Homeostasis Flashcards
Explain the importance of maintaining constancy of the internal enviorment
he body needs the ECF to be maintained in a state compatible with the survival of the individual cells.
o 80% of ECF is ISF
o 20% is Plasma
Define tissues
Tissues: Groups of cells that share the same characteristics or specialization.
Define Organs
Organs: Collections of tissues, usually of several different types, that synchronize to perform a particular function.
Define the term homeostasis
The regulation of a relatively constant internal environment in which all processes work optimally even when it varies with external surroundings and changes in demand. E.g the laws of demand mean that as energy demand increases (during exercise), supply of substrates required to produce energy must also increase in order to meet that demand and prevent disturbance in the system.
Define the principles behind -ve feedback (3)
- Magnitude of change in a monitored variable (such as body temperature) is sensed by a receptor, which feeds that information to an integrating center where it is compared with a reference level.
- Any difference between the actual level and the reference level generates another signal, which is fed to an effector mechanism, in such a way as to produce a response (e.g shivering or sweating), which corrects the original change.
- The magnitude of the generated signal is proportional to the magnitude of difference from normal and also the magnitude of the response.
Explain what is meant by feed forward control
- More sophisticated form of negative feedback, additional receptors permits system to anticipate change and therefore activate response earlier. – e.g temperature receptors in our skin detect external temperature and activate response before any significant change in core temperature occurs.
- Positive feedback has the opposite effect of –ve feedback. Where –ve feedback aims to restore optimum with positive feedback initial disturbance set off a train of events that lead to an even greater disturbance.
- ^ such cycles usually lead to instability, common in pathophysiology, rare in normal physiology
Illustrate the concept of homeostasis by outlining daily water balance in a man
input = loses
- Input is regulated by the thirst mechanism
- Output is regulated by urinary loss
- other processes are regulated but their control is not orientated towards water balance (e.g sweating)
Identify the different body fluid compartments
- Water makes up around 60% of body weight, woman are less ‘wet’ as they have more fat.
- The water in the body is split into 3 compartments:
1) Intracellular fluid (ICF)
2) Interstitial fluid (fluid between cells) (ECF)
3) Plasma (fluid component of blood) (ECF)
What is the method of practice of dilution principle?
1) inject substance that will stay in one compartment only
2) then calculate the volume of distribution:
= amount injected (minus any removed by excretion or metabolism) divided by concentration in the sampled fluid.
How do we measure plasma volume (PV)?
Plasma volume (PV): Since plasma proteins cannot across the capillary walks, can use dyes or radioactive labels that attach to plasma proteins (Evans blue or l125 albumin)
How do we measure Extracellular Volume (ECF)?
Extracellular Volume (ECF): Need something that freely crosses capillary walls, but cannot cross cell membranes, e.g inulin, sucrose, mannitol, which are all too large to cross cell membrane or 24Na+, 36Cl- which are actively extruded from cells.
How do we measure total body water (TBW)?
Total Body Water (TBW): There is no barrier to water in the body, so can use a loading dose of heavy water / deuterated water (D2O)
How do you measure other compartments that cannot be directly sampled? (ISF and ICF)
ISF = ECF – PV
ICF = TBW - ECF
