Question

Q. Discuss the details of secretion, regulation and function on target tissue of hormone Oxytocin.

Answer 1

- Oxytocin is a peptide hormone which is produced by the neurosecretory cells of the paraventricular nucleus of hypothalamus (some amount of oxytocin is also produced by supraoptic nucleus although it mainly produces vasopressin).

- From the hypothalamus, oxytocin is transported to the posterior pituitary gland where it is temporarily stored and later released when needed.

- Oxytocin is secreted in response to the cervical stretching during childbirth or due to suckling of the nipples by the baby during breastfeeding. During childbirth, cervical dilation and stretching sends signals to the hypothalamus which produces oxytocin. Oxytocin is released from the posterior pituitary gland which travels through bloodstream and reach the uterus where it causes severe contraction of uterine musculature which further dilates the cervix thus helping in childbirth.

- Oxytocin also regulates "mild let down" reflex. During breastfeeding when the baby sucks the nipples it causes secretion and release of oxytocin from the brain that acts on the mammary glands and cause contraction of myoepithelial cells releasing the milk. Although milk production in the mammary glands is controlled by the hormone prolactin secreted from the anterior pituitary gland. Oxytocin regulates the release of milk from the mammary glands during breastfeeding.

- Oxytocin acts on its target tissues (mainly mammary glands and uterus) through G-protein coupled receptors. The binding of oxytocin to the cell membrane of its target tissue (mainly the myoepithelial cells of mammary glands and myometrium of uterus) causes influx of calcium ions which increases the level of calcium ions inside the cells helping in contraction of the muscle cells.