Download Endocrine System, Maintaining Homeostasis

Endocrine System,
Maintaining Homeostasis
Chemical Control vs
Electrochemical Control
• Cells communicate electrochemically
(nerve impulse) very rapidly. Cells also
communicate chemically (hormones).
Chemical communication is slower but the
results last longer.
• Hormones are chemical regulators
produced by cells in one part of the body
that affect cells in another part of the body.
• In most animals, chemical communication
takes place through the glands. Glands
are specialized to secrete substances
needed by the body. The two major types
of glands are:
1. Exocrine Glands – release chemicals
into ducts that empty into an organ where
the chemical produces its effect.
Examples of Exocrine Glands
a) Salivary glands – release saliva into the
mouth
b) Sweat glands – release sweat to the
skin’s surface
c) Digestive glands – release enzymes that
digest food
2. Endocrine Glands – release chemicals
directly into the bloodstream to carry
chemicals to areas where they are
needed. Lacking ducts, they are
sometimes called ductless glands.
Endocrine glands produce chemicals
called hormones.
Examples of Endocrine Glands
a) Adrenal gland – produces adrenaline
b) thyroid – produces thyroxine
Types of Hormones
Hormones are divided into two main classes
based on their chemical structure.
1. Protein hormones – are composed of
long chains of amino acids’
2. Steroid hormones – are made from
cholesterol
How Hormones Work
• Glands are made up of regulator cells.
• These cells detect change in the
environment (internal or external).
• When these cells detect a change, they
respond by producing a hormone.
• The hormone circulates throughout the
blood stream and is delivered to the cells
that respond to change.
• The cells affected by hormones are called
target cells.
One-messenger model
• The one-messenger model of hormone
action means hormones enter the cell
membrane directly to exert their effect.
• Steroid hormones work this way.
Two-messenger model
• Some hormones cannot pass directly through
the cell membrane. First, they attach to a
special protein on the cell’s surface called a
receptor.
• The interaction between the hormone and the
receptor activates an enzyme which causes the
production of a second messenger that
produces the desired effect.
• This is called the two-messenger model of
hormone action. Protein hormones work this
way.
• Assigned Readings: P. 372, 373, 374