15.1 The Principles of homeostasis Flashcards
What is homeostasis?
Maintaining of a dynamic equilibrium with small fluctuations over a narrow range of conditions
What are sensory receptors?
Cells detecting changes in the internal and external environment of an organism
What internal changes do sensory receptors monitor?
pH of the blood
Core body temperature
Concentrations of urea and sodium ions in the blood
What are effectors?
Muscles or glands that react to the motor stimulus to bring about a change in response to a stimulus
How does a negative feedback system work?
A small change in one direction is detected by sensory receptors
- > Effectors work to reverse the change and restore conditions to their base level
- > Initial stimulus is reversed
What are examples of a negative feedback system?
Control of blood sugar levels by insulin and glucagon
Temperature control
Water balance of the body
How does a positive feedback system work?
Sensory receptors detect a change in the internal environment
- > Stimulates effectors to reinforce the change
- > Increases response
What are two examples of a positive feedback system?
Blood clotting cascade
Childbirth and oxytocin
Can you explain the blood clotting cascade?
Blood vessel is damaged
- > Platelets stick to the damaged region
- > Release factors that initiate clotting and attract more platelets
- > Continues until a clot forms
Can you explain how a baby is born?
Head of the baby pushes against the cervix
- > Stimulates production of oxytocin
- > Oxytocin stimulates uterus to contract
- > Head of the baby is pushed even harder against the cervix
- > Triggers release of more oxytocin
- > Continues until baby is born
What does cell signalling allow?
Transfer of signals locally using neurotransmitters
E.g. Between neurones at synapses
Transferring signals across large distances using hormones
What is an example of signals being transferred across large distances?
Cells of pituitary glands secrete ADH
Acts on cells in the kidney
To maintain water balance in the body
What is homeostasis?
Coordinating the functions of organs to maintain a relatively constant internal environment
