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Biology Chapter 26
Hormones and the Endocrine System
by Emily Bower
26.1 Chemical signals Coordinate body
Functions
• Animals rely chemical signals to regulate their body
functions
• Hormone- is a chemical signal that is carried by the
circulatory system (usually in blood) and communicates
regulatory messages throughout the body
• Hormones are made and secreted by of endocrine glands
• Collectively known as the endocrine system. One of the
two systems the body uses to communicate messages
• Endocrine system makes slower but longer lasting
responses then the nervous system
• Can take hours or day to act because of the time it
takes for hormones to be made and transported, and
because of cellular response time
• Hormones are important in controlling whole body
activities and responses to stimuli (ex. Stress,
dehydration, low blood glucose levels, and long term
development process- growth, maturation, and
reproduction
• Secretory vesicles in the endocrine cell are full of
molecules of the hormone
• The endocrine cell secretes the the molecules into
the circulatory system
• From there hormones may travel to ALL parts of the
body
• But only TARGET CELLS are equipped to respond
• A single hormone molecule may dramatically alter a
target cell’s metabolism by turning on or off the
production of a number of enzymes
• Hormones are the body’s long distance chemical
regulators, they convey info via the blood stream to
target cells throughout the body
• Local Regulators- (other chemical signals) are
secreted into the interstitial fluid and effect only
nearby target cells
• Pheromones are another kind of chemical signal that
carry messages between different individuals of the
same species, as in mate attraction
• Neurosecretory cells perform functions of both the
nervous and the endocrine systems
• They conduct nerve cells but also make and secrete
hormones in the blood
• Few chemicals serve as both hormones in the
endocrine system and chemical signals in the
nervous system (Epinephrine or adrenaline serves as
both, allows fight or flight)
• Another example is the neurotransmitter- carries info
from one nerve cell to another or from a nerve cell to
another kind of a cell that will react.
• Unlike most hormones neurotransmitters usually do
not travel in the bloodstream
26.2 Hormones affect target cells by two
main signaling mechanisms
• There are 2 major classes of molecule functions in
vertebrates
1. Amino acid derived hormones (proteins, peptides,
and amines) they are all hydrophilic
2. Steroids which are all hydrophobic
• Regardless of the structure signaling by any of these
molecules involves three key events- reception,
signal transduction and response
1. Reception- when a hormone bonds to a specific
receptor or on/in the target cell. The binding of a
signal molecule to a receptor protein triggers events
within the target cell.
2. Signal Transduction- that convert the signal from
one form to another
3. Response- a change in the cells behavior. Cells that
lack receptors for a particular chemical signal do not
respond to hat signal
• While both hormones carryout the 3 steps
above they do so in different ways
• Water-soluble hormones are embedded in the
plasma membrane of target cells and project
outward from the cell surface
1. Hormone molecule binds to receptor proteinactivating it
2. This initiates a signal transduction pathway, a series
of changes in the cellular proteins that covert an
extracellular chemical signal to a specific
intracellular response
3. Molecule activates a protein that carries out the
cell’s response either in the cytoplasm or in the
nucleus. One hormone may trigger a variety of
responses
Lipid soluble hormones bind to receptors inside the cell
Steroid hormones- (sex hormones) are lipids made
from cholesterol
1. The steroid hormone enters the cell. If it is a target cell
then
2. Binds to a receptor protein in the cytoplasm or nucleus.
The hormone receptor complex itself usually carries out
the transduction of the hormonal signal. The complex
acts as a gene activator
3. The hormone receptor complex attaches to a specific
site on the cell’s DNA in the nucleus
4. The binding of the complex to DNA stimulates
trasncroption of certain genes into RNA which is
translated into new proteins. All steroid hormones react
by turning on or off a gene. Different kinds of cells
respond differently
26.4 The hypothalamus, which is
closely tied to the pituitary, connect
the nervous and endocrine system
Hypothalamus- the part of the brain that
receives info from nerves about the internal
condition of the body and about the external
environment.
It responds by sending out the appropriate
nervous or endocrine system.
It dirrectly controls the Pituitary gland and thus
exerts massive control over the endocrine
system by using the pituitary to relay
directives to other gland.
Pituitary gland- has two parts
1. Posterior Pituitary- nervous tissue and is an
extension of the hypothalamus. Store and secretes
two hormones made in the hypothalamus
2. Anterior Pituitary- endocrine cells that synthesize
and secrete numerous hormones into the blood.
Both are situated in a pocket of skull bone at the base
of the hypothalamus.
Releasing Hormones- stimulate the anterior pituitary to
secrete hormones
Inhibiting Hormones- induce the anterior pituitary to
stop secreting hormones
• There is a structural function between the
hypothalamus and the pituitary
• A set of neurosecrtory cells extend form the
hypothalamus into the posterior pituitary.
• The hormones in the body can be channeled through
the neurosecretory cells into the posterior or
anterior pituitary depending on what they are meant
to do
Thyroid-stimulating hormone (TSH)- a hormone
secreted by the anterior pituitary that stimulates the
thyroid gland to secrete its’ hormones
Prolactin (PRL)- hormone secreted by the anterior
pituitary that stimulates different effects in different
species
Growth hormone (GH) - hormone secreted by the
anterior pituitary that promotes development and
growth and stimulates metabolism
Endorphins- A pain inhibiting hormone produced by
the brain and anterior pituitary, also serves as a
neurotransmitter (natural painkillers & runners high)
TSH-releasing hormone (TRH)- secreted by the
hypothalamus. A peptide hormone that triggers the
release of TSH which in turn stimulates the thyroid
gland
• Precise regulations of the TRH-TSH-thyroxin system
keeps the hormones at levels that maintain
homeostasis
26.9 The adrenal glands mobilize responses
to stress
Adrenal Gland- One of the endocrine glands, located
atop each kidney in mammals is made up of 2 parts
1. Adrenal Medulla-central portion. Produces the fight
or flight hormone. Ensure rapid, short-term
responses to stress. It secretes 2 hormones
1.epinephrine- adrenaline
2. norepinephrine- noradrenalin
2. Adrenal Cortex- outer portion of the adrenal gland.
Controlled by the anterior pituitary, secretes
hormones called glucocorticoids and mineral
corticoids
Both parts respond to stress
Stressful stimuli activate certain nerve cells in
the hypothalamus
1. Cells send nerve cells via the spinal cord to the adrenal
medulla
2. Stimulating it to secrete epinephrine and
norepinephrine into the blood. Epinephrine and
norepinephrine have somewhat different responses.
Both contribute to short term response. Hormones
secreted by Adrenal medulla are short-term and
hormones secreted by the Cortex are long term.
3. The Hypothalamus secretes a hormone
4. Stimulates target cell in the anterior pituitary to
secrete the hormone ACTH
5. In turn ACTH stimulates cells of the adrenal cortex to
secrete the hormones that cause long-term stress
Short term stress response
1. Glycogen broken down to glucose; increased
blood glucose
2. Increased blood pressure
3. Increased breathing rate
4. Increased metabolic rate
5. Change in blood-flow patterns, leading to
increased alertness and decreased digestive
and kidney activity
Long-term stress response
Mineralocorticoids
Glucocorticoids
1. Retention of
1. Proteins and fats
sodium ions and
broken down
water by kidneys
and converted
to glucose,
leading to
increased blood
glucose
2. Increased blood 2. Immune system
volume and blood may be suppressed
pressure
Mineralocorticoids- a corticosteroid hormone
secreted by the adrenal cortex that helps
maintain salt and water balance and may
increase blood pressure in response to long
term stress
Glucocorticoids- a corticosteroid hormone
secreted by the adrenal cortex that increases
the blood glucose level and helps maintain the
body’s response to long-term stress.