Introduction to Medical Sciences & Homeostasis Flashcards
General organisation of body systems
Cells are organised into tissue, tissue is organised into organs and organs are organised into organ systems
Outline the role of each major system in maintaining health and optimal homeostasis
Nervous, endocrine and musculoskeletal – to seek and supply and access nutrients
Respiratory – to supply 02 and disposal
Alimentary – break down food to usable forms and absorb across gut wall to blood stream and disposal
Cardiovascular – transport O2 and nutrients into bloodstream and transport C02 and waste from cells
Nervous and endocrine - cooordinate and control all these processes
Define the term homeostasis
Homeostasis is the maintenance of similar but not identical conditions in the internal environment to keep variables within a set range
Importance of maintaining constancy of the internal environment
The internal environment must remain relatively consistent to allow cells to produce energy, carry out their functions and for processes to occur optimally – despite changes in both the internal and external environment
Describe the principles of negative feedback
- Self-limiting – the condition that triggers the homeostatic response becomes switched off/removed by that response
- Size of response is proportional to size of disturbance
- Restores the regulated condition after its initial disturbance but cant prevent it happening
Describe the principles of feed forward control
More sophisticated and involves additional receptors to anticipate change
Therefore a response can be activated before the change occurs
Describe the principles of positive feedback
The opposite effect to negative feedback
Triggers a response which results in an even greater disturbance
Commonly associated with pathology
Outline daily water balance in a person
Process that is homeostatically controlled
water makes up 60% of body weight
water effects the concentration of everything else in the body
What are the different fluid compartments
Intracellular fluid = ICF (fluid within cells)
Interstitial fluid = ECF extracellular fluid ECF (fluid between cells)
Plasma (fluid component of blood) = extracellular fluid
composition of the ECF is very, VERY important.
Describe the characteristics of the natural barriers which separate body compartments
Water can move freely between the intracellular, interstitial and plasma fluid
Movement is subject to forces such as osmosis
The body can survive only as long as the composition of the ECF is maintained in a state compatible with the survival of its individual cells
Define the dilution principle
C=m/v or v=m/c
Explain how the dilution principle can be used to measure body fluid compartments
- Inject a substance that will stay in one compartment only (plasma, ECF, TBW)
- Then calculate the volume of distribution = amount injected (minus any removed by excretion or metabolism), divided by the concentration of the sampled fluid
How can each compartment be measured using the dilution principle
Only plasma can be sampled – therefore only compartments of which plasma is a component can be measured (plasma, ECF, TBW)
Plasma volume (PV) = use dyes or radioactive labels that attach to plasma proteins
eg. Evans blue or 1125 albumin
Extracellular volume (ECF) = use something that can freely cross capillary walls, but can’t cross cell membrane
eg. Insulin, sucrose or Na+, Cl-
Total body water (TBW) = no barriers to water in body so can use a loading dose of heavy water/ deuterated water (D2O)
ISF = ECF-PV OR TBW-ECF
