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Key Words
Module 1 - Communication and Homeostasis
Cell - Secrete the hormone glucagon and are found in the islets of Langerhans.
Acetylcholinesterase - An enzyme in the synaptic cleft. It breaks down the transmitter substance acetylcholine.
Action Potential (An) - Is achieved when the membrane is depolarised to a value of about +40mV. It is an all-or-nothing response.…read more

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Carbon dioxide for example if it builds up in the tissue fluid outside the cells could disrupt the
activity of enzymes by altering the pH of the environment around the cell
Maintaining the internal environment of cells
o Composition of tissue fluid is maintained by blood
The movement of blood transports substance to and from the cells
So any waste or toxins accumulating in tissue fluid are likely to enter the blood and be carried away
o To prevent their accumulation in the blood they…read more

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This destabilises the system and is usually harmful
o For example when the body gets too cold
Below a core temperature enzymes become less active
If they are less active the exergonic reactions that release heat are slower and
release less heat
o The body cools further, slowing downing the enzyme controlled
reactions even more
So the body temperature spirals downwards
Sometimes it can be beneficial
o At the end of pregnancy to bring about the dilation of the cervix, as it begins to stretch…read more

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Sweat glands in skin
If core body temperature is too high, they secrete more sweat onto the skin, the water in which evaporates using heat from blood to
supply latent heat of vaporisation
If core body temperature is too low, less sweat is secreted , less evaporation of water, so less loss of latent heat
o Lungs, mouth and nose
If core body temperature is too high, panting increases evaporation of water from lungs, tongue and other moist surface using
latent heat as in sweat.…read more

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The Endocrine System
Signalling via hormones
o The endocrine system is another communication system in the body
It uses blood circulation to transport its signals
This means it can be transferred all over the body
o The signals released by the endocrine system are called hormones
Hormones are released from endocrine glands
These are ductless glands - they consist of a group of cells that produce and release
hormones straight into the blood capillaries that surround the gland
Endocrine or exocrine
o There are two…read more

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These have a variety of roles in the body:
The mineralocorticoids
o Help to control the concentrations of sodium and potassium in the blood
Example is Aldosterone
The glucocorticoids
o Help to control the metabolism of carbohydrates and proteins in the liver
Example is Cortisol
The Regulation of blood glucose
The Pancreas
o Is a small organ lying below the stomach
It has both exocrine and endocrine functions
Secretion of enzymes
o The majority of pancreatic cells manufacture and release digestive enzymes
This is its…read more

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A low blood glucose concentration is detected by cells
In response the cells secrete the hormone glucagon
Its target cells are the hepatocytes
o They have the specific complementary receptor for glucagon
The effects of glucagon on the cell are
o Conversion of glycogen into glucose
Glycogenolysis
o Use of more fatty acids in respiration
o The production of glucose by conversion from amino acids and fats
Gluconeogenesis
The overall effect of these changes is to increase the blood glucose concentration
Regulation of insulin levels…read more

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It usually starts in childhood
o Thought to be a result of an autoimmune response in which the body's own immune system attacks the cells and destroys them
It may also be a result from a viral attack
o The body is then no longer able to manufacture sufficient insulin and cannot store excess glucose as glycogen
Type 2 Diabetes
o Also know as non-insulin-dependent diabetes
o A person with this type of diabetes can still produce insulin
However as people age their responsiveness to…read more

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This has a set frequency varying from person to person, at which it initiates waves of excitation
The frequency of waves is typically 60 - 80 per minute
o However the frequency of these excitation waves can be controlled by the cardiovascular centre in the
medulla oblongata
o There are many factors that affect heart rate
Movement of the limbs is detected by stretch receptors or muscle spindles in the muscles
These send impulses to the cardiovascular centre informing it that extra oxygen may soon…read more

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