Homeostasis Flashcards
What is the general equation of life?
Nutrients + O2 = Waste (CO2) + Energy
What works together to support the equation of life?
Co-operating body systems.
What gives rise to homeostasis?
The threat of disruption to the balance of the equation of life.
What does homeostasis mean?
Home = similar/ Stasis = state
Similar condition
What is homeostasis?
Homeostasis is the regulation of an internal steady environment in the body in response to disruption.
What does a failure to maintain a constant internal balance cause?
Pathology.
What are common disruptions to the internal state?
Temperature
Diet
Exercise
What is the difference between external and internal variables in homeostasis?
External- activity (e.g. eating doughnut)
Internal- temp/pH, conc etc.
When is homeostasis less effective?
Extreme conditions.
What mechanisms are used to maintain homeostasis?
Negative feedback
Feed-forward control
Positive feedback
What is the most important mechanism of homeostatic control?
Negative feedback.
How does negative feedback work?
When a condition that is homeostatically regulated is sensed to have shifted from the normal range, a signal is generated that produces a response which corrects the original disturbance and brings the condition back to normal.
What is the homeostatic response proportional to?
The disturbance to condition caused.
What are the characteristics of negative feedback?
Oscillation around a set point
Restores the internal condition AFTER disturbance
What is feed-forward control?
Sophisticated form of negative-feedback control in which additional receptors recognise changes in the environment PRIOR to them causing a disruption and allow a response to be activated earlier. (E.g. going back for a coat in the cold after sensing temp).
What is positive feedback control?
Opposite of NFC. Whilst this tries to restore less disruption, positive feedback control triggers further disruption to the system.
Where is positive feedback control usually seen?
Pathology- although seen in some physiological processes such as nerve transmission.
How is the integration of distal body systems achieved in homeostasis?
Endocrine / nervous system.
What homeostatic mechanisms of the endocrine/nervous system are active?
Neural/endocrine reflexes.
Why is homeostatic maintenance of water important?
Water controls everything else in the body.
What is water input regulated by?
Thirst mechanism.
What is water output regulated by?
Excretion / urinary tract mechanism (kidney function).
What is prioritised above water regulation?
Body temperature
What 3 compartments is water split between?
- Intracellular fluid
Extracellular fluid
- Interstitial fluid
- Plasma
What is intracellular fluid?
Fluid within the cells.
What does the extracellular fluid consist of?
Interstitial fluid
Plasma
What is the interstitial fluid?
Fluid in-between cells.
What is plasma?
Fluid component of blood.
What are the barriers that must be crossed between compartments?
Plasma > Interstitial fluid
(Plasma membrane- plasma proteins filtered out)
Intersistial fluid > Intracellular fluid
(Cell membrane)
How is water distributed across the fluid compartments?
1/3 extracellular, 2/3 intracellular.
Why does H20 distribution vary with gender?
Females have more fat- fat is 10% water whereas water is 70% water.
Why does H20 distribution vary with age?
Elderly have lower water concentration- again due to fat and muscle distribution.
What does plasma do?
Freely exchanges nutrients with the ISF- they are homogeneous with the exception of plasma proteins being unable to cross the capillary wall.
What is the dilution principle?
M=CV
What must be sampled in the dilution principle?
Plasma- least barrier reduction; only compartments of which plasma is a component can be measured directly.
What compartments can be measured using the Dilution Principle?
Plasma proteins- since these cannot cross the plasma membrane, dyes or radioactive tags are used.
Extracellular volume- freely crosses capillary walls but cannot cross cell membrane due to size.
Total body water- no barriers to water in the body.
