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Endocrine System
Endocrine and Exocrine
 Endocrine
functions:
communication and control, via
hormones
 Exocrine functions: secrete
products into ducts that empty
on a surface or into a cavity
Endocrine
 Secretes
HORMONES into the blood
 Endocrine Organs are located
throughout the body: head, neck,
chest, abdomen, pelvis.
 Endocrine secretions (hormones)bind
to specific cells ( target organ cell)
that have receptors for that specific
hormone.
Mechanisms of Hormone Action
 Two
Major classes of hormones:
 Protein & Steroid
 Differ in mechanisms by which
they influence target cells
Protein Hormones
 Protein
hormones serve as “first
messengers”..that is they send
message to a specific target organ
for functions to take place. Then a
number of chemical reactions occur.
These reactions activate molecules
inside the cell…”second messengers”
 Second messengers provide
communication within a hormones
target cells.
Steroid Hormones
 Pass
directly through cell membrane
 Enters the nucleus of the cell
 Forms hormone receptor complex
that acts on the DNA
 New protein is formed in the
cytoplasm that causes a specific
effect in the target cell
Regulation of Hormone Secretion
 Controlled
by homeostatic feedback
 Negative Feedback: reverses the
direction of change in a physiological
system. Ex: Pancreatic Insulin to
lower blood sugar
 Positive Feedback: amplifies
physiological changes. Ex: Oxytocin
release during labor to advance birth
Endocrine Disease
 Caused
by:
 Hypersecretion: too much
hormone secreted
 Hyposecretion: too little
hormone secreted.
 See Table 10-1, pages 302-303