Introduction to Medical Sciences and 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 - o0ordinate and control all these processes
Define the term homeostasis
Prevention of disturbance in the system
Importance of maintaining constancy of the internal environment
Homeostasis maintains optimal conditions for enzyme action throughout the body, as well as all cell functions. It is the maintenance of a constant internal environment despite changes in internal and external conditions.
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
Principles of feed forward control
More sophisticated and to some extent predict and prevent change
Additional receptors permit system to anticipate change and therefor activate response earlier – “pre-empts” change in condition
Principles of positive feedback
Has opposite effect to negative feedback
Sets of a train of events that lead to 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
Interstitial fluid (between cells)
= extracellular fluid ECF
Plasma (fluid component of blood)
Importance 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
Use of dilution principle 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 measures using the dilution principle
Only plasma can be sampled – only compartments of which plasma is a component (plasma, ECF, TBW)
Plasma volume (PV) = use dyes or radioactive labels that attach to plasma proteins eg. Evans blue or I125 dbumin
Extracellular volume (ECF) = need something that freely crosses 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
