Communication & Homeostasis Basics

Plants & Animals - increase chances of survival by responding to external environment changes & internal environment. e.g. temp
Means conditions optimal for metabolism (chem reactions).
Stimulus - any change in internal/external.

• Receptors detect stimuli.
• Specific - detect one particular stimulus. e.g. light, pressure etc.
• Many different types for different stimuli.
• Some are cells e.g photoreceptors connect to nervous system.
• some are proteins on cell surface membranes e.g. glucose receptors on pancreatic cells.

• bring a response to stimulus
• produce an effect
• e.g. muscle cells, cells in glands (pancreas)

• Receptors communicate with effectors via nervous / hormonal system or both.
• Both are examples of cell signalling.

Changes in external envir. can affect internal. e.g. blood + tissue fluid
Homeostasis - involves control systems
                       - keeps internal envir constant which is vital to function normally + to stop damage.

Important - maintaining core body temp as it affects enzyme activity. Enzymes control rate of metabolic reactions.

• Body temp too high (e.g. 40°C) - enzymes denature (molecules vibrate too much, breaks H bonds which holds 3D shape, active site changed + no longer works as catalyst). Metabolic reactions less efficient.
• Body temp too low - enzyme activity reduced. Rate of metabolic reactions slowed down.
• Highest rate of enzyme activity - optimum temp (about 30°C)

Important - maintaining glucose concentration in blood for respiration

• mechanism that restores to around norm.
• e.g. body temp kept within 0.5°C above/below 37°C
• change can't be too big b/c effectors can't counteract
  
• e.g. big body temp drop from prolonged cold weather - too big a change to counteract
  

• Amplifies change
• Effectors increase level away from norm
• Rapidly activates something

e.g. blood clot:

• Platelets activiated
• Release chemical
• More platelets activated
• Platelets quickly form blood clot at injury
• Negative feedback - body detects blood clot has formed.

Positive feedback - not involved in homeostasis b/c doesn't keep internal envir. constant.

Homeostatic systems - receptor, communication system, effector.
Receptor - detect too high/low
Communication system - sends stimulus from receptor to effector by hormonal/nervous sys.
Effector - respond to counteract change to norm.
Enzyme conditions - need to be kept constant to be optimum.
Negative feedback - mechanism that restores back to norm.
Positive feedback - amplifies change.