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Find out about the hormones involved in Birth & Lactation

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Fiona White Physiology & Anatomy Hormones in Reproduction Find out about the hormones involved in Birth & Lactation. For each one, state where it is secreted from and what its effects are. Describe whether the mechanisms involved are negative or positive feedback. There are several different hormones that influence the female reproductive system and the two most fundamental hormones are progesterone and oestrogen. Progesterone is a steroid hormone and has a number of physiological effects on the body such as normalising blood clotting and vascular tone, zinc and copper levels, cell oxygen levels, and the use of fat stores for energy and it also assists in the thyroid function. It is usually required to normalise or restore changes caused by oestrogen. It affects all aspects of pregnancy, prepares breasts for lactation and the relaxation of joints and ligaments in preparation of childbirth. It can affect bowel movements usually causing constipation and back pain and raises the body temperature. ...read more.


The feedback loop causes the detector (pituitary gland) to either inhibit or stimulate the production of oestrogen or progesterone when required and keep the levels from deviating from the 'norm'. However, there is a more direct form of labour, which is caused from the release of the hormone oxytocin, a nine amino acid peptide hormone, synthesised in the neurosecretory cells in the hypothalamus which instructs the posterior lobe of the pituitary gland to secrete. The oestrogen encourages the uterine muscle to be more sensitive to oxytocin and therefore the uterine contracts further. This is known as positive feedback as when the mechanism causes the detector to increase, not decrease its message to the controller, the loop is positive. In this case, the hormone oxytocin is released during childbirth and stimulates the contractions of the uterus, which in turn stimulates more oxytocin production leading to further rapid contractions until the baby is born (parturition). ...read more.


After childbirth, prolactin levels fall as the internal stimulus for them is removed and therefore suckling from the baby on the nipple will promote further prolactin release and maintain the ability to continue to lactate. When the demand for breastfeeding is no more the lactation will usually cease with one to two weeks. High prolactin levels also tend to suppress the ovulatory cycle by inhibiting FSH. Oxytocin also plays a role in lactating, as it is this hormone that stimulates the myoepithelial cells causing the milk to be ejected into the ducts of the mammary glands. Suckling by the baby on the nipple again will stimulate oxytocin release. The release of oxytocin in this instance, and prolactin are controlled by negative feedback unlike the release of oxytocin during childbirth. Based on information taken from: 1. Biology a Functional Approach by MBV Roberts, 4th Edition 2. http://en.wikipedia.org/wiki/lactation 3. Pregnancy and Birth by Miriam Stoppard Published 1986 * * * * * ...read more.

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