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