what is homeostasis

• maintenance of stable internal environment within restricted limits in organisms

• ensures cells function normally despite changes in external environment

why homeostasis is important

1. keeps internal environment constant for metabolic reactions

2. ensures cells function properly + avoid damage

3. helps organisms respond + adapt to external changes

control mechanisms in homeostasis

homeostasis coordinated by several diff control mechanisms, consisting of receptors, coordinators + effectors throughout body

roles of receptors, coordinators + effectors in homeostasis:

• receptors - sensory receptors detect stimuli + send signals to brain abt changes in internal environment ex. changes in blood pH + temperature

• coordinator - receives + interprets info from receptors + sends instructions to an appropriate effector

• effectors - muscles/glands that act on signals from brain + cause responses to reverse changes + regain equilibrium ex. sweating to reduce high temp

control mechanisms aim to maintain conditions around optimum point: point where system operates best

negative feedback systems

involve coordination between receptors + effectors to control conditions around set optimum points (system works best). derivation from optimum point leads to changes that bring system back to optimum point

how neg feedback works

1. receptors detect change in one direction ex. rising blood glucose

2. signals trigger effectors to produce responses that reverse initial change ex. releasing insulin = lower blood glucose

3. conditions return to set range

examples of neg feedback mechanisms

1. maintaining blood glucose conc

   • importance - glucose needed for respiration, too much glucose can affect water potential in blood + cells

   • how achieved - insulin + glucagon adjust blood glucose conc to maintain healthy supply of glucose

2. maintaining blood pH

   • importance - changes in pH can impair enzyme action

   • how achieved - adjustments made to acid-base balance in blood to maintain optimum pH

3. maintaining temperature

   • importance - changes in temp can impair enzyme action

   • how achieved - adjustments made ex. sweating/shivering to maintain optimum temp

4. water regulation

   • importance - too much/little water in blood + cells → cells burst/shrink bc osmosis

   • how achieved - water removed/reabsorbed from blood/tissue fluid to maintain optimum water pot.

positive feedback systems

amplifies changes not reversing them. deviation from optimum causes changes that result in even greater deviation from optimum point

how pos feedback works

1. initial change occurs ex. clotting factors release after blood vessel injury

2. effectors stimulated + enhance change ex. more clotting factors released

3. change continues until endpoint met ex. clot fully formed.

examples of pos feedback mechanisms

less common than neg feedback in homeostasis bc uncontrolled responses can disrupt body's equilibrium. tight regulation ESSENTIAL to prevent harm when changes intensify

• blood clotting - clotting factors activate further clotting

• childbirth - oxytocin activate more uterine contractions

cell signalling

process by which cells communicate. can occur between adjacent cells ex. when neurones release neurotransmitters to stimulate nearby nerve/muscle cells or between v distant cells

how cell signalling occurs between distant cells:

1. cells can communicate (releasing hormones)

2. hormones travel in blood + signal to target cells that may be far away

3. cell-surface receptors let cells recognise + respond to these hormones