Endocrine System
Communication
The endocrine system is one of the major body
systems used for communication.
A major function of the endocrine system is to
maintain homeostasis.
It is composed of tissue called glands.
The messages sent are in the form of hormones.
A hormone is a compound produced in one part
of the body, travels to another area in the body
and performs its function there.
Hormones
A
Hormones can be
classified as:

1. Steroid Hormones –
B
A. are lipid soluble and pass through the
plasma membrane of a cell.
B. The hormone then complexes with a
receptor and triggers a response
(usually protein production).
C
C. mRNA is created in the process of
__________________.
D. The mRNA is then brought to the
cytoplasm where it is turned into a
protein via ___________________.
D
Hormones

2. Non steroid aka Amino Acid
Hormones- cannot pass
through the membrane.
A
A. Target cells have receptors
for the hormone OUTSIDE the
cell membrane.
B. When the two bind a
chemical reaction causes a
chain of events INSIDE the cell
to trigger the desired response.
C. The message reaches the
nucleus which creates mRNA
in response to the external
signal.
B
C
Feedback Mechanisms
Homeostasis
in the body is
maintained by
feedback
mechanisms
called
negative
feedback.
How it works: Once the body deviates from a set level,
the body detects this and reacts to return the levels to
normal and then shuts off.
Think of how a thermostat regulates the temperature in
your house.
Negative Feedback
As particular conditions in the
body change from a set point
(blood glucose levels for
example), the body detects
these changes.
In reaction to the changes a
hormonal “switch” is turned on
to return the condition to the
acceptable level.
The “switch” is then shut off
again until the levels change
again.
Endocrine Glands
Pituitary Gland
The pituitary gland is a tiny
gland found at the base of
the brain.
It is the most important of
all, sometimes called the
“master gland”.
The pituitary regulates body
functions as well as
regulating other glands.
Pituitary Hormones
Gland
Hormone
Action
Anterior
Follicle-stimulating hormone (FSH)
Stimulates production of sperm and
eggs.
Luteinizing hormone (LH)
Posterior
Stimulate ovaries and testes.
Prepares uterus for implantation
of a fertilized egg.
Thyroid-stimulating hormone (TSH)
Stimulate thyroid gland to make and
release thyroxine.
Adreno-corticotropic hormone
(ACTH)
Stimulate Adrenal glands to
produce specific hormones.
Growth hormone (GH)
Stimulates general protein
synthesis and cell growth.
Prolactin
In nursing mothers, stimulates milk
production.
Melanocyte-simulating hormone
(MSH)
Causes melanocytes in skin to
produce melanin (pigment).
Antidiuretic hormone (ADH)
Stimulates kidneys to absorb water.
Oxytocin
Stimulates contractions in uterus.
Releases milk in nursing mothers.
Thyroid and Parathyroid Glands
The thyroid gland produces a
hormone called throxine. This
hormone acts on the entire
body to increase metabolism.
The thyroid also produces
calcitonin. Calcitonin is
important for regulating calcium
levels in the blood.

Calcitonin triggers bone cells
to absorb the calcium, lowering
the amount in the blood.
The parathyroid releases
parathyroid hormone, which
has the opposite effect on
calcium levels.
Pancreas
The pancreas is vital for
digestion.
It also acts as a gland secreting
insulin and glucagon – two
hormones used to regulate
blood sugar levels.
**This is another example of
maintaining homeostasis!
Pancreas


Insulin stimulates cells to
convert glucose to glycogen –
lowering blood sugar levels
and storing it.
Glucagon has the opposite
effect, triggering cells to break
glucagon down to glucose
and flooding the blood with
the sugar.
Adrenal Glands
The adrenal glands are found on top of the kidneys.
There are two parts of the gland, the outter (cortex)
portion secretes aldosterone which is a hormone that
affects the kidneys, causing sodium absorption.

A second hormone, cortisol is involved in
imflammation (swelling) reduction and raising blood
glucose levels.
The inner portion of the adrenal glands (medulla) is
responsible for the “fight or flight” response.

Under high stress the adrenal glands release
adrenaline (epinephrine) which increase heart rate,
blood pressure, breathing and sugar levels.

To counteract the effects of this hormone
norepinephrine is released, having the opposite
effects when danger has passed.
Reproductive Glands
Gonads: Produce gametes and
sex hormones
Males – the glands are called the testes

The male sex hormone is testosterone and
required for sperm production.

Also responsible for secondary sex
characteristics: facial hair, increased body size,
deep voice.
Females – glands are called ovaries

Ovaries produce estrogen and progesterone.
Estrogen is needed for proper egg development and
secondary sex characteristics: widen hips, breast
production, and mature reproductive system.
Progesterone is needed to prepare the uterus for embryo
development.
Endocrine Dysfunction
Without proper development and function of the endocrine glands a number
of disorders can arise.
Improper GH –
Too little GH can lead to dwarfism (body is not proportional)
Too much GH can lead to giantism
Acromegally – Too much GH during adolescence – huge flat head, odd walk. Andre
the Giant is an example.
Improper Thyroid function –



Cretinism can result from improper thyroxine production
The skeletal and nervous system do not develop properly.
Hyperthyroidism – Too much thyroxine  fast metabolism, nervous, bulging eyes.
Hypothyroidism – Too little thyroxine  excessive obesity
Insulin malfunctions

Diabetes – the cells of the body do not properly respond to insulin.
Type I is autoimmune (develops before the age of 15). Insulin is not properly produced.
Type II develops later in life and results in cells not responding to normal levels of
insulin.