Homeostasis 2 Flashcards
Homeostatic reflexes are represented by reflexes which may be..?
Neural
Hormonal
What do the mechanisms of homeostasis maintain?
O2 and CO2
Waste and ions
Blood pressure and blood volume
Nutrient level
What percentage of body weight does water make up?
60%
Why is homeostatic regulation of water crucial?
Because water affects the concentration of everything else
How is water regulated?
Input by thirst mechanism
Output by regulation of kidney function
Other processes which are not regulated towards water balance, such as sweating which is for temperature regulation
What three compartments is water split between?
Intracellular fluid (ICF)
Interstitual fluid (ISF, fluid between cells)
Plasma (fluid component of blood)
ISF and plamsa make up extracellular fluid (ECF)
How does water move between compartments?
Water can move through all three compartments freely, but movement is subject to forces such as osmosis
How does fluid pass from ECF and ICF
Crosses the cell membrane
How does fluid move between plasma and ISF?
Crosses the capillary wall
Explain the permeability of the cappilary wall?
Permeable to everything except plasma proteins
Explain the permibility of the cell membrane?
Selective permeability
What is the ratio of water distribution across the compartments?
1/3 in ECF and 2/3 in ICF
How is water distributed in ECF
80% in ISF
20% in plasma
What do proportions of water vary with?
Sex and age
Woman and older people have higher proportions of fat than muscle (70% of muscle is water whereas 10% of fat is water)
Why is plasma described as the dynamic component of the ECF?
Because it is continuously moving through vessels by the pumping action of the heart
What nutrients does plasma exchange with ISF through the cappilary wall?
O2
Glucose
Ions
CO2
Urea
Can exchange take place through large vessels like arteries?
No because the walls are too thick for exchange to take place
Is the composition of blood and ISF the same?
Yes, apart from plasma proteins which are too large to pass through the cappilary wall
What is the dilution principle?
c = m/V
What can the dilution principle be used to measure?
Body fluids
What should be remembered when using the dilution principle?
- c = m/V becomes V = m/c
- Only plasma can be sampled, so only compartments which plasma is a component of can be measured directly
- The nature of barriers which seperate compartments is crucial in determining the test substance
What components can be measured directly?
- Plasma volume (measure plasma protein using dye)
- ECF (something that crosses cappilary wall but not the cell membrane like 24Na+
- Total body water, TBW (water because no barriers, use heavy water D2O)
What compartments can be calculated indirectly?
ISF and ICF
ISF = ECF - PV
ICF = TBW - ECF
What do you need to remember when calculating fluid levels?
To subtract any secretions or metabolism
Why is the composition of the ECF very different from the ICF?
Because the cell membrane acts as a selective barrier
How do ion concentrations of the ECF compare to the ICF?
More Na+ and Cl- outside the cell
More K+ inside the cell
Why must large concentration gradients of ions be maintained?
For nerve function
What does hyper mean?
Greater than normal
What does hypo mean?
Less than normal
What does aemia mean?
In the blood
What does uria mean?
In the urine
What does ‘glyc’ mean?
Relates to glucose
