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Feedback and Homeostasis _NXPowerLite_.ppt - PEER

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					FEEDBACK
MECHANISMS
                   M AINTAINING
                   E QUILIBRIUM

   Living versus non-living
       Living organisms have the ability to
        sense and respond to changes in
        environment
   The cells of living organisms function best
    in a constant, balanced internal
    environment
   Organisms must maintain a “steady state”
    called homeostasis to survive
                    M AINTAINING
                    E QUILIBRIUM

   Cells, tissues, organs, and organ systems
    must work together to adjust to
    changing conditions
   Cold temperatures: humans respond by
    shivering to increase body temperature
    by muscle movement
   Hot temperatures: humans may
    respond by sweating to cool off
   W HAT         IS    F EEDBACK ?

Feedback is the process in which part of the
output of a system is returned to its input in
order to regulate its further output.
     N EGATIVE F EEDBACK

   Have you ever been scolded for not cleaning your room?

   Cleaning your room is how you respond to being scolded.

   A negative feedback system involves the detection of an
    undesirable condition and the response to make that
    condition ideal.

                                     Negative Feedback
                                             +




                                             _
    N EGATIVE F EEDBACK

Basic structure:

 INPUT    DETECTION   RESPONSE   OUTPUT   SHUT OFF
    N EGATIVE F EEDBACK


   Negative feedback occurs when the output
    of a system acts to oppose changes to the
    input of the system
   A thermostat is an example of a negative
    feedback system
                      Room temp                  Set point
                       increases
                                                is reached




Room temp is                                                      Room temp is
  below the              THERMOSTAT                                above the
   setpoint                                                         setpoint




                       Set point               Room temp
                       is reached               decreases




A thermostat is a device for regulating the temperature of a system so that the
system's temperature is maintained near a desired setpoint temperature.
         N EGATIVE F EEDBACK
                 IN B IOLOGY

   Negative feedback also
    regulates many systems
    in organisms
   The endocrine system
    is one example
   This diagram shows a
    negative feedback loop
    for stress hormones
   Areas of negative
    feedback are indicated
    with a minus sign, (-)
KEEPING THE
 BODY IN
 BALANCE!
                  E NDOCRINE SYSTEM

   The endocrine system is
    composed of glands that
    produces chemical
    messengers called
    hormones

   Hormones are produced in
    one part of the body and
    travel to target organs
    through the bloodstream
                             E NDOCRINE S YSTEM


   The brain continuously sends signals to the endocrine glands
    to secrete and release hormones
   The glands, in turn, send feedback to the nervous system

   The hypothalamus in the brain is
    the master switch that sends
    signals to the pituitary gland
    which can release up to eight
    hormones into the bloodstream
   The hormone travels to its target
    organ and usually results in the
    release of another hormone into
    the bloodstream
                    E NDOCRINE S YSTEM


   The hypothalamus then detects the rising
    hormone levels from the target organ
    and decreases the release of hormones
    from the pituitary which results in a
    decrease in hormone release from the
    target organ


   The process of maintaining normal body
    function through negative feedback
    mechanisms is called homeostasis
                        G LUCOSE     AND I NSULIN


                                        Pancreas
   Glucose intake occurs during
    digestion of food that is
    needed for energy
    expenditure to perform
    routine physical activities.
   The pancreas is the key organ
    that regulates the glucose           Liver
    levels in body by secreting
    two hormones, insulin and
    glucagon.
   The liver also helps to store
    the excess glucose in form of
    glycogen to be utilized later.
G LUCOSE AND I NSULIN N EGATIVE F EEDBACK L OOP

                                Increases
                                 Glucose
                                  Levels
     Eating cake
                                                     Stimulates β cells of
                   (-)                            pancreas to secrete insulin
 Lowers Blood                  CYCLE 1
 Glucose levels


                         Insulin stimulates the
                            cells to take up
                           glucose from the
                                  blood
Low Blood Glucose Levels
                                               Stimulated Alpha Cells in
                                                       Pancreas
        (-)


  High blood glucose levels
                                     CYCLE 2
   and Cycle 1 continues
                                               Glucagon is released


Glucagon stimulates liver cells to
 release glucose into the blood
     G LUCOSE AND I NSULIN N EGATIVE
                     F EEDBACK L OOP

   Two primary Hormones

        Insulin                        Glucagon



Lowers Blood Glucose              Raises Blood Glucose
       Levels                             Levels

The opposite actions of these two hormones helps to maintain
  normal blood sugar levels in the body hence maintain
  homeostasis of the body.
    TAKE A B REAK AND C HAT W ITH
                 YOUR N EIGHBOR !

   Turn to the person behind or in front of you
    and discuss the following topics:

       What is a feedback and an example of a
        negative AND positive system?

       What is the endocrine system and why is it
        important?

       Define homeostasis and how normal body
        function is maintained with feedback
        mechanisms.
        K IDNEYS   AND   WATER R EGULATION


    The kidneys play a key role in maintaining
    water regulation.
K IDNEY AND WATER R EGULATION



              The nephron is the
               most important
               functional part of the
               kidney.
              It filters nutrients like
               salts and amino acids
               in the Bowman’s
               capsule into ascending
               loop and filters the
               urine.
        K IDNEY AND WATER R EGULATION
Anti-Diuretic Hormone, ADH (also called vasopressin), is secreted
by the pituitary gland and acts on the nephron to conserve water
and regulate the tonicity of body fluids.




                            Anti-
                            Diuretic
                            Hormone

                                       ADH acts on Nephron to
                                       reabsorb water and decrease
                                       blood osmolality (saltiness)
ADH REGULATED WATER CONSERVATION IN KIDNEYS

            Less water in the                            Excess water in
                 blood                                      the blood



        Stimulates osmoreceptors in               Stimulates osmoreceptors in
      hypothalamus to send signals to           hypothalamus to send signals to
            the pituitary gland                       the pituitary gland



         Pituitary glands secretes                  Pituitary glands secretes
            high levels of ADH                          low levels of ADH




 ADH makes the tubules more permeable             Less ADH makes the tubules less
and more water is reabsorbed back into the    permeable and less water is reabsorbed
   bloodstream (urine is concentrated).      back into the bloodstream (urine is dilute).
                 ADH     REGULATED WATER
              CONSERVATION IN KIDNEYS



   Osmoregulators send negative feedback to
    the hypothalamus about the concentration
    of water in the bloodstream.
   The hypothalamus then stimulates the
    pituitary glands to secrete high or low
    concentrations of anti-diuretic hormone.
   ADH then makes the tubules more or less
    permeable and hence, maintains water and
    electrolyte homeostasis.
TEMPERATURE REGULATION OF BODY


     Animals that are capable of maintaining
      their body temperature within a given
      range are called homeotherms.
     Temperature is regulated by negative
      feedback control.
     Thermoreceptors located in hypothalamus
      detect temperature fluctuations in the
      body.
    T EMPERATURE R EGULATION OF THE
                              B ODY

   Increased temperature causes vasodilatation
    (blood vessels near the surface of the skin
    dilate).

   The large surface area allows heat to be lost
    from the blood and lowers the body
    temperature.

   Sweating also helps lower the temperature.

   Decreased temperature causes
    vasoconstriction (blood vessels constrict)
    and minimal heat loss occurs which helps
    maintain body temperature.

   Hair on the body provides insulation and
    helps maintain body temperature.
                    P OSITIVE F EEDBACK

   A positive feedback loop occurs when the output
    of a system acts to enhance the changes to the
    input of the system.
   One example of a biological positive feedback
    loop is the onset of contractions in childbirth.
       When a contraction occurs, the hormone
        oxytocin is released into the body, which
        stimulates further contractions.
       This results in contractions increasing in
        amplitude and frequency.
                  P OSITIVE F EEDBACK

   Another example is blood clotting.
       The loop is initiated when injured tissue
        releases signal chemicals that activate
        platelets in the blood.
       An activated platelet releases chemicals
        to activate more platelets, causing a
        rapid cascade and the formation of a
        blood clot.
   Lactation involves positive feedback so that
    the more the baby suckles, the more milk is
    produced.
                  P OSITIVE F EEDBACK

   In most cases, once the purpose of the feedback
    loop is completed, counter-signals are released
    that suppress or break the loop.
       Childbirth contractions stop when the baby
        is out of the mother's body.
       Chemicals break down the blood clot.
       Lactation stops when the baby no longer
        nurses.
                O THER K INDS OF
                       F EEDBACK
Feed-forward
      Not technically feedback,
       but similar.
      The system responds in
       anticipation of a change
      Hunger is an example of
       feed-forward. If you
       typically eat lunch at
       noon, your body will
       begin to make digestive
       enzymes in anticipation.

				
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