Endocrine System
Chapter 34
Hormones
 A hormone is a chemical signal that is secreted into
the circulatory system and communicates regulatory
messages within the body.
 Hormones may reach all parts of the body, but only
certain types of cells, target cells, are equipped to
respond.
Systems of Internal Communication
 Animals have two systems of internal communication
and regulation:
 The nervous system
 The endocrine system
Systems of Internal Communication
 The nervous system conveys high-speed electrical signals along
specialized cells called neurons.
 The endocrine system, made up of endocrine glands, secretes
hormones that coordinate slower but longer-acting responses to
stimuli.
 These 2 systems work in together in maintaining homeostasis.
 Example: The endocrine system is all about hormones and growth,
the nervous system signals to the glands that there is a need for a
hormone.
Hormones
 Advantages of using chemical messengers:
 Chemical molecules can spread to all tissues through the
blood.
 Chemical signals can persist longer than electrical ones.
 Many different kinds of chemicals can act as hormones;
different hormones can target different tissues.
 Each gland can secrete more than 1 type of hormone
 Ex. Pituitary gland secretes 9 different hormones including
GH (growth hormone), oxytocin, TSH (thyroid)
Glands
 Many hormones are secreted by ductless endocrine
glands.
 Obtain raw materials from and secrete hormones directly
into the bloodstream.
 Example: pituitary
 Exocrine glands have ducts for discharging secretions
onto a free surface.
 Sweat glands, salivary glands, enzyme-secreting glands
in the digestive tract.
Control Pathways and Feedback
Loops
 A common feature of
control pathways is a
feedback loop connecting
the response to the initial
stimulus.
 Feedback inhibition: an
increase in a substance
causes the production of that
substance to decrease.
The Pancreas
 The pancreas is located
behind the stomach and is
connected to the small
intestine by a small tube.
 It secretes digestive
enzymes into the digestive
tract (exocrine function).
 Endocrine function –
production of insulin and
glucagon.
Glucose Homeostasis
 The islets of Langerhans:
-Beta cells in the
pancreas secrete insulin
and glucagon. (regulate
blood sugar
 Insulin removes glucose
from the blood.
 Glucagon returns
glucose to the blood.
Diabetes Mellitus
 Endocrine disorder
 Body fails to produce or properly respond to
insulin
 Type I: develops before age 15, immune
system kills beta cells, little/no secretion of
insulin
 Type II: after age 40, produce low to normal
amts of insulin. Body does not respond to the
hormone. Can be caused by obesity
Sex hormones
 Puberty: rapid growth and development, occurs
between ages 9-15
 Female reproductive hormone, estrogen:
responsible for, breast development, and
widening hips
 Male reproductive hormone, testosterone:
responsible for facial hair, increased muscle
development and deepening of the voice.