Hormonal Communication - OCR A-Level Biology

what is the endocrine system?

communication using hormones as signalling molecules

what are the two types of hormone?

protein and peptide hormones and steroid hormones

which type of hormone can enter cells and which type are not soluble so bind to receptors on the surface membrane?

protein hormones are not soluble so bind to receptors but steroid hormones enter the cell and have a direct effect on DNA

what is different about endocrine glands?

they are groups of cells without ducts that are associated with capillaries

what is the 1st messenger?

non steroid hormones that bind to receptors on the cell surface membrane

what is the 2nd messenger?

the signalling molecule released inside the cell after the signal from the 1st. the 2nd messenger stimulates activity in the cell

describe the chain of events after a 1st messenger binds to the cell

They activate a G protein that activates an effecter (commonly adenyl cyclase) than converts a molecule into the 2nd messenger. ATP is used to convert the molecule into cAMP the 2nd messenger. This can act directly or start a series of enzyme controlled reactions

what are the two parts of the adrenal gland?

the adrenal cortex and adrenal medulla

what are the three layers of the adrenal cortex?

the zona glomerulosa, zona fasciculata and zona reticularis

what is secreted in the andrenal medulla?

adrenaline and noradrenaline

what type of hormones are produced by the adrenal cortex?

steroid based hormones produced using cholesterol

how do steroid hormones act in cells?

They dissolve in the cell surface membrane and bind with a specific receptor in the cytoplasm, these enter the nucleus and bind to another receptor. This stimulates production of mRNA which codes for protein synthesis

what do mineralocorticoids do?

control concentrations of Na+ and K+ in the blood and contribute to maintaining blood pressure

what do glucocorticoids do?

help control metabolism of carbs, fats and proteins in the liver

what do precursor androgens do?

they are taken up by ovaries or testes and converted to sex hormones

what is the effect of adrenaline on the body?

increased heart rate, dilated pupils, increased mental awareness and body hair standing up

what is the exocrine function of the pancreas?

exocrine cells are in small groups called acinus that group together in lobules with a tubule at the centre. These tubules form the pancreatic duct that secretes enzymes

what is the benefit of the fluid from the pancreas being alkaline?

it helps neutralise the acidic contents of the digestive system

what is the endocrine function of the pancreas?

islets of langerhans contain alpha and beta cells that secrete glucagon and insulin

what do beta cells in the pancreas secrete?

insulin

what do alpha cells in the pancreas secrete?

glucagon

which of insulin and glucagon reduces blood glucose concentration?

insulin

how do beta cells release insulin?

Potassium ions flow out of channels in the cell surface membrane. When blood glucose concentration is high glucose moves into the cell where it is metabolised to produce ATP which closes the potassium channels. Because the potassium ions accumulate the potential difference across the cell membrane is increased which causes the calcium ion channels to open so calcium enters the cell. When these open vesicles of insulin fuse with the cell membrane releasing insulin by exocytosis.

what is the normal blood glucose concentration?

4-6 mmoldm-3

what is the difference between hypoglycaemia and hyperglycaemia?

hypo is when the blood glucose concentration drops and stays low too long. hyper is when blood glucose concentration is too high which can lead to organ damage.

which hormone is released when the blood glucose concentration is too low

glucagon

what happens when insulin binds to a receptor?

It activates tyrosine kinase which causes phosphorylation of inactive enzymes in the cell and a series of enzyme controlled reactions take place

What is the effect of insulin on the cell?

more glucose transporter proteins are are placed on the cell surface membrane so more glucose enters the cell, glucose is converted to glycogen for storage (glycogenesis) and more glucose is used in respiration

what is the role of glucagon?

alpha cells detect low blood glucose concentration and secret glucagon which targets hepatocytes and binds to receptors on their surface which stimulates a G protein that activates adrenal cyclase. ATP is used to convert inactive molecules into cAMP and phosphorylase A converts glucagon to glucose (glycogenolysis)

what type of feedback is used to maintain blood glucose concentration?

negative feedback

on which cells does insulin act?

liver and muscle cells

what is diabetes?

when the body cannot produce enough insulin to control blood glucose concentration

what is type 1 diabetes?

This type usually starts in childhood, they are insulin dependent and must inject insulin several times daily. Glucose cannot be broken down so they may experience a long period of high blood glucose concentration. The opposite of this is that when blood glucose concentration is low there is no reserve of glycogen so they may experience a hypo

what is type 2 diabetes?

When not enough insulin is produced so the blood glucose concentration is permanently raised. Obesity, lack of exercise and genetics can contribute to type 2

What are treatment options for type 1 diabetes?

insulin injections, blood glucose concentration monitoring or an insulin pump that pumps insulin through a permanently inserted needle, islet cell transplants (beta cells implanted to produce insulin), complete pancreas transplant or recently stem cell use developments mean new beta cells could be produced.

What are treatment options for type 2 diabetes?

changes in lifestyle, weight loss, exercise and medication can be used. Insulin injections may also be necessary.

Where is insulin for diabetics use sourced?

Bacteria that have been genetically modified produce it. This is cheaper and poses less risks than extracting it from the pancreas of other animals