Homeostasis Flashcards
What is homeostasis?
Prevention of disturbance in a system to maintain similar (not identical) conditions
What are examples of challenges to internal environment?
1.) external temperature
2.) access to nutrients
3.) exercise
What is negative feedback?
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
Characteristics of negative feedback?
- oscillation around set point
- restores the regulated condition after its initial disturbance, but cannot prevent it happening
What is feedforward control?
Additional receptors permit system to anticipate change and therefore activate response earlier
- more sophisticated form of control
What is positive feedback?
Sets off a train of events that lead to an even greater disturbance
- opposite effect of negative feedback
- more commonly associated with pathology
What percentage of body weight is water?
Roughly 60%
What are the three compartments what water is split between?
1.) ICF
2.) ISF
3.) plasma
What are properties of plasma?
- blood cells
- inside the blood vessel (capillaries)
- contains plasma proteins
What is the volume of water in plasma?
3 litres
Where is ISF found?
In between cells and capillary wall
What volume of water is in ISF?
11 litres
Where is ICF found?
In the cells
What volume of water is in ICF?
28 litres
What components make up ECF?
Plasma and ISF
What is the capillary wall permeable to?
Everything apart from blood cells and plasma proteins
What is plasma?
The dynamic component of ECF, and freely exchanges nutrients with ISF as they are identical apart from blood cells and plasma proteins
What is the formula for the dilution principle?
c = m/v or v = m/c
What compartment can be sampled for the dilution principle?
Only ones that have plasma as a component (plasma, ECF, TBW)
How can plasma be measured?
Using Evans blue or I^125 albumin to attach to plasma proteins
How can ECF be measured?
Using something that can freely cross capillary walls but not cell membranes (insulin, sucrose, mannitol, ^24Na+, ^36Cl-)
How can TBW be measured?
Using a loading dose of heavy water/deuterated water (D2O)
How can a compartment that doesn’t contain plasma be measured?
Indirectly, using formulas such as ISF = ECF - plasma and ICF = TBW - ECF
What is the method of the dilution principle?
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
What are normal values?
- healthy male
- 21 year old
- 70 kg
Who has a lower body water percentage than normal?
- females as they have a higher proportion of body fat
- older people for the same reason above
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
D
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
B
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
C
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
C
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
B
