Читать книгу Understanding Anatomy and Physiology in Nursing - John Knight - Страница 72

The term positive feedback is used to describe situations where deviations from the physiological set point are amplified and made larger. In humans the classic example of positive feedback occurs during childbirth (Figure 2.3). As the time of delivery nears at around 9 months, the muscular wall (myometrium) of the uterus is progressively stretched. This activates stretch receptors in the uterine wall and nerve impulses are generated and relayed to the brain. The posterior pituitary gland releases the hormone oxytocin, which circulates in the blood before binding to receptors on the smooth muscle cells of the myometrium, initiating uterine contraction.

This process is then perpetuated with uterine contraction leading to further oxytocin release, which then itself leads to further uterine contraction. This establishes a positive feedback loop during which the uterine contractions get more and more powerful and closer together until eventually the baby is delivered. Levels of oxytocin remain high in the mother’s blood following delivery; this hormone is often referred to as the ‘love hormone’ since it promotes feelings of love and affection which play a key role in the bonding between mother and newborn baby. Oxytocin also stimulates the ‘let-down reflex’ which pushes milk into the milk ducts of the breast towards the nipple to allow the baby to feed.

Figure 2.3 Childbirth (parturition)

Source: OpenStax (2013) Anatomy and Physiology. Rice University. Available at: https://openstax.org/books/anatomy-and-physiology/pages/preface

Now that you have completed the chapter, attempt the multiple-choice questions in Activity 2.3 to assess your knowledge.