Packet 18 Notes
Aim: The Endocrine System
(A) HORMONES
 Hormones: substances secreted (released) by cells that act to regulate the activity of other cells in the body
 Functions of hormones are:
1. to regulate growth, development, behavior, and reproduction
2. to coordinate the production, use and storage of energy
3. to maintain homeostasis through temperature regulation, metabolism,
excretion and water and salt balance
4. to respond to stimuli outside the body
 Hormones act as chemical messengers, carrying instructions that cause cells to change their activities
 The instructions a hormone carries are determined by both the hormone itself and the cell it affects
 Each hormones is very specific about which types of cells can receive its instructions
 Similar to enzymes and their lock-and-key model
(B) ENDOCRINE GLANDS AND TISSUES
 Endocrine glands: ductless organs that secrete hormones directly into the bloodstream
 All of the endocrine glands and hormone secreting tissues make up the endocrine system—which coordinates
all of the body’s sources of hormones
 Exocrine glands: deliver substances through ducts which transport the substances to specific locations inside
and outside the body
(C) HOW HORMONES WORK
 Each hormone works with a specific target cell
 They bond to specific receptor molecules (proteins) found on the cell membrane—this causes a change inside
the target cell
 Some hormones pass right through the cell membrane
 Only small amounts of hormones are usually needed to produce the required effect
(D) FEEDBACK MECHANISMS
 Endocrine system plays a very important role in homeostasis—it must maintain the amounts of various
hormones that are needed within the body
 Feedback mechanisms—detect the amount of hormones and then adjust as needed
1. positive feedback—if high levels of a hormone are detected,
the output of even more hormone is then
stimulated
2. negative feedback—a change in one direction stimulates the
control mechanism to counteract further
change in the same direction
(E) HUMAN ENDOCRINE SYSTEM
NAME
FUNCTION
LOCATION
HORMONES
Hypothalamus
Makes hormones that control
In the brain
Releasing hormones
Pituitary
Secretes hormones that
Base of the skull
Oxytocin
the pituitary gland
directly regulate many body
Growth hormone (GH)
functions and controls the
FSH
actions of several other
LH
endocrine glands
Thymus
Helps to regulate the immune
Chest cavity
thymosin
Adrenal
Help the body respond to
On the top of each kidney
Epinephrine and
Thyroid
Regulates metabolism
neck
thyroxine
Pancreas
Regulates the level of glucose
Near the liver
Insulin and glucagon
Ovary
Regulate female reproductive
In females—lower abdomen
Estrogen and progesterone
Regulate male reproductive
In males—outside of the body
testosterone
processes—sperm formation;
in the scrotum
response
stress
norepinephrine
in the blood
processes—egg production;
secondary sex characteristics
Testes
secondary sex characteristics
( F) THE NERVOUS SYSTEM
**Nearly all multicellular organisms have communication systems.—humans have ________________________ and
______________________.
** The nervous system controls
____________________________________________________________________________________
____________________________________________________________________________________
Stimulus: ____________________________________________________________________________
____________________________________________________________________________
(1) NEURONS
 Messages carried by the nervous system are electrical signals—impulses
 _______________________________: the cells of the nervous system that transmit these impulses
1. sensory neurons: ____________________________________________________
____________________________________________________
____________________________________________________
2. motor neurons: _____________________________________________________
____________________________________________________
____________________________________________________
3. interneurons: _______________________________________________________
_______________________________________________________
_______________________________________________________
Structure of a neuron
 Cell body: ___________________________________________—contains the nucleus and much of the
cytoplasm—
____________________________________________________________________
 Dendrites:
________________________________________________________________________
_______________________________________________________________________
—carry impulses from the ________________________________________or from other
neurons to _________________________________
 Axon:
________________________________________________________________________
________________________________________________—ends with axon terminals
 Myelin sheath: __________________________________________________________
(2) NERVE IMPULSE
 Resulting reaction to a stimulus is a __________________________________
 EXAMPLE: when you touch a hot iron, you automatically pull your hand away. The hot iron is the
________________________ and you pulling your hand away is the __________________________.
 Nerve cells do not touch each other
 Important chemicals are released by the ends of one nerve cell—
________________________________________________________________________
_______________________________________________________—then are picked up by the second nerve cell
(3) DIVISIONS OF THE NERVOUS SYSTEM
 Nervous system of vertebrates includes two divisions
(4) DISEASES/DISORDERS
 Cerebral palsy: _________________________________________________________
_________________________________________________________
 Multiple sclerosis (MS): ________________________________________________
________________________________________________
 Alzheimer’s: progressive, degenerative disease which results in
___________________________, inability to _________________,
___________________ or ________________________________________
 Parkinson’s: involves a particular group of nerve cells in the brain—results in
______________________, _______________________________ and
______________________________________________________