Anatomy and Physiology (Homeostasis and Regulation)


stability of the internal environment and the mechanisms that maintain the stability

Dynamic Equilibrium

maintained where the rate of loss balances out with the rate of gain

Feedback Mechanisms

evolved to help maintain homeostasis in organisms

(+) Feedback Mechanisms

the output (or product) of a system intensifies the response

(+) Feedback Mechanisms Examples

child birth, fruit ripening

(-) Feedback Mechanisms

the output (or product) of a system causes a counter response to return a set point

(-) Feedback Mechanisms Examples

body temperature, water concentration, blood sugar regulation


sensory organ that receives the stimulus


an action that evokes a response


an organ that does the response


the effect, caused by the stimulus

Mistake in a Feedback Loop

homeostasis is thrown off

Mistake in a Feedback Loop Example

Type 1 Diabetes


substances that speed up the reactions without being permanently altered


biological catalysts are proteins

Regulate Metabolism

cells can control the amount of an enzyme

Feedback Inhibition

output of a process is used as an input to control the behavior of the overall process itself

Activity of Enzyme

can be regulated

Chemical Inhibitors

can bind to enzymes and slow reaction rates

Environmental Conditions

play a role in enzyme function

Passive Transport

requiring no extra energy as molecules move down the gradient

Active Transport

requiring extra energy to move molecules against the gradient

Simple Diffusion

the spreading of molecules across the membrane until equilibrium is reached

Transport Protein

acts to help facilitate the diffusion of molecules that couldn't pass through the cells' membrane

Can't Pass Through The Cell Membrane

large and polar molecules


allows molecules through


binds to substances to carry across the cell membrane


the simple diffusion of water across the cell membrane


moves from areas of high concentration to areas of low concentration

Low Solute

high concentration

High Solute

low concentration

Hyper Tonic Solutions ^

water is lower than the cells cytoplasm

Water Out of Cells

cell shrivels

Hypo Tonic Solutions v

water is higher than the cells cytoplasm

Water Into a Cell

cell swells

Isotonic Solutions ^ v

identical water to cells cytoplasm

Molecular Pumps

when a cell uses energy to pump molecules across the membrane

Protein Channel

moves molecules across the membrane


moves particles into the cell


export materials out of the cell

Cell Signalling

allows cells to process information from their environment and communicate to other cells


molecules that bind to other molecules for signalling

Signal Transduction Pathway

signal -> message transduced -> desired response

Autocrine Signals

self"; affect the same cell that releases them

Paracrine Signals

diffuse to nearby cells

Juxtacrine Signals

require direct contact between the signalling cell and the receiving cell

Hormones (Endocrine Signalling)

signal travels to distant cells


protein where the signal is received on the target cell

Intracellular Receptors

located inside a cell

Intracellular Receptors (Ligands?)

ligands are small and nonpolar

Membrane Receptors (Ligands?)

ligands are large and polar


not strong


can block the normal ligands to prevent communication


the passing along the signal until the desired response is reached

Changing the Shape

passing along the message


addition of phosphate groups (by kinases)


removal of phosphate groups (by phosphatases)

Second Messenger

a molecule that serves as an intermediate between the receptor and the cascade of responses after

Key for Regulation?

second messenger

Opening of Ion Channels

changing the balance of ion concentration inside and outside of cell

Alternations in Gene Expression

genes may be switched on (unregulated) or off (regulated)

Response Example

alternation of enzyme activities