Slides about Chemical Messengers, Hormones, Pheromones, Types of Chemical Messengers, Biochemistry of Chemical Messengers, Feedback Mechanisms of Hormones

1. Topic: Chemical Messengers
Submitted to: Ma'am Lubna Kanwal
Presented by: Muhammad Ahmad
BS (Hons) Zoology
UNIVERSITY OF OKARA
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2. Chemical
Messengers,
Biochemistry Of
Hormones &
Their Feedback
Mechanism
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3. Chemical Messengers
 Definition:
 Chemical messengers are
molecules that specialized cells
synthesize and secrete.
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4. Chemical Messengers
Chemical messengers can be
categorized as follows:
 Local chemical messengers
 Neurotransmitters
 Neuropeptides
 Hormones
 Pheromones
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5. Local chemical messengers
 Many cells secrete chemicals that alter
physiological conditions in the
immediate vicinity.
 Most of these chemicals act on the same
cell (autocrine agents) or adjacent cells
(paracrine agents) and do not
accumulate in the blood.
 Vertebrate examples include some of
the chemicals called lumones that the
gut produces and that help regulate
digestion. In a wound, mast cells secrete
a substance called histamine that
participates in inflammatory response.
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8. Neurotransmitters
 Neurons secrete chemicals called
neurotransmitters (e.g., nitric oxide
and acetylcholine) that act on
immediately adjacent target cells.
 These chemical messengers reach
high concentrations in the synaptic
cleft, act quickly, and are actively
degraded and recycled.
 Ex: Acetylcholine : causes
contraction of skeletal muscles.
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10. Neuropeptides
 Some specialized neurons (called
neurosecretory cells) secrete
neuropeptides (neurohormones).
 The blood or other body fluids transport
neuropeptides to nonadjacent target cells,
where neuropeptides exert their effects
(figure).
 In mammals, for example, certain nerve
cells in the hypothalamus release a
neuropeptide that causes the pituitary
gland to release the hormone oxytocin,
which induces powerful uterine
contractions during the delivery of
offspring.
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12. Hormones
 Endocrine glands or cells secrete
hormones that the bloodstream
transports to nonadjacent target
cells (figure).
 Ex: Insulin is secreted by pancreas
and regulates energy metabolism.
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14. Pheromones
 Pheromones are chemical
messengers released to the
exterior of one animal that
affect the behavior of another
individual of the same species.
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16. Interlinkage of Nervous System &
Endocrine System
 Scientists now recognize that the
nervous and endocrine systems work
together as an all-encompassing
communicative and integrative
network called the neuroendocrine
system.
 In this system, feedback systems
regulate chemical messengers in their
short- and long-term coordination of
animal body function to maintain
homeostasis.
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17. Hormone
 Derivation: Gr. Hormaein,to set in
motion or to spur on.
 Hormone is a specialized chemical
messenger that an endocrine gland
or tissue produces and secretes.
 The study of endocrine glands and
their hormones is called
endocrinology.
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18. Action Of Hormones
 Hormones circulate through body
fluids and affects the metabolic
activity of a target cell or tissue in a
specific way.
 A target cell has receptors to which
chemical messengers either
selectively bind to or on which they
have the effect.
 Only rarely does a hormone operate
independently.
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19. BIOCHEMISTRY
OF HORMONES
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20. Contribution of Hormones in
control of Biochemical
Reactions Hormones are effective in extremely small
amounts.
 Only a few molecules of a hormone may be
enough to produce a dramatic response in a
target cell. In the target cell, hormones help
control biochemical reactions in three ways:
1. A hormone can increase the rate at which
other substances enter or leave the cell.
2. It can stimulate a target cell to synthesize
enzymes, proteins, or other substances.
3. It can prompt a target cell to activate or
suppress existing cellular enzymes.
 As is the case for enzymes, hormones are not
changed by the reaction they regulate.
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21. Classes of Hormones
Proteins
Amines
Steroids
Eicosanoid
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22.  Hormones that the vertebrate
pancreas secretes are proteins.
 Those that the thyroid gland
secretes are amines.
 The ovaries, testes, and cortex of
the adrenal glands secrete
steroids.
 Produced from 20-carbon fatty
acid, arachadonic acid.
Produced in all cells except
RBCs. Involved in inflammation.
.
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24. Feedback Control System Of
Hormone Secretion
 A feedback control system
monitors
changes in the animal or in the
external environment and sends
information to a central control unit
(such as the central nervous
system), which makes adjustments.
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25. Feedback Systems
Positive Feedback System
Negative Feedback System
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26. Positive Feedback System
 A positive feedback system
reinforces the initial stimulus.
 Positive feedback systems are
relatively rare in animals because
they usually lead to instability or
pathological states.
 Surges of Hormones can occur with
Positive feedback system.
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28.  One example of Positive feedback
system is the surge of Luteinizing
Hormone (LH) that occurs as a result
of the stimulatory effect of estrogen
on the anterior pituitary before
ovulation. The secreted LH then acts
on the ovaries to stimulate additional
secretion of estrogen, which return
causes more secretion of the LH.
Eventually, LH reaches an approach
an appropriate concentration, and
typical negative feedback control of
hormones secretion is then exerted.
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30. Negative Feedback System
 A feedback system that produces a
response that counteracts the
initiating stimulus is called a
negative feedback system.
 Negative feedback systems monitor
the amount of hormone secreted,
altering the amount of cellular
activity as needed to maintain
homeostasis.
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32.  For example, suppose that the rate of
chemical activity (metabolic rate) in the
body cells of a dog slows (figure). The
hypothalamus responds to this slow rate by
releasing more thyrotropin releasing
hormone (TRH), which causes the pituitary
gland to secrete more thyrotropin, or
thyroid-stimulating hormone (TSH). This
hormone, in turn, causes the thyroid gland
to secrete a hormone called thyroxin.
 Thyroxin increases the metabolic rate,
restoring homeostasis. Conversely, if the
metabolic rate speeds up, the
hypothalamus releases less TRH, the
pituitary secretes less TSH, the thyroid
secretes less thyroxin, and the metabolic
rate decreases once again, restoring
homeostasis.
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33. THANKS
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