HOMEOSTASISUnit 3

WHAT IS HOMEOSTASIS? 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 39⁰C 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?

7.1 – HOMEOSTASIS AND CONTROL SYSTEMS

Ideal conditions of a human body 37⁰ 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.

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.

BASIC COMPONENTS OF A HOMEOSTATIC CONTROL SYSTEM

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.

EXAMPLE: BODY DEALING WITH INCREASED CO2

Exercise CO2 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 CO2 from the body.

Exercise O2 decreased in blood receptor in neck artery detects low O2 nerve impulse sent to the brain impulses sent to muscles that control breathing

DYNAMIC EQUILIBRIUM & HOMEOSTASIS

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.

LEVELS REMAIN CONSIDERABLY STABLE WITH CHANGES IN ENVIRONMENT

HOMEOSTASIS AND FEEDBACK

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).

NEGATIVE FEEDBACK

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.

POSITIVE FEEDBACK

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

SEATWORK/HOMEWORK

Page 337, 1-5

7.2 - THERMOREGULATION

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

processes?

ECTOTHERMS VS. ENDOTHERMS

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”

HEAT STRESS

Rise in body temperature hypothalamus sweat glands (sweat).

Rise in body temperature hypothalamus blood vessels dilate increase in ‘cooled’ blood blood cools internal organs.

COLD STRESS

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.

PROLONGED COLD STRESS

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.

FREEZING CELLS

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.

SEATWORK/HOMEWORK

Page 341#1-4, 6-8, 10.