The Endocrine
System
• A system that controls
homeostasis by releasing
chemical messengers called
Hormones into the blood.
HOMEOSTASIS
• a process in which a constant
internal environment is
maintained, despite changes in
the external environment.
• Ex: Evaporation of water helps
regulate body temperature
To maintain Homeostasis the
endocrine system works in
conjunction with the nervous
system.
• Nervous system allows for the
body to adjust quickly to
changes whereas the time
required for a hormonal
response is much longer but the
effect is longer lasting.
• Hormones secreted from an
endocrine gland directly into the
bloodstream to be transported to a
target tissue is called an
Endocrine Hormone
Diagram of Endocrine Glands
Hormones effect the body in 4 ways:
• 1. Regulate the chemical
composition of the body
• 2. Help the body cope with
emergency demands like stress
and infection.
• 3. Help in growth and
development
• 4. Contribute to the basic
processes of reproduction.
Hormone Classification
1. Activation Site
Target Hormones
– affect specific cells or target
tissues.
Non-Target Hormones
- affect many cells or target tissues
2. Chemical Nature
Steroid – Fat soluble hormones
Diffuse into a specific cell and bind
with receptor molecules in the
cytoplasm which signals the cell to
produce a specific protein.
Protein – Water soluble hormones
Bind to receptor sites on the cell
membrane which activates
enzymes in
the cytoplasm to carry out a
specific function.
3. Tropic vs Non-Tropic
Tropic – have endocrine glands as
their target.
Non-Tropic – don’t have endocrine
glands as their targets.
***Diagram Booklet
HORMONE CONTROL:
• the amount of hormone
released is determined by the
need for it by the body, it is
regulated so there is not over or
under production of the
hormone.
• This type of control is called
NEGATIVE FEEDBACK
• Negative Feedback
maintains stability because
the product inhibits the
production of itself.
• To show negative feedback, we
use a flow chart called a Negative
Feedback Loop
• Two types depending on the type
of hormone:
1. Hormones controlled by Tropic Hormones
Environmental Change
Hypothalamus
Releasing Hormone
Pituitary Gland
Tropic Hormone
Gland
Non Tropic Hormone
Effect
(-)
2. Non Tropic Hormones Not Controlled
by a Tropic Hormone
Environmental Change
Gland
Hormone
Effect
(-)
Examples:
Low Metabolism
Hypothalamus
Releasing Hormone
Pituitary Gland
TSH
Thyroid Gland
Thyroxin
Increased Metabolism
(-)
High Ca 2+ Levels
ThyroidGland
Calcitonin
Increased
Ca 2+ uptake by bones
(-)