Oxytocin Oxytocin is a peptide hormone. It is produced by secreted from the posterior pituitary and synthesized in neurones paraventricular and supraoptic nuclei of the hypothalamus. The functions are contraction of uterine smooth muscle during labor. Contraction of myoepithelial cells around breast ducts and alveoli to stimulate milk flow and it is queried as to whether oxytocin release actually causes the onset of labor. Oxytocin primarily affects uterine smooth muscle – increasing both the frequency and duration of action potentials during uterine contractions.
Oestrogen enhances the effects of oxytocin by lowering the membrane potential of smooth muscle cells. As the fetus enters the birth canal the lower segment of the uterus, the cervix and then the vagina are dilated; this causes reflex release of oxytocin. Strong uterine contraction cause further descent of the fetus, further distention and further release of oxytocin. The oxytocin is also involved in lactation. The lactation process occurs when stimulation of the nipple produces a neurohormonal reflex that causes the secretion of oxytocin.
In turn oxytocin causes contraction of myoepithelial cells of the mammary ducts and the ejection of milk. Regulation: Hypothalamic nuclei are under neurological control. Excitatory cholinergic and inhibitory neurones make contact with the neurosecretory neurones. It increases intracellular calcium leads to oxytocin secretion. Oxytocin binds to its receptors on targets cells (breast tissue and uterus). During labor the Oxytocin release may be triggered by cervical dilatation and also increase synthesis of oxytocin receptors during labor may be due to the increase in the oestrogen:progesterone ratio (progesterone falls during labor).
The milk ejection process, in which, the suckling from the newborn stimulates sensory neurones in the nipple and areolus. The impulses are then conducted in afferent fibres the spinal cord. It ascends via lateral, dorsal, and ventral spinothalamic tracts the midbrain. Then the excitatory fibres project from the midbrain to oxytocin neurones of the hypothalamus. Finally, the Oxytocin releases. Homeostasis depends on the action and interaction of a number of body systems to maintain a range of conditions within which the body can best operate.
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