Download The Endocrine System

The Endocrine System
Mrs. Hartley
Anatomy and Physiology
2004-2005
Functions
 Works with nervous system to control body
activities
 Primary role is to help maintain homeostasis
 Communication using chemicals called
hormones
 Regulate processes including metabolism,
growth and development, reproduction, and
regulation of stress
 Control of these processes is essential to
survival
Composition of Endocrine
System
 Composed of organs that produce and
secrete hormones
 Perform a secretory function therefore
are referred to as glands
 Two types: endocrine and exocrine
glands
Nervous vs. Endocrine
 Often work together
 Parts of the nervous sytem stimulate or
inhibit the release of hormones and viceversa
 Endocrine system typically acts more
slowly than the nervous system
Endocrine Glands
 Secrete products into
extracellular space
surrounding the cells
 Products = hormones that
enter bloodstream
 Pituitary gland, thyroid gland,
parathyroid glands, adrenal
glands, pancreas, and gonads
are primary endocrine glands
 Pineal and thymus gland play
small role
 Hormones received by
kidneys, stomach, small
intestine, placenta
Hormones
 Chemical units produced by endocrine glands
 Means by which glands provide control of body
activities
 Hormones are released into the bloodstream
which in turn delivers to all body cells
 The cells that recognize a particular hormone
will be the one to respond (target cell)
Hormonal Action
 Released in very small
quantities
 Diffuse through bloodstream
 Will have an effect only on a
particular type of cell called
the target cell
 Effect limited to target cell
because of protein molecules
acting as receptors that are
specific to a particular
hormone
 Cells other than the target cell
are not affected by a hormone
because they lack appropriate
receptors
Hormonal Action Cont.
 Hormone unites with receptor and exerts it’s effect
(generally altering metabolic processes)
 May change rate of activity, rate of protein synthesis,
rate of secretion, etc largely determined by the nature
of the hormone
LIPID BILAYER
Water Soluble Hormones
 Include molecules that are composed of amino acids
 Cannot pass through the lipid plasma membrane
 How can they produce an effect on the cell then? They
must use a second messenger system located in the
cell.
 Most common is cyclic AMP
 Hormone (first messenger) activates second
messenger which in turn exerts the effect in the cell.
 Examples: epinephrine, norepinephrine (NE),
antidiuretic hormone (ADH), oxytocin (OT), calcitonin
(CT), and parathyroid hormone (PTH)
Lipid-Soluble Hormones
 Include mainly steroid hormones
 Can pass directly through the bilayer by diffusion to the
target cell easily
 Binds to receptor in cell which binds to the DNA of the
nucleus
 “Turns on” the synthesis of specific protein molecules
by DNA
 Activate genes to synthesize new proteins and
enzymes
 Examples: aldosterone, cortisol, testosterone,
estrogen, thyroxine
Prostaglandins
 Chemicals with regulating effect on cells
 Act only on nearby cells whereas hormones
can travel distances, often called “local
hormones”
 Interact with hormones to regulate activities
 Reduce blood pressure and open airways OR
stimulate smooth muscle contraction for the
opposite effect
Hormonal Control
 How does an endocrine gland “know”
how much hormone to produce and
release? - - Feedback is provided by way
of chemical signals sent to the endocrine
gland
 Two systems: negative and positive
feedback
Negative Feedback
Systems
 Provides a response
in the opposite
direction to that of
the stimulus
 Signal is secreted by
the hormone or its
products which
exerts the negative
effect on the
endocrine gland
HOMEOSTASIS
Decreased blood
NORMAL BLOOD
Level Ca2+
LEVEL Ca2+
Decreased
Blood Level
Ca2+
Stimulates
Parathyroid
gland
Inhibits
Parathyroid
Gland
Increased
Blood level
Ca2+
Ca2+ Blood levelHOMEOSTASIS
Rises above NORMAL BLOOD
normal
LEVEL Ca2+
Positive Feedback
Systems
 Regulate hormone secretion by providing
a response in the same direction as the
stimulus
 Endocrine gland increases its rate of
hormone release and more responses
are stimulated
 Cause extreme conditions in the body
therefore quite unstable and uncommon
1. The baby moves deeper into the mother's pelvic region. (See
handout, Figure 29.16)
2.Special sensory nerve cells that are pressure receptors in the
cervix are stimulated and send nerve impulses to the
hypothalamus.
3. Specialized neurosecretory cells in the hypothalamus make
oxytocin hormone that travels down long extensions of these
cells into the posterior pituitary where it is stored. (See Fig. 5.3, p.
76 and read the text section titled Posterior Pituitary on p. 77.)
4. The posterior pituitary releases oxytocin hormone into the
blood.
5. Oxytocin hormone stimulates the uterus muscle lining, the
myometrium, to contract.
6. Uterine contraction pushes the baby deeper into the birth canal
and pressure receptors in the cervix are again triggered.... see #2.
This positive feedback loop continues until the baby is born.
--> When doctors induce labor, the woman receives several doses
of a synthetic oxytocin to get the positive feedback loop of labor
going.
FYI
 What triggers the start of the labor
positive-feedback loop?
 Doctors do not know, however, it has
been the generally accepted hypothesis
that the baby sends out the initial
message. Most recently, scientists have
discovered a protein released by the
baby's lungs that acts as a hormone
signaling mom to begin labor.
Pituitary Gland
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Aka hypophysis
Located at base of brain
Connected to hypothalamus
Two portions: anterior lobe 75% and
glandular; posterior composed of nerve
tissue
 Release of hormones regulated by
hypothalamus
Anterior/Posterior
Hormones
 Growth Hormone (GH)
 Prolactin (PRL)
 Thyroid-stimulating
hormone (TSH)
 Adrenocroticotropic
hormone (ACTH)
 Follicle-Stimulating
hormone (FSH)
 Luteinizing hormone
(LH)
 Oxytocin (OT)
 Antidiuretic hormone
(ADH)
 **Stored but not
produced here!!!
Thyroid Gland
 Prominent organ in
neck made of two
large lobes
 Hormones: Thyroxine
(T4), Triiodothyronine
(T3), and Calcitonin
(CT)
Parathyroid Glands
 Four or five peashaped masses of
glandular epithelium
 Secrete one
hormone called
parathyroid hormone
(PTH)
Adrenal Glands
 Paired, triangular
masses that lie on
each kidney
 Two areas: inner
medulla and outer
cortex
 Function as distinct
glands
Hormones of
Medulla/Cortex
 Medulla
 Epinephrine
 Norepinephrine
 Cortex
 Steroid hormones
 Mineralocorticoids:
aldosterone
 Glucocorticoids: cortisol,
corticosterone, cortisone
 Sex hormones:
androgens and
estrogens
Pancreas
 Part of endocrine and
digestive system
 Alpha cells secrete the
hormone glucagon
 Beta cells secrete the
hormone insulin
 http://cal.man.ac.uk/stud
ent_projects/2000/mnby
7lc2/factors_affecting_se
cretion.htm
Gonads
 Sex organs
 Produce the sex cells
and secrete primary
sex hormones
 Females = ovaries
which secrete
estrogens and
progesterone
 Males = testes which
secrete testosterone
Pineal Gland
 Small structure in
cranial cavity
associated with brain
 Secretes one
hormone called
melatonin
Thymus Gland
 Prominent in infants
but diminishes in size
with advancing age
 Soft, irregulary
shaped structure on
the top of the heart
 Early, secretes
thymosin
Assignment: Create a
powerpoint presentation for
your assigned hormones

Presentation must answer the following questions:
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From where does the hormone come?
What effects do these hormones have on the human body?
What organs do the hormones target?
Why are these hormones important to homeostasis in the
body?
What are the feedback mechanisms and antagonistic
hormones?
What happens when this gland does not work properly?
What can be medically done to correct malfunctions?
Presentation must include at least three
illustrations/diagrams