Homeostasis 2 Flashcards
Where is the water in our bodies?
ICF
ISF
Plasma
What is transcellular fluid?
ECF which exists in special areas
How is water distributed in an average 70Kg, 21yo man?
Plasma 3L
ISF 11L
ICF 28L
What is the capillary wall permeable to?
Everything but protein
What is the ratio of ISF to plasma?
80% of ECF is ISF
20% of ECF is plasma
Why are females considered ‘less wet’?
They have a higher proportion of body fat which has less water content than muscle
When do women start to show proportionally less body water than men?
From puberty onwards
What is plasma?
The fluid component of blood
Why is plasma considered the dynamic component of the ECF?
It continuously moves through blood vessels by the pumping action of the heart
What is the relationship between plasma and the ISF?P
Plasma freely exchanges nutrients and waste with the ISF
When does exchange of particles occur?
As blood passes through the capillaries of the body. Large vessels like arteries have walls too thick for exchange
What is the only difference in composition between the plasma and the ISF?
Plasma proteins which are too large and therefore restricted to the plasma
What 3 things must be remembered when measuring body fluids?
- Dilution principle
- Only plasma can be sampled therefore only compartments of which plasma is a component can be measured directly
- The nature of barriers which separate compartments is crucial in determining the test substance.
What are the criteria for test substances in measuring body fluid?
- Non-toxic
- Evenly distributed in the compartment being measured
- Must not affect the distribution of water
- Must be unchanged by the body
- Must be easy to measure
What compartments can be measured directly using the dilution principle?
Plasma volume
ECF
TBW
How can the compartments that cannot be directly sampled be calculated?
ISF = ECF - PV
ICF = TBW - ECF
How can plasma volume be measured directly?
Since plasma proteins cannot cross the capillary walls, can use dyes or radioactive labels that attach to plasma proteins
How can ECF volume be measured directly?
Need something that freely crosses capillary walls, but cannot cross cell membranes
How can TBW be measured directly?
There is no barrier to water in the body so can use a loading dose of radioactive water
What is the method of practice of dilution principle?
- Inject a substance that will stay in one compartment only
- Then calculate the volume of distribution (amount injected divided by the concentration in the sampled fluid)
Hyper
greater than normal
Hypo
less than normal
Aemia/emia
in the blood
Uria
in the urine
Glyc
related to glucose
What is the result of the breakdown of homeostatic control mechanisms?
Disease states and illness
Coma and death
