Download Chemical signals in animals

Key concepts







Hormones are compounds produced in one part of the body and
transported to another location to produce specific responses;
small amount s can induce substantial responses.
Chemical signals produced by the body are mostly produced by
glands.
Hormones either affect a target effector organ directly or via the
signal transduction pathway.
Effects of hormones vary depending on whether they bind to a
receptor in the plasma membrane or within the nucleus of a cell.
Action of hormones is controlled by feedback mechanisms.
Hormones are classified by mode of transport or through chemical
composition.
Diseases in the endocrine system occur when levels of hormones
released are at an abnormal level or when receptors of that
particular hormone are damaged.
Endocrine system




Hormone-secreting
cells
Chemical signals
secreted into body
fluids, eliciting
responses in target
cells
Functions with NS in
maintaining
homeostasis
Effects are slower and
longer-lasting
Maintenance of Homeostasis by the ES and NS


Neurosecretory cells
– nerve cells that
secrete hormones into
bloodstream (eg.
epinephrine)
Feedback regulation
 Positive feedback
○ Suckling  release of
oxytocin  milk
secretion
 Negative feedback
○ Control of blood calcium
and glucose levels
Invertebrate Endocrine Systems



Hydra –control method
of reproduction
Mollusks –controls egglaying
Arthropods – extensive
endocrine systems for
molting and maturity
 Ecdysone  molting and
promotion of adult
features
 Brain hormone (BH) 
regulates production of
ecdysone
 Juvenile hormone (JH)
 retention of larval
characteristics
Chemical signals and their modes of action
Hormones bind to
specific receptor
proteins on/within target
cells
Signal
transduction
pathway is
initiated
Target cell
changes its
behavior to
produce a
response
most peptides, proteins and glycoproteins
steroids and thyroid hormones
Importance of signal transduction pathways
1) Different pathways in
different cells  different
responses to the same signal
2) Amplification of the single
signal allows small amounts of
hormones to have a large effect
Vertebrate endocrine
systems


Hypothalamus
integrates
endocrine and
nervous functions
Neurosecretory
cells of the
hypothalamus
produce hormones
 Stored and secreted
by posterior pituitary
 Affect anterior
pituitary’s release of
own hormones
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Table 45.1 (continued)
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Feedback control loops: a closer look
Regulation of
thyroid hormones
Regulation of glucose in the
blood
Hormones control the
reproductive cycle of
human females