Objectives To understand homeostasis in more depth. To compare and contrast positive and negative...
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Objectives To understand homeostasis in more depth. To compare and contrast positive and negative feedback. To list examples of the two types of feedback in our body.
Objectives To understand homeostasis in more depth. To compare and contrast positive and negative feedback. To list examples of the two types of feedback
Objectives To understand homeostasis in more depth. To compare
and contrast positive and negative feedback. To list examples of
the two types of feedback in our body.
Slide 3
Principles of Homeostasis... THE MAINTENANCE OF STATIC OR
CONSTANT CONDITIONS IN THE INTERNAL ENVIRONMENT... External
Environment Internal Environment
Slide 4
External Environment Internal Environment Homeostasis is about
staying the same... but... things dont stay the same... They
CHANGE! Conditions change here constantly... Where they cannot
change is here... The Internal Environment
Slide 5
Homeostasis is about staying alive! staying alive!staying
alive! For the bodys cells to survive and function properly, the
composition and temperature of the fluids around the cells
(interstitial fluid) must remain much the same. An organism is said
to be in homeostasis when the internal environment contains: The
optimal concentration of gases The optimal concentration of
nutrients The optimal concentration of ions and water At the
optimal temperature
Slide 6
Activities such as exercise change the rate at which we
breathe... Which changes the pH of the blood... Which is dangerous
Potentially fatal, unless... Which increases the amount of CO 2 in
our blood The body responds homeostatically by changing the volumes
of air we breathe and adjusting blood pH with buffers (HCO3, Hb and
others) Our lab will be on this!!
Slide 7
Homeostasis operates by means of control systems Homeostasis
operates by means of control systems Sensory receptors Control
center Effectors
Slide 8
Homeostasis is characterized by Negative Feedback Homeostasis
is characterized by Negative Feedback...response is negative to the
initiating stimulus...the control system initiates a series of
changes that return the factor toward a certain mean value... thus
maintaining homeostasis.
Slide 9
Slide 10
Maintaining Homeostasis The various organ systems of the body
act to maintain homeostasis through a combination of hormonal and
nervous mechanisms. In everyday life, the body must regulate
respiratory gases, protect itself against agents of disease
(pathogens), maintain fluid and salt balance, regulate energy and
nutrient supply, and maintain a constant body temperature. All
these must be coordinated and appropriate responses made to
incoming stimuli. In addition, the body must be able to repair
itself when injured and be capable of reproducing (leaving
offspring).
Slide 11
Oxygen must be delivered to all cells and carbon dioxide (a
waste product of cellular respiration) must be removed. Breathing
(inhalation and exhalation) brings in oxygen and expels CO 2. The
rate of breathing is varied according to the oxygen requirement.
Both gases are transported around the body in the blood; the oxygen
mostly bound to hemoglobin.
Slide 12
All of us are under constant attack from pathogens (disease
causing organisms). The body has a number of mechanisms that help
to prevent the entry of pathogens and limit the damage they cause
if they do enter the body. The skin, the digestive system and the
immune system are all involved in limiting damage.
Slide 13
Food and drink must be taken in to maintain the body's energy
supplies. Steady levels of energy (as glucose) is available to
cells through hormonal regulation of blood sugar levels. Insulin,
released by the endocrine cells of the pancreas, causes cells to
take up glucose after a meal. Glucagon causes the release of
glucose from the liver.
Slide 14
Damage to body tissues triggers the inflammatory response.
There is pain, swelling, redness, and heat. Phagocytes and other
white blood cells move to the injury site. The inflammatory
response is started (and ended) by chemical signals (e.g. from
histamine and prostaglandins) released when tissue is damaged.
Slide 15
The levels of water and ions in the body are maintained mainly
by the kidneys, although the skin is also important. Osmoreceptors
monitor the fluid and ion levels of the blood and bring about the
release of regulatory hormones; the kidneys regulate reabsorption
of water and sodium from blood in response to levels of the
hormones ADH and aldosterone.
Slide 16
The body is constantly bombarded by stimuli from the
environment. The brain sorts these stimuli into those that require
a response and those that do not. Responses are coordinated via
nervous or hormonal controls. Simple nervous responses (reflexes)
act quickly. Hormonal responses take longer to produce a response
and the response is more prolonged.
Slide 17
Negative Feedback Scenario: You are outside enjoying your last
moments of summer on the beach DTS unfortunately, you fall asleep!
Your body temperature starts to rise what does your body do to
maintain homeostasis??? Something called thermoregulation
Slide 18
Increase in body temperature leads to increase in blood
temperature. Increase in blood temperature detected by receptors in
the hypothalamus... it is the hypothalamus that causes various
responses in the body designed to lower temperature. Blood vessels
carrying blood to the skin dilate, carrying more blood to the
surface. Heat loss from the blood by radiation Sweat glands become
active and produce sweat Loss of heat by radiational cooling and
through evaporation of sweat lead to a decrease in blood
temperature (negative feedback) Decrease in blood temperature will
be detected by the receptors in the hypothalamus which will
decrease dilation of blood vessels in the skin and stop sweat
production.
Slide 19
Example # 1
Slide 20
Example # 2
Slide 21
This would result in positive feedback A positive feedback
mechanism reinforces the existing state, i.e. would cause a further
increase in temperature. A further increase in temperature would
cause enzymes to work faster, increasing heat production and
leading to denaturation of enzymes and ultimately death. **What
would be the consequences if this negative feedback mechanism for
thermoregulation failed?**
Slide 22
Generally --- but not always --- this is bad news for the body
as it generally leads to a vicious cycle. Unlike negative feedback
which tends to dampen the original stimulus, positive feedback acts
to intensify that stimulus.
Slide 23
A system exhibiting positive feedback, in response to
perturbation, acts to increase the magnitude of the perturbation.
That is, "A produces more of B which in turn produces more of A". A
vicious cycle!perturbation In contrast, a system that responds to a
perturbation in a way that reduces its effect is said to exhibit
negative feedback.negative feedback Positive Feedback? The Tacoma
Narrows Bridge collapsed in 1940, due to a design flaw that allowed
positive feedback to dominate. Alarm or panic can spread by
positive feedback among a herd of animals to cause a stampede In
sociology a network effect can quickly create the positive feedback
of a bank run. Some examples...
Slide 24
Example # 1
Slide 25
A panic attack... or stress of ANY kind... causes high levels
of adrenaline to be released from the adrenal medulla. The body
responds by preparing to either run away or fight for its life
(fight or flight response) If no actual confrontation occurs then
more anxiety results and the body responds by releasing ACTH from
the anterior pituitary gland which acts on its target gland the
adrenal medulla to produce yet more adrenaline.. And hence the
vicious cycle continues... Positive feedback for sure!
Slide 26
Example # 2
Slide 27
The normal heart pumps about 5 L of blood/m in Volume of blood
(L) W ith the withdrawal of 2L of blood the heart becomes
progressively less effective in terms of its pumping effectiveness.
This leads to less blood being delivered to tissues which in turn
further weakens the heart making it even less able to effectively
pump... A vicious cycle of positive feedback that without
intervention quickly leads to eternity. N ote that with only 1L of
blood loss the heart is capable of returning (via negative
feedback) to normal function.
Slide 28
Example # 3 Childbirth... oxytocin a (usually) non-fatal
example See explanation on next page
Slide 29
Now this is somewhat of an exception in our examples of
positive feedback. Depending on your point of view, you see,
positive feedback in this case results in nothing more disastrous
than a wee crying baby. What happens is that labour is set in
motion by contractions of the walls of the uterus. These
contractions are stimulated by the hormone oxytocin (a posterior
pituitary hormone). More contractions result in more oxytocin
release causing more and deeper contractions until the little baby
is finally born. Bravo for positive feedback! If the uterus is not
contracting sufficiently to expel a fully developed fetus,
commercial preparations of oxytocin are sometimes used to stimulate
uterine contractions, thus inducing labour. Also, such preparations
are often administered to the mother following childbirth to ensure
that the uterine muscles will contract enough to squeeze broken
blood vessels closed, minimizing the danger of haemorrhage.
Slide 30
So what have we learned today? What is homeostasis and how is
it important? What is negative feedback? Give an example What is
positive feedback? Give an example