Biology, Eighth Edition (Raven)

Chapter 46: The Endocrine System

Positive and Negative Feedback

What is the difference between positive and negative feedback? Many molecular and physiological processes are controlled by feedback mechanisms. In a feedback loop the product of a process, such as the breakdown of proteins into amino acids, has an effect on the rate of the process. Negative feedback occurs when the rate of the process decreases as the concentration of the product increases. Positive feedback occurs when the rate of a process increases as the concentration of the product increases. Negative feedback controls the rate of a process to avoid accumulation of a product. The rate of a process will continuously accelerate under positive feedback as long as substrate is available and the product is not consumed by some other process.

View the animation below, then complete the quiz to test your knowledge of the concept.


1.	Which of the following ovarian hormones is involved in a positive feedback loop with the hypothalamus and the anterior pituitary?

		A)	progesterone
		B)	luteinizing hormone
		C)	gonadotropin releasing hormone
		D)	estrogen
		E)	gonadotropin

2.	Which of the following hormones is released by the anterior pituitary as a part of that positive feedback loop between it and the ovary?

		A)	progesterone
		B)	luteinizing hormone
		C)	gonadotropin releasing hormone
		D)	estrogen
		E)	gonadotropin

3.	Which of the following hormones is released by the corpus luteum after ovulation and causes a negative feedback loop with the hypothalamus and the anterior pituitary?

		A)	progesterone
		B)	luteinizing hormone
		C)	gonadotropin releasing hormone
		D)	estrogen
		E)	gonadotropin

4.	A positive feedback loop causes a self-amplifying cycle where a physiological change leads to even greater change in the same direction.

		A)	True
		B)	False

5.	A negative feedback loop is a process in which the body senses a change, and activates mechanisms to reverse that change.

		A)	True
		B)	False