Hormones, F214, Biology, OCR

Detailed notes on the hormones section of the OCR F214 Biology specification.
Not the best notes if you just want a quick summary but hopefully they will of good use to others :) 

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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 cells may have receptors for one or more hormones or other chemicals.
When the hormone binds to the receptor, it results a response specific to that cell type.
Endocrine Glands: organs that secrete hormones directly in the blood e.g. pituitary, adrenal, ovaries,
adrenal, thyroid.
Exocrine Glands: organs that secrete products (NOT hormones) into ducts which lead directly into the
external site of action e.g. sweat glands, salivary glands, mammary glands, stomach, liver and
pancreas.
Endocrine vs. Exocrine Glands
Endocrine glands have secretory cells which Exocrine glands secrete their products into
directly pass secretions into the blood within ducts which carry them to their target site.
the nearest capillaries.
Endocrine products are released into the Exocrine products are released into the external
internal environment. environment.
Endocrine products produce slower responses Exocrine products produce faster responses as
as they have travel through blood stream. they go straight to target site.
Describe, with the aid of diagrams and photographs, the histology of the pancreas, and outline its
role as an endocrine and exocrine gland.
The Pancreas ­ Exocrine Gland a
The exocrine function is the manufacture and
secretion of pancreatic fluids which contain
digestive enzymes such as lipase, amylase and
trypsin and alkaline sodium hydrogen
carbonate. Small groups of cells called acini (1x
acinus) surround tiny tubules, in which they
synthesise and secrete the pancreatic fluids
into. The tubules join up to form a pancreatic
duct which carries the fluid into the duodenum.
The digestive enzymes can then hydrolyse
macromolecules of food, whilst the sodium
hydrogen carbonate helps to neutralise the
acidic contents from the stomach entering the
small intestine.

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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 liver and skeletal muscle
to hydrolyse glycogen into glucose so some can enter
the blood.…read more

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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 glucose concentrations were to get too high, the water potential of the blood would
become too high, causing water from cells to enter the blood.…read more

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This causes the vesicles to move towards
the plasma membrane and fuse with it, so that the insulin can be released by exocytosis.
Diabetes Mellitus
Compare and contrast the causes of Type 1 and Type 2 diabetes mellitus.
Diabetes mellitus is a disease in which the body is no longer able to control its blood glucose
concentration. This can lead to hyperglycaemia after a meal rich in sugars, and hypoglycaemia after
exercise or fasting.…read more

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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. Due to the
body's low pKa, they increase the acidity of the blood by so much that the body's buffering system
cannot keep up.…read more

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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 day.
However, small quantities have very large effects and most endocrine glands can secrete hormones
very quickly in response to stimuli, in order to help the organism survive.…read more

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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 system in order to supply tissues with
the oxygen and nutrients that they require. Waste products are also removed, such as carbon
dioxide, from the tissues by the blood, so that they do not accumulate and inhibit cell metabolism.…read more

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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 carbon dioxide levels in the blood: This increases
pH so is detected by chemoreceptors in the carotid
arteries, the aorta and the brain. The chemoreceptors
send fewer impulses to the cardiovascular centre.…read more

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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.…read more

Comments

Holly Leslie


this is really useful! cheers x

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