Transcript The Endocrine System

The Endocrine System
Main Function
The endocrine system is made up of eight major glands that each
secrete different types of hormones that regulate metabolism,
growth and development, sexual reproduction and mood among
other things. Its main function is to establish and keep homeostasis
(equilibrium) within the body.
Major Glands and Associated Functions
Hypothalamus- integrates the nervous and vertebrate endocrine
systems by receiving information from nerves throughout the body
and other parts of the brain
• Once the hypothalamus receives this info, it works to initiate
endocrine systems that are appropriate for environmental
conditions
• The Hypothalamus regulates all other endocrine glands via the
pituitary gland
Pituitary Gland- the pituitary gland is made up of the anterior and
posterior pituitary glands which are found at the base of the brain
and surrounded by bone
• Although known as the “master gland” it obeys hormonal orders
from the hypothalamus
Posterior Pituitary Gland- an extension of the brain which
develops from a small bulge of the hypothalamus and remains an
extension of the hypothalamus
• Stores and secretes antidiuretic hormone (ADH) and oxytocin
Anterior Pituitary Gland- develops from a fold of tissue at the roof
of the developing embryo’s mouth and grows upward toward the
brain, eventually disconnecting from the mouth
• Consists of endocrine cells that synthesize and secrete several
hormones directly into the blood
• Unlike the posterior, it is not an extension of the brain
Thyroid gland- covers the
windpipe from the front,
right, and left sides
• Produces T3 and T4
hormones that stimulate
and maintain metabolic
processes
• Regulated by thyroid
stimulating hormone
(TSH)
• Secretes calcitonin which
lowers blood calcium
levels
• Regulated by
calcium in the blood
•
Plays a vital role in
homeostasis
• In adult mammals,
thyroid hormones
help to maintain a
normal blood
pressure, heart rate,
muscle tone,
digestion and
reproductive
functions
Parathyroid gland- small
glands located in the neck
behind the thyroid
• Releases parathyroid
hormone which raises
blood calcium levels
•
Parathyroid hormone(PTH) is regulated
by calcium in the blood
Pineal gland- small mass of tissue located
near the center of the brain
• Secretes the hormone melatonin which
is involved in biological rhythms and is
regulated by light/dark cycles
• Melatonin signals your body that it
is nighttime and assists it in sleep
Pancreas- This is a gland located in the
abdomen, more specifically, below and
behind the stomach.
• Produces a number of essential
chemicals such as insulin and glucagon
• Inulin is responsible for lowereing
blood sugar level and is regulated
by sugar in the blood
•
Adrenal glands- located on the
top of both kidneys and are
divided into an outer portion
(adrenal cortex) and an inner
portion (adrenal medulla) which
specialize in different hormone
functions
Adrenal Cortex- creates
glucocorticoids and
mineralocorticoids
• Glucocorticoids- steroids that
raise blood sugar levels and
are regulated by
Adrenocorticotropic hormone
(ACTH)
• Mineralocorticoids- steroids
that promote the reabsorption
of sodium ions and excretion
of potassium ions in kidneys
Adrenal Medulla- creates and
secretes epinephrine and
norepinephrine which are more
commonly known as adrenaline
Both of these dictate metabolic
response within the body which
include oxygen release in muscles,
blood vessel dilation and
constricting/ raising blood pressure
Gonads- These are the glands that
produce and secrete hormones
necessary for growth and development,
sexual behavior, and regulation of
reproductive cycles. The ovaries and the
testes are the two glands in this
category.
Ovaries- situated on either side of the
uterus and contain egg cells for
reproduction as well as produce
Estrogens and Progesterone
• Estrogens- responsible for promotion
of development and maintenance of
female secondary sex characteristics
and also stimulate the growth of the
uterine lining
• Progesterone- a steroid that
promotes uterine lining growth
Testes- located on the outside of the
male body
• Androgens generally support sperm
formation and promote the
development and maintenance of
male secondary sex characteristics
• Main androgen hormone is
testosterone
Feedback Mechanisms
To maintain homeostasis within our bodies, the endocrine system
uses two important feedback systems. These mechanisms are known
as positive and negative feedback.
Negative feedback
system- This mechanism
is important for
maintaining homeostasis
and most endocrine
glands are under its
control. The way this
system’s loop works can
be thought of as the way
a thermostat works to
maintain a desirable
temperature in a house. It
senses change in our
bodies and triggers glands
accordingly, as does the
thermostat when it
switches the air
conditioning on and off in
an attempt to find an
ideal temperature. In the
case of our bodies, the
ideal that this system
works toward is
homeostasis. This
negative feedback system
is constantly working
throughout our bodies.
Positive feedback system- This
mechanism works to control selfperpetuating changes that do not
require continuous adjustment. Unlike
negative feedback, positive feedback is
rarely used to maintain homeostatic
functions. Positive feedback is only
needed on occasion rather that
continuously as is the case with negative
feedback.
An example of positive feedback is childbirth. In the above picture,
the positive feedback loop is being shown. When an expecting
mother is in labor, the head of the baby will push against the cervix
sending nerve impulses from the cervix to be transmitted to the
brain. From these impulses, the brain stimulates the pituitary gland to
secrete oxytocin. Oxytocin is then carried in the bloodstream to the
uterus. Oxytocin stimulates uterine contractions and pushes the baby
toward the cervix and the baby will then push its head against it. This
loop continues until the baby is born and until the mothers body can
again reach homeostasis.