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Flashcards in Homeostasis Deck (18):
1

define homeostasis

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

2

which systems control homeostasis? (2)

nervous and endocrine

3

why is maintaining internal conditions important?

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

4

Explain the principles behind negative feedback

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

5

Explain what is meant by a feed forward system

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

6

Explain positive feedback

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

7

what is physiology?

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

8

what are the three different body fluid compartments?

- intracellular fluid
- interstitial fluid (ECF)
- plasma (ECF)

9

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

intracellular fluid = 2/3 (66%)
extracellular fluid = 1/3 (33%)

10

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

- 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

11

define the dilution principle

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

12

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

- 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

13

name a substance that can be used to meausre plasma volume

radioactive dyes attached to plasma proteins

14

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

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

15

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

radioactive water

16

can intracellular fluid and interstitial fluid be measured directly?

No
- interstital fluid volume = ECF - plasma volume
- intracellular fluid volume = total body water - ECF

17

how is the volume of distribution calculated?

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

18

how does compostion of water vary among the population?

- 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