Communication and Homeostasis Flashcards
Receptor
A cell or protein on the cell surface membrane that detects a stimulus and creates action potentials (nervous impulse)
Effector
A cell that brings about a response
Stimulus
A change in an environment that causes a response
Response
Change in behaviour/physiology because of a stimulus
Internal environment
Conditions inside an organism
External environment
The conditions outside an organism
Cell signalling
Communication between cells to help them work together to coordinate their actions
Cell signalling process
- cell signalling can occur between adjacent cells or between distant cells
- to produce a response, receptors need to communicate with effectors
- cell surface receptors allow cells to recognise the chemicals involved in cell signalling
- the 2 communication systems that work by cell signalling are the neuronal and hormonal system
Nervous system
peripheral nervous system: nerves, ganglion
Central nervous system: brain, spinal cord
Messenger: electrical impulses
Endocrine system
Hypothalamus, pineal gland, pituitary gland, thyroid gland, thymus, adrenal gland, pancreas, ovary/testis
Messenger: chemical hormones
Communication mechanism
Neuronal: electrical impulses. Hormonal: hormones
nature of communication
N: electrical H: chemical
transmitted via
N: neurones. H: hormones (bloodstream)
speed of transmission
N: very rapid. H: slow
effect caused by response
N: short lasting. H: long lasting
Speed of response
N: rapid. H: slow
duration of communication
N: short lived. H: can be long term
duration of effect
N: short term + temporary H: short term + temp. or long term + permanent
Negative feedback
Normal level— level changes from normal— receptors detect change— communication via nervous or normal system— effectors response— levels back to normal
E.g. body temperature, BGL, osmoregulation
Positive feedback
Normal level— levels change from normal— receptors detect change— communication via nervous or normal system— effectors response — change amplified
E.g. blood clot formation, hypothermia, oxytocin+childbirth
Behavioural responses to maintain body temperature
- seek shade
- fan yourself
- wear more/less clothing
Physiological responses to maintain body temperature
- shivering
- sweating
Ectotherms
E.g. reptiles, fish
- can’t control their body temperature internally
- their internal temperature depends on the external temperature
- activity level is dependent on external temperature
- have a variable metabolic rate and they generate very little heat themselves
Endotherms
E.g. mammals birds
- can control their body temperature internally through homeostasis, and also change their behaviour
- internal temperature is less effected by external temperature
- activity level is dependent on external temperature
- have high metabolic rate and generate lots of heat themselves
- mainly use physiological
Physiological responses to temperature
• body temperature is maintained by the hypothalamus, it receives information from the hypothalamus
• Thermoreceptors in hypothalamus detect blood temperature
• Thermoreceptors in skin (peripheral temperature receptors) detect skin temperature
• Thermogenic set point in humans is 36.8+_0.5
Physiological response to reduce temperature
vasodilation
- supplies capillaries with a greater volume of blood, which then loses heat via radiation
- arterioles smooth muscle relaxes causing the vessels to dilate
sweating
- cools the skin by evaporation which uses heat energy from the body to convert water to water vapour
- therefore less effective in humid conditions
flattening hairs
- stops them from forming an insulating layer
- allows air to circulate over skim and heat to leave by radiation
Physiological response to increase temperature
boosting metabolic rate
- hair erector muscles contract, causing hairs to stand up
- this traps air and forms an insulating layer
shivering
- reflex action, muscles contract and relax rapidly, the metabolic reactions required to facilitate this generates heat
vasoconstriction
- arterioles smooth muscle contract causing the vessels to constrict and reduce blood flow
- blood is diverted through shunt vessels minimising heat loss via radiation
Changes to body temperature summary
Increase in body temp—> thermoreceptors in hypothalamus —> 1.increase sweating
| and skin detect change 2.Vasodilation
Normal body temp. 3.Hairs lie flat
|
Decrease in body temp —> thermoreceptors in hypothalamus —> 1.vasoconstriction
and skin detect change 2.Shivering
3.Skin hairs erect
Homeostasis
The maintenance of the internal environment within an optimum range
What does homeostasis control
- temperature
- blood pH
-blood glucose
Homeostasis control over temperature
Low temperature
- if temperature falls below the optimum range, enzyme activity declines
- decreased enzyme activity causes the rate of important reactions (e.g. respiration) to slow down
high temperature
- if body temperature rises above the optimum range, enzymes denature
- the higher temperature causes the hydrogen bonds that maintain the enzyme structure to break
- this alters the enzyme active site is the enzyme active site so the enzyme can no longer catalyse reactions e.g. respiration
Homeostasis control on blood ph
- if blood pH rises above (too alkaline) or falls below (too acidic) the optimum range, enzymes denature
- denatured enzymes can no longer catalyse important reactions
- optimum pH range is normally around pH7
- some enzymes have very different optimum ranges e.g. enzymes in the stomach have acidic optimum pH)
Homeostasis control of blood glucose
High blood glucose
- homeostasis maintains blood glucose concentration
- if blood glucose levels rise above the optimum range, the water potential of the blood is reduced
- low water potential in the blood causes water to diffuse out of the cells by osmosis and into the blood
- this makes cells flaccid and they die
Low blood glucose
- homeostasis maintains blood glucose concentration
- if blood glucose levels fall below the optimum range, there is not sufficient glucose for respiration
- respiration rate decline and energy levels fall
Negative feedback
The mechanism that restores systems to the original level
Steps involved in negative feedback
- Detect change
- change in the internal environment (stimulus) is detected by receptors
- receptors are stimulated when the level is too high or too low - Counteract change
- receptors send a signal to the effectors through the nervous system
- the effectors counteract the change
- negative feedback can maintain the internal environment within a specific range. If a change is too dramatic, negative feedback may not be able to prevent it
Multiple negative feedback mechanisms
Provide a greater degree of control of the internal environment
More control
- because they body can respond to multiple changes away from the optimum
E.g. body temperature can be reduced or increased by multiple mechanisms
Faster responses
- because the body can respond in more ways to a change away from the optimum
E.g. if the body temperature decreases, negative feedback can increase body temperature by both shivering and vasoconstriction
Is positive feedback homeostasis
No, positive feedback isn’t involved in homeostasis because it doesn’t keep your internal environment constant
