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Ch. 39-1 & 39-2:
I. Endocrine System
FUNCTION: Transmit
chemical messages to
control growth, development
& metabolism
A. Hormones & Glands
Hormone = secreted
chemical in blood stream or
ducts that affects cells
Ex: Human growth
hormone (HGH), insulin
Gland = organ that releases
hormones into body
B. Compared to
nervous system
Message delivered
throughout the body
Body’s response is slower
than nerve impulse
C. Two Gland Types:
1) EXOCRINE gland –
secrete substance through
ducts (Ex: sweat, tears)
2) ENDOCRINE gland –
secretes hormones into
bloodstream
D. Endocrine Glands:
1. Pituitary gland (in brain)
• most important
•regulates other glands
2. Thyroid (in neck)
• makes thyroxine;
regulates metabolism
3. Adrenal glands (above
each kidney)
• makes epinephrine
(adrenaline) ; response to
stress
4. Pancreas
• makes insulin; regulates
glucose levels
E. Feedback
Mechanism
• adjusts to regulate
hormone levels
• maintains HOMEOSTASIS
Ex. Thyroid  thyroxine
Thyroid gland controlled by
hypothalamus & pituitary
gland
Hypothalamus sense low
levels of thyroxine in blood
& sends a message to
pituitary releases hormone
Signals
the thyroid to
produce & release
thyroxine
Thyroxine sent to cells to
speed metabolism
Low Hormone Level
Decrease
Hormone
Production
Increase
Hormone
Production
High Hormone Level