endocrine system

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define the following key terms

Hormones Molecules that are released in the endocrine glands directly into the blood. They act as messengers carrying a signal from the endocrine gland to a specific target organ or tissue.   

Endocrine gland A gland that secretes hormones directly into the blood. They have no ducts   

Exocrine gland   A gland that secretes molecules into a duct that carries the molecules to where they are used  

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how must the signal be targeted?

The cell receiving the hormone must have a specific complementary receptor on their plasma membrane  where the hormone can bind. The cells that have these specific receptors are called target cells and are grouped as a target tissue

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what are the 2 types of hormones involved?

protein and peptide hormones and derivatives of amino acids- not soluble

steroid hormones- can pass through the membrane

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describe and explain the action of adrenaline

Adrenaline is an amino acid derivative and it is unable to enter the target cell, therefore it may cause an effect inside the cell without being in the cell itself,

Adrenaline receptor is complementary to the shape of adrenaline and it is associated with an enzyme on the inner surface of the cell membrane called adenyl cyclase

Adrenaline binds to the specific receptor on the cell membrane, the adrenaline molecule is called the first messenger

It then activates the enzyme adenyl cyclase and converts ATP into cyclic AMP (cAMP). This is the second messenger.

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what is the function of the adrenal glands?

The adrenal glands are found just above the kidneys. Each can be divided into the medulla and cortex region

  medulla Found in the centre of the gland the cells release adrenaline in response to stress or shock It can effect us in the following way relax smooth muscles in bronchioles increase stroke volume of heart increase heart rate dilate pupils cause hair on body to erect

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what is the function of the adrenal glands?

cortex

It uses cholesterol to produce certain hormones which have a variety of roles:

mineralocortocoids help control concentration of potassium and sodium in the blood

the glucocortides help to control the metabolism of carbohydrates and proteins in the liver

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what is the pancreas?

A small organ lying below the stomach and it has endocrine and exocrine functions

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describe the pancreas excretion of cells

The exocrine function of the pancreas is to manufacture and release digestive enzymes. The pancreatic duct carries the fluid containing the enzymes into the first part of the small intestine.

It contains the following enzymes:

amylase

trypsinogen

lipase

It also contains sodium hyrogencarbonate which makes it an alkaline and helps to neutralise the contents of the digestive system.

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describe the secretion of hormones in the pancreas

The islets of Langherns in the pancreas contain the following types of cells. Alpha cells that manufacture and secrete the hormone glycogen. Beta cells that manufacture and secrete the hormone insulin. The islets are well supplied with blood capillaries meaning the hormones are directly secreted into the blood. This is the endocrine function.

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describe the control of blood glucose

The concentration of blood glucose is carefully regulated. The cells in the islets of Langerhans monitor the concentration of glucose in the blood. The normal concentration is 90mg 100cm-3. If the concentration rises or falls then alpha and beta cells detect the stimulus and release a hormone.

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What happens if glucose is to high

Beta cells detect a high blood glucose, in response to this they secrete insulin.

The target cells are: liver cells ,muscle cells and body cells in the brain and they all posses the specific membrane bound receptor for insulin

When the insulin binds this activates adenyl cyclase in which coverts ATP to cAMP. This activates a series of enzyme controlled reactions in the cell:

  • more glucose channels are placed into the cell surface membrane
  • more glucose enters the cell
  • glucose is converted into glycogen
  • more glucose is converted to fats
  • more glucose is used in respiration

The increased entry of glucose through the specific channels reduces the blood glucose concentration.

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what happens if glucose is to low

A low blood glucose concentration is detected by alpha cells, in response they secrete the hormone glucagon and  it's target cell is hepatocytes (liver cells) which posses the specific receptor for glucagon.

The effects include:

  • conversion of glycogen to glucose
  • use of more fatty acids in respiration
  • the production of glucose by conversion from amino acids and fats

The overall effect of these changes is to increase the blood glucose concentration.

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