Transcript Endocrine System, Part 2

Endocrine System, Part 2
Ashlee Black
Kelsey Hunter
Melanie O’Bar
Homeostasis!
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There are simple and complex pathways in the
endocrine system. The 4 named in your text are:
simple endocrine, simple neurohormone, simple
neuroendocrine, and complex neuroendocrine.
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Simple endocrine: stimulus > receptor protein on endocrine
cell > secretion goes to blood vessel > to target effectors >
response.
Simple neurohormone: stimulus > sensory neuron connected
to hypothalamus/posterior pituitary > secretion through
neurosecretory cell > blood vessel > target effectors >
response.
Simple neuroendocrine: stimulus > sensory neuron on
hypothalamus > neurosecretory cell secretes hormonereleasing hormone > blood vessel > receptor site on
endocrine cell > blood vessel > target effectors > response.
Homeostasis, cont.
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Complex neuroendocrine pathways are those in which a
hormone secreted by one endocrine gland produces a
response in another endocrine gland. (Pituitary gland) Seems
very similar to simple neuroendocrine…
In endocrine and neuroendocrine pathways, the
outgoing signal is called an efferent signal and is
either a hormone or neurohormone.
Feedback Loops: connect the response to the initial
stimulus.
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Negative feedback: the effector response reduces the stimulus and the
response eventually stops. Prevents overreaction of the system and
“wild” fluctuations in the environment. Contributes to the hormonal
control of blood glucose and calcium levels.
Positive feedback: Reinforces the stimulus and initiates
greater response. Release of milk is an example
(neurohormone pathway).
Regulation of Body Temperature
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Body temperature is the balance between
the heat produced by the body and the heat
lost from the body. In humans, as other
mammals, the core temperature of the
body remains constant despite the
temperature of the surrounding
environment.
For the body to function optimally, the
temperature must be maintained within
narrow limits. There are two kinds of body
temperature: core temperature and surface
temperature. Core temperature is the
temperature of the deep tissues of the
body. It normally remains constant at about
98.6 degrees Fahrenheit (37.0 degrees
Celsius). However, body temperature varies
from person to person and is affected by
factors such as exercise, sleep, eating and
drinking, and time of day.
Something We Floridians Are All Too
Familiar With…
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The sweat pores allow loss of fluid
as part of temperature control of the
body. As a rise in external
temperature is sensed by the nerve
endings in the skin, the message is
relayed to the hypothalamus, the
temperature-regulating area of the
brain. The brain then sends nerve
impulses to the sweat (eccrine)
glands stimulating them to release
sweat until the skin receptors detect
that the skin's temperature is back
to normal. The brain then sends
messages to stop the release of
sweat. The human body has
between two and three million
eccrine
glands
that
secrete
moisture on the skin primarily to
cool the body through evaporation.
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Body heat is transferred
from skin and blood to
the sweat, The sweat
evaporates transferring
heat away and in doing
so cools the body
The Hypothalamus Is Back…
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The body's surface temperature rises and falls
in response to the environment. Body
temperature is maintained by the
hypothalamus, which constantly monitors blood
temperature and activates mechanisms to
compensate for changes.
When the body's surface temperature falls, the
hypothalamus sends nerve impulses to the skin
to stimulate shivering, which generates heat by
muscle activity, and to restrict the blood
vessels in the skin (skin arterioles), which limits
heat loss. When the surface temperature rises,
the hypothalamus stimulates the sweat glands
in the skin to produce sweat and dilates the
skin arterioles to increase heat loss.
The message that is responsible for the
restriction and dilation of skin arterioles is
hormonal, and is sent through the bloodstream
from the pituitary gland.
Primary Methods of Temperature
Regulation
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Hairs with the erector pili muscle
(controlled by nerves)
Sweat glands (controlled by nerves and
hormones)
Blood arterioles (controlled by hormones)
Shivering: When core temperature falls
an uncontrolled phase of rapid muscular
contraction occurs which generates heat
that is used to raise the core temperature
(controlled by nerves)
When the Body Temperature Falls:
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Blood flow to the surface
via arterioles in reduced.
Notice that (a) is dilated
but (b) & (c) are
vasoconstricted: Less
heat is lost to the
environment by
radiation, heat is
retained in the core.
When the Body Temperature Rises:
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Blood flow to the surface
is increased.
(a) is closed and (b) and
(c) arterioles are open:
vasodilation
Blood flows closer to the
surface
More heat is lost to the
external environment
Core temperature is
reduced
Nerves vs. Hormones
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Nerves are faster (one ten thousandth
of a second) while hormones are
slower-acting.
Nerves have a shorter effect while
hormones last longer in the
bloodstream.
Nerves are electrical impulses while
hormones are chemical.
Nervous system performs short term
crisis management while Endocrine
system regulates long term ongoing
metabolic processes
Paracrine communication involves
chemical messengers between cells
within one tissue while Endocrine
communication is carried out by
endocrine cells releasing hormones
Further Comparison
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Together, the nervous and endocrine systems
coordinate the functions of all body
systems. How does the nervous system
achieve this?
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The nervous system achieves this through the use of
nerve impulses and the secretion of neurotransmitter
substances that either excite or inhibit the effector.
How does the endocrine system achieve
this control?
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The endocrine system, in contrast, regulates body
functions by releasing chemical messengers called
hormones (“to urge on” or “to set in motion”) into the
bloodstream for delivery throughout the body.
And more…
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The nervous system causes muscles to
contract and glands to secrete. The endocrine
system regulates metabolic activities, growth
and development, and reproduction.
The nervous system tends to act in
milliseconds. The endocrine system acts in
seconds, minutes, hours, weeks, months, even
years, depending upon the hormone.
Each nerve affects one part of your body. On
the other hand, hormones can affect lots of
parts of the body at the same time
Remember…
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One way of keeping hormones and nerves straight in
your mind is to compare them to radio and telegraph
communication systems. Whereas nerves are relatively
hard-wired from one spot to another, hormones are
broadcast into the circulatory system. Carried in the
blood, they come into contact with every cell in the
body, just as we are bathed in radio waves all of the
time. But only those cells with the correct receptor cells
will bind, and thus respond to, any give hormone.
Hormones can therefore be highly specific, just as
nerves; they can also be very general, eliciting
responses from all the cells in an organ or organ system
without having to directly innervate each one.
Blood Glucose Concentration
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Insulin and glucagon regulate the sugar level in the
body. These two hormones are manufactured in the
pancreas and through circulation are carried to the liver
where they perform their functions. Enzymes that
convert glucose to glycogen though a condensation
reaction are stimulated by Insulin. Enzymes that
hydrolyze glycogen to glucose are stimulated by
glucagon. Receptors in the pancreas are sensitive to the
changes in sugar level, thus releasing the necessary
requirements of insulin and glucagon depending on the
needs of the body. The beta cells found in the islets of
the pancreas make insulin and the alpha cells make
glucagon.
The Pacreas is Back, Too…
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If there is too much glucose in the blood, then receptors in the
pancreas detect this. They send a message to the cerebrum,
inducing feelings of satiety (so that intake of food is decreased).
They also send messages to the Islets of Langerhans (the B-cells)
to produce insulin. This insulin is released into the bloodstream via
capillaries, and has various effects. It increases the intake of
glucose by all cells, and stimulates the conversion of glucose into
glycogen. This reduces the amount of glucose in the blood, so that
they return to equilibrium.
If there is too little glucose in the blood, then the same receptors in
the pancreas detect this. They send a message to the cerebrum,
inducing feelings of hunger (so that intake of food is increased).
They also send a message to the A-cells in the islets of langerhans
to produce glucagon.
A-cells make glucagon and affect mainly liver cells, to break down
glycogen.
B-cells make insulin and affect all cells, to take in glucose.
Return of the Pancreas, cont.
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Glucagon is released into the bloodstream via capillaries and
stimulates the conversion of glycogen into glucose in liver. The liver
is also stimulated to convert amino acids into glucose. Thus, the
levels of glucose in the blood increase so that equilibrium is
reached.
To elevate glucose levels, glucagon binds to receptors on
hepatocytes (liver cells) and other cells (e.g. muscle cells). This
activates an enzyme, glycogen phosphorylase, inside the
hepatocyte to hydrolyse glycogen to glucose. This process is called
glycogenolysis. In rodents, alpha cells are located in the periphery
of the islets, however in humans the islet architecture is generally
less organized and alpha cells are frequently observed inside the
islets as well. When being viewed by an electron microscope, alpha
cells can be identified by their characteristic granules with a large
dense core and a small white halo.
Alpha Cells!
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endocrine cells in the islets of Langerhans of
the pancreas. They make up 15-20% of the
cells in the islets. They are responsible for
synthesizing and secreting the peptide
hormone glucagon, which elevates the
glucose levels in the blood.
Beta Cells!
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are a type of cell in the pancreas in areas called the islets of Langerhans.
They make up 65-80% of the cells in the islets.
Beta cells make and release insulin, a hormone that controls the level of
glucose in the blood. There is a baseline level of glucose maintained by
the liver, but it can respond quickly to spikes in blood glucose by releasing
stored insulin while simultaneously producing more. The response time is
fairly quick, taking approximately 10 minutes.
Apart from insulin, beta cells release C-peptide, a byproduct of insulin
production, into the bloodstream in equimolar quantities. C-peptide helps
to prevent neuropathy, and other symptoms of diabetes related to vascular
deterioration[1]. Measuring the levels of C-peptide can give a practitioner
an idea of the viable beta cell mass.
β-cells also produce amylin, also known as IAPP, islet amyloid
polypeptide. Amylin functions as part of the endocrine pancreas and
contributes to glycemic control. Amylin's metabolic function is now
somewhat well characterized as an inhibitor of the appearance of nutrient
[especially glucose] in the plasma. It thus functions as a synergistic partner
to insulin. Whereas insulin regulates long term food intake, increased
amylin decreases food intake in the short term.
Diabetes
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One in 20 of the world's adult population now
suffers from diabetes. Diabetes currently
affects 246 million people worldwide and is
expected to affect 380 million by 2025. It is the
fourth leading cause of global death by disease.
The westernisation of people's lifestyles is
leading to a rapid spread of type 2 diabetes,
particularly in developing countries.
In 2007, the five countries with the largest
numbers of people with diabetes were India
(40.9 million), China (39.8 million), the United
States (19.2 million), Russia (9.6 million)
and Germany (7.4 million).
Diabetes, cont.
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Type 2 or adult onset diabetes is associated with
obesity, poor eating habits and a sedentary lifestyle.
It is caused by lack of insulin in the body and
resistance to insulin that is naturally produced.
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The main risk factors for Type 2 diabetes are being
overweight, aged over 40, having a family history of
diabetes and being Asian or Afro-Caribbean.
Up to 80% of Type 2 diabetes is preventable by
adopting a healthy diet and exercise.
Prof. Alberti, who is president of the Royal College of
Physicians said: "Diabetes causes an enormous
burden to people and economies world-wide.
Common complications include circulatory disease,
including strokes and amputations as well as kidney
problems and blindness.
Kidney Failure
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Kidneys remove waste from the blood.
Failing kidneys lose their ability to filter out
waste products, resulting in kidney disease, also
called nephropathy.
In the kidneys, capillaries with even smaller
holes in them act as filters. As blood flows
through the blood vessels, small molecules such
as waste products go through the holes. These
become part of the urine. Useful substances,
such as protein and red blood cells, are too big
to pass through the holes in the filter and stay in
the blood.
Kidneys, cont.
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High levels of blood sugar, as in diabetes,
make the kidneys filter too much blood. After
having to work so hard, the kidneys start to
leak. Useful protein is lost in the urine.
Having small amounts of protein in the urine
is called microalbuminuria. When kidney
disease is diagnosed early, treatments may
keep kidney disease from getting worse.
Having larger amounts is called
macroalbuminuria. When kidney disease is
caught later, end-stage renal disease, or
ESRD, usually follows.
Waste builds up in the blood.
Kidneys, Kidneys, Kidneys
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Treatment: centers around tight control
of blood glucose and blood pressure,
exercise, losing weight, eating less salt,
avoiding alcohol and tobacco
Once kidneys fail, dialysis is necessary.
(Hemodialysis or Peritoneal dialysis)
A kidney transplant may also be an
option.
Ta Da!
Also…