pituitary Axis
- The hypothalamus is part of the brain that controls many bodily functions including the hypothalamic-pituitary-gonadal axis (HPG axis), which is responsible for regulating reproductive functions.
- The pituitary gland, often called the "master endocrine gland," is regulated by the hypothalamus and produces various hormones such as LH, FSH, oxytocin, and prolactin, involved in growth, stress, and reproduction.
- The pituitary gland has two parts:
- Anterior pituitary (adenohypophysis): develops from the roof of the mouth.
- Posterior pituitary (neurohypophysis): develops from neural outgrowth.
- GnRH, a hormone produced by the hypothalamus, stimulates the release of LH and FSH from the anterior pituitary, leading to the production of sex hormones by the gonads.
- The hypothalamus, specifically the arcuate nucleus, acts as a GnRH pulse generator, controlling GnRH secretion in a pulsatile pattern.
- Feedback mechanisms regulate testosterone, estrogen, and progesterone production in the gonads, impacting LH and FSH levels.
- Inhibin, another hormone produced by the gonads, provides negative feedback to the pituitary, suppressing FSH production.
Posterior Pituitary Hormones
- Oxytocin and arginine vasopressin (AVP) are two nonapeptides produced by the posterior pituitary.
- Oxytocin plays a crucial role in:
- Luteolysis (destruction of the corpus luteum)
- Uterine contractions during labor
- Milk ejection during lactation
- Nursing behavior in mothers
- Contractions of seminiferous tubules and epididymis
GnRH Secretion
- The frequency of GnRH pulses varies depending on the species and reproductive state.
- Continuous GnRH administration leads to a reduction in LH and FSH production, as the pituitary GnRH receptors become downregulated.
Experimental Models
- Experiments involving gonadectomy, hypophysectomy, and pituitary stalk lesions provide insights into the roles of different hormones in regulating HPG axis function.
- Gonadectomy (removal of the gonads): Studying the effects of removing gonads and hormonal replacement allows researchers to investigate the influence of gonadal hormones on LH/FSH levels.
- Hypophysectomy (removal of the pituitary gland): Studying the effects of removing the pituitary gland and administering exogenous GnRH helps understand the pituitary's role in gonad function.
Regulation of Testis Function
- Testosterone exerts negative feedback on the hypothalamus and pituitary, controlling LH and FSH production.
- Castration of males leads to increased LH and FSH production due to the absence of negative feedback from testosterone.
- Testosterone can be converted to estrogen, but dihydrotestosterone (DHT) cannot.
HPG Axis in Ram
- Castrated rams with testosterone, DHT, or estrogen treatments show a decrease in LH and FSH production, along with a reduced GnRH pulse frequency.
- Hypothalamo-pituitary disconnected wethers, with GnRH pulses infused every 2 hours, show little effect of testosterone, DHT, or estrogen treatments on LH and FSH, indicating negative feedback at the hypothalamic level.
- Testosterone treatment in castrated wethers decreases GnRH concentrations in portal blood, reducing both pulse frequency and amplitude.
Regulation of Steroid Production
- GnRH, released by the hypothalamus, stimulates the pituitary to release LH and FSH.
- FSH, in the ovary, stimulates the growth of follicles, leading to increased estrogen production.
- The rise in estrogen triggers an LH surge due to a positive feedback mechanism, increasing the sensitivity to GnRH.
- After ovulation, estrogen exerts negative feedback on FSH and LH production.
Sexual Dimorphism in the HPG Axis
- Neonatal androgen exposure during development affects the HPG axis, preventing the response to estrogen in adults, resulting in sexual dimorphism.
- Neonatal androgen presence does not fully masculinize the hypothalamus.
Prolactin in Reproduction
- Prolactin, a protein hormone secreted by the pituitary gland, has circadian rhythmic release patterns.
- It plays a role in lactation and acts as a luteotrophin in some species.
- Prolactin surges with GnRH before ovulation in rats, but this pattern isn't clear in humans.
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Description
Explore the critical roles of the hypothalamus and pituitary gland in regulating bodily functions. This quiz focuses on the hypothalamic-pituitary-gonadal axis, the hormones involved, and the anatomy of the pituitary gland. Test your knowledge on the mechanisms behind reproductive hormone regulation.
