How is childbirth a positive feedback mechanism

The cervix contains stretch-sensitive nerve cells that monitor the degree of stretching the sensors. These nerve cells send messages to the brain, which in turn causes the pituitary gland at the base of the brain to release the hormone oxytocin into the bloodstream.

Oxytocin causes stronger contractions of the smooth muscles in of the uterus the effectors , pushing the baby further down the birth canal. This causes even greater stretching of the cervix. The cycle of stretching, oxytocin release, and increasingly more forceful contractions stops only when the baby is born. At this point, the stretching of the cervix halts, stopping the release of oxytocin.

A second example of positive feedback centers on reversing extreme damage to the body. Following a penetrating wound, the most immediate threat is excessive blood loss.

Less blood circulating means reduced blood pressure and reduced perfusion penetration of blood to the brain and other vital organs. If perfusion is severely reduced, vital organs will shut down and the person will die. The body responds to this potential catastrophe by releasing substances in the injured blood vessel wall that begin the process of blood clotting.

As each step of clotting occurs, it stimulates the release of more clotting substances. This accelerates the processes of clotting and sealing off the damaged area. Clotting is contained in a local area based on the tightly controlled availability of clotting proteins.

This is an adaptive, life-saving cascade of events. Homeostasis is the activity of cells throughout the body to maintain the physiological state within a narrow range that is compatible with life. Homeostasis is regulated by negative feedback loops and, much less frequently, by positive feedback loops.

Medication can lower blood pressure and lower the set point in the system to a more healthy level through a process of alteration of the set point in a feedback loop. Changes can be made in a group of body organ systems in order to maintain a set point in another system. This is called acclimatization. This occurs, for instance, when an animal migrates to a higher altitude than one to which it is accustomed. In order to adjust to the lower oxygen levels at the new altitude, the body increases the number of red blood cells circulating in the blood to ensure adequate oxygen delivery to the tissues.

Another example of acclimatization is animals that have seasonal changes in their coats: a heavier coat in the winter ensures adequate heat retention, while a light coat in summer assists in keeping body temperature from rising to harmful levels.

Learning Objectives Discuss the ways in which the body maintains homeostasis and provide examples of each mechanism. Key Points Negative feedback loops are used to maintain homeostasis and achieve the set point within a system. Negative feedback loops are characterized by their ability to either increase or decrease a stimulus, inhibiting the ability of the stimulus to continue as it did prior to sensing of the receptor.

Positive feedback loops are characterized by their ability to maintain the direction of a stimulus and can even accelerate its effect.

Acclimatization is characterized by the ability to change systems within an organism to maintain a set point in a different environment. During parturition, oxytocin cells increase their basal activity, and hence oxytocin secretion increases. In addition, the oxytocin cells discharge a burst of action potentials as each fetus passes through the birth canal. Each burst causes the secretion of a pulse of oxytocin, which sharply increases uterine tone; these bursts depend upon auto-stimulation by oxytocin released from the dendrites of the magnocellular neurons in the supraoptic and paraventricular nuclei.

Email address: Your name:. Example Question 9 : Feedback And Homeostasis. Possible Answers: equilibrium. Correct answer: positive feedback. Explanation : When production of a product in a system then causes more of the same product to be created it is known as positive feedback. Report an Error. Example Question 10 : Feedback And Homeostasis. Which of the following is an example of positive feedback? Possible Answers: Oxytocin causes uterine contractions, which cause more release of oxytocin.

Blood pressure rises, which causes vasodilation to lower blood pressure. Blood sugar rises, which causes the body to release insulin, which lowers blood sugar. Hunger causes metabolism to slow down, which reduces hunger.

Body temperature rises and causes sweat glands to open up and reduce body temperature. Correct answer: Oxytocin causes uterine contractions, which cause more release of oxytocin. Explanation : During positive feedback the production of an effect stimulates amplification of the same effect. Example Question 1 : Understanding Positive Feedback.

The control of which of the following hormones is regulated by positive feedback? Possible Answers: Glucagon. Correct answer: Oxytocin.

Explanation : Contraction of the uterus during childbirth causes the release of oxytocin, which stimulates stronger contractions of the uterus, causing more oxytocin release.

Example Question 2 : Understanding Positive Feedback. Which of the following is an example of a positive feedback loop? Possible Answers: A species of plant goes extinct, and over time, another species of plant adapts to fill the extinct plant's ecological niche. Plant and animal life slowly return to the slopes of a volcano following an eruption. Correct answer: A warming climate thaws out frozen methane a greenhouse gas in Siberia, leading to further warming.

Explanation : In a positive feedback loop, an increase in quantity A leads to an increase in quantity B. Example Question 3 : Understanding Positive Feedback. Possible Answers: Blood osmolarity.