- know where oxytocin is synthesized
- know whic gland secretes oxytocin
- know what the effects of oxytocin are
- know what the target tissues for oxytocin are
- know how oxytocin secretion is regulated
This packet covers the hormone oxytocin: synthesis, secretion, target tissues, effects, and regulation. This hormone will be discussed again when the topic of reproductive physiology comes up (parturition and breast feeding).
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Oxytocin is secreted from the posterior pituitary (neurohypophysis) and is regulated by the paraventricular nuclei of the hypothalamus. This hormone is synthesized by the neurons of the paraventricular nucleus and are transported and stored in the neurohypophysis. When the neurons of the paraventricular nuclei become stimulated, they will generate action potentials to the neurohypophysis and stimulate the secretion of oxytocin.
One of the target tissues for oxytocin is the myometrium of the uterus (smooth muscle). When the fetus of a pregnant female starts to exert enough pressure on the cervix this will stimulate mechanoreceptors (pressure receptors) to start generating action potentials to the brain (hypothalamus). Then this will stimulate the secretion of oxytocin. When oxytocin interacts with its receptors on within the uterus this will stimulate the muscle tissue to contract; forcing the fetus to push even harder against the cervix. As more pressure is applied to the cervix more action potentials are generated to the brain, which will increase oxytocin levels until the fetus is completely birthed/expelled from the mother. Once the child is born oxytocin levels and labor contractions will slowly decline as the cervix returns back to normal. This is one of the few examples of a positive feedback loop in the human body.
The other target tissues for oxytocin, or where oxytocin receptors are found, are the mammary glands. Oxytocin and prolactin work together to make the process of breast feeding occur. Recall that prolactin stimulates the production of milk, but only the production and not the ejection. Oxytocin is the hormone that stimulates the ejection of milk during breast feeding. Once the child begins to suckle on the nipple of the mother it will stimulate mechanoreceptors around the areola (colored part of the nipple). These will in turn generate action potentials to the brain (hypothalamus) and stimulate the secretion of oxytocin. Once oxytocin reaches the mammary glands, mile will be ejected and the child will be recieve the milk. Physical contact isn't the only stimulus that can stimulate the release of oxytocin in this situation, sometimes just a baby cyring or the smell or sight of a baby can activate the hypothalamus and stimulate the secretion of oxytocin; which can cause lactation when the mother is not breast feeding.
It is also said that oxytocin plays a role in behavior but this is just a theory. It is believed that breast feeding causes a sort of "bonding" between the mother and the child. Again, this is something that hasn't been proved, it's just theory.
Source: Mind of Aaron
Source: Self made
Source: Self made