Endocrine system
•Made of glands that
secrete substances
into the bloodstream.
(Exocrine glands
secrete substances
into ducts.)
•Function:
Communication &
control
•Same functions as
nervous system, but
works slower
How do hormones cause change?
• Hormones are chemicals
released from one part of
the body and carried
through the bloodstream to
affect another part of the
body.
• Hormones are released in
small quantities and are
very specific.
• Target cells have receptors for
specific hormones. If the
hormones contact cells
without these target cells, they
will have no effect.
•Hormones produce one or more
changes in target cells:
1. Alter plasma membrane permeability,
potential, or both
2. Stimulate protein synthesis
3. Activate/Deactivate enzymes
4. Induce a secretory activity
5. Stimulate mitosis
•There are 2 major types of hormones:
•Water-soluble hormones (amino acid)
•Lipid-soluble hormones (steroids)
Lipid-soluble
•Steroids
•Can pass directly
through the target
cell membrane
forming a
hormone-receptor
complex, which
alters the actions
of the cell
Water-soluble
•Amino acid-based
molecules
•Not able to pass
through the membrane
•Bind to receptors on
the outside of the
target cell, which
activate a 2nd
messenger to mediate
the response to the
target cell.
•Like a molecular relay.
How are endocrine glands
activated?
•Glands are activated in 3 ways:
1. Hormonal Stimuli
• Glands are encouraged by hormones secreted by other
glands.
• Ex: Hypothalamus stimulates pituitary
2. Humoral Stimuli
• Levels of nutrients and ions in the blood can cause glands to
secrete hormones.
• Ex: Blood calcium levels stimulate parathyroid glands
3. Neural Stimuli
• Nerve impulses cause glands to secrete hormones.
• Ex: Sympathetic nervous system during stress causes release
of epinephrine from adrenal glands.
Summary
•When an endocrine gland is
stimulated by another gland, ions, or
nerves, chemicals called hormones
are released. These hormones alter
target cells either directly or by using
a second messenger depending on
their ability to cross the cell
membrane.
What are the functions of
the pituitary gland?
• The pituitary gland is a small bulb found on the underside of
the brain.
• It has 2 lobes: anterior pituitary and posterior pituitary.
• Called the “master gland” because it controls many other
glands in the body.
Thyroid-stimulating Causes thyroid to
hormone (TSH) produce thyroxine
Adrenocorticotropic Stimulates adrenal
hormone (ACTH) glands
Stimulates growth in
Growth Hormone (GH)
bones and muscles
Melanocyte stimulating Stimulates melanocytes to
hormone (MSH) produce melanin
Stimulates production of
Prolactin (PRL)
breast milk
Stimulates release of sex hormones
Luteinizing hormone
Gonadotropins
Follicle stimulating
hormone Stimulates egg or sperm production
Antidiuretic hormone Increases water retention in kidneys, decreasing
(ADH) or vasopressin urine production
Stimulates contraction of uterus during childbirth
Oxytocin (OT) and promotes release of breast milk
What are the functions of the
hypothalamus?
• The hypothalamus is located just above the pituitary gland
and is about the size of an almond.
• Its main function is to control the pituitary gland by
hormonal and neural stimulation.
• This allows for functions like:
• Control of brain stem & spinal cord
• Center of emotional response
• Body temperature regulation
• Regulation of food intake
• Controls thirst
• Regulates sleep &
wake cycles
What is the function of the
pineal gland?
• The pineal gland is a tiny cone-
shaped gland near the
cerebellum.
• The main secretion of the
pineal gland is melatonin.
Rise and fall during day and night causing sleep
Melatonin
and wake cycles.
Summary
•The glands within the brain include
the pineal gland which regulates
sleep cycles and the pituitary and
hypothalamus which work
cooperatively to control many body
functions. The pituitary is divided into
anterior and posterior lobes.
What are the functions of
the thyroid gland?
• The thyroid gland is located
at the base of the neck.
• It has 2 distinctive halves
resulting in a butterfly shape.
Calcitonin Reduces the calcium levels in the blood
Thyroxine (T4) Regulate metabolism and body
Thyroid Hormones
heat production, controls cellular
(TH)
oxygen usage, and maintains
Triiodothyronine (T3) blood pressure
What is the function of the
parathyroid glands?
•The parathyroid glands
are attached to the back
of the thyroid.
•Produces parathyroid
hormone, which has the
opposite function from
calcitonin.
•Parathyroid hormone
brings calcium out of the
bones and into the
bloodstream for use by
cells.
What are the functions of
the adrenal glands?
• The adrenal glands sit atop each kidney
• Each gland has an outer layer (adrenal cortex)
and an inner layer (adrenal medulla) that
have different functions.
Regulate the “fight or flight”
epinephrine response to emergency situations.
Adrenal medulla Increases heart rate, blood
pressure, blood flow, intake of
norepinephrine oxygen for immediate energy.
Glucocorticoids
Regulate ion levels for quick energy
Adrenal cortex (ex: cortisol &
aldosterone)
What are the functions of
the pancreas?
• Pancreas has both exocrine (using
ducts) and endocrine (ductless)
glands.
• The endocrine part of the
pancreas is made of groups of
cells called the islets of
Langerhans that look like tiny
islands.
• The islets of Langerhans produce
insulin and glucagon.
Beta cells Insulin Lower blood glucose levels
Pancreas
Alpha cells Glucagon Raise blood glucose levels
What are the functions of
the thymus gland?
•Located near the
sternum
•Produces thymopoietin,
thymic factor, and
thymosin, which is
involved in the
development of the
immune system.
Summary
•The thyroid, parathyroid and adrenal
glands have wide-reaching effects on
the body. The pancreas and thymus
are endocrine glands, as well, but also
have functions within other body
systems (digestive & immune).
What are the endocrine
functions of the gonads?
Gonads= reproductive organs
that produce sex cells and
secrete sex hormones
Females- ovaries
Males- testes
Estrogen Maturation of reproductive organs and secondary sex
characteristics
Progesterone Cause breast development and control of menstrual cycle
MALES
Testosterone Maturation of reproductive organs and secondary sex
characteristics, production of sperm
Secretes atrial natriuretic peptide: reduces blood volume and
Heart pressure
Stomach &
Several digestive hormones that regulate multiple digestive
Small
processes
Intestine
Placenta Steroid and protein hormones that influence pregnancy
Erythropoietin: signals bone marrow to produce more red blood cells
Kidneys
Produces Vitamin D, which allows digestive system to absorb
Skin Calcium from food
Fatty Produces leptin, which controls appetite
Tissue
How are hormones regulated?
• Control of hormone secretion is required to
regulate the amount of hormones released into the
body.
• Often this control comes from feedback
mechanisms.
• Example: The thyroid gland secretes
the hormone thyroxine (T4). It
won’t secrete thyroxine, though,
until it is stimulated by other
hormones from the hypothalamus
and anterior pituitary glands. If the
level of thyroxine in the blood
becomes too high, the
hypothalamus and pituitary will stop
producing the stimulating
hormones, thus slowing the thyroid
from producing thyroxine.
Endocrine system When thyroxine levels
get too high, the
Hypothalamus secretes
hypothalamus is
hormones into the
triggered to stop the
pituitary
(specifically thyrotropin- impulse
releasing hormone)
HOMEOSTASIS
Thyroid secretes
Pituitary secretes thyroxine into blood,
thyroid-stimulating which increases
hormone metabolism
What happens when
endocrine glands function
improperly?
•Improper functioning of an endocrine gland may
cause:
•Hyposecretion- not enough hormone is
released
•Hypersecretion- too much hormone is released
•All endocrine disorders are caused by either
the hyposecretion or hypersecretion of
hormones.
Summary
•The endocrine system is controlled by
feedback loops, like that of the
hypothalamus – pituitary – thyroid
system. If the glands of the endocrine
system malfunction, it often results in
the hypersecretion or hyposecretion
of hormones.
