Lecture 1
Homeostasis:
Why things don’t (usually) go wrong!
Homeostasis:
• Maintain stability of internal
environment (fluid bathing cells)
in face of changes to external &
internal environment by body
systems
• Blood pressure, body
temperature, water
content, food intake, etc.
BODY FLUID COMPARTMENTS
TOTAL BODY WATER (TBW) = 60% BWkg
Normal BW 70 Kg so TBW = 42 L
INTRACELLULAR FLUID
Volume = 28 L, 2/3 TBW
H 2O
INTERSTITIAL
FLUID
Volume = 11 L
80% of ECF
H 2O
H2O
SALTS
PLASMA
Volume
=3L
20%
of ECF
H2O
SALTS
EXTRACELLULAR FLUID
Volume = 14 L, 1/3 TBW
Homeostasis:
Why things DON’T (usually) go wrong!
Homeostasis:
• Stability – balancing inputs & outputs
• dynamic compensatory processes
• Keep regulated variable within normal
range
• Cell function maintained by constancy of
internal environment (ECF): pH, volume,
ionic composition, energy level
COMPONENTS OF FEEDBACK SYSTEMS
Stimulate
or inhibit
Start
1
4
Stimulate
or inhibit
2
3
Stimulate
or inhibit
NEGATIVE Feedback System
1. Response of body in
opposite direction of change
in that variable
2. Most variables in body
under negative feedback
control
3. Blood pressure, blood
glucose, body temperature
POSITIVE Feedback System
1. Response of body in same
direction of change in that
variable
2. Exacerbates or amplifies
change
3. Rare in body – destabilizing
4. Blood clotting, nerve &
muscle action potential,
parturition
Intracellular Homeostasis
1. Ionic Homeostasis
• Cell membrane integrity
• Passive transport
• Diffusion, osmosis, filtration
• Active transport
• 10, 20, co- & countertransport
• Membrane potential to
maintain internal
environment:
• Channels & transporters
• Nutrient & waste transport
Fig 4.15
Intracellular Homeostasis
2. Volume homeostasis
• ECF stabilizes ICF
3.pH Homeostasis
• Enzyme regulation
• Metabolic control
4.Energy Homeostasis
• [ATP] regulates energy flux
Lecture 2
TERMINOLOGY:
• Tonicity–qualitative-relativeconcentration of 2 solutions
thatdetermines the direction and extent ofdiffusion of water
• Isotonic soln: no net diffusionof water
• Hypotonic soln: water moves into cells causing them toswell
• Hypertonic soln: water moves out of cellscausing them toshrink
Tonicity-Relative Response of Cells in Solution
TERMINOLOGY:
• Isosmotic- sameosmolarity as plasma
• hypoosmotic - below
• hyperosmotic - above
Major Cations & Anions
TERMINOLOGY:
• Oncotic pressure
( ; mmHg)–a type of osmoticpressure generated bymolecules too
large to crosssemipermeable membranes(usuallyproteins):
“pullingpressure”
• Hydrostatic pressure
(P; mmHg)–pressureexerted by gravity effects orpumping
ofliquids:“pushing
• pressure,”e.g. bloodpressure
Body Fluid Compartments
Terminology
• Oncotic pressure (pi; mmHg)– a type of osmotic pressure generated
by molecules too large to cross semipermeable membranes (usually
proteins)
• “Pulling Pressure”
• Hydrostatic pressure (P; mmHg)– pressure exerted by gravity effects
or pumping of liquids
• “Pushing Pressure” e.g. BP
IV Fluids
• Main types of IV Fluids
– Isotonic fluids
– Hypotonic fluids
– Hypertonic Fluids
• Groupings of IV Fluids
– Blood & blood products
– Crystalloids: electrolytes
– Colloids: create oncotic pressure,
albumin
– Plasma expanders
Lecture 3
Solubility in Water
Molecules with ionic or polar covalent bonds have
an electrical attraction to water molecules.
Fig 2.4
•
When NaCl is placed in water, the polar water molecules are attracted to the
charged sodium and chloride ions.
•
Clusters of water molecules surround the ions, allowing the sodium and chloride
ions to separate from the salt crystal and enter the water… or to DISSOLVE.
Lipids
Lipids are non-polar and have a very low solubility in water.
Lipids can be divided into four subclasses:
 Cholesterol/steroids
 Fatty acids
 Triglycerides
 Phospholipids
Lipids provide a valuable source of energy, are a major component
of all cellular membranes and are important signaling molecules.
Phospholipid Bilayer
*Image via Bing
This is our CELL MEMBRANE!!