Summary
Summary A* Homeostasis notes
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A* Homeostasis notes
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HomeostasisWhat is homeostasis?
The maintenance of a constant internal environment within restricted limits in organisms, in
response to changes in internal and external conditions
What in the body needs to be controlled?
Core body temperature, blood glucose concentration, stable blood pH and water potential
Give three reasons why homeostasis is important?
1) maintain enzyme activity and functions of other proteins
2) regulate water potential of blood and tissue fluid to prevent osmotic cell death
3) maintain stable blood glucose concentration to provide respiratory substrates
What is a coordinator?
Where information from various places is brought together and sends impulses out to stimulate
change
What is a response?
Outcome of the process
What is an effector?
A muscle or gland which brings about the changes needed?
What is a receptor?
What detects any deviation from the optimum point (stimulus) and sends impulses to a central base
What is a stimulus?
An external or internal change in conditions
Give an overview of feedback mechanisms?
Process by which a receptor detects a stimulus creating a desired change to the system, brought
about by an effector which often restores the optimum point
What is negative feedback?
Feedbacks which restore systems to their original level- when a change is produced which causes a
change in the stimulus detected by the receptor and turn the system off
Negative feedback systems have…
Separate mechanisms to control departures in different directions from the original state, giving a
greater deal of control
What is positive feedback?
Occurs when deviation from the optimum causes changes that result in an even greater deviation
from the normal
, Give an advantage of positive feedback?
A small stimulus can bring about a large and rapid response
AQA example= neurones
Stimulus leads to a small influx of sodium ions which increases the permeability of the neurone to
sodium ions causing more ions entering leading to a further increase in permeability and an even
more rapid entry of ions
What are the two principal coordination systems in animals?
The nervous system- rapid, and the hormonal system- slower
Describe these systems
Both interact to maintain constancy in the internal environment and both systems use chemical
messengers- the hormonal system exclusively and the nervous system through neurotransmitters
and chemical synapses
WYSAK about the hormonal system
Chemical messengers, produced in and secreted by glands, carried by the blood plasma, effect on
specific target cells, effective in low concentrations and often have long lasting effects
How do hormones have an effect on target cells?
1) bind to receptors on target cells
2) use the second messenger model
How do they bind to receptors on target cells?
These target cells have specific protein receptors on their cell surface membranes that are a
complimentary shape to a specific hormone
What is the second messenger model?
A two-step action where an initial hormone (messenger one) binds to a cell surface receptor causing
intercellular changes that produce a second messenger which has an effect in the cell
How is blood glucose concentration controlled?
By the pancreas and the liver
What is the pancreas made up of?
Cells which make the digestive enzymes but also have groups of hormone producing cells called
islets of Langerhans
What are the two types of these cells?
Alpha cells which are larger and produce glucagon, and beta cells which are smaller and produce
insulin
The role of the liver
Glycogenesis, glycogenolysis and gluconeogenesis
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