Homeostasis
Maintaining the Balance
Year 12 Biology
TERM 2
Homeostasis
noun
(Science: Biology)
(1) The tendency of an organism or a cell to regulate its internal conditions, usually by a system of
feedback controls, so as to stabilize health and functioning, regardless of the outside changing
conditions
(2) The ability of the body or a cell to seek and maintain a condition of equilibrium or stability within
its internal environment when dealing with external changes
(3) homeostasis is the maintenance of the constant internal environment which include the function
of kidney, liver, skin, and other body systems.
Positive Feedback
Positive feedback builds upon itself and
never leads to resolution and balance.
If the body’s systems relied on positive
feedback responses, homeostasis could
not be achieved.
So Positive Feedback is actually a
negative thing, most of the time...
Positive Feedback Mechanism
Negative Feedback
The human body functions through a series of negative feedback pathways. The human organ
systems work together to achieve homeostasis. There are a variety of mechanisms and vital functions
that are maintained through homeostasis; blood glucose, blood pH, blood pressure, body
temperature, O2 and CO2 levels, etc.
“What does the word “feedback” mean? With what do you associate this term?”
“What would you consider normal or acceptable range for your grades? What happens when you fall
outside of (below) that range?”
“What things/processes in the human body need to be kept within a particular range?”
The negative feedback system is about restoring balance.
Body Systems - Endocrine
Endocrine glands make chemicals called hormones and pass them straight into the bloodstream.
Hormones can be thought of as chemical messages.
From the blood stream, the hormones communicate with the body by heading towards their target cell to
bring about a particular change or effect to that cell. The hormone can also create changes in the cells of
surrounding tissues (paracrine effect). The endocrine system works with the nervous system and the
immune system to help the body cope with different events and stresses.
Some of the roles of the endocrine system include: Growth, Repair, Sexual reproduction, Digestion,
Homeostasis.
The endocrine system is a tightly regulated system that keeps the hormones and their effects at just the right
level. One way this is achieved is through ‘feedback loops’. The release of hormones is regulated by other
hormones, proteins or neuronal signals.
The released hormone then has its effect on other organs. This effect on the organ feeds back to the original
signal to control any further hormone release. The pituitary gland is well known for its feedback loops
The Internal Environment - Temperature
In humans, body temperature is
controlled by the thermoregulatory centre
in the hypothalamus.
It receives input from two sets of
thermoreceptors: receptors in the
hypothalamus itself monitor the
temperature of the blood as it passes
through the brain (the core temperature),
and receptors in the skin (especially on
the trunk) monitor the external
temperature.
Diabetes and homeostasis
Homeostasis and diabetes are related because of the system of homeostatic checks and balances
that allows for the proper rise and fall of glucose levels in the blood stream and within bodily tissues.
Three homeostatic imbalances that can lead to diabetes are:
1. When the body does not produce enough of the hormone insulin and sometimes glucagon.
2. When the body overproduces the hormone insulin.
3. When a person’s body possesses nonfunctional receptor sites within target cells that cause the
body to become insensitive to these same chemicals.
Example - Diabetes
Simulations
I don't feel so good…
Treadmill man
Outside guy