Cell Signalling

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  • Created by: Siobhan
  • Created on: 15-01-13 21:08
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Cell Signalling
Communication between cells can use either:
o Nervous system
Impulses sent along neurones
Very fast
Results in a short lived response
Has specific nerve pathways
o Hormones
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
conditions.
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).
Homeostasis requires:
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)
Thermoregulation
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.
2.…read more

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