hormones n homeostasis wady edt
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Hormones, Endocrine System
& Homeostasis
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LOs
Describe hormones and endocrine system in
human
List several examples of hormones and their
functions
Explain the concept of homeostasis
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What are hormones?
Hormones are chemical signals that are secreted into the
circulatory system and communicate regulatory messages
within the body
Hormones reach all parts of the body, but only target cells
have receptors for that hormone
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How do cells communicate?
Two systems coordinate communication throughout the body:
the endocrine system and the nervous system
The endocrine system secretes hormones that coordinateslower but longer-acting responses including reproduction,
development, energy metabolism, growth, and behavior
The nervous system conveys high-speed electrical signalsalong specialized cells called neurons; these signals regulate
other cells
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Endocrine Signaling
Hormones secreted into extracellular fluids by endocrine cells
reach their targets via the bloodstream
Endocrine signaling maintains homeostasis, mediatesresponses to stimuli, regulates growth and development
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Endocrine Tissues and Organs
In some tissues, endocrine cells are grouped together in
ductless organs called endocrine glands
Endocrine glands secrete hormones directly into surrounding
fluid
These contrast with exocrine glands, which have ducts and
which secrete substances onto body surfaces or into cavities
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Major endocrine glands:
Hypothalamus
Pineal gland
Pituitary gland
Thyroid gland
Parathyroid glands(behind thyroid)
Adrenal glands
(atop kidneys)
Pancreas
Ovaries (female)
Testes (male)
Organs containingendocrine cells:
Thymus
Heart
Liver
Stomach
Kidneys
Smallintestine
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Hormone Actions
Affects parts distant from gland
May affect numerous parts of the body
Effects take longer than nervous system
Effects may be long lasting
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Hormone Activity
Affect only target cells
Hormone must bind to a receptor
Receptor activates chain of events
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Classes of Hormones
Peptide hormones (most common) Steroid hormones (gonads & adrenal cortex)
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Feedback Regulation
A negative feedback loop inhibits a response by reducing theinitial stimulus, thus preventing excessive pathway activity
Positive feedback reinforces a stimulus to produce an even
greater response
For example, in mammals oxytocin causes the release of milk,
causing greater suckling by offspring, which stimulates the
release of more oxytocin
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Growth Hormone
Controls normal growth
Hypersecretion
Gigantism
Acromegaly
Bones of hands & face
thicken
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Growth Hormone
Acromegaly
Bones of hands & face thicken
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Pineal Gland
Embedded within brain
Produces melatonin
Increase in secretion at night
Helps set circadian rhythms
physical, mental and behavioral changes that follow
a roughly 24-hour cycle, responding primarily to
light and darkness in an organisms environment can influence sleep-wake cycles, hormone release,
body temperature and other important bodily
functions
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Thyroid Gland
Below level of voice box
Hormones that regulate metabolism
Most body cells have receptors
Negative feedback loop regulates release
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Thyroid Disorders
Graves disease
Hyperthyroidism
Rapid heart rate
Nervousness
Protrusion of eyes
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Thyroid Disorders
Goiter
Hypothyroidism
Slow growth Caused by insufficient
iodine in diet
Thyroid enlarges
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Pancreas
Endocrine portion in islets of Langerhans
Hormones that regulate levels of glucose
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Diabetes
High levels of glucose in blood
Lack of insulin
Inability of tissue to respond to insulin
Two types
Type I = insulin dependent
Pancreas does not produce enough insulin
Type II
Often occurs later in life
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Gonadal Sex Hormones
The gonads, testes and ovaries, produce most of the
sex hormones: androgens, estrogens, and progestins
All three sex hormones are found in both males and
females, but in significantly different proportions
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Sex hormones
The testes primarily synthesize androgens, mainly
testosterone, which stimulate development and
maintenance of the male reproductive system
Testosterone causes an increase in muscle and bone
mass and is often taken as a supplement to cause
muscle growth, which carries health risks
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Sex hormones
Estrogens are responsible for maintenance of the
female reproductive system and the development of
female secondary sex characteristics
In mammals progesterone are primarily involved in
preparing and maintaining the uterus
Synthesis of the sex hormones is controlled by FSH
and LH from the anterior pituitary
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Effects of anabolic steroid
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Homeostasis
Copyright 2009 Pearson Education, Inc.
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Homeostasis is an internal steady state
Animals regulate their internal environment
Copyright 2009 Pearson Education, Inc.
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Externalenvironment
Homeostaticmechanisms
Internal
environment
Smallfluctuations
Largefluctuations
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Humans promote homeostasis by
Adding clothing when we are cold
Drinking water when we are dehydrated
Eating when our calories are running low Urinating when our bladders are full
Copyright 2009 Pearson Education, Inc.
Animals regulate their internal environment
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Sweat glands secrete sweat
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Sweat glands secrete sweat
that evaporates, cooling body
Blood vessels inskin dilate and
heat escapes
Temperaturedecreases
Thermostat shuts offcooling mechanisms
Temperature risesabove normal
Temperature fallsbelow normal
Thermostat shuts offwarming mechanisms
Homeostasis:Internal body temperature
of approximately 3638C
Temperatureincreases
Blood vessels in skinconstrict, minimizingheat loss
Skeletal muscles
rapidly contract,
causing shivering,
which generates heat
Thermostat inbrain activateswarming mechanisms
Thermostat in brainactivates coolingmechanisms
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