Homeostasis

Question 1

Define homeostasis

Answer 1

Body’s ability to maintain optimum conditions within the range

Question 2

Importance of maintaining health and homeostasis?

Answer 2

Loss of homeostasis leads to illness or disease

Question 3

Explain negative feedback

Answer 3

When homeostasis is disturbed, a signal is sent to produce a response to correct the disturbance and bring conditions back within normal range

Question 4

Characteristics of negative feedback

Answer 4

• Oscillations around set point

- Restores regulated condition after initial disturbance, cannot prevent it happening

Question 5

Explain feed forward system

Answer 5

Sophisticated form of negative feedback. Additional receptors allow system to anticipate change and activate a response earlier.
(Example: pre-empts state of dehydration, hence more concentration of urine, conserving water)

Question 6

Explain positive feedback mechanism

Answer 6

Leads to greater disturbance of condition

Question 7

Describe return of homeostasis of water balance

Answer 7

• Body loses water
• Body fluids become more concentrated (due to feed forward mechanism)
• Receptors sense disturbance of homeostatic condition
• Thirst pathway stimulated
• Person seeks water (negative feedback)
• Water returned to homeostatic conditions

Question 8

Fluid compartments

Answer 8

-Intracellular fluid (33%)

• Interstitial fluid —-> Extracellular fluid (66%)
• Plasma ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Question 9

(!!!) Explain the importance of the nature of the barriers which separate the body
compartments

Answer 9

Separates ions from each compartment, but water can move freely.

Question 10

Measurement of body fluid volumes (dilution principle)

Answer 10

• > c=m/v, hence v=m/c (dilution principle)
• > Only plasma can be sampled, hence compartments which plasma is a component can be measured directly (plasma, ECF, Total Body Water)
• > Nature of Barriers which separate compartments are crucial in determining the test substance

Question 11

Substances to measure each compartment directly

Plasma Volume, ECF, TBW

Answer 11

Plasma Volume: Dyes or radioactive labels that attach to plasma proteins (e..g Evans blue or i125 albumin)
ECF: Something freely crossing capillary walls but not cell membranes (e.g. Insulin, sucrose)
TBW: Heavy water / deuterated water (D2O)

Question 12

Indirectly measure compartments (that plasma is not a component)

Answer 12

ISF = ECF - PV
ICF = TBW - ECF