Introduction to Medical Sciences & Homeostasis

Question 1

General organisation of body systems

Answer 1

Cells are organised into tissue, tissue is organised into organs and organs are organised into organ systems

Question 2

Outline the role of each major system in maintaining health and optimal homeostasis

Answer 2

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

Question 3

Define the term homeostasis

Answer 3

Prevention of disturbance in the system

Question 4

Importance of maintaining constancy of the internal environment

Answer 4

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.

Question 5

Principles of Negative Feedback

Answer 5

1. Self-limiting – the condition that triggers the homeostatic response becomes switched off/removed by that response
2. Size of response is proportional to size of disturbance
3. Restores the regulated condition after its initial disturbance but cant prevent it happening

Question 6

Principles of feed forward control

Answer 6

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

Question 7

Principles of positive feedback

Answer 7

Has opposite effect to negative feedback

Sets of a train of events that lead to an even greater disturbance

Commonly associated with pathology

Question 8

Outline daily water balance in a person

Answer 8

Process that is homeostatically controlled

water makes up 60% of body weight

water effects the concentration of everything else in the body

Question 9

What are the different fluid compartments

Answer 9

Intracellular fluid = ICF (fluid inside 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.

Question 10

Importance of the natural barriers which separate body compartments

Answer 10

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

Question 11

Define the dilution principle

Answer 11

C=m/v or v=m/c

Question 12

Use of dilution principle to measure body fluid compartments

Answer 12

1. Inject a substance that will stay in one compartment only (plasma, ECF,TBW)
2. Then calculate the volume of distribution = amount injected (minus any removed by excretion or metabolism), divided by the concentration of the sampled fluid

Question 13

How can each compartment be measures using the dilution principle

Answer 13

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