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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_m
ode=true&safe=active&persist_safety_mode=1
Example of Dangerous positive feedback loops
1. 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?
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=PL1MDalK3VB
WvAOO1zcgE3NxsRnS8lD86i&index=2&safety_mode=true&safe=acti
ve&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.