What are the properties of hormones?
- Produced in glands , secrete hormones directly into the blood (endocrine glands)
- Carried in the blood plasma to the cells on which they act (target cells - specific receptor on their cell surface membrane that is complmentary to hormone)
- Effective in low concentration but have widespread and long-lasting effects
What is the second messenger model?
Mechanism is used by two hormones involved in the regulation of blood glucose concentration (adrenaline and glucagon)
Steps of the second messenger model:
- Adrenanline binds to the transmembrane protein receptor within the cell-surface membrane of liver cell
- Binding of adrenanline causes the protein to change shape of the inside of membrane
- Change of protein shape leads to the activation of an enzyme called adenly cyclase
- Activiated adenly cyclase converts ATP to cyclic AMP (cAMP)
- cAMP acts as a second messenger that binds to the protein kinase enzyme , changing its shape and activating it
- Active protein kinase enzyme cataylses the conversion of glycogen to glucose (glycogneolysis)which moves out of liver cell by faciliated diffusion and into the blood by channel proteins
Diagram of second messenger model
Appearence of pancreas
It is a large, pale-coloured gland that is situated in the upper abdomen behind the stomach
What is the function of the pancreas?
It produces enzymes (protease, amylase and lipase) for digestion and hormones (insulin and glucagon) for regulating blood glucose concentration
What is seen under the pancreas microscopically?
- Made up largely of cells that produce its digestive enzymes
- Scattered throughout the cells are groups of hormone-producing cells known as islets of Langerhans
What are the cells of islets of Langerhans inclucde?
- Alpha cells which are larger and produce the hormone glucagon
- Beta cells which are smaller and produce the hormone insulin
Where is the liver located in?
Below the diaphragm
Has a mass up to 1.5kg and made up of cells called hepatocytes
What is the role of the liver?
- Serves a variety of roles
- Regulating blood glucose concentration
- While the pancreas produce hormones of insulin and glucagon its the liver thar has the effects
What are the three important processes regulating the blood sugar which takes place in the liver?
What is glycogensis?
It is the conversion of glucose into glycogen
When does glycogenesis happens?
When the blood glucose concentration is higher than normal
Liver removes glucose from the blood and coverts to glycogen
It can store 75-100g of glycogen which is sufficient to maintain human blood glucose concentration for 12 hours in absence of other sources
What is glycogenolysis?
It is the breakdown of glycogen to glucose
When does glycogenolysis happen?
When the blood glucose concentration is lower than normal
Liver can convert stored glycogen back into glucose
This can diffuse into the blood to restore the normal blood glucose concentration
What is gluconeogenesis?
It is the production of glucose from sources other than carbohydrate
When does gluconeogenesis happen?
When its supply of glycogen is exhausted
The liver can produce glucose from non-carbohydrate sources such as glycerol and amino acids
What is glucose a source for?
It is a substrate of respiration
providing the source of energy for almost all organisms
Therefore, it is essential that blood of mammals contains a relatively constant concentration of glucose for energy
What happens if the blood glucose concentration falls below the normal?
Cells will be deprived of energy and die especially brain cells are sensitive to this as they only respire glucose
What happens if the blood glucose concentration rises too high?
It lowers the water potential of blood and creates osmosis problems
causes dehydration and equally dangerous
Wha factors influence the blood glucse concentration?
This is where blood glucose from from three sources
- Diet - in form of glucose absorbed following hydrolysis of other carbohydrates such as starch, maltose and sucrose
- Glycogneogensis (hydrolysis in small intestine of glycogen) stored in lvier and muscle cells
- Gluconeogenesis - which is the production of glucose from sources other than carbohydrates
What is insulin?
A globular protein made up of 51 amino acids
What cells do not have glycoprotein receptors on cell surface membrane?
Red blood cells
Almost all body cells have this
What happens when the insulin binds into the glycoproteins receptor on cell-surface membrane ?
- A change in tetiary structure of gluocse transport carrier proteins , causing them to change shape and open
- This allows glucose to move in cell by facilitaed diffusion
- Increase in carrier proteins responsible for transport of cell-surface membrane. At low insulin , protein which channels are part of membrane of vesicles
- A rise in insulin concentration result in these vesicles fusing increasing no of glucose transport chain
- Activation of enzymes to convert glucose to glcygoen and fat
How is blood glucose concentration is lowered in one or more of the fllowing ways?
- Increasing rate of absorbption of glucose into muscle cells
- Increasing respiration rate of cell using more glucose
- Increasing the conversion of glucose into glycogen (glycogenesis) in the cells of liver and muscles
- Increasing the rate of conversion of glucose to fat
What is the glucagon’s actions at secreting at blood plasma?
- Attaching specific protein receptor on cell-surface membrane of liver cells
- Activating enzymes that convery glycogen to glucose
- Activating enzymes involved in the conversion of amino acid and glycerol into glucose (=gluconeogensis)
What is the effect of adrenanline in blood gluocse concentration?
When is adrenanline produced and produced by?
Produced by the adrenal glands
This is produced by times of excitment and stress
Where is the adrenal glands located at?
Above the kidney
How does adrenaline gland increase the blood glucose concentration by?
- Attaching to protein receptors on cell surface membrane of target cells
- Activating enzymes that causes the breakdown of glycogen to glucose in liver
How does insulin and glucagon hormones act anatgonistically?
The system is self-regulating through negative feedback
The concentration of glucose in blood determine the quantity of insulin and glucagon produced
Only when falls - insulin produced
Only when rises - glucagon produced
Explain why the events shown in diagram can be described as an example of negative feedback?
Because it has changes to bring it back to normal level
It changes from the normal
What happens if blood glucose concentration increases above the normal?
- B cells (islets of Langerhans) detect the change (receptors)
- B cells release insulin (found in blood plasma)
- This targets organs of liver and muscles
- This increase the glucose uptake
- Increase the glucose transport proteins in all cells
- Increase glycogenesis
- Increase rate of respiration
- This decreases the blood glucose level
What happens if blood glucose concentration decreases above the normal?
- Alpha cells in iselts of Langerhans detect the change
- Alpha cells release glucagon in blood plasma
- Target organs liver and muscles
- This increase glycogenolysis (glycogen to glucose)
- This decreases glcuose uptake
- Decrease rate of respiration
- IGluconeogenesis - glucose from amino acids + glycerol
- Decrease glucose transport proteins
What processes increase during second messeger model?
Adrenanline acts as a 1st messenger