homeostasis

Question 1

What is the equation of life?

Answer 1

Nutrients + O2 = energy (usually ATP) + CO2 + waste products

Question 2

What is the goal of all body systems working together?

Answer 2

To bring in nutrients and eliminate waste. This creates an optimal internal environment in which all cells can function.

Question 3

What are the 2 main activities of cells?

Answer 3

1) those that keep that actual cell alive such as protein synthesis 2) those that contribute to survival of the whole organism

Question 4

What is ECF made from?

Answer 4

Plasma (20%) and ISF (80%)

Question 5

What is the dynamic component of ECF and what is its function?

Answer 5

Plasma. In capillaries, it exchanges CO2 and waste with ISF as blood passes through capillaries of the body.

Question 6

Which movements occur across capillary walls?

Answer 6

There is free movements except plasma proteins which are too large. These are restricted to the capillaries. ECF is homogenous excluding plasma proteins.

Question 7

What happens when there is a failure of capillary perfusion?

Answer 7

Gangrene occurs.

Question 8

How is water distributed in the body?

Answer 8

1/3 ECF and 2/3 ICF.

Question 9

What % of the body is water?

Answer 9

Around 60%

Question 10

Do males or females carry less water and why?

Answer 10

Females as they have more fat. Fat is 10% water and muscle is 70%. Older people also carry less water.

Question 11

What is the definition of homeostasis?

Answer 11

Maintenance of constant conditions in the internal environment of an organism.

Question 12

What is the homeostatic plateau?

Answer 12

A range at which the internal environment can be maintained across.

Question 13

What is the upper temperature limit to life?

Answer 13

The temperature at which proteins are denatured.

Question 14

What is the advantage of homeothermy?

Answer 14

Body temperature can be kept constant at 37 degrees over a range of external temperatures. However, this has a high energy cost.

Question 15

What is the overall outcome of homeostasis?

Answer 15

Internal conditions are regulated independently of the internal environment.

Question 16

Describe negative feedback.

Answer 16

Magnitude of controlled variable is sensed as a stimulus to a receptor. Fed to an integrating system which is compared to a reference level. Any difference between actual level and reference level generates an error signal which is fed as an effector mechanism.

Question 17

In negative feedback, what is the factor that decides how big a response will be?

Answer 17

The magnitude of the error is proportional to the size of the response and deviation.

Question 18

What adaptations occur on exposure to hot/cold?

Answer 18

Hot - decreased heat production and increased heat loss. Increased blood flow to skin and heal loss by sweating/evaporation. Cold - increased heat production by shivering and minimised heat loss by shutting down blood flow to the skin. Also behavioral measures.

Question 19

What are the 2 main characteristics of negative feedback systems?

Answer 19

1) they can restore the regulated variable after its initial displacement, but cannot prevent this happening, 2) there is oscillation around the set point

Question 20

What is feed-forward control?

Answer 20

A more sophisticated version of negative-feedback. Receptors permit the system to anticipate change and therefore activate the response earlier.

Question 21

What is positive feedback?

Answer 21

Initial disturbance leads to a chain of events that lead to an even greater disturbance. Common in pathophysiology.

Question 22

Give 1 physiological example of a positive feedback system.

Answer 22

Action potentials

Question 23

Which processes regulate water input and output?

Answer 23

Input - thirst mechanism. Output - urinary losses.

Question 24

What is the dilution principle?

Answer 24

c = m/v therefore v = m/c, from this can calculate the volume of distribution.

Question 25

Which substances can be used to measure volume of distribution?

Answer 25

Need to inject a substance that will stay in only 1 compartment. Needs to be: non-toxic; evenly distributed in the compartment being measured; must not affect the distribution of water; must be unchanged by the body; and easy to measure.

Question 26

Which compartments can be measured directly?

Answer 26

Only those of which plasma is a component - only plasma can be sampled.

Question 27

Name 3 examples of compartments that can be measured directly.

Answer 27

1) plasma volume as plasma proteins cannot cross capillary walls so attach radioactive labels/dyes to them, 2) ECF - use something that freely crosses capillary walls but doesn’t cross cell membranes like sucrose or mannitol, 3) total body water using heavy water/deuterium

Question 28

Which compartments are measured indirectly?

Answer 28

ISF = ECF - PV and ICF = TBW - ECF

Question 29

Which organ regulates K+?

Answer 29

Kidney

Question 30

What causes disease/illness?

Answer 30

Perturbation/breakdown of homeostatic control mechanisms. Eg. in diabetes there is a breakdown in the normal regulation of blood glucose which leads to hyperglycaemia.

Question 31

What is the aim of clinical intervention?

Answer 31

To restore changes outwith the normal range - pathophysiological disturbances.