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Hormones
Define the terms endocrine gland, exocrine gland, hormone and target tissue.

Hormone: a chemical messenger which travels to the target tissue via the bloodstream e.g.
oestrogen, testosterone, adrenaline.

Target Tissue: some or all cells in the tissue express receptors that are complementary in shape to a
specific hormone, though…

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The endocrine function is the secretion of the
hormones insulin or glucagon in response to blood
sugar levels. Areas of the pancreas called islets of
Langerhans contain different types of cells, including
beta-cells and alpha-cells. When blood sugar levels are
too low, alpha-cells secrete glucagon into the
bloodstream, stimulation the…

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- Insulin also causes more glucose to be converted into fats and increased glucose uptake by
respiring cells.
- These effects cause the blood glucose concentration to fall, which is sensed by beta-cells and they
reduce their secretion of insulin ­ this is a negative feedback mechanism.
- If blood…

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ion voltage gated channels to open so that calcium ions diffuse into the cell from the surrounding
tissue fluid and bind to receptors on the vesicles of insulin. This causes the vesicles to move towards
the plasma membrane and fuse with it, so that the insulin can be released by…

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- Ketoacidosis: the absence of insulin causes fatty acids to be released from adipose tissue, which
go to the liver to be converted into ketone bodies. These bodies can be used in respiration in the
absence of glucose but in diabetics, they are produced faster than they are used up.…

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bilayer. Therefore, the receptors for steroid hormones are in the cell cytoplasm. Protein hormones
are not soluble in lipids so their receptors are on the outer surface of the membrane of their target
cell.
The concentrations of hormones within the blood are very small and very little is secreted each…

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for eczema and asthma.
- Mineralocorticoids: Involved in regulation of potassium and sodium levels in the blood.

Control of Heart Rate in Humans

Outline the hormonal and nervous mechanisms involved in the control of heart rate in humans.

The role of the heart is to pump blood around the circulatory…

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cardiovascular centre, informing that extra oxygen may soon be needed.
- Adrenaline: Hormone secreted by adrenal glands in response to stress, shock, anticipation or
excitement. The presence of adrenaline in the blood increases heart rate in order to prepare the
body for activity.

Stimuli that decrease heart rate:
- Low…

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- These drugs can also improve sports performances that require steadiness and concentration, such
as snooker. However, they are banned from this sport as they could give an unfair advantage.

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Holly Leslie

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this is really useful! cheers x

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