Dr. Gossett – BSC 1309 / BSC 1409 Chapter 10 pt. 1 of 3 The Endocrine System.

Chapter 10– The
Endocrine System.
The endocrine
system communicates
sending chemical
messages called hormones.
Hormones influence growth.
They influence development,
behavior, and metabolism.

The main function of
the endocrine system
is to coordinate
the body systems
and to help maintain
The endocrine system works
with the nervous system,
but it's a more leisurely
system of communication
than the nervous system.

Endocrine glands contain cells
called secretory cells that
release their products called
hormones into the extracellular
fluid where they diffuse
into the bloodstream.
Therefore, there means
a more leisurely acting
than communication with
that of the nervous system.
Hormones are one type
of chemical messenger
found in the human body.

This image shows
the hormone diffuses
from the secretory
cell contained
within these either endocrine
glands or other organs
of the body that have
endocrine functioning.
The hormones go and diffuse
from that fluid, extracellular
fluid, into the
bloodstream where
it's going to travel throughout
the body to target sales.
The major endocrine glands are
the pituitary, the thyroid,
parathyroid, adrenals,
and pineal glands.
Organs with some
endocrine tissue
include the hypothalamus, the
thymus, pancreas, ovaries,
testes, heart, placenta,
stomach, intestines,
and kidneys.
Some of these organs we will
be studying their hormones
within Chapter 10.
Some of the other organs,
such as the kidneys, heart,
we will study in
future chapters.
And so this is just the
layout of the organs
and the endocrine
glands within the body,
and the different hormones
that they secrete.
We will cover some of these
more in-depth as we progress
through the chapter.

Hormones travel in
the bloodstream,
that's previously noted.
And although they
come into contact
with virtually all cells
because they are contained
in the blood, they typically
affect a particular type
of cell.
And this type of cell
is called a target cell.
In other words, cells
that are designed
to respond to
antidiuretic hormone
will only respond to that
antidiuretic hormone.
Every cell in the body will not.
Target cells have
specific receptors.

In the previous
example, if they will
respond to antidiuretic
hormone, then they
have an antidiuretic
hormone receptor.
The target cells, as noted,
have these receptors.
These are just going to
be protein molecules.
It's going to be located on
the plasma membrane and bind
and recognize that
specific hormone.
Receptors, these
target receptors,
are often lacking
in cancerous cells.
Thus, resulting in a
failure of a response
to that particular hormone.

Other cells in the body,
other than the target cells,
lack the correct
receptors and are
unaffected by a
particular hormone
if they do not have the
specific receptor for that.
The mechanism by which a
hormone influences target cell
depends on the chemical
makeup of the hormone.
And there are two main
types, lipid-soluble and
Lipid-soluble hormones
include the steroid hormones
derived from cholesterol.
And the main organs and glands
that secrete steroid hormones
are the ovaries, the testes,
and the adrenal glands.

These lipid-soluble
hormones move easily
through the cell's plasma
membrane because, recall,
it is a phospholipid
bilayer itself.

Lipid-soluble hormones once
inside the target cell.
The steroid hormone combines
with a receptor molecule.
In the nucleus, the
hormone receptor complex
attaches to the DNA and
can activate certain genes
to synthesize specific proteins.
This activation
leads the target cell
to synthesize proteins,
including enzymes
that may stimulate or inhibit
a particular metabolic pathway.

This shows the imagery of
a steroid hormone derived
from cholesterol.
So in step one,
the steroid hormone
diffuses through the plasma
membrane of the target cell.

Once inside the
cell, it will bind
to a receptor located in the
cytoplasm of that target cell.
Be transported into the nucleus.

Binds to the DNA in step four
and activates certain genes.

Once the DNA is transcribed
to messenger RNA,
it's transported back
out through the cytoplasm
to the ribosome, where
proteins, including enzymes,
which is just
proteins, synthesize.
And the enzymes alter
the activity of the cell.

Water-soluble hormones,
on the other hand,
are made of amino acids and they
cannot pass through the lipid
bilayer of the plasma membrane
and require a second messenger
to exert their effects.
Water-soluble hormones are
considered first messengers.
They exert their
effects indirectly
by binding to receptors on
the surface of this plasma

They simulate second
messengers within the cell
to carry out the effect of
that particular hormone.
So a water soluble is made
of amino acid, considered
a first messenger.
It's going to bind to a receptor
on the cell membrane, which
is going to activate a second
messenger within the cell.
A common second messenger is
cyclic adenosine monophosphate,
or otherwise known as cAMP.
Hormones bind to
the receptor site
on the target cell membrane,
prompting the conversion of ATP
to cAMP within the cell.
cAMP activates an enzyme within
the cell called a protein
kinase, which in turn activates
another enzyme and so on.
The end result of
the enzyme cascade
is the activation of an enzyme.
In this case, that catalyzes
the breakdown of glycogen
to glucose within the
liver or skeleton muscles.

Again, this is the example
of a water-soluble hormone.
So it's considered
a first messenger.
So it's going to bind
on the cell surface.
It will not diffuse
directly through.
In this example,
it's going to bind.
The binding activates the enzyme
responsible for producing cAMP,
considered the second
messenger from ATP.
cAMP is going to initiate
an enzyme cascade.

This one's going to
break down glycogen
to glucose within the cytoplasm.
You notice it never goes
within the nucleus itself.
This is all occurring
within the cytoplasm.

Summary of the lipid-soluble
versus water-soluble.
Lipid-soluble moves
into a cell and can
stimulate the
synthesis of proteins.
Whereas, water-soluble proteins
activate proteins already
present within the cell.
And they do this without
ever entering the cell.
They will bind on
the cell surface.
Some research now indicates
that steroid hormones
may have additional mechanisms
of action, including
interacting with certain
membrane receptors.

Negative feedback mechanism
is the most common.

Negative feedback mechanism
is the major mechanism
of the body to
maintain homeostasis.
And homeostasis just keeps the
body's internal environment
relatively constant, such as
our set point for temperature,
Our levels of glucose,
our levels of capsicum.

Increased blood level
of a specific hormone
inhibits its further release.
Some endocrine
glands are sensitive
to a particular
condition they regulate
rather than to the level
of hormone they produce.
For example, a pancreas
stops secreting insulin
when levels of blood
glucose begin to decline.

Positive feedback mechanism,
on the other hand–
there are some processes
within the body that
go through positive
feedback mechanism.
And positive feedback mechanism,
the outcome of a process
further stimulates the process.
A primary example of this
is the hormone oxytocin
and uterine contractions
of childbirth.
It also includes milk ejection.
Oxytocin will also
stimulate milk ejection
in nursing mothers.
So in this example
during childbirth,
the pituitary glands
release a specific hormone
called oxytocin,
which stimulates
the uterus to contract.
Uterine contractions
stimulate the release
of more oxytocin, stimulating
more contractions.
Till eventually, expulsion
of the baby and the placenta
terminate this feedback.
So it's increasing in intensity.

between hormones can
be antagonistic,
synergistic, or permissive.
Antagonistic is when the
effect of one hormone
opposes that of another,
such as glucagon and insulin.
Glucagon is going to
increase blood glucose.
Whereas, insulin is going
to decrease blood glucose.
Synergistic is the
response of a tissue
to a combination of hormones.
It's much greater
than its response
to either individual hormone.
Such as epinephrine
from the adrenal
glands and glucagon
from the pancreas
prompt the liver
to release glucose.
Permissive is when
one hormone must
be present for another
hormone to exert its effect,
such as thyroid hormone must
be present for the hormone
aldosterone produced
by the adrenal glands
to stimulate re-absorption
of sodium within the kidneys.

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