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Unit 3.  Homeostasis: process by which a constant internal environment is maintained despite the changes in the external environment. “homoios” = similar,

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Presentation on theme: "Unit 3.  Homeostasis: process by which a constant internal environment is maintained despite the changes in the external environment. “homoios” = similar,"— Presentation transcript:

1 Unit 3

2  Homeostasis: process by which a constant internal environment is maintained despite the changes in the external environment. “homoios” = similar, “stasis” = standing still.  Severe strenuous excersize: body temperature can increase to more than 39 ⁰C  temperature associated to fever.  Heat is dissipated through __________.  How does your body respond to an increase in body temperature?  Sweat  loss of water  drop in blood pressure  pressure on kidneys (to conserve water)  Sweat  salts (nerve function, muscle contraction)  pressure on kidney’s to maintain electrolyte balance.  Energy needs  blood glucose needs to be kept constant to maintain ATP supplies  etc. etc. etc.  What dangers exist if your body is unable to regulate the fluid balance of your tissues?

3  Ideal conditions of a human body  37 ⁰ C.  0.1% blood sugar level  pH = 7.35  External environments in Canada  -40 ⁰ C and 40 ⁰ C.  Foods rarely contain 0.1% blood sugar level and pH of 7.35.  Pressures you put on your body  Excercise  Digesting large meals  Drinking to much water/not enough water  Eating too much salt  Etc.


5 Homeostasis requires the interaction of several regulatory systems. Information about blood sugar, fluid balance, body temperature, oxygen levels, and blood pressure are relayed to a nerve coordinating centre once they move outside the normal limits. From the coordinating centre, regulators bring about the needed adjustments.

6  All homeostatic control systems have three functional components: 1) A monitor  Located in organs  Sends signal to coordinating centre when organ operates outside of its normal limits. 2) A coordinating centre  relays information to appropriate regulator 3) A regulator  Helps to restore the normal balance.

7  Exercise  CO 2 increased  receptors in brain stem stimulated  nerve cells carry impulses to muscles which control breathing  muscles increase depth and rate of breathing  helps flush excess CO 2 from the body.  Exercise  O 2 decreased in blood  receptor in neck artery detects low O 2  nerve impulse sent to the brain  impulses sent to muscles that control breathing

8 Dynamic:  dy·nam·ic (d-nmk)adj. also dy·nam·i·cal (--kl)  1. a. Of or relating to energy or to objects in motion.  2. Characterized by continuous change, activity, or progress  3. Marked by intensity and vigor;  4. Of or relating to variation of intensity, as in musical sound. Equilibrium:  e·qui·lib·ri·um (kw-lbr-m, kw-)n. pl. e·qui·lib·ri·ums or e·qui·lib·ri·a (-r-)  1. A condition in which all acting influences are cancelled by others, resulting in a stable, balanced, or unchanging system.  3. Physics The state of a body or physical system at rest or in unaccelerated motion in which the resultant of all forces acting on it is zero and the sum of all torques about any axis is zero.  4. Chemistry The state of a chemical reaction in which its forward and reverse reactions occur at equal rates so that the concentration of the reactants and products does not change with time. DYNAMIC EQUILIBRIUM: CONDITION THAT REMAINS STABLE WITHIN FLUCTUATING LIMITS. Homeostasis is often referred to as a dynamic equilibrium.


10  Negative feedback: process by which a mechanism is activated to restore conditions to their original state.  Positive feedback: process in which a small effect is amplified (less common).

11  Makes adjustments to bring body back within acceptable range.  Change in the variable being monitored triggers the control mechanism to COUNTERACT any further change in the same direction.  Resists change.  Prevents small changes from becoming too large.  Analogy: room temperature regulation  Monitor (thermometer): monitors the temperature. If temperature falls below a set point, sends info to thermostat.  Coordinating centre (thermostat): sends info to the regulator.  Regulator (furnace): is switched on when it receives this information. Normal conditions are re-established.  Opposite would occur with temperature above the set point.

12  Reinforce change  Move controlled variable further away from steady state.  Allows small physiological event to be accomplished rapidly.  Example: BIRTH.  Decrease in progesterone  contractions  release of oxytocin  STRONGER contractions  baby to cervix  stronger contraction  baby OUT


14  Page 337, 1-5

15  Thermoregulation: maintenance of body temperature within a range that enables cells to function efficiently.  How can extreme temp. affect cell processes?

16  Ectotherm: invertebrates, most fish, amphibians, reptiles.  Depend on air temp. to regulate metabolic rates  Activity partially regulated by environment  Behavioural adaptations: ‘basking,’ retreating to shaded areas.  Endotherm: mammals and birds.  Can maintain constant body temp regardless of surroundings.  Cold: increase cellular resp. (generate heat)  Hypothalamus: region of the vertebrate’s brain responsible for coordinating many nerve and hormone functions  “thermostat”

17  Rise in body temperature  hypothalamus  sweat glands (sweat).  Rise in body temperature  hypothalamus  blood vessels dilate  increase in ‘cooled’ blood  blood cools internal organs.

18  Temperature drops  thermoreceptors (skin)  hypothalamus  blood flow limited  limits heat loss from skin  retains heat in internal organs.  Temperature drops  thermoreceptros (skin)  hypothalamus  smooth muscles (in skin: ‘goosebump’)  hair traps air next to skin  reduced heat loss.  What type of animal would this be most effective?  Temperature drops  thermoreceptros (skin)  hypothalamus  skeletal muscles  shivering.

19  Hormonal response  Elevates metabolism  ‘brown fat’: adipose tissue capable of converting chemical energy into heat.  Newborns: lack ability to shiver.  Hypothermia  Body core falls below normal temp. Range.  Mammalian diving reflex:  When in cold water  heart rate slows  blood diverted to VITAL organs.


21  Possible?  Ice crystals form  Act as little knives: membranes are torn, tissues destroyed.  Melting  Cells fill with water  lyse  Frogs  Frozen in winter.  Can ‘defrost’ and live afterwards.  How?!  Antifreeze: protein that prevents ice crystals from forming.


23  Page 341 #1-4, 6-8, 10.

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