Control of blood glucose

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  • Created by: Hindleyc
  • Created on: 14-04-19 12:56
What controls blood glucose
the pancreas- detector and effector
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What is it
large pale coloured gland known as endocrine gland that secretes substances directly into blood stream as many bloody vessels near
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where is it found
in upper abdomen behind the stomach
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what does it produce
enzymes for digestion (protease, amylase, lipase) and independent hormones for regulating bloody glucose- insulin and glucagon so very important organ
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When studies under a microscope what is the pancreas
largely made up of cells that produce the digestive enzymes eg cells that secrete enzymes and cells that secrete hydrogen carbonate ions
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What are scattered throughout these cells
the groups of cells which secrete hormones which control blood sugar known as the islets of Langerhans
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What do they do
monitor and respond to blood sugar, not to do with digestion only blood glucose control- cells constantly monitor blood glucose conc
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what 2 types of cells does it contain
alpha that secretes hormone glucagon and Beta cells that secretes insulin
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What is there many of surrounding alpha and beta cells
many blood vessels (capillaries)
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What does blood glucose conc need to be
controlled at relatively constant levels
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if it drops too low
cells will be deprived of energy and die
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If levels rise too high
it lowers the water potential of the blood and creates osmotic problems that can lead to dehydration
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If high
secret insulin
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if low
secrete glucagon
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in a healthy human how much glucose per 100ml of blood
80-100 mg
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What are these limits
not broad (narrow limits) because conc of solutes important in WP
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If blood glucose falls below this
cells may be short of glucose
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If blood glucose goes much above this
normal behaviour of the cell is upset- WP too high so water into cell
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3 sources of blood glucose
Directly from the diet - in form of glucose resulting from breakdown of other carbohydrates, from breakdown of glycogen (glycogen stored in liver and muscles) excess glucose in diet converted into glycogen called glycogenesis or gluconeogenesis
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What is gluconeogenesis
this is production of new glucose from sources other than carbohydrates
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What can the liver make
glucose from glycerol (fattys acids) and amino acids
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Glucose to glycogen
glycogenesis when blood sugar rises- insulin
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Glycogenesis
making glycogen
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Gluconeogenesis
making new glucose
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Too much glucose
B cells secrete insulin so glucose goes into glycogen (glycogensis)
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If little glucose
A cells glucagon so glycogen into glucose - glycogenolysis
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What does amount of glucose flucatuate depending on
diet and level of mental and physical activity
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3 main hormones that operate to maintain a constant blood glucose level
insulin, glucagon and adrenaline
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Where is insulin secreted into
bloodstream to anywhere (all parts of body)
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What do the B cells of the IOL detect and how do they respond
rise in blood glucose, secreting hormone directly into blood plasma
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What is insulin
globular Protein
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What do almost all body cells (not red blood cells) have
glycoprotein receptors on their CSM that bind with insulin
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Mainly
muscles and liver cells have receptors complementary to insulin because only have receptors so will only affect these cells
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When it combines with receptors what does it bring about
change in the 3. structure of glucose transport protein channels=cause to change shpe&open&allow more glucose into cells (ones already there), An inc in no, carrier molecules in CSM, activation of enzymes that convert glucose to glycogen and fat
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How does it increase number of carrier molecules in CSM
Insulin binds to receptors on CSM intercellular chemical signal triggering fusion of carrier containing vesicles with CSM so can move and fuse so glucose can move by FD therefore less glucose in blood
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What does , addition glucose carriers do
increase glucose permeability so more glucose in cell
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As a result of what is brought about, how is the blood glucose level lowered
increasing rate of absorption of glucose into cells- especially muscle cells from blood, increasing respiratory rate of cells which therefore use up more glucose thus inc uptake of glucose from the blood (inc conc gradient)
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, if excess of glucose
Increase rate of conversion of glucose to glycogen as large so doesn't affect WP (glycogenesis) in the cells of the liver and the muscles or inc conversion of glucose to fat as if already high rate doesn't need any more so convert to glycogen/fat
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What is the effect of these processes is
to remove glucose from the blood and to return its level to normal
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What does this lowering of blood glucose level cause
B cells to reduce their secretion of Insulin (negative feedback) which is slower
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How does it cause it to decrease
by glucose going from blood to liver and muscle cells and store
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What do chemical signals trigger
formation of vesicles containing glucose carrier proteins
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further signal
vesicles fuse with CSM
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Therefore more
glucose moves from blood to cell
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Glucose to glycogen stores using
insulin
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Target cells for adrenaline
Liver and muscles
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Glucagon
liver
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Insulin
liver and muscle
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What does adrenaline do
Inc HR and BR so more respiration needed
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What there about
4 other hormones apart from glucagon that can increase blood glucose levels but best known is adrenaline
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When is adrenaline produced and what from
By adrenal gland at times of stress
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How does adrenaline raise blood glucose levels
Activating an enzyme that causes the breakdown of glycogen to glucose in the liver and inactivating an enzyme that synthesises glycogen from glucose (any that would make glucose)
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What do the alpha cells of the IOL detect
fall in blood glucose
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how do they respond to it
secrete the hormone glucagon directly into the blood plasma
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What cells only have receptors that bind to glucagon
liver
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so
only liver cells respond
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how do they respond
Activating an enzyme that coverts glycogen to glucose or increasing the conversion of AA and glycerol into glucose (glucogenesis)
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overall effect
therefore increase the amount of glucose in the blood and return to its normal level
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what do glucose and adrenaline follow
secondary messenger model
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What does the raising of the blood glucose level cause
A cells to reduce their secretion of glucagon (negative feedback)
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but what does this take
time for pancreas to detect and for liver to respond to glucagon
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What do the 2 hormones insulin d glucagon act in
opposite directions
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what does insulin do
lower the blood glucose level where as glucagon raises it
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So how are the 2 hormones said to act
antagonistically
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What is the system and what does this mean
self- regulating In that it is the level of glucose in the blood that determines the quantity of insulin and glucagon produced
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In this way what does the interaction of the 2 hormones allow
highly sensitive control of the blood glucose level
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What does the level of blood glucose fluctuate aroun
a set point because of the way negative feedback mechanisms work
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only when what happens is insulin secretion produced
when blood glucose level falls below the set point (negative feedback) leading to a rise in blood glucose
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In the same way only when levels exceed the set point what happens
glucagon secretion is reduced (negative feedback) leading to a fall in blood glucose
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What is the regulation of blood glucose an example of
how different hormones interact in achieving homeostasis
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How do hormones differ from each other
chemically
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But what certain characteristics do they have in common
produced by glands which secrete hormones directly into the blood- endocrine glands, carried in the blood plasma to target cells which have receptors on CSM that are complementary to the hormone, effective in V small quantities
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but what do they have
long lasting and widespread effects
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What is the secondary messenger model
mechanism used by 2 hormones involved in regulation of blood glucose (adrenaline and glucagon)
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how does it work
hormone is the first messenger that binds to specific receptors on the CSM of target cells to form hormone receptor complex then this activates an enzyme inside the cell that results in the production of a chemical that acts as a 2nd messenger
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What does this second messenger do
cause a series of chemical changes that produce the required response
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How does adrenaline act
in same way as glucagon except its a adrenaline receptor and muscle and liver cells
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overall concept of 2ndary messenger model
bind doesn't directly cause change- produces 2ndary messenger that causes change
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hormone =
primary
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what sometimes happens
just normal activation or inactivation
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steps
glucagon binds to receptor causing Adenyl cyclase and G protein to convert many molecules of ATP into many molecules of cyclic AMP (secondary messenger) that activates kinases allowing glycogen into glucose that enters blood stream
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steps
1 hormone approached transmembrane protein, fuses to receptor causing it to change shape on inside of membrane activating an enzyme called adenyl cyclase inside the membrane that converts ATP to cyclic AMP which acts as a second messenger
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in turn. what happens to the cyclic AMP
changes the shape of and activates protein kinase enzymes and these catalyse the conversion of glycogen to glucose
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What is diabetes
metabolic disorder caused by an inability to control blood glucose levels due to a lack of the hormone insulin or a loss of responsiveness to insulin (high to low)
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first form
type 1 (insulin dependent) due to body being unable to produce insulin
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when
that normally begins in childhood
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What may it be a result of
an autoimmune response where body IS attacks its own cells in this case B cells of IOL
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How quick
develops quickly over a few weeks
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what are symptoms like
symptoms normally obvious
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What can it be
genetic but autoimmune most common
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2nd type
Type 2 (insulin dependent) and is normally due to glycoprotein receptors on the body cells losing their responsiveness to insulin
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however what may it also be due to
inadequate (reduced) supply on insulin from pancreas
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when does it usually develop
in people over 40 years however incidence is increasing in adolescents due to poor diet and increase obesity
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how does it develop
slowly
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what are symptoms
normally less severe and may go unnoticed
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who are more likely to develop type 2 diabetes
overweight and is most common form
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how is type 1 controlled
injections of insulin
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why cannot it be taken by mouth
as it is a proteins and would be digested in the the alimentary canal so therefore has to be injected directly into the blood 2 or 4 times a day
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how much insulin is injected must be matched exactly to
glucose intake
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What if take too much insulin
his/her blood glucose can drop too low and this can result in unconsciousness
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So what are used to monitor blood glucose to ensure correct dose
Biosensors
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how is Type 2 controlled
by regulating the intake of carbohydrate in the diet and matching this to the amount of the exercise taken or injections of insulin or use of drugs that stimulate insulin production
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What do other drugs do
Slow down the absorption of glucose from the intestine
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How is it sometimes medicated
interfere with the sodium glucose co transporter occasionally drugs to stimulate production of insulin
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Glycogenesis
glucose to glycogen (liver removes G from blood)
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Glycogenolysis
glycogen to glucose ?(liver convert stored glycogen into glucose which diffuses into blood to restore normal blood glucose conc )
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Gluconeogenesis
Glucose from other source than carbs when supply of glycogen exhausted liver produce glucose from non-carb sources such as glycerol and amino acids
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large pale coloured gland known as endocrine gland that secretes substances directly into blood stream as many bloody vessels near

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where is it found

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what does it produce

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