Changes

 

==Introduction==

==Introduction==

Reproductive hormones often have multiple roles and operate via [[Negative_Feedback_-_Anatomy_%26_Physiology|negative feedback systems]]. The information below will provide the main reproductive hormones in domestic species and their functions.

Reproductive hormones often have multiple roles and operate via [[Negative_Feedback_-_Anatomy_%26_Physiology|negative feedback systems]]. The information below will provide the main reproductive hormones in domestic species and their functions.

<br />

<br />

<br />

<br />

Although the hypothalamus via GnRH stimulates the secretion of LH and FSH, it cannot regulate LH and FSH independantly. Therefore another hormone produced from the developing ovarian follicle in the female and sertoli cells in the male acts as a negative feedback mechanism for FSH. Sex hormones also alter the level of production of GnRH from the hypothalamus via a negative feedback system. High concentrations of progesterone or testosterone will reduce the secretion of GnRH and also therefore the secretion of LH and FSH.

Although the hypothalamus via GnRH stimulates the secretion of LH and FSH, it cannot regulate LH and FSH independently. Therefore another hormone produced from the developing ovarian follicle in the female and sertoli cells in the male acts as a negative feedback mechanism for FSH. Sex hormones also alter the level of production of GnRH from the hypothalamus via a negative feedback system. High concentrations of progesterone or testosterone will reduce the secretion of GnRH and also therefore the secretion of LH and FSH.

===Luteinising Hormone (LH)===

===Luteinising Hormone (LH)===

<br />

<br />

<br />

<br />

Male sex hormones are regulated by negative feedback systems that operate at various levels within the male sex hormone system. The starting point for the production of testosterone (and therefore the production of spermatozoa)is the hypothalamus. The hypothalamus contains neuroendocrine cells that are capable of secreting a substance called '''Gonadotropin-releasing hormone''' or GnRH. GnRH stimulates cells in the anterior pituitary, via the "portal system" to secrete two intermediate hormones within the male sex hormone cycle; '''Luteinizing hormone''' (LH) and '''Follicle-Stimulating Hormone''' (FSH).  

Male sex hormones are regulated by negative feedback systems that operate at various levels within the male sex hormone system. The starting point for the production of testosterone (and therefore the production of spermatozoa)is the hypothalamus. The hypothalamus contains neuroendocrine cells that are capable of secreting a substance called '''Gonadotropin-releasing hormone''' or GnRH. GnRH stimulates basophilic cells in the adenohypophysis, via the "portal system" to secrete two intermediate hormones within the male sex hormone cycle; '''Luteinizing hormone''' (LH) and '''Follicle-Stimulating Hormone''' (FSH).  

<br />

<br />

<br />

<br />

A further non-reproductive role of activin is it's role in skin lesions where it is thought to stimulate keratinocytes.

A further non-reproductive role of activin is it's role in skin lesions where it is thought to stimulate keratinocytes.

===Prostaglandin F_2αO===

===Prostaglandin F_2α===

Prostaglanin is a C₂O fatty acid and is produced within the uterine endometrium and vesicular glands. Estradiol stimulates prostaglandin synthesis while progesterone inhibits it. The target tissue in the female is the [[Corpus_Luteum_Regression_-_Anatomy_%26_Physiology|corpus luteum]], uterine myometrium and ovulatory follicles. In the female PGF_2α cause luteolysis and can also cause the induction of tone and contractions within the uterus. It plays an important role in partuition in ruminants.

Prostaglanin is a C₂O fatty acid and is produced within the uterine endometrium and vesicular glands. Estradiol stimulates prostaglandin synthesis while progesterone inhibits it. The target tissue in the female is the [[Corpus_Luteum_Regression_-_Anatomy_%26_Physiology|corpus luteum]], uterine myometrium and ovulatory follicles. In the female PGF_2α cause luteolysis and can also cause the induction of tone and contractions within the uterus. It plays an important role in partuition in ruminants.

<br />

<br />

<br />

<br />

If a pregnancy is to remain viable then luteolysis needs to be avoided and this is achieved where concentrations of PGF_2α remain below a threshold level allowing the corpus luteum to continue to secrete progesterone and thus maintain pregnancy. There are two main factors involved in the regulation of uterine secretions of PGF_2α; oxytocin secretions from the corpus luteum and molecules secreted by the developing embryo that facilitate the maternal recognition of pregnancy.

If a pregnancy is to remain viable then luteolysis needs to be avoided and this is achieved where concentrations of PGF_2α remain below a threshold level allowing the [[Corpus_Luteum_Regression_-_Anatomy_%26_Physiology|corpus luteum]] to continue to secrete progesterone and thus maintain pregnancy. There are two main factors involved in the regulation of uterine secretions of PGF_2α; oxytocin secretions from the [[Corpus_Luteum_Regression_-_Anatomy_%26_Physiology|corpus luteum]] and molecules secreted by the developing embryo that facilitate the maternal recognition of pregnancy.

Oxytocin secretion via the  [[Corpus_Luteum_Regression_-_Anatomy_%26_Physiology|corpus luteum]] stimulates endometrial production of PGF_2α and by the end of the [[Oestrous_Cycle_-_Anatomy_%26_Physiology|luteal phase]] the concentration of oxytocin and the number of oxytocin recptors within the endometrium allow the production of enough PGF_2α to breach the threshold level and cause luteolysis. During pregnancy the embryonically produced [[Maternal_Recognition_of_Pregnancy_-_Anatomy_%26_Physiology|pregnancy recognition]] molecules inhibit the secretion of PGF_2α from the endometrium ensuring that luteolysis cannot occur.

<br />

<br />

<br />

<br />

Oxytocin secretion via the corpus luteum stimulates endometrial production of PGF_2α and by the end of the luteal phase the concentration of oxytocin and the number of oxytocin recptors within the endometrium allow the production of enough PGF_2α to breach the threshold level and cause luteolysis. During pregnancy the embryonically produced [[Maternal_Recognition_of_Pregnancy_-_Anatomy_%26_Physiology|pregnancy recognition]] molecules inhibit the secretion of PGF_2α from the endometrium ensuring that luteolysis cannot occur.

Normally the concentration of PGF_2α in arterial blood is relatively low due to extensive metabolism by PGF_2α-dehydrogenase (in especially the lungs). These levels are below the threshold required to cause luteolysis as PGF_2α production in early gestation is low.

<br />

<br />

<br />

<br />

Normally the concentration of PGF_2α in arterial blood is relatively low due to extensive metabolism by PGF_2α-dehydrogenase in especially the lungs). These levels are below the threshold required to cause luteolysis as PGF_2α production in early gestation is low.

The  [[Ovary_-_Anatomy_%26_Physiology#Arterial_Supply|ovarian artery]] is wrapped around the uterine vein. This creates a countercurrent mechanism by which the lipid soluable prostaglandins are able to diffuse from the uterine vein into the [[Ovary_-_Anatomy_%26_Physiology#Arterial_Supply|ovarian artery]]. During the latter stages of the [[Oestrous_Cycle_-_Anatomy_%26_Physiology|luteal phase]] as PGF_2α production increases luteolysis will occur as PGF_2α Is able to reach its target in the ovary before being metabolized in systemic circulation.

<br />

<br />

<br />

<br />

The ovarian artery is wrapped around the uterine vein. This creates a countercurrent mechanism by which the lipid soluable prostaglandins are able to diffuse from the uterine vein into the [[Ovary_-_Anatomy_%26_Physiology#Arterial_Supply|ovarian artery]]. During the latter stages of the luteal phase as PGF_2α production increases luteolysis will occur as PGF_2α Is able to reach its target in the ovary before being metabolized in systemic circulation.

Horses and pigs do not poses this countercurrent mechanism. In these spp. the [PGF_2α-dehydrogenase] in systemic circulation is much lower in order to induce luteolysis when Prostaglandin concentration rises.

===Prostaglandin (PGE₂)===

===Prostaglandin (PGE₂)===

<br />

<br />

<br />

<br />

In females it's target tissue is the [[Corpus_Luteum_Regression_-_Anatomy_%26_Physiology|corpus luteum]] and the oviduct where it helps induce ovulation and the secretion of progesterone from the corpus luteum. PGE₂ also plays an important role during labour where it aids the softening of the cervix and aids stimulation of uterine contractions.

In females it's target tissue is the cervix (it is a potent cervical dilator), [[Corpus_Luteum_Regression_-_Anatomy_%26_Physiology|corpus luteum]] and the oviduct where it helps induce ovulation and the secretion of progesterone from the corpus luteum. PGE₂ also plays an important role during labour where it aids the softening of the cervix in animals with a soft-type cervix(equine and human) and aids stimulation of uterine contractions. It can thus be used to prepare the tract for parturition.

===Human Chorionic Gonadotrophin (hCG)===

===Human Chorionic Gonadotrophin (hCG)===

[[Category:To Do - Review]]

[[Category:To Do - Review]]

[[Category:Reproductive System - Anatomy & Physiology]]

[[Category:Reproductive System - Anatomy & Physiology]]