Hypothalamus-Pituitary Complex and Feedback Control The hypothalamus-pituitary complex functions using negative feedback. This means that when the hypothalamus detects there is too little of a hormone in the blood stream it will send a message via hormones to the pituitary gland to send hormones to stimulate the gland that produces the needed hormone.

However, if the hypothalamus detects that there is too much of a particular hormone in the bloodstream, it will send a message via a hormone to the pituitary gland, which will stimulate the gland to produce less hormone.

Figure 13.13 on page 432

Negative Feedback Loops http://bcs.whfreeman.com/thelifewire/content/chp42/4202s.swf

Positive Feedback Loops This is a situation in which the body detects a change and works to increase that changes. Rarely does it aid in homeostasis but often disrupts the balance of life and can be life threatening.

Examples of beneficial positive feedback 1. Blood clotting the enzyme that produces the blood clot also produces more thrombin that further accelerates the reaction. 2. Childbirth the stretching of the uterus causes oxytocin to be secreted which in turn stimulates uterine contractions.

Feedback Loops http://www.youtube.com/watch?v=_QbD92p_EVs&safety_mode=true&safe=active&persist_safety_mode=1

Example of Dangerous positive feedback loops A small area of the heart is damaged in a hard attack, then the heart will then pump less blood. The heart is deprived of more blood flow and more of the heart muscle dies. Many diseases are positive feedback loops.

What is the difference between negative and positive feedback What is the difference between negative and positive feedback? Negative feedback occurs when the rate of the process decreases as the concentration of the product increases. It wants to avoid accumulation of a product. Positive feedback occurs when the rate of a process increases as the concentration of the product increases. http://www.youtube.com/watch?v=CLv3SkF_Eag&list=PL1MDalK3VBWvAOO1zcgE3NxsRnS8lD86i&index=2&safety_mode=true&safe=active&persist_safety_mode=1

Explain negative feedback using an example. Ex: Body Temperature Too hot, negative feedback will try to return your body to normal temp by making you sweat Too cold, negative feedback will try to return your body to normal temp by making you shiver

Explain positive feedback using an example. Ex: Breast Feeding - The baby nurses The more the breast is stimulated the more milk is produced If the baby stops breastfeeding, milk production stops

Practice Question Explain, using a negative feedback loop, what would happen if a tumor on the thyroid gland prevented the release of thyroxine.