Here are my notes on homeostasis. They are all of my notes for this topic condensed and arranged in a way that makes sense to me.

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Homeostasis: the maintenance of a stable internal environment within an organism.
Homeostasis has 2 main categories:
Behavioural homeostasis: behaviour to aid survival
Internal homeostasis (usually referred to as just homeostasis): usually a negative feedback loop
including neurons or hormones to maintain a stable internal environment.
Examples of homeostasis include; water balance, glucose levels, body temperature, blood pH and
[salt/ion] of the blood.
Homeostasis relies on coordination between organs and differentiated cells within them to maintain
a stable condition for the whole organism; and so there are specialized cells to monitor changes in
these conditions called Receptors. Neurones are cells which then relay the information while cells
which coordinate a response signal for a response from the appropriate effector cell.
Homeostasis relies on cell signalling and is achieved by hormones being secreted into the blood
streams and reaching cells in target organs. (E.g. the pituitary release FSH at puberty to cause ovaries
and testes to begin forming eggs and sperm)
Cell signalling: The ability of cells in one part of the body to pass "messages" to cells in other parts of
the body to initiate a response. It can also be defined as chemicals crossing a neuronal synapse.
Negative feedback e.g. temperature; when it falls receptors will be stimulated to bring temperature
back to normal. Negative feedback opposes the change and tries to get back to the normal.
Positive feedback is where instead of opposing the change when receptors are stimulated it
continues the change away from the normal; this further change increases the stimulus therefore
continuing the cycle. E.g. Childbirth when the head of a neonate presses against the cervix the
stretching stimulates receptors. These cause the anterior pituitary which acts as both effecter and
coordinator to release oxytocin. Oxytocin causes the uterus to contract more, the neonates head
stretching the cervix more thus causing more oxytocin to be secreted and so on.
Axon at rest

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Originating from either the coordinator or the receptor an electrical impulse will travel down the
axon when the positive ions rush back across the membrane to initiate an action potential.
What happens at the receptor?
Receptors are modified dendrites and with sufficient stimulus will open Na+ channels. This causes the
Na+ to flood in down the electrochemical gradient initiating a chain reaction.
It is the voltage change which initiates the chemical reaction.…read more

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Many drugs such as pain killing drugs affect the synapse. This is because they act like
neurotransmitters and compete with the actual neurotransmitters for the receptors, or the enzyme
of the synapse that is responsible for the breaking down of the neurotransmitters.
Temporal summation is where several action potentials are fired in a short time and so a greater
number of neurotransmitters are to be released.…read more

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Neuromuscular function...
To enable muscle contraction an action potential travels along a motor neurone to the muscle; here a
synapse is crossed like at a nerve junction (at the axon terminals). These are called motor end plates.
There are many neuromuscular functions on each muscle, the more neuromuscular junctions are
stimulated, the stronger the contraction. This is called gradation of response.
Thermoregulation an example of Negative feedback.
Humans are endotherms this means they are warm blooded and keep their body temperature within
strict limits.…read more

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In environments significantly colder than our body temperature we tend to wrap up warmly to
prevent radiative heat losses from our skin or by cold winds via convection.
Animals that live in extreme cold have natural insulation in the form of blubber while animals who live
in extreme heat tend to have larger surface areas for radiative heat loss.
Thermoregulation how it works...
The simple theory centre in the hypothalamus is stimulated by temperature changes.…read more

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Cell signalling has 2 types:
1. Local Signalling which includes paracine signalling and synaptic signalling.
2. Long Distance Signalling (hormonal) includes endocrine signalling.
Antigenic Communication is where antigens on the cells are recognised as self by white blood cells.
This leads to problems with transplant patients as the white blood cells cannot recognise the
antigens of transplant cells.
Hormones are released by endocrine glands and travel in the blood to a target organ with a specific
receptor or internal binding site.…read more

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Heart rate increase.
Conversion of glycogen to glucose to be stimulated.
Dilute the pupils.
How does it work?
1. Adrenaline binds with its specific receptor on the target cell which has enzymes attached
to it on the intracellular side.
2. This then activates the enzymes and so adrenaline is known as a first messenger
3. The enzyme adenyl cyclise catalyses a reaction which converts ATP into a form called
cyclic AMP or cAMP.
4.…read more

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Insulin is an example of negative feedback and without these homeostatic feedback loops blood
glucose would swing between highs and lows depending on our feeding patterns.
The problems with diabetes are; that the retina can be affected and glucose changes the viscosity of
the blood.
After a meal the digestive system breaks down sugars relatively quickly into glucose. However,
complex carbohydrates will take longer.…read more

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Its effects on the cell are:
It increases the cell's permeability to glucose as protein channels rise into the membrane.
Adenyl cyclise is activated.
cAMP activates enzyme controlled reactions.
Glycogenesis occurs as glucose is converted to glycogen.
Some glucose is converted into fat.
More glucose is used in respiration.
An average liver can store 75-100g of glycogen which is enough to supply the average person with
up to 12 hours under the influence of glucagon. Muscles store about 300g.…read more

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Obesity is a risk factor for type II diabetes as the non-receptitiveness to insulin means that
injections will become pointless.
A diet high in levels of sugar.
Family history
The production of insulin:
In the past we have relied on pig insulin, this caused problems for religious ground on pigs,
vegetarians while also having issues with contamination and allergic reactions.
In the present it is now produced by biotechnology and is perfectly complementary to insulin
The process...
1.…read more


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