BIO1022 Chapter Notes - Chapter Prescribed: Osmoregulation, Gonadotropin, Erectile Tissue
30 May 2018
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BIO1022 – Readings – Week 6
chapter 45 - hormone and endocrine system
- in animals - hormones are secreted into the extracellular fluid, circulate in the
blood and communicate regulatory messages through the body.
- each hormone binds to specific receptors in the body
- chemical signalling by hormones is the function of the endocrine system
- hormones and other signalling molecules bind to target receptors , triggering
specific response pathways
- intercellular communication
• endocrine signalling
•
o hormones secreted into extracellular fluid by endocrine cells reach
target cells via the bloodstream
o one function is to maintain homeostasis
o hormones regulate properties that include blood pressure and
volume, energy metabolism and allocation and solute
concentrations in body fluids.
o mediates responses to environmental stimuli
o regulates growth and development
o triggers physical and behavioural changes underlying sexual
maturity and reproduction.
• paracrine and autocrine signalling
•
o many types of cells produce and secrete local regulators, molecules
that act over short distances and reach their target cells solely by
diffusion
o depending on the target cell, signalling by local regulators can be
either paracrine or autocrine.
o paracrine
o
▪ target cells lie near the secreting cell
o autocrine
o
▪ the secreting cells themselves are the target cells
o both play roles in many physiological processes, including blood
pressure regulation, nervous system function and reproduction
• synaptic and neuroendocrine signalling
•
o synaptic signalling
o
▪ neurons form specialised junctions called synapses with
target cells such as other neurons and muscle cells
▪ at most synapses - neurons secreted molecules called
neurotransmitters that diffuse a very short distance to bind
to receptors on target cells
o neuroendocrine signalling
o
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▪ specialised neurons called neurosecretory cells secrete
neurohormones which diffuse from nerve cell endings into
the blood stream
• signalling by pheromones
•
o some animal species communicate to each other via pheromones -
chemicals that are released into the external environment
o serve a wide range of functions - defining territories, warning of
predators and attracting potential mates
- chemical classes of local regulators and hormones
• classes of local regulators
•
o one group of local regulators, the prostaglandins are modified fatty
acids
o many other local regulators, including cytokines and growth
factors are polypeptides, some are gases
o nitric oxide - NO
o
▪ a gas
▪ functions in the body as both a local regulator and
neurotransmitter
▪ when the level of oxygen in the blood falls, endothelial cells
in blood vessel walls synthesis and release NO
▪ after diffusing into the surrounding smooth muscle cells -
the result is vasodilation - which increases blood flow to
tissues
▪ in human male’s, NO’s ability to promote vasodilation
enables sexual function - increasing blood flow to the penis
• classes of hormones
•
o fall into three major chemical classes
o
▪ polypeptides
▪ steroids
▪
▪ lipids that contain four fused carbon rings
▪ all derived from cholesterol
▪ amines
▪
▪ synthesised from a single amino acid
- cellular response pathways
• differences between the response pathways for water-soluble and lipid
soluble signalling molecules
• in endocrine signalling
• difference in cellular hormone response pathways is the location of the
target cell’s receptor proteins
• water soluble hormones are secreted by exocytosis and travel freely in
the bloodstream
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• these hormones bind to cell-surface receptors as they are insoluble in
lipids and cannot diffuse through the plasma membranes of target cells, -
this induces changes in cytoplasmic molecules and sometimes altering
gene transcription
• in contrast - lipid soluble hormones diffuse out across the membranes of
endocrine cells - outside the cell, they bind to transport proteins that keep
them soluble in the aqueous environment of the blood.
•
o upon leaving the blood they diffuse into target cells and typically
bind to receptors in the cytoplasm or nucleus
- a single hormone can elicit multiple responses if target cells differ in their
receptor type or in molecules that produce the response
- endocrine tissues and organs
• some endocrine cells are found in organs that are part of other organ
systems.
• more often, endocrine cells are grouped in ductless organs called
endocrine glands - e.g. thyroid or gonads
• endocrine glands secrete hormones directly into the surrounding fluid.
• in constrast, exocrine glands, such as salivary glands, have ducts that
carry secreted substances onto body surfaces or into body cavities
- feedback regulation and coordination with the nervous system are common in
endocrine signalling
- simple hormone pathways
• simple endocrine pathway
•
o endocrine cells respond directly to an internal or environmental
stimulus by secreting a particular hormone
o the hormone travels in the bloodstream to target cells where it
interacts with specific receptors
• neuroendocrine pathways
•
o include additional steps and involve more than one cell type
o in a simple neuroendocrine pathway, the stimulus is received by a
sensory neuron which stimulates a neurosecretory cell - this then
secretes a neurohormone which diffuses into the bloodstream and
travels to target cells.
- feedback regulation
• a feed back loop linking the response back to the initial stimulus is
characteristic of control pathways
• often regulation involves negative feedback - in which the response
reduces the initial stimulus
• negative feedback dampens a stimulus
• positive feedback reinforces a stimulus, leading to an even greater
response
- coordination of endocrine and nervous systems
• invertebrates
• vertebrates
•
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find more resources at oneclass.com
Document Summary
Bio1022 readings week 6 chapter 45 - hormone and endocrine system. In animals - hormones are secreted into the extracellular fluid, circulate in the blood and communicate regulatory messages through the body. Each hormone binds to specific receptors in the body. Chemical signalling by hormones is the function of the endocrine system. Hormones and other signalling molecules bind to target receptors , triggering specific response pathways. A single hormone can elicit multiple responses if target cells differ in their receptor type or in molecules that produce the response. Feedback regulation and coordination with the nervous system are common in endocrine signalling. Hormonal regulation of growth: growth hormone - secreted by the anterior pituitary - stimulates growth through tropic and non-tropic effects. Endocrine glands respond to diverse stimuli in regulating homeostasis, development and behaviour: parathyroid hormone and vitamin d - control of blood calcium, adrenal hormones - response to stress steroid hormones from the adrenal cortex.
