1. Hormones & Homeostasis
Endocrine System
Hormones & Homeostasis

2. Homeostasis Homeostasis maintaining internal balance in the body
organism must keep internal conditions stable even if environment changes
also called “dynamic equilibrium”
example: body temperature
humans:
too cold = shiver
too warm = sweat
lizard:
too cold = bask in sun
too warm = hide in shade

3. Regulation How we maintain homeostasis nervous system endocrine system
nerve signals control body functions
endocrine system
hormones
chemical signals control body functions

4. Controlling Body Temperature
Nervous System Control
Feedback
Controlling Body Temperature
nerve signals
brain
sweat
dilates surface blood vessels
high
body temperature
low
constricts surface blood vessels
shiver
brain
nerve signals

5. Hormones Why are hormones needed?
chemical messages from one body part to cells in other parts of body
communication needed to coordinate whole body
maintaining homeostasis
growth hormones

6. Endocrine System Endocrine system releases hormones
glands which secrete (release) chemical signals into blood
chemicals cause changes in other parts of body
growth hormones
sex hormones
response hormones
metabolism hormones
and more….
Hormones coordinate slower but longer–acting responses to stimuli such as stress, dehydration, and low blood glucose levels. Hormones also regulate long–term developmental processes by informing different parts of the body how fast to grow or when to develop the characteristics that distinguish male from female or juvenile from adult. Hormone–secreting organs, called endocrine glands, are referred to as ductless glands because they secrete their chemical messengers directly into extracellular fluid. From there, the chemicals diffuse into the circulation.

7. Responding to hormones
Lock and key system
hormone fits receptor on “target” cell
target cell
secreting cell
non- target cells
can’t read signal
can’t read signal

8. Glands Pineal Pituitary Thyroid Adrenal Pancreas Ovary Testes
melatonin
Pituitary
many hormones: master gland
Thyroid
thyroxine
Adrenal
adrenaline
Pancreas
insulin, glucagon
Ovary
estrogen
Testes
testosterone

9. Positive vs. Negative Feedback
Positive- Causes the variable to accelerate the change in the same direction of the initial disturbance. or
Negative- Causes the variable to change in a direction opposite to that of the initial change.

10. Maintaining homeostasis
Feedback
Maintaining homeostasis
hormone 1
gland
lowers body condition
high
specific body condition
low
raises body condition
gland
hormone 2

11. specific body condition
Negative Feedback
Response to changed body condition
if body is high or low from normal level
signal tells body to make changes that will bring body back to normal level
once body is back to normal level, signal is turned off
hormone 1
gland
lowers body condition
high
specific body condition

12. Regulation of Blood Sugar
Endocrine System Control
Feedback
Regulation of Blood Sugar
insulin
body cells take up sugar from blood
liver stores sugar
reduces appetite
pancreas
liver
high
blood sugar level
(90mg/100ml)
low
liver releases sugar
triggers hunger
pancreas
liver
glucagon

13. Positive or Negative Feedback? Oxytocin Production during birth
Baby pushes on the cervix
Nervous system sends a signal to the hypothalamus
Hypothalamus manufactures oxytocin
Oxytocin is transported to the posterior pituitary gland and released
Oxytocin stimulates uterine contraction
Loop stops when the baby leaves the birth canal

14. Positive or Negative Feedback? Thyroid Gland and TRH production
Hypothalamus senses that the thyroxine level in the blood is low
Hypothalamus secretes thyrotropin-releasing hormone (TRH)
TRH stimulates the anterior pituitary to secrete thyroid-stimulating hormone (TSH)
TSH stimulates the release of thyroxine by the thryoid gland
High levels of thyroxine in the blood inhibit the secretion of TRH and TSH (stops the release of additional thyroxine)
*This loop keeps the level of thyroxine in the blood relatively constant.

15. Feedback
Suppose the secretion of a certain hormone causes an increase in the concentration of substance X in the blood. A low concentration of X causes the hormone to be released. What is the effect on the rate of hormone secretion if an abnormal condition causes the level of X in the blood to remain very low?