1. Homeostasis

2. When things work...
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3. 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?

4. 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

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

6. dynamic equilibrium

7. Analogy dynamic equilibrium Response No heat produced Heater turned
Room
temperature
decreases
Heater
turned
off
Set point
Too
hot
Set
point
Control center:
thermostat
increases on
cold
Heat
dynamic equilibrium

8. Feedback Systems
negative feedback system - buildup of the end product of the system shuts the system off
blood pressure drops
brain
blood pressure rises
nerve pathway
heart rate increases
arteries constrict
The response counteracts further change in the same direction

9. Feedback Systems
positive feedback (feed-forward) system - a change in some variable that triggers mechanisms that amplify the change
Decrease in progesterone
Uterus (contractions)
increased contractions
Baby creates pressure
on cervix
Progesterone inhibits uterine contractions
hypothalamus
Oxytocin released

10. 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

11. Local Signaling Animal and plant cells
Have cell junctions that directly connect the cytoplasm of adjacent cells
Plasma membranes
Plasmodesmata
between plant cells
Gap junctions
between animal cells
Figure 11.3
(a) Cell junctions. Both animals and plants have cell junctions that allow molecules
to pass readily between adjacent cells without crossing plasma membranes.

12. Specificity! Cell-cell recognition Figure 11.3
(b) Cell-cell recognition. Two cells in an animal may communicate by interaction
between molecules protruding from their surfaces.

13. diffuses across synapse
In other cases, animal cells
Communicate using local regulators
(a) Paracrine signaling. A secreting cell acts on nearby target cells by discharging molecules of a local regulator (a growth factor, for example) into the extracellular fluid.
(b) Synaptic signaling. A nerve cell releases neurotransmitter molecules into a synapse, stimulating the target cell.
Local regulator
diffuses through
extracellular fluid
Target cell
Secretory
vesicle
Electrical signal
along nerve cell
triggers release of
neurotransmitter
Neurotransmitter
diffuses across synapse
is stimulated
Local signaling
Figure 11.4 A B

14. Long-distance signaling
Hormone travels
in bloodstream
to target cells
(c) Hormonal signaling. Specialized endocrine cells secrete hormones into body fluids, often the blood Hormones may reach virtually all body cells.
Long-distance signaling
Blood
vessel
Target
cell
Endocrine cell
Figure 11.4 C
Both plants and animals use hormones

15. How are external signals converted to responses in the cell?
Three stages of cell signaling
EXTRACELLULAR
FLUID
Receptor
Signal
molecule
Relay molecules in a signal transduction pathway
Plasma membrane
CYTOPLASM
Activation
of cellular
response
Figure 11.5
Reception 1
Transduction 2
Response 3

16. 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

17. Intracellular Receptors
Hormone
(testosterone)
EXTRACELLULAR
FLUID
Receptor
protein
DNA
mRNA
NUCLEUS
CYTOPLASM
Plasma
membrane
Hormone-
receptor
complex
New protein
Figure 11.6
Are proteins found within cytoplasmic or nucleus
Signal molecules that bind are small or hydrophobic
can readily cross the plasma membrane 1
The steroid
hormone testosterone
passes through the
plasma membrane.
Testosterone binds
to a receptor protein
in the cytoplasm,
activating it. 2
The hormone-
receptor complex
enters the nucleus
and binds to specific
genes. 3
The bound protein
stimulates the
transcription of
the gene into mRNA. 4
The mRNA is
translated into a
specific protein. 5

18. Membrane Receptors There are three main types of membrane receptors
G-protein-linked
Tyrosine kinases
Ion channel

19. G-protein-linked receptors
Plasma Membrane
Enzyme
G-protein (inactive)
CYTOPLASM
Cellular response
Activated
enzyme
Activated Receptor
Signal molecule
Inctivate
Segment that
interacts with
G proteins
GDP
GTP
P i
Signal-binding site
Figure 11.7
Seven α helices
Yeast mating factors, epinephrine, many hormones and neurotransmitters
active

20. Receptor Tyrosine Kinases
Important in cell growth and reproduction!
e.g. growth factor
Signal molecule
Signal-binding sitea
CYTOPLASM
Tyrosines
Signal molecule
Helix in the
Membrane
Tyr
Dimer
Receptor tyrosine kinase proteins (inactive monomers) P
Cellular response 1
Inactive relay proteins
Activated relay proteins
Cellular response 2
Activated tyrosine-
kinase regions
(unphosphorylated
dimer)
Fully activated receptor
tyrosine-kinase
(phosphorylated
6 ATP ADP
Figure 11.7

21. Ion Channel Receptors E.g. ligand-gated ion channels
Cellular response
Gate open
Gate close
Ligand-gated
ion channel receptor
Plasma Membrane
Signal molecule (ligand)
Figure 11.7
Gate closed
Ions
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

22. Step 2: Transduction Multistep pathways Can amplify a signal
Provide more opportunities for coordination and regulation

23. Signal Transduction Pathway
At each step in a pathway the signal is transduced into a different form, commonly a conformational change in a protein
Signal molecule
Active
protein
kinase 1 2 3
Inactive
protein kinase
Cellular
response
Receptor P
ATP
ADP PP
Activated relay
molecule i
Phosphorylation cascade P 
A relay molecule
activates protein kinase 1. 1 2
Active protein kinase 1
transfers a phosphate from ATP
to an inactive molecule of
protein kinase 2, thus activating
this second kinase.
Active protein kinase 2
then catalyzes the phos-
phorylation (and activation) of
protein kinase 3. 3
Enzymes called protein
phosphatases (PP)
catalyze the removal of
the phosphate groups
from the proteins,
making them inactive
and available for reuse. 5
Finally, active protein
kinase 3 phosphorylates a
protein (pink) that brings
about the cell’s response to
the signal. 4

24. Second Messangers
Are small, nonprotein, water-soluble molecules or ions
Cyclic AMP (cAMP)
Is made from ATP
Figure 11.9 O –O N O P OH
CH2
NH2
ATP
Ch2
H2O HO
Adenylyl cyclase
Phoshodiesterase
Pyrophosphate
Cyclic AMP
AMP i

25. Many G-proteins
Trigger the formation of cAMP, which then acts as a second messenger in cellular pathways
ATP
GTP
cAMP
Protein
kinase A
Cellular responses
G-protein-linked
receptor
Adenylyl
cyclase
G protein
First messenger
(signal molecule
such as epinephrine)
Figure 11.10

26. Step 3: Response Each protein in a signaling pathway In the cytoplasm
Glucose-1-phosphate (108 molecules)
Glycogen
Active glycogen phosphorylase (106)
Inactive glycogen phosphorylase
Active phosphorylase kinase (105)
Inactive phosphorylase kinase
Inactive protein kinase A
Active protein kinase A (104)
ATP
Cyclic AMP (104)
Active adenylyl cyclase (102)
Inactive adenylyl cyclase
Inactive G protein
Active G protein (102 molecules)
Binding of epinephrine to G-protein-linked receptor (1 molecule)
Transduction
Response
Reception
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

27. Other pathways
Regulate genes by activating transcription factors that turn genes on or off
Reception
Transduction
Response
mRNA
NUCLEUS
Gene P
Active
transcription
factor
Inactive
DNA
Phosphorylation
cascade
CYTOPLASM
Receptor
Growth factor
Figure 11.14

28. Thermoregulation

29. 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

30. Modes of Heat Exchange Radiation is the emission of electromagnetic
waves by all objects warmer than absolute
zero. Radiation can transfer heat between
objects that are not in direct contact, as when
a lizard absorbs heat radiating from the sun.
Evaporation is the removal of heat from the surface of a
liquid that is losing some of its molecules as gas.
Evaporation of water from a lizard’s moist surfaces that
are exposed to the environment has a strong cooling effect.
Convection is the transfer of heat by the
movement of air or liquid past a surface,
as when a breeze contributes to heat loss
from a lizard’s dry skin, or blood moves
heat from the body core to the extremities.
Conduction is the direct transfer of thermal motion (heat)
between molecules of objects in direct contact with each
other, as when a lizard sits on a hot rock.

31. Balancing Heat Loss and Gain
Insulation
Circulatory Adaptations
Cooling by Evaporative Heat Loss
Adjusting Metabolic Heat Production

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

33. 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

34. 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!)

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

36. 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

37. 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

38. 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

39. 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 conc’n of mitochondria)
Babies have higher amount of brown fat – they don’t shiver

40. What regulates our temperature?
Hypothalamus - contains a group of nerve cells that function as a thermostat

41. Internal body temperature
Thermostat in
hypothalamus
activates cooling
mechanisms.
Sweat glands secrete
sweat that evaporates,
cooling the body.
Blood vessels
in skin dilate:
capillaries fill
with warm blood;
heat radiates from
skin surface.
Body temperature
decreases;
thermostat
shuts off cooling
Increased body
temperature (such
as when exercising
or in hot
surroundings)
Homeostasis:
Internal body temperature
of approximately 36–38°C
increases;
shuts off warming
Decreased body
temperature
Vasoconstriction, diverting
blood from skin to deeper tissues
and reducing heat loss
from skin surface.
Skeletal muscles
rapidly contract,
causing shivering,
which generates
heat.
activates
warming
Cold Response

42. Internal body temperature
Heat Response
Thermostat in
hypothalamus
activates cooling
mechanisms.
Sweat glands secrete
sweat that evaporates,
cooling the body.
Vasodilation,
Blood vessels
relax and fill
with warm blood;
heat radiates from
skin surface.
Body temperature
decreases;
thermostat
shuts off cooling
Increased body
temperature
Homeostasis:
Internal body temperature
of approximately 36–38°C
increases;
shuts off warming
Decreased body
Vasoconstriction, diverting
blood from skin to deeper tissues
and reducing heat loss
from skin surface.
Skeletal muscles
rapidly contract,
causing shivering,
which generates
heat.
activates
warming

43. Extreme Cold
Why does your body allow you to get frost bite? Why is hypothermia such a concern?

44. Classwork/Homework Section 7.1 – Pg. 337 #1-5, 7-9