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science for medicine > Homeostasis 2 > Flashcards

Homeostasis 2 Flashcards

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1
Q

Homeostatic reflexes are represented by reflexes which may be..?

A

Neural

Hormonal

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2
Q

What do the mechanisms of homeostasis maintain?

A

O2 and CO2

Waste and ions

Blood pressure and blood volume

Nutrient level

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3
Q

What percentage of body weight does water make up?

A

60%

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4
Q

Why is homeostatic regulation of water crucial?

A

Because water affects the concentration of everything else

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5
Q

How is water regulated?

A

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

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6
Q

What three compartments is water split between?

A

Intracellular fluid (ICF)

Interstitual fluid (ISF, fluid between cells)

Plasma (fluid component of blood)

ISF and plamsa make up extracellular fluid (ECF)

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7
Q

How does water move between compartments?

A

Water can move through all three compartments freely, but movement is subject to forces such as osmosis

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8
Q

How does fluid pass from ECF and ICF

A

Crosses the cell membrane

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9
Q

How does fluid move between plasma and ISF?

A

Crosses the capillary wall

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10
Q

Explain the permeability of the cappilary wall?

A

Permeable to everything except plasma proteins

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11
Q

Explain the permibility of the cell membrane?

A

Selective permeability

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12
Q

What is the ratio of water distribution across the compartments?

A

1/3 in ECF and 2/3 in ICF

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13
Q

How is water distributed in ECF

A

80% in ISF

20% in plasma

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14
Q

What do proportions of water vary with?

A

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)

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15
Q

Why is plasma described as the dynamic component of the ECF?

A

Because it is continuously moving through vessels by the pumping action of the heart

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16
Q

What nutrients does plasma exchange with ISF through the cappilary wall?

A

O2

Glucose

Ions

CO2

Urea

17
Q

Can exchange take place through large vessels like arteries?

A

No because the walls are too thick for exchange to take place

18
Q

Is the composition of blood and ISF the same?

A

Yes, apart from plasma proteins which are too large to pass through the cappilary wall

19
Q

What is the dilution principle?

A

c = m/V

20
Q

What can the dilution principle be used to measure?

A

Body fluids

21
Q

What should be remembered when using the dilution principle?

A
  1. c = m/V becomes V = m/c
  2. Only plasma can be sampled, so only compartments which plasma is a component of can be measured directly
  3. The nature of barriers which seperate compartments is crucial in determining the test substance
22
Q

What components can be measured directly?

A
  1. Plasma volume (measure plasma protein using dye)
  2. ECF (something that crosses cappilary wall but not the cell membrane like 24Na+
  3. Total body water, TBW (water because no barriers, use heavy water D2O)
23
Q

What compartments can be calculated indirectly?

A

ISF and ICF

ISF = ECF - PV

ICF = TBW - ECF

24
Q

What do you need to remember when calculating fluid levels?

A

To subtract any secretions or metabolism

25
Q

Why is the composition of the ECF very different from the ICF?

A

Because the cell membrane acts as a selective barrier

26
Q

How do ion concentrations of the ECF compare to the ICF?

A

More Na+ and Cl- outside the cell

More K+ inside the cell

27
Q

Why must large concentration gradients of ions be maintained?

A

For nerve function

28
Q

What does hyper mean?

A

Greater than normal

29
Q

What does hypo mean?

A

Less than normal

30
Q

What does aemia mean?

A

In the blood

31
Q

What does uria mean?

A

In the urine

32
Q

What does ‘glyc’ mean?

A

Relates to glucose

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