Homeostasis Flashcards
What is homeostasis?
> The maintenance of an internal environment within restricted limits in organisms
What is negative feedback?
> Negative feedback is when the change produced by the control system leads to a change in the stimulus detected by the receptor and turns the system off
What is positive feedback?
> Positive feedback occurs when a deviation from an optimum causes changes that result in an even greater deviation form the normal
The role of the liver in regulating blood sugar
> The pancreas produces the hormones insulin and glucagon, and it is in the liver where they have their effects
> There are 3 important processes associated with regulating blood sugar which takes place in the liver:
• Glycogenesis
• Glycogenolysis
• Gluconeogenesis
Glycogenesis ?
> Conversion of glucose into glycogen
> When blood sugar concentration is higher than normal the liver removes the glucose and converts it into glycogen
Glycogenolysis ?
> Glycogenolysis is the breakdown of glycogen to glucose
> When the blood glucose concentration is lower than normal, the liver can convert stored glycogen back into glucose which diffuses into the blood to restore the normal bloody glucose concentration
Gluconeogenesis ?
> Gluconeogenesis is the production of glucose from sources other than carbohydrates
> When it’s supply of glycogen is exhausted, the liver can produce glucose from sources such as glycerol and amino acids
Insulin and the Beta cells of the pancreas
> When glycoprotein receptors combine with insulin, insulin brings about:
• A change in the tertiary structure of the glucose transport carrier proteins, causing them to change shape and open, allowing more glucose into the cells by facilitated diffusion
• A rise in insulin concentration results in the vesicles fusing with the cell surface membrane so increasing the number of glucose transport channels
• Activation of the enzymes that convert glucose to glycogen
Glucagon and the Alpha cells of the pancreas
> The alpha cells of the islets of langerhans detect a fall in blood glucose concentration, glucagons actions include:
• attaching to specific protein receptors on the cell-surface membrane of liver cells
• activating enzymes that convert glycogen to glucose
• activating enzymes involved in the conversion of amino acids and glycerol to glucose (Gluconeogenesis)
Role of adrenaline in regulating the blood glucose level
> Adrenaline is produced by the adrenal glands
> Adrenaline raises the blood glucose concentration by:
• attaching to protein receptors on the cell-surface membrane of target cells
• activating enzymes that cause the breakdown of glycogen to glucose
Secondary messenger model
( Adrenaline and glucagon )
> Adrenaline binds to a protein receptor within the cell-surface membrane of a liver cell
> This causes the protein to change shape on the inside of the membrane
> The change of protein shape leads to the activation of an enzyme called adenyl cyclase
> This converts ATP to cyclic AMP
> This cAMP acts as a secondary messenger that binds to protein kinase enzyme, changing its shape
> This catalyses the conversion of glycogen to glucose which moves out of the liver cell by facilitated diffusion
