Homeostasis Flashcards
1
Q
Homeostasis definition
A
- Homeostasis is maintaining the right conditions for various physiological and biochemical systems to operate within optimal parameters.
- Different biological systems may require different “optimal” conditions - can become quite complex/ difficult
- Maintaining homeostasis may involve many physiological systems acting simultaneously.
- Maintaining homeostasis in a challenging env is an active process (our body is always working to maintain homeostasis)
- Homeostasis is maintained by the process of allostasis: “the maintenance of stability through active intervention”
2
Q
CONTROL SYSTEMS: DESIGN OF THE HOMEOSTATIC MECHANISM
A
- Controlled variable (thing that is being controlled + has possibility to change + generally will be trying to make sure that controlled variable is at its set point)
- Way we do that is by using a homeostatic mechanism which is built on this basic design:
SENSOR –> AFFERENT PATHWAY –> CONTROLLER –> EFFERENT PATHWAY –> EFFECTOR
2
Q
CONTROL SYSTEMS: DESIGN OF THE HOMEOSTATIC MECHANISM
A
- Controlled variable (thing that is being controlled + has possibility to change + generally will be trying to make sure that controlled variable is at its set point)
- Way we do that is by using a homeostatic mechanism which is built on this basic design:
SENSOR –> AFFERENT PATHWAY –> CONTROLLER –> EFFERENT PATHWAY –> EFFECTOR
3
Q
Control of BP
A
- Control of BP is a good example: we know we have a target BP
- Because if our blood pressure gets too high (hypertension)?
- Hypertension can cause damage to blood vessels.
- Hypertension can increase the workload on the heart leading to permanent damage. - Because if our blood pressure gets too low (hypotension)?
- Insufficient blood supply to the brain can cause fainting. - Blood pressure needs to be kept within a normal range.
- Control of blood pressure is achieved using a negative feedback control system: changes in blood pressure are resisted so that an appropriate blood pressure is maintained.
- Control system for blood pressure:
- Controlled variable: blood pressure
- Set point: normal/target BP
- Sensors: baroreceptors
- Afferent pathway: nerves
- Controller: cardiovascular centre in medulla
- Efferent pathways: autonomic nervous system, hormones
- Effectors: heart, smooth muscle in vessels
4
Q
Negative feedback system
A
- Negative feedback control system: negative as it is negating/reversing the change = trying to return the controlled variable back to where it was / and its feedback because it is looking backwards to reverse a change that has already occurred
- OR reverses (negates) the effect of a change that has already occurred
- Think that is curing a problem that has occurred
5
Q
CONTROL of BODY TEMP
A
Controlling body temperature.
- The body’s core temperature is tightly regulated in the “thermoneutral zone” 36.5°C - 37.5°C
- Stable core temp is maintained by balancing heat production + loss.
- Doesn’t mean it can’t change/ don’t need to prevent it = it can be good e.g. to warm up muscles before sport, after injury using an ice pack to cool inflammation
- Just wants to make sure that in the long-term the controlled variable is where it should be
Control system
- Sensors: central, visceral, muscle = sensors all over the body to get a good overview of what the body temp is exactly like
- Controller: hypothalamus = part of brain = is a central controller in the body
- Effectors: blood vessels (change diameter of bv to stop heat being lost from the skin to the env), skeletal muscles (shiver = to increase body temp), hair, behaviour (know if hot can go to a shady place = helps to regulate body temp)
- immediate control via the autonomic nervous system,
- delayed control by the endocrine system
6
Q
More on body temp
A
- Over long term can get long-term adaptations = acclimatisation
- Hyperthermia is an increase in body temp above the setpoint = neg feedback system will be working to return body to normal temp
- Maybe no effect or be beneficial – eg exercise
- Maybe an adverse effect
- altered cell function –decreased performance, seizures
- permanent cell damage
- death
- Exercise increases core body temp which optimises physiological processes.
- Increased muscle temp due to warm-up:
- decreases tissue stiffness,
- increases nerve-conduction rate,
- alters muscle contraction characteristics and- increases anaerobic energy provision
7
Q
Fever
A
- Fever is due to an increase in the hypothalamic (normal) set point = but in a fever what has happened is that the set point has changed
- When we have an infection in our body we get production of chemicals that are called pyrogens e.g. bacterial infection will produce pyrogens and because they are from outside the body they are called exogenous pyrogens
- the bacteria will trigger an immune response and the immune cells will produce endogenous pyrogen → both go to the hypothalamus → where they cause the production of chemicals known as prostaglandins →
- the effect of those prost.. Is to increase the set point → our body (or homeostatic mechanism) then tries to increase normal body temp up to that new set point →
- say it’s new set point is 40 and it gets to 38.5 (body temp is higher than usual but lower than the set point) = so at that stage a person will feel cold + start shivering even though temp is higher than normal = still lower than set point =
- body will still try to institute changes to try and reach the set point which is whole point of feedback systems
8
Q
Feedforward systems
A
- anticipates a likely change and tries to prevent it from occurring
- Some control systems become operational before the controlled variable has changed – these are feedforward systems.
- We can anticipate changes that are going to occur. = e.g. in the env that could impact on the controlled variable in the future = are looking forward into the future = changes that haven’t occurred yet but could
- Are all about prevention = will implement responses that will stop the controlled variable from changing
- Feedforward can work in combination with feedback.
EXAMPLES:- Mechanisms to retain heat are switched on as soon as we go into a very cold environment – before the controlled variable has changed.
- Heart rate and respiratory rate increase before exercise begins.
9
Q
POSITIVE FEEDBACK SYSTEM
A
- Positive feedback control systems accentuate/ continuing the change in the controlled variable once it has begun
EXAMPLE: Labour - Women labour = contractions start mild, initially a long while a part
- As labour continues = contractions get stronger + closer together = change is due to positive feedback system
- Controlled variable = diameter of the cervix (opening at base of uterus)
- As the cervix is dilating, the controlled variable is changing = we want cervix to open so baby can pass through = want to continue dilation
- Way we do that is that dilation of the cervix causes the release of the hormone oxytocin = that release of oxytocin results in a stronger contraction of the uterus which means the baby’s head gets pushed further into the cervix
- Which means cervix becomes more dilated, so more oxytocin gets released so the uterus starts to contract even more strongly → so cervix = more dilated
2ND EXAMPLE: blood clotting - once the change has begun, the homeostatic mechanism is designed to make the change even bigger
