Homeostasis

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Homeostasis
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When things work...

• Honda COG Commercial

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Homeostasis

• homeostasis constant physiological adjustments
  of the body in response to external environment
  changes
• also known as dynamic equilibrium
• What happens to your body when you exercise?

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Exercise and Homeostasis

• evaporation of sweat to cool off
• heart rate increases to increase blood flow (to
  get O2 levels back up)
• pancreas signals breaking down of biomolecules to
  get energy needed to exercise

• body temperature increases
• O2 levels being used up
• increased cellular metabolism

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Homeostatic Control System

1. Receptor organs that detect changes or sense
   when conditions are not within normal range
2. Control Centre organs which process information
   it receives from the receptor and send signals to
   another part of the body
3. Effector coordinating centre sends signals to
   an organ / tissue which will normalize the
   original organ

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dynamic equilibrium
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Analogy
dynamic equilibrium
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Feedback Systems

• negative feedback system - buildup of the end
  product of the system shuts the system off

blood pressure drops
brain
nerve pathway
blood pressure rises
heart rate increases
arteries constrict

• The response counteracts further change in the
  same direction

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Feedback Systems

• positive feedback (feed-forward) system - a
  change in some variable that triggers mechanisms
  that amplify the change

Decrease in progesterone
Uterus (contractions)
Baby creates pressure on cervix
increased contractions
hypothalamus
Oxytocin released
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How are external signals converted to responses
in the cell?

• Cells in a multi-cellular organism communicate
  via chemical messengers
• Local and long-distance signaling

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Local Signaling

• Animal and plant cells
• Have cell junctions that directly connect the
  cytoplasm of adjacent cells

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• Cell-cell recognition

Specificity!
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• In other cases, animal cells
• Communicate using local regulators

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Long-distance signaling

• Both plants and animals use hormones

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How are external signals converted to responses
in the cell?

• Three stages of cell signaling

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Step 1 Reception

• The binding between signal molecule (ligand) and
  receptor is highly specific
• A conformational change in a receptor is often
  the initial transduction of the signal
• Can have intracellular and membrane receptors

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Intracellular Receptors

• Are proteins found within cytoplasmic or nucleus
• Signal molecules that bind are small or
  hydrophobic
• can readily cross the plasma membrane

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Membrane Receptors

• There are three main types of membrane receptors
• G-protein-linked
• Tyrosine kinases
• Ion channel

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G-protein-linked receptors
Yeast mating factors, epinephrine, many hormones
and neurotransmitters
Seven a helices
active
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Receptor Tyrosine Kinases
Important in cell growth and reproduction!
e.g. growth factor
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Ion Channel Receptors

• E.g. ligand-gated ion channels
• Region acts like a gate
• E.g. Sodium and Calcium channels important in the
  nervous system

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Step 2 Transduction

• Multistep pathways
• Can amplify a signal
• Provide more opportunities for coordination and
  regulation

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Signal Transduction Pathway At each step in a
pathway the signal is transduced into a different
form, commonly a conformational change in a
protein
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Second Messangers

• Are small, nonprotein, water-soluble molecules or
  ions
• Cyclic AMP (cAMP)
• Is made from ATP

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• Many G-proteins
• Trigger the formation of cAMP, which then acts as
  a second messenger in cellular pathways

Figure 11.10
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Step 3 Response

• Each protein in a signaling pathway
• Amplifies the signal by activating multiple
  copies of the next component in the pathway
• In the cytoplasm
• Signaling pathways regulate a variety of cellular
  activities

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• Other pathways
• Regulate genes by activating transcription
  factors that turn genes on or off

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Thermoregulation
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Thermoregulation

• Process by which animals maintain an internal
  temperature within a tolerable range.
• Critical to survival because biochemical and
  physiological processes are sensitive to changes
  in temperature.
• Enzymatic reactions
• Properties of membranes

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Modes of Heat Exchange
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Balancing Heat Loss and Gain

1. Insulation
2. Circulatory Adaptations
3. Cooling by Evaporative Heat Loss
4. Adjusting Metabolic Heat Production

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Insulation

• Feathers, hair or fat layers
• Reduces the flow of heat between an animal and
  its environment
• Lowers the energy cost of keeping warm

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• In mammals, the insulating material is associated
  with the integumentary system (skin, hair and
  nails)

Hair
Epidermis
Sweat pore
Muscle
Dermis
Nerve
Sweat gland
Hypodermis
Adipose tissue
Blood vessels
Oil gland
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• Most land animals and birds react to cold by
  raising their fur or feathers
• Traps a thicker layer of air
• Increasing its insulating power (the more still
  air the better!)

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Goosebumps

• Raise hair on our body
• Inherited from our furry ancestors
• We rely more on a layer of fat just beneath the
  skin

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Circulatory Adaptations

• We can alter the amount of blood (and hence heat)
  flowing between the body core and the skin.

Vasodilation Muscles in superficial blood
vessels relax Increases the diameter of vessels
more blood Increases heat transfer, warming
the skin
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• Vasoconstriction
• Muscles in superficial blood vessels contract
• Smaller diameter of blood vessels less blood
• Reduces heat transfer, preventing heat loss
• Keeps blood (and heat) in interior of body where
  it is needed

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Evaporative Heat Loss

• When environmental temperatures are above body
  temperature we
• Sweat, pant, bathe, spread saliva over body
  surfaces
• Heat is carried away with water molecules as they
  change into a gas

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Adjusting Metabolic Heat Production

• Shivering and Moving - Heat production is
  increased by muscle activity
• Non-shivering Thermogenesis (NST) - Certain
  hormones can cause mitochondria to increase their
  metabolic activity and produce heat
• Brown Fat Specialized tissue for rapid heat
  production (has higher concn of mitochondria)

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What regulates our temperature?

• Hypothalamus - contains a group of nerve cells
  that function as a thermostat

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Cold Response
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Heat Response
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Extreme Cold

• Why does your body allow you to get frost bite?
• Why is hypothermia such a concern?

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Classwork/Homework

• Section 7.1 Pg. 337 1-5, 7-9
• Section 7.2 Pg. 341 1-9,11