Homeostatic Drugs
I.
Overview
of Homeostasis and Drug Action
A.
Homeostasis
- maintenance of internal stability; often biochemical in nature
1.
In other
words, there is a balance that is constantly readjusting to current conditions.
2.
A dynamic
balance.
3.
The
adjustments to the body occur as a result of chemical reactions.
4.
The
chemicals having the greatest impact are hormones and neurotransmitters
II.
Comprehensive
Explanation of Homeostatic Systems
A.
The
Building Blocks of the Nervous System
1.
The
Neuron: The Basic Structural Unit of the Nervous System
2.
synapse -
site of communication between a message-sending neuron and its message-receiving
target cell
3.
synaptic
cleft - a minute gap between the neuron and target cell, across which
neurotransmitters travel
4.
dendrites
- short branches of the neuron that receive transmitter signals
B.
Introduction
to Nervous Systems
1.
Neurotransmitters
- chemical messengers released by neurons
2.
Neurons -
specialized nerve cells that make up the nervous system
3.
Axon - an
extension of the neuronal cell body along which electrochemical signals travel
4.
Receptor
- a special region in a membrane that is activated by natural substances or
drugs to alter cell function
5.
Psychoactive
- drugs that affect mood or alter the state of consciousness
C.
The
Nature of Drug Receptors
1.
receptors
are special proteins located in the membranes of receiving neurons and other
target cells
2.
opiate
receptors - receptors activated by opioid narcotic drugs, such as heroin and
morphine
3.
endorphins
- neurotransmitters that have narcotic-like effects
D.
Agonistic
and Antagonistic Effects on Drug Receptors
1.
agonistic
- a type of substance that activates a receptor
2.
antagonistic
- a type of substance that blocks a receptor
E.
Neurotransmitters:
The Messengers
1.
Acetylcholine
(ACh) - one of the major neurotransmitters in the autonomic portion of the
peripheral nervous system
2.
muscarinic
- a receptor type activated by ACH; usually inhibitory
3.
nicotinic
- a receptor type activated by ACH; usually excitatory
4.
Catecholamines
- a class of biochemical compounds including the transmitters norepinephrine,
epinephrine, and dopamine
5.
Serotonin
F.
Major
Divisions of the Nervous System
1. The
Central Nervous System
2. The
Reticular Activating System - one major function is to control the brain's state
of arousal
3. anticholinergic
- agents that antagonize the effects of acetylcholine
4. The
Basal Ganglia - primary centers for involuntary and fine-tuning of motor
functions
5. The
Limbic System - regulates emotional activities, memory, modulation of basic
hypothalamic functions, and activities such as mating, procreation and caring
for the young
6. The
Cerebral Cortex - receives sensory input, interprets incoming information, and
initiates voluntary motor behavior
7. The
Hypothalamus - the control center for the autonomic nervous system
8. The
Autonomic Nervous System - controls the unconscious functions of the body
a.
Sympathetic
- generally speeds up body systems
b.
Parasympathetic
- generally slows down body systems
G.
The
Endocrine System and Drugs
1. hormones
- regulatory chemicals released by endocrine systems
2. Endocrine
Glands and Regulation
a.
Pituitary
gland - the master gland
b.
Adrenal
glands - releases epinephrine and corticosteroids
c.
Steroids
- hormones related to the corticosteroids released from the adrenal cortex
d.
Androgens
- male sex hormones
3. The
Abuse of Hormones: Anabolic Steroids
a.
Anabolic
steroids - compounds that chemically resemble the steroids, which stimulate
production of tissue mass
III.
Homeostatic Drugs
A.
Drugs
cause intended or unintended effects by altering the activity of
neurotransmitters and the sites at which they act. Some of these substances also
have an impact on hormones.
B.
Alterations
in body chemistry occur as a response to changes in temperature, metabolism,
nutrient absorption, organ functions and emotions.
C.
The cells
responsible for transmitting information are neurons. The human brain contains
more than 10 billion neurons.
D.
Neurotransmitters
may stimulate activity (excitatory) or decrease it (inhibitory).
E.
The
neurotransmitter that appears to be affected to the greatest extent by
psychoactive drugs is dopamine.
F.
Dopamine
is the major neurotransmitter in the pleasure center of the brain.
IV.
Drugs affect neurotransmitters in a number of ways
A.
Up or
down regulation
B.
Altering
synthesis, storage, release or deactivation of neurotransmitters
C.
Modify or
block information
D.
Mimic a
neurotransmitter
E.
A drug
agonist mimics the effect(s) of a chemical normally found in the body.
(endorphins and heroin).
F.
The
agonist tricks the body into reacting as if the endogenous chemical were present
or it enhances the effects of the endogenous chemical.
G.
An
antagonist blocks the effects of a chemical already working in the body or
blocks the effects of a chemical introduced into the body (naltrexone and
heroin).
H.
Repeated
use of any drugs of abuse forces the neurons to go through the process of
neuroadaptation. Up and down regulation affect the person's response to that
drug over time (tolerance).
I.
When the
body adapts to one substance, it also has tolerance for other chemicals in the
same classification.
V.
The kidney is the second most frequent target of serious adverse effects
of non-steroidal antiinflammatory drugs (NSAIDs). The renal side effects of
NSAIDs related to inhibition of cyclooxygenase (COX) comprise reduction in renal
blood flow (RBF) and glomerular filtration rate (GFR), sodium/water retention,
water intoxication and hyperkalemia.
VI.
Conclusion
A.
All
psychoactive drugs affect brain activity by altering the ability of neurons to
send and receive messages.
B.
Many
scientists believe that elucidating how substances of abuse affect nervous
systems will lead to new and more effective methods for treating drug addiction.
Drugs
and Society Online. http://www.jbpub.com/dsonline/6e/chapterindex.cfm.
1996-2000. Jones and Bartlett Publishers.
Psychopharmacological
Concepts. http://www.rci.rutgers.edu/~lwh/drugs/chap03.htm.
2000. Rutgers. edu