The Endocrine System
Communication
throughout the body
What is the endocrine System?
• It is one of the 2 regulatory
systems in the human body
• It is made up of endocrine glands
that secrete chemical messengers
called hormones
• Hormones travel through the
blood allowing communication
through all parts of the body
Jobs of the Endocrine System
• Regulation of metabolism and
tissue maturation
• Regulation of ion concentrations
in the blood
• Maintaining water balance
• Helps control production of
immune cells
• Helps control heart rate and blood
pressure
. . . Still more!
• Controls blood glucose and other
nutrients
• Controls reproductive functions
• Regulates uterine contractions
and milk production
What is an endocrine gland?
• They are ductless organs that secrete their
hormones directly into the blood
• Hormones cause a response in other cells,
called target cells, but only if the other cells
have receptors.
Are there different types of hormones?
•
•
•
•
Yes!
There are two major categories:
Steroid hormones (lipid soluble)
Protein or peptide hormones (water soluble)
Steroid Hormones
• Can pass through the cell
membrane
• Have receptor molecules inside
the cell
• Usually take a longer period of
time to act
• Can be reproductive hormones
• Can be taken orally because they
will pass through the stomach
walls
Protein Hormones
• Cannot cross the cell membranes
• Need receptor molecules on the
outside of target cells
• Usually act very quickly
• Cannot be taken orally because
they cannot pass through the
stomach wall and will be digested
• A small amount can have a very
big affect due to signal
amplification
How do Steroid Hormones Work?
• 1. They pass through the cell membrane
• 2. They bind a receptor in the cytoplasm of a
target cell
• 3. The receptor/Hormone complex enters the
nucleus
• 4. Gene expression is started and new gene
products are formed
How do Protein hormones work?
• 1. The water-soluble hormone binds a
receptor on the outside of the cell membrane
• 2. A G protein activates an enzyme
(adenylate cyclase)
• 3. This causes a series of intracellular
changes that can amplify the original signal
• 4. Intracellular changes result in a change in
productivity, enzyme activation, gene
expression, cell shape, or cell motion
How are Hormones controlled?
• The Pituitary gland is the “master gland” that
controls the endocrine system
• The pituitary gland is controlled by its close
neighbor, the hypothalamus (part of the
nervous system)
Two types of feedback:
Negative:
• Used to maintain
values in a normal
range
• Maintains
homeostasis
• Ex: Insulin and
glucagon keep blood
glucose levels
constant
Positive:
• Used to break
homeostasis
• Levels of hormones
cause more hormone
to be produced.
• Ex: Oxytocin in child
birth causes
stronger and
stronger
contractions