What stimulates the hypothalamic pituitary gonadal axis?
During puberty the HPG axis is activated by the secretions of estrogen from the ovaries or testosterone from the testes. This activation of estrogen and testosterone causes physiological and psychological changes.
At what age during the fetal and childhood periods is the hypothalamic pituitary axis most active?
During foetal life, the activity peaks at midgestation and decreases towards birth, possibly due to the suppressive effects of placental hormones, especially oestrogens. At birth, gonadotrophin levels are low, but at around 1 week of age the hypothalamic-pituitary axis becomes active again.
What is the function of hypothalamic pituitary gonadal axis?
The hypothalamic–pituitary–gonadal (HPG) axis is primarily responsible for regulating reproductive activity and the release of ovarian hormones in animals and humans (Couse et al., 2003; Meethal and Atwood, 2005).
What specifically causes the activation of the HPG axis?
HPG axis activity increases with the onset of puberty, as evidenced by increasing numbers and amplitude pulses of gonadotropins, LH, and follicle stimulating hormone (FSH). Based on the pulsatile secretion feature, basal gonadotropin measurements poorly discriminate between prepubertal and early pubertal children (23).
Where is the hypothalamic pituitary adrenal axis located?
The hypothalamic-pituitary-adrenal axis, or HPA axis as it is commonly called, describes the interaction between the hypothalamus, pituitary gland, and adrenal glands. The hypothalamus and pituitary gland are located just above the brainstem, while the adrenal glands are found on top of the kidneys.
What is hypothalamic-pituitary dysfunction?
The hypothalamic-pituitary-ovarian (HPO) axis is a tightly regulated system controlling female reproduction. Group I ovulation disorders involve hypothalamic failure characterized as hypogonadotropic hypogonadism. Group II disorders display a eugonadal state commonly associated with a wide range of endocrinopathies.
What is the fetal hypothalamic pituitary adrenal axis?
The fetal hypothalamus-pituitary-adrenal (HPA) axis is at the center of mechanisms controlling fetal readiness for birth, survival after birth and, in several species, determination of the timing of birth.
Which hormone is responsible for the negative feedback loop of ovulation?
Progesterone is chiefly responsible for a negative feedback effect at the hypothalamic level, which decreases GnRH pulse frequency. Estradiol exerts both a positive and negative feedback effect, mostly at the pituitary level, and the use of steroids to prevent ovulation combines both effects.
What happens when HPA axis is suppressed?
HPA axis suppression resulting in reduced cortisol response may cause an impaired stress response and an inadequate host defence against infection, which remain a cause of morbidity and death. Suppression commonly occurs in the first days after cessation of glucocorticoid therapy, but the exact duration is unclear.
What is hypothalamic pituitary dysfunction?
How would the body be affected if the hypothalamus stopped functioning?
The hypothalamus instructs the adrenal glands to release adrenaline and cortisol into the bloodstream. If the hypothalamus is not functioning properly, the adrenal glands will also stop functioning. This can lead to adrenal insufficiency, which causes: Weight loss.
How does negative feedback control the function of the hypothalamic pituitary gonadal HPG axis?
The HPG axis is controlled by a negative feedback loop. In the healthy brain, the hypothalamus releases gonadotropin-releasing hormone (GnRH) into the median eminence, and then GnRH is transported via the hypophyseal portal system to the anterior pituitary where it acts on its receptor (GnRHR).
How is the hypothalamic pituitary and gonadal axis related?
The hypothalamic–pituitary–gonadal axis ( HPG axis) refers to the hypothalamus, pituitary gland, and gonadal glands as if these individual endocrine glands were a single entity. Because these glands often act in concert, physiologists and endocrinologists find it convenient and descriptive to speak of them as a single system.
Where are the GnRH neurons located during puberty?
Mechanism The mechanism of the initiation of puberty is not entirely understood; however, it is known that the GnRH neurons are the primary role player in the initiation of puberty. The GnRH neurons develop in the olfactory placode and then migrate to the area of the hypothalamus during the gestational period.
How does the hypothalamus control the initiation of puberty?
GnRH neurons of the hypothalamus control the initiation of puberty. The pulsatile secretion of GnRH by these neurons causes the changes of puberty. Currently, there are increasing amounts of evidence showing that kisspeptin neurons in the arcuate nucleus release neurokinin B and dynorphin to generate the pulsatile secretion of GnRH.[1]
When does central precocious puberty occur in girls?
Precocious puberty is characterized by the development of secondary sexual characteristics before the age of eight years in girls and nine years in boys. The premature activation of GnRH secretion leading to central precocious puberty has remarkable female gender predominance and more than 90 percent of the affected girls have the idiopathic form.