132583
Descrição
Mapa Mental por harry_bygraves, atualizado more than 1 year ago
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Criado por harry_bygraves
mais de 11 anos atrás
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Control of
blood glucose 2
- Insulin is a small protein secreted by special cells called beta cells in the islets of
Langerhans, endocrine tissue within the pancreas. When the blood glucose
concentration rises above the set point, more insulin is secreted form the pancreas
- In order to act on cells, insulin molecules bind to an exposed glycoprotein receptor on
the cell surface membranes, in much the same way as a substrate binds to an enzyme.
The membrance-bound insulin brings about a number of cellular responses which
reduce the blood glucose concentrations. The repsonses include changes in both cell
surface membrane permeability and enzyme activity which lead to four main effects;
- 1. An increase in the uptake of glucose in amino acids into cells. 2.
An increase in the rate of cellular respiration and the use of glucose
as a respiratory substrate molecule. 3. An increase in the rate of
conversion of glucose to fat in adipose cells. 4. An increase in the
rate of conversion of glucose to glycogen in liver and muscle cells
- 1. An increase in the uptake of glucose in amino acids into cells. 2.
An increase in the rate of cellular respiration and the use of glucose
as a respiratory substrate molecule. 3. An increase in the rate of
conversion of glucose to fat in adipose cells. 4. An increase in the
rate of conversion of glucose to glycogen in liver and muscle cells
- Adrenaline. In times of acute stress or excitment, adrenaline is screted.
Adrealine causes the breakdown of glycogen in the liver, boosting blood
glucose concentrations
- The second messanger model. Both adrenaline and glucagon stimulate glycongenolsis in liver cells. this
hydrolysis of glycogen to glucose causes the blood glucose concentration to increase. Neither adrenaline nor
glucagon enter liver cells. Instead both hormones act by binding to specific receptors on the surface of the cell
surface membrane of liver cells. The binding of the first messanger activates adenyl cyclase. This is an enzyme
that accelerates the production of cyclic adenosine monophosphate (cAMP). cAMP is a small molecule that acts
as the second messenger within the cytoplasm. It duffuses through the cytoplasm of the liver cell where it iniates
a complex chain reaction that ends with the breakdown of glycogen to glucose phosphate,a source of glucose
- This second messenger model pathway involves
a complex chain reaction that produces a
cascade effect which amplifies the response to
the hormone. Throughout the chain, each
enzymes molecule activates many substrate
molecules which become the next enzyme in the
chain. This means that a small signal results in a
very large response- in this case, a rapid
increase in the blood glucose conc. Although
adrenaline and glucogon use the same second
messenger pathway, each hormone binds to its
own specific receptor site. owever, a amximum
production of cAMP by one hormone cannot be
increased any further by a second hormone
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