Chapter 1 & 6:Homeostasis 9/5/14 7:33 PM
Homeostasis- keeping internal environment stable relative to the outside
Law of mass balance- what comes in must equal what comes out
Two options:
Excretion- elimination of material from the body
Convert substances through metabolism
Mass flow=concentration of x * volume flow
Clearance-rate at which something leaves the body.
Homeostasis is not equilibrium
Instead it’s a dynamic steady state
To maintain the body regulates certain variables at a setpoint
There is an input signal, integrating center, output signal then a
response
Local control- starts in one tissue and is handled in that tissue
Reflex control uses long distance signaling
Two parts: a response and feedback loop
Three parts to a response loop: input signal, integrating center and
an output signal
Negative feedback loops are homeostatic
Positive feedback loops are not homeostatic
Feedforward loops anticipate change
Chapter 5: Membrane Dynamics 9/5/14 7:33 PM
Tonicity: how cell volume would be affected if placed in a certain solution
Hypotonic- cell gains water
Hypertonic-cell loses water
Isotonic-nothing happens
Tonicity depends on the concentration of non-penetrating particles
only
Diffusion:
Passive transport that uses kinetic energy of molecules
Higher to lower concentration-down concentration gradient
Occurs until the concentration is equal everywhere
Faster over short distances
Faster with high temperatures
Faster with smaller particles
Diffusion directly across a phospholipid bilayer is called simple
diffusion
o Only nonpolar lipophilic molecules can diffuse
o Exception is water-depends on concentration of membrane
o Rate of diffusion is determined by surface area
o Fick’s law of diffusion and membrane permeability determine
diffusion rate
Protein-Mediated Transport-carried out by transporters
4 classes: structural proteins, enzymes, receptors and transporters
Structural proteins
o Connect membrane to cytoplasm
o Create cell junctions
o Attach cells to the extracellular matrix
Transport proteins are either channel or carrier
o Most channel ones are water filled
o Selectivity of a channel protein is determined by the diameter
and the amino acid charge of the protein its membrane
Facilitated Diffusion uses carrier proteins
For example GLUT transporters
Takes advantage of concentration gradient
Active transport is opposite-requires energy
Down concentration gradient
Primary uses ATP, secondary “freeloads” by using the concentration
gradient potential energy of another molecule
Sodium-Potassium pump-primary active transport
SGLT transporter-secondary
Vesicular Tranport
Phagocytosis-think amoeba
Endocytosis-creates smaller vesicles
Chapter 8 9/5/14 7:33 PM