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Foundation of Medicine (Year 1) > Homeostasis > Flashcards

Homeostasis Flashcards

1
Q

What is homeostasis?

A

Prevention of disturbance in a system to maintain similar (not identical) conditions

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2
Q

What are examples of challenges to internal environment?

A

1.) external temperature
2.) access to nutrients
3.) exercise

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3
Q

What is negative feedback?

A

When a condition is shifted from normal a signal is generated that produces a response that corrects the original disturbance and brings it back to normal range

  • size of response is proportional to size of disturbance
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4
Q

Characteristics of negative feedback?

A
  • oscillation around set point
  • restores the regulated condition after its initial disturbance, but cannot prevent it happening
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5
Q

What is feedforward control?

A

Additional receptors permit system to anticipate change and therefore activate response earlier

  • more sophisticated form of control
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6
Q

What is positive feedback?

A

Sets off a train of events that lead to an even greater disturbance

  • opposite effect of negative feedback
  • more commonly associated with pathology
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7
Q

What percentage of body weight is water?

A

Roughly 60%

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8
Q

What are the three compartments what water is split between?

A

1.) ICF
2.) ISF
3.) plasma

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9
Q

What are properties of plasma?

A
  • blood cells
  • inside the blood vessel (capillaries)
  • contains plasma proteins
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10
Q

What is the volume of water in plasma?

A

3 litres

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11
Q

Where is ISF found?

A

In between cells and capillary wall

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12
Q

What volume of water is in ISF?

A

11 litres

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13
Q

Where is ICF found?

A

In the cells

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14
Q

What volume of water is in ICF?

A

28 litres

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15
Q

What components make up ECF?

A

Plasma and ISF

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16
Q

What is the capillary wall permeable to?

A

Everything apart from blood cells and plasma proteins

17
Q

What is plasma?

A

The dynamic component of ECF, and freely exchanges nutrients with ISF as they are identical apart from blood cells and plasma proteins

18
Q

What is the formula for the dilution principle?

A

c = m/v or v = m/c

19
Q

What compartment can be sampled for the dilution principle?

A

Only ones that have plasma as a component (plasma, ECF, TBW)

20
Q

How can plasma be measured?

A

Using Evans blue or I^125 albumin to attach to plasma proteins

21
Q

How can ECF be measured?

A

Using something that can freely cross capillary walls but not cell membranes (insulin, sucrose, mannitol, ^24Na+, ^36Cl-)

22
Q

How can TBW be measured?

A

Using a loading dose of heavy water/deuterated water (D2O)

23
Q

How can a compartment that doesn’t contain plasma be measured?

A

Indirectly, using formulas such as ISF = ECF - plasma and ICF = TBW - ECF

24
Q

What is the method of the dilution principle?

A

1.) inject a substance that will stay in one compartment only (plasma, ECF, TBW)
2.) calculate the volume of distribution: amount injected (minus any excreted or metabolised) divided by the concentration in the sampled fluid

25
Q

What are normal values?

A
  • healthy male
  • 21 year old
  • 70 kg
26
Q

Who has a lower body water percentage than normal?

A
  • females as they have a higher proportion of body fat
  • older people for the same reason above
27
Q

Homeostasis:

A - Is fundamental for life
B - Maintains monitored variables within a set range
C - Allows us to live in hot countries and eat donuts
D - All of the above

A

D

28
Q

Negative feedback regulation:

A - Is the least common type of feedback
B - Causes return to a set point
C - Amplifies the response
D - Disrupts homeostasis

A

B

29
Q

Positive feedback regulation:

A - Is the most common type of feedback
B - Causes return to a set point
C - Amplifies the response
D - Predicts and prevents disruption of set point before it happens

A

C

30
Q

You drink 1L of water. How is that water distributed in the body?

A - Contained in the ECF
B - Contained in the ICF
C - 1/3 in ECF, 2/3 in ICF
D - 2/3 in ECF, 1/3 in ICF
E - 1/2 in ECF, 1/2 in ICF

A

C

31
Q

A healthy 20 year old female with [K+]ecf of 4.2mmol/l doubles her normal K+ intake. After a week, which of these is most likely to be her [K+]plasma?

A - 2.1mmol/l
B - 4.2mmol/l
C - 8.4mmol/l
D - 12.6mmol/l

A

B

Foundation of Medicine (Year 1) (6 decks)

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