Homeostasis

Question 1

Define the term homeostasis

Answer 1

The stable condition of the body and it’s internal environment and the maintainance or regulation to keep it in an optimum state

Question 2

How does a negative feedback control system work?

Answer 2

A variable is monitored against a reference level, any change of the variable is sensed by a receptor which produces an effector mechanism which produces a response

Question 3

What is the aim of negative feedback?

Answer 3

To restore the internal environment to optimal conditions

Question 4

What are the two characteristics of negative feedback systems?

Answer 4

There is oscillation around the set point AND it restores the regulated variable after inital displacemnt BUT cannot prevent it happening

Question 5

What can feed forward control do that negative feedback can’t?

Answer 5

Additional receptors permit the system to anticipate change and activate response earlier

Question 6

What does positive feedback do?

Answer 6

The signal from the initial disturbance sets off a train of events that lead to an even greater disturbance

Question 7

What is a feature of positive feedback?

Answer 7

Self-amplification

Question 8

What are examples of positive feedback?

Answer 8

Diabetes, childbirth, nerve action potential

Question 9

What percentage of body weight is water?

Answer 9

60%

Question 10

What are the three compartments where water is found in the body?

Answer 10

Intracellular fluid, interstitial fluid, plasma

Question 11

What makesup extracellular fluid?

Answer 11

Interstitial fluid and plasma

Question 12

Where is 2/3s of the water found?

Answer 12

Intracellular fluid (ICF)

Question 13

The capillary wall is permeable to everything but?

Answer 13

Plasma protein

Question 14

What has selective permeability?

Answer 14

Cell membrane

Question 15

What is roughly the volume of total body water?

Answer 15

42L

Question 16

What do we have twice as much as?

Answer 16

Twice as much ICF as ECF

Question 17

What percentage of ECF is ISF?

Answer 17

80%

Question 18

What percentage of ECF is plasma?

Answer 18

20%

Question 19

What is the dynamic component of the ECF?

Answer 19

Plasma

Question 20

What freely exchanges nutrients and waste with the ISF?

Answer 20

Plasma

Question 21

Where does plasma exchange with the ISF?

Answer 21

Capillaries

Question 22

What is only found in plasma due to it being restricted by size?

Answer 22

Plasma proteins

Question 23

What can be sampled when trying to determine body fluid volumes?

Answer 23

ONLY compartments where plasma is a component (plasma, ECF, TBW)

Question 24

What can be used to measure plasma volume?

Answer 24

Evans blue

Question 25

What can be used to measure extracellular volume (ECF)?

Answer 25

Something that freely crosses capillary walls but cannot cross cell membranes e.g. Insulin, sucrose or Na/Cl isotopes

Question 26

What can be used to measure total body water (TBW)?

Answer 26

Loading dose of heavy/deuterated water

Question 27

How would you measure interstitial fluid volume (ISF)?

Answer 27

ECF - PV

Question 28

How would you measure intracellular fluid volume (ICF)?

Answer 28

TBW - ECF

Question 29

How would you calculate volume of distribution (using dilution principle)?

Answer 29

Inject substance that will stay in one compartment only

Volume of distribution = amount injected - any removed by excretion or metaboism / concentration in sampled fluid

Question 30

Why is the large concentration gradient between ICF and ECF necessary?

Answer 30

For nerve and muscle function

Question 31

Where is Na+ concentration higher?

Answer 31

ECF

Question 32

Where is K+ concentration higher?

Answer 32

ICF

Question 33

Where is Cl- concentration higher?

Answer 33

ECF