Problem 2

Background and context

Homeostasis refers to the ability of an organism to maintain a state of equilibrium despite the dynamic external environment. Temperature, heart rate, blood pressure, oxygen, calcium, water, and sodium are some of the physiological variables that must be maintained within a particular range; failure to do so may disrupt normal body function and lead to disease. In humans, different regulatory mechanisms are present to maintain homeostasis and have four major components: a stimulus, a receptor, a control center, and an effector. The homeostasis mechanism can be in the form of a positive feedback loop or a negative feedback loop.

A positive feedback loop intensifies the change in a system causing it to move away from the state of equilibrium. A positive feedback loop is uncommon and is considered normal only when it has a definitive endpoint.

• As shown in Figure 33.12, childbirth is an example of a positive feedback loop mechanism.
• The stimulus is the first uterine contractions during labor that push the baby towards the cervix and cause it to stretch.
• The receptors in the cervix communicate this change to the brain (control center) that causes the pituitary gland to secrete oxytocin.
• Oxytocin causes stronger contractions of the uterine muscles (effectors).
• Once the baby is born, which is the endpoint, the cervix stops stretching and oxytocin is no longer released.