Homeostasis Flashcards
Define homeostasis
Our body monitors its internal state, responding to threats which could disturb/prevent optimum “similar
conditions”.
Homeostasis describes the processes by which the internal environment of the body is kept reasonably constant in such a way that it optimises all physiological and biochemical processes that support life.
Why must we maintain a consistant internal environment?
Without homeostasis we would die; it is fundamental to life. Without it, vital biochemical processes would not occur, meaning energy cannot be generated to power cellular function.
Our bodies are not tolerant to substantial change to internal environment and respond in ways to minimise these changes. failure to adequately correct imbalances results in illness and disease, or pathology
What does homeostasis require (since it is so complicatied)?
Integration of organ systems to mainteain this optimal internal environment, allowing cells to function and ultimately produce energy. This requires regulation at a cell, tissue and system level.
Give everyday challenges to our internal environment and what they impact on?
External temp, access to nutrients, exercise. Impact on body fluid composition, energy stores, body temp and physiological mechanisms must act to counteract these potential threats to homeostasis.
What happens to homeostasis at extremes?
it becomes less effective
Explain Negative feedback
When a condition that is homeostatically regulated (e.g. body temperature), is sensed to have shifted from the normal range, a signal (usually nervous or endocrine), is generated that produces a response (e.g. shivering or sweating), that corrects the original disturbance and brings the regulated condition back within the normal range.
It causes a return to a set point
Why is it “negative” feedback?
the condition that triggered the homeostatic response becomes switched off/removed by that response.
Give some characteristics of negative feedback systems?
- Size of response proportional to the size of the disturbnce
- there is oscillation around a set point
- restores the regulated condition after its intitial disturbance but cannot prevent that disturbacne from happening
Explain feedforward control
More sphisticated form of -ve feedback. Additional receptors permit the ststem to anticipte the change and activate a response earlier - almost predicting and preventing change
Give an example of -ve vs feedforward feedback?
While negative feedback prompts the thirst response, the kidney detects the increased body fluid concentration and pre-empts a state of dehydration. It responds by producing smaller volumes of urine, and a more concentrated form of urine, thus conserving water.
Outline daily water balance in man?
Person working in hot day –> looses body water y evaporation –> body fluids become concentrated –> internal receptors sense change in internal concentration –> thirst pathway stimulated –> person seeks out and drinks water –> water added to body fluids decreases their concentation - negative feedback between two
Explain positive feedback?
Where negative feedback restores disturbed conditions to optimum, positive feedback sets off a train of events that** lead to an even greater disturbance**. It AMPLIFIES the response but cannot predict/prevent disruption before it happens.
Such cycles usually lead to instability and are common in pathophysiology/pathology but rare in normal physiology
Where could positive feedback mechanisms occur?
In nerve action potential, in ovulation and sexual behaviour
give an example of a positive feedback mechanism
Action potential: initial trigger allows +vely charged Na ions to enter nerve cell. influx of Na, meaning charge inside becomes more positive (depolarisation). Na permeability increases… leading to influx… cycle repeats - self amplification
What is the aim of medicine (in relation to homeostasis)
Restoring this homeostatic control when it is disturbed by illness or disease
What key process is homeostatically controlled and why?
Water balance - its homeostatic maintenance is crucial beacuse water affect the conc of everything else in the body (water in must = water out)
What is regulated to maintain water balance
- Input regulated by thirst mechanism
- Output by regulation of kidney function (urinary loss)
- Other processes to alter water balance are regulated too, but their control is not aimed at maintaining water balance (e.g. sweating to control temp regulation, but by-product of water loss leads to confilc between water and temp regulation
