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Communication between cells can use either:
o Nervous system
Impulses sent along neurones
Results in a short lived response
Has specific nerve pathways
Secreted into the blood
Generally slower acting (one exception being adrenaline)
Long lasting response
Wide acting, with one hormone affecting a range of tissues.
Homeostasis the maintenance of constant internal conditions regardless of fluctuations
in external environment.
Negative feedback where any deviation from normal internal conditions triggers
mechanisms to oppose and counteract the change resulting in a return to optimum
Endotherm an organism that can maintain its own internal body temperature
regardless of external factor by use of homeostasis (e.g. rabbits).
Ectotherm an organism whose body temperature fluctuates with external temperature
and relies on external factors to maintain body temperature (e.g. lizards).
o Receptors to detect any changes (e.g. Thermoreceptors)
o A communication system (hormones and the NS)
o Effectors to respond to the change (muscles and glands)
Body temperature should be 37°C ± 0.5°C
Mostly under nervous control with only minor hormonal influence.
Some hormonal influence
o Adrenaline causes a short-term increase in metabolic rate.
o Thyroxine causes a long-term rise in metabolic rate (e.g. when a person moves
to a colder climate).
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Hormones (Blood Glucose Regulation)
Steroids Lipid soluble so are able to easily pass through phospholipid membranes
and effect cells.
Protein/Polypeptides Can not pass through cell membranes so need to use
Secondary (2°) messengers in order to effect cells.…read more
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Pancreas Responsible for blood glucose regulation.
o Exocrine gland Secretes enzymes into the pancreatic duct and then into the
small intestine to aid digestion.
o Endocrine gland
Islets of Langerhans
Alpha () Cells make/secrete GLUCAGON
Beta () Cells make/secrete INSULIN
Both insulin and glucagon are protein messengers so must use the secondary
messenger system to effect cells.
How Beta Cells secrete Insulin
1. K+ channels open in the cell membrane so potassium ions diffuse out.
Potential difference of -70mV.