Homeostasis

Question 1

define homeostasis

Answer 1

a process in which an optimal internal condition is maintained
- this process requires integration of all organ systems

Question 2

which systems control homeostasis? (2)

Answer 2

nervous and endocrine

Question 3

why is maintaining internal conditions important?

Answer 3

The body has a narrow range in which they can work effectively (homeostatic plateau), failure of homeostasis therefore leads to pathology

Question 4

Explain the principles behind negative feedback

Answer 4

receptors respond to a change in environment (stimulus) –> information sent to integration centre –> level checked against reference level –> diffrence in level cuases a change to be sent to an effector –> change in conditions is counteracted
- THIS IS SELF-LIMITING

Question 5

Explain what is meant by a feed forward system

Answer 5

additional receptors allow the body to anticipate change and stimulate a response before the change occurs

Question 6

Explain positive feedback

Answer 6

positive feedback aims to amplify the disturbance to create a greater deviation from the norm value

Question 7

what is physiology?

Answer 7

it is the study of how the body works normally with all systems working optimally

Question 8

what are the three different body fluid compartments?

Answer 8

• intracellular fluid
• interstitial fluid (ECF)
• plasma (ECF)

Question 9

what proportion of total body water does each fluid compartment contain?

Answer 9

intracellular fluid = 2/3 (66%)

extracellular fluid = 1/3 (33%)

Question 10

explain the nature of the barriers which separate the body compartments?

Answer 10

• water can move freely between all 3 compartments
• ions cannot move freely across the cell membarne
• plasma proteins cannot move across the capillary walls
  THIS IS IMPORTANT AS IT ALLOWS ELECTROCHEMICAL GRADIENTS TO BE MAINTAINED

Question 11

define the dilution principle

Answer 11

volume (v) = mass (m) / concentration (c)

Question 12

what are the criteria for substances used to measure fluid compartment volume (5)

Answer 12

• non-toxic
• evenly distributed in the compartment
• must not affect the distribution of water
• must be unchnaged by the body
• must be easy to meausre
• note only plasma can be sampled

Question 13

name a substance that can be used to meausre plasma volume

Answer 13

radioactive dyes attached to plasma proteins

Question 14

name a substance that can be used to measure extracellular fluid volume

Answer 14

• inulin
• sucrose
• *any other substance that can cross capillary walls but not cell membranes

Question 15

name a substance that can be used to measure total body water

Answer 15

radioactive water

Question 16

can intracellular fluid and interstitial fluid be measured directly?

Answer 16

No

• interstital fluid volume = ECF - plasma volume
• intracellular fluid volume = total body water - ECF

Question 17

how is the volume of distribution calculated?

Answer 17

volume = amount/mass injected (minus any excreted or metabolised) / concentration in fluid sample

Question 18

how does compostion of water vary among the population?

Answer 18

• average male has about 60% water
• females have a lower % of water
• obese/overweight people have a lower % of water
• % of water decreases with age as muscle mass is lost
• fat is 10% water whereas muscle is 70% water