Chapter 7 - Endocrine system Flashcards
Hormones
chemicals that are secreted in one part of
the body and have effects in other parts of the body
Are Hormones are secreted directly into the bloodstream for
transport
Yes
What are hormones secreted by
Hormones can be secreted by endocrine glands
(sometimes large organs, sometimes individual cells) or
by neurons
If secreted by neurons what are hormones called?
neurohormones
Hormones act as chemical messengers
and they initiate
changes in target cells (alterations of metabolic activity,
growth/differentiation, etc.). Only cells that have specific
receptors for a hormone will respond to that hormone.
Endocrine system function
The endocrine system, along with the nervous system,
functions to regulate the activities of the body.
Endocrine system contrast with nervous system
In contrast to the nervous system, where information is
transmitted rapidly through electrical signals, the release
of hormones occurs in a slower, more persistent manner.
* In addition, the effects of the endocrine system generally
last longer.
* Although the nervous system tends to mediate more
rapid changes in the body, and the endocrine system
tends to mediate longer-lasting effects, they can work
together to regulate processes.
Peptide hormones
strings of amino
acids (3 – 300 amino acids).
* Generally bind to receptors on the surface
of target cells. Often have their effects
through the activation of existing enzymes.
Effects are therefore often rapid.
Steroid hormones
Synthesized from
cholesterol.
Secreted primarily by the gonads and the
adrenal glands.
* The sex steroids include progesterone,
estrogens, and androgens. They are
chemically very similar.
Generally bind to receptors on the insides
of target cells to affect gene expression
and protein synthesis. Therefore, effects
can take some to be seen, and they may
produce relatively long-lasting effects.
How do Hormones Influence Behavior?
- Sensory Mechanisms
- Development in or Activity of the Central
Nervous System - Muscles used in Execution of Behaviors
Effects on Sensation
Hormones can affect the ability to detect
certain stimuli, and they can affect the
responses to and preferences for
particular stimuli.
Effects on Sensation
* Rough-skinned Newts (Taricha granulosa)
When identifying potential mates, the male first
uses visual cues (size, shape, color) and then
switches to olfactory cues to confirm species,
gender, and reproductive state.
* If appropriate, the male will clasp the female for
several hours in a posture called amplexus.
* During this time, the female becomes receptive
and will pick up the spermatophore from the
male.
Vasotocin
a peptide hormone found in non-
mammalian vertebrates.
* Vasotocin affects how male Rough-skinned
Newts react to visual, tactile, and chemical
stimuli from females.
* Males injected with vasotocin spend more
time in the vicinity of visual and olfactory cues
from females, and they show enhanced
tactile responsiveness during amplexus
Hormones have been found to affect several
characteristics of the brain
- Volume of brain tissue.
- Number of cells.
- Size of cell bodies.
- Extent of dendritic branching.
- Percentage of neurons sensitive to particular
hormones. - Survival of neurons.
Example – Singing Behavior in Zebra Finches
(Taeniopygia guttata)
Effects on Muscles
Hormones can affect behavior by affecting
muscles and motor neurons.
* Example – Calling behavior in the African
Clawed Frog (Xenopus laevis)
Calling behavior in the African
Clawed Frog (Xenopus laevis)
Males emit six different calls. The most common
is the advertisement call, which consists of
alternating fast and slow trills.
* The advertisement call allows females to locate
males in murky waters.
* Sexually-receptive females will approach males
and produce a rapping call; the pair then duets.
* Receptive females allow males to clasp them
around the waist for several hours while they
release eggs.
* Non-receptive females produce a ticking sound.
Adult males have eight times the number of
fibers in their larynx as females.
* The rate at which calls are produced is different
in males and females (71 contractions per
second in males vs. 6 contractions per second in
females).
* Males mostly have fibers that are fast-twitch and
fatigue-resistant, while those in females tend to
be slow-twitch and fatigue-resistant.
- What causes the differences in male and female
calls?
At metamorphosis, the number of muscle
fibers in the larynx of both males and
females is the same as the number of
fibers in the larynx of adult females.
* As males mature, the levels of androgens
increase, and this causes a) new fibers to
be added, and b) development of more
fast-twitch muscle fibers.
How can we investigate the relationships
between hormones and behavior?
Interventional Studies
Correlational Studies
Interventional Studies
Involves removal of the
endocrine gland, followed by observation of
behavior. Can also replace the hormone with
implants or injections; this is also followed by
observations of behavior
Green Anole – Anolis carolinensis
Correlational Studies
Involves comparisons of
hormone levels with the presence of absence of
behaviors.
Song Sparrow – Melospiza melodia
Organization Effects
When hormones organize
neural pathways that are responsible for certain
behaviors. Can also include effects outside the
nervous system (e.g. development of anal fin in
western mosquitofish). Organizational effects
occur early in life; they tend to be permanent.
Activational effects
occur in adulthood and tend
to last only as long as the hormone is present.
May involve subtle changes to previously
established connections within the central
nervous system.
Mating Behavior in Rats
Adult male and female rats differ in their
sexual behavior.
* Males: Social investigation, mounting,
intromission, ejaculation.
* Females: Solicitation and
acceptance.
Lordosis
These differences in behavior are due to differences
in the brains of male and female rats that were
caused by the irreversible actions of androgens
early in life.
* Early in life, all rats have the potential to develop
“male” brain anatomy and “female” brain anatomy in
the areas that control sexual behavior.
* Neonatal testosterone causes development down
the male pathway. The absence of testosterone
leads to the development of a “female” brain. These
are organizational effects.
Interestingly, the testosterone in males is
actually converted to estradiol after it enters the
neurons in question. Thus, it is estradiol binding
to estradiol receptors that actually induces the
development of the “male” brain.
* So, why doesn’t estradiol have this effect in
young female rats?
– Low amounts of estradiol
– Alpha-fetoprotein
Steroid hormones also have activational
effects on sexual behavior in both male
and female rats.
* Adult females with high levels of estrogen
and progesterone display sexual
behaviors; the absence of these hormones
leads to a lack of those behaviors.
* In males, testosterone is necessary for the
performance of copulatory behavior.
