BIO1022 Lecture 11: BIO1022 – Lecture 11 – Week 6 – Hormones
30 May 2018
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BIO1022 – Lecture 11 – Week 6 – Hormones
- hormones - a chemical signal that is secreted into the circulatory system and
communicates regulatory messages within the body
• may reach all parts of the body but only certain types of cells (target cells)
are equipped to respond
• specific cells have receptors that can bind to these hormones
- regulatory systems
• nervous system
•
o conveys high speed electrical signals along specialised cells called
neurons
o these messages control movement of body parts in response to
sudden environmental change
• endocrine system
•
o comprises all of an animal’s hormone secreting cells
o in contrast to NS - hormones coordinate slower but longer acting
responses to stimuli - e.g. stress
o hormones also regulate long term developmental process - e.g.
growth, development of primary and secondary sexual
characteristics
o hormone secreting organs called endocrine glands - secrete
hormones directly into the extracellular fluid, where they diffuse
into the blood - then transported around the body
• overlap
•
o structurally, chemically and functionally related
o neurosecretory cells secrete hormones - known as neurohormones
into the blood
o some chemicals (epinephrine) serve as both hormones of the
endocrine system and chemical signals in the nervous system
o nervous system also plays a role in certain sustained responses -
e.g. day/night - cycles by increasing or decreasing secretions from
endocrine glands
- control pathways
• a receptor. or sensor which detects a stimulus and sends information to a
control centre
• after comparing the incoming information a set point - desired value - the
control centre sends out a signal directions an effector to respond
• in endocrine and neuroendocrine pathways - this outgoing single called
an efferent system is a hormone or neurohormone which acts on
particular effector tissues and elicit specific physiological or
developmental changes
- hormone control pathways
• simple endocrine pathways
• simple neurohormone pathways
• simple neuroendocrine pathways
- feedback loops
• common feature of control pathways
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• connecting the response to the initial stimulus - causes the response to
cease
• negative feedback - the effector response reduces the initial stimulus and
eventually response ceases positive feedback - reinforces the stimulus
and leads to an even greater response - e.g. suckling
- hormones and how they work
• convey information via the blood stream to target cells
• three major classes of molecules functions as hormones in vertebrates
•
o proteins and peptides
o amines derived from amino acids
o steroids - not water soluble
• signalling by any of theres molecules involves three key events
•
o reception of the signal occurs when the molecule binds to a
specific receptor protein in or on the target cell - this triggers
signal transduction within the target cell resulting in a response
• transmission of hormones
•
o water soluble
o
▪ receptors are imbedded in plasma membrane
▪ secretary cell - transport vesicle - released into
extracellular fluid - released into blood stream - eventually
encounters hormone receptor
▪ binding of hormone to its receptor initiates a transduction
pathway - series of changes that converts an extracellular
chemical signal to an intracellular response
o lipid soluble hormones
o
▪ cannot be transported through bloodstream
▪ cannot be dissolved in blood stream
▪ transported with transport protein
▪ bind with some kind of receptor on target cell - receptor
located inside the target cell
▪ hormone form completes with receptors inside cell
▪ these protein-receptor complexes bind onto DNA and
induce changes in gene expression
- hormonal interaction
• opposing interaction where effect of one hormone opposes the effect of
another
• synergistic interaction - where combined action of two or more hormones
are required to produce a particular effect
• permissive interaction where a hormone exerts an effect on a cell only
after another hormone has primed the target cell - hormone a will do
nothing unless hormone b is active
- vertebrate endocrine system
• hypothalamus
•
find more resources at oneclass.com
find more resources at oneclass.com
