Homeostasis Flashcards
Explain the importance of maintaining constancy of the internal environment.
Bodies are not tolerant to substantial changes in the internal enviorment (e.g temp, pH, conc. of hormones etc) failure to adequately correct any imbalances and disruptions to the constancy result in illness and disease or pathology.
The ECF needs to maintained in a state compatible with the survival of individual cells.
What is the ECF made up of?
80% ISF and 30% plasma.
Define tissue
Group of cells that share the same characteristics or specialisation.
Define organs.
Collections of tissues, usually several different types, that synchronise to perform a particular function.
Defne homeostasis
Homeostasis is 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.
Give an example of how homeostasis works using energy.
The laws of demand mean that as energy demand increases (e.g during exercise), supply of substrates required to produce energy must also increase in order to meet that demand and prevent disturbance in the system.
Describe the principles behind negative feedback control systems.
- magnitude of change in a monitored variable (such as body temp) is sensed by a receptor, which feeds that info 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 magnitude of the response.
Explain what is meant by feed forward control.
- More sophisticated form of neg feedback - additional receptors permit system to anticipate change and therefore activate response earlier - e.g temp receptors in our skin detect external temp and activate response before any significant chance in core temp occurs.
Describe positive feedback.
Pos feedback has the opposite effect of -ve feedback. Where -ve feedback aims to restore optimum, +ve feedback initial disturbance set off a train of events that lead to an even greater disturbance away from norm.
What are the different body fluid compartments?
- Water makes up around 60% of body weight - women are more ‘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) - plasma is the dynamic component of blood.
Explain the importance of the nature of the barriers which seperate the body compartments.
- Capillary wall is permeable to everything but plasma protein.
- Cell membrane has selective permeability
- Barriers important to keep ICF 1/3, ECF 2/3
Define the dilution principle.
C = m / v , v = m / c
- Method of practice of dilution principle:
1) Inject a 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 you measure PV ?
Plasma volume: Since plasma proteins cannot cross the capillary walls, can use dyes or radioactive labels that attach to plasma proteins (use either Evans blue or l125 albumin)
How do you measure ECF?
Extracellular Volume: Need something that freely crosses the capillary walls but cannot cross cell membranes, e.g insulin, sucrose, mannitol, which are all too large to cross cell membrane or 24 Na+, 36 Cl- which are actively extruded from cells.
How do you measure TBW?
Total body water, there is no barrier to water in the body so can use a loading dose of heavy water / deuterated water (D20)
