Organisms Respond To Changes In Their Environments: - Hormones And The Regulation Of Blood Glucose Concentration

- Hormones and their mode of action - 

Hormones differ chemically but there are characteristics which would be the same also. 

Hormones :

- Produced in glands // secrete hormones directly into blood

- Carried in blood plasma to cells which are acted on // target cells // specific receptors on their cell-surface membrane // complementary to specific hormones.
- Effective in very low concentrations // widespread // long-lasting.

 Second Messenger Model 

2 hormones are used - Adrenaline and glucagon 

1. Adrealine binds to the transmembrane protein receptor within the cell-surface membrane of the liver cell. 
2. Binding of the adrealine causes the protein to change the shape on the inside of the membrane
3. Change in shape of the protein leading to the activation of an enzyme - adenly cyclase // activated adenly cyclase converts ATP to cyclic AMP (cAMP) 
4. cAMP acts as second messenger that binds to the protein kinase enzyme, its activiated by changing its shape.
5. Active protein kinase enzyme catalyses the conversion of glycogen to glucose which moves out of the liver cell // facilitated diffusion // in to the blood through channel proteins. 

Role of the Pancrease in regulating blood glucose 

It produces enzymes - 

Protease, amylase and lipase for digestion and hormones. 

Insulin and glucagon for regulating blood glucose concentration. 

There are groups of hormone-producing cells - islets of Lnagerhans - cells of the islets of Langerhans:

- ɑ cells, larger and produce the hormone glucagon

- 𝛽 cells, smaller and produce the hormone insulin 

Role of the liver in regulating blood sugar 

There are three important processes involved with regulating blood sugar which takes place in the liver:

Glycogenesis - this is the conversion of glucose into glycogen. 

This occurs when the blood glucose concentration is higher than normal. The liver removes the glucose from the blood and converts it into glycogen. 

Glycogenolysis - this is the breakdown of glucagon into glucose.

This occurs when the blood glucose concentration is lower than normal. The liver converts glycogen into glucose which is then diffused into the blood. 

Gluconeogenesis - this is production of glucose from sources other than carbohydrates. 

This occurs when glycogen supply is exhausted. The liver produces glucose from non-carbohydrate sources - amino acids and glycerol. 

Regulation of blood glucose concentration 

Factors that influence blood glucose concentration

1. Directly from the diet = glucose is absorbed from the hydrolysis of carbohydrates 
2. From the hydrolysis of glycagon in the small intestine = glycogenolysis // stored in liver and muscle cells 
3. From gluconeogenesis 

Insulin and the 𝛽 cells of the pancreas 

when combined with receptors insulin brings about:

- Change in tertiary strucute of the glucose transport carrier proteins - changing shape and open - allows more glucose into the cells by facilitated diffusion.

- Increase in number of carrier proteins responsible for glucose transport in the cell-surface membrane. Protein from which these channels are made is part of the vesicles. // rise in insulin concentration the vesicles fusing with the cell-surface membrane increasing the number of glucose transport channels. 

- Activation of enzyme that convert glucose to glycogen and fat. 

Blood glucose is lowers through the following ways:

- Increasing the rate of absorption of glucose into the cells - muscle cells

- Increasing rate of respiration of the cells // uses more glucose // increasing the uptake from the blood

- Increasing glycogenesis in liver and muscle cells

- Increasing the rate of conversion of glucose to fat. 

The processes taking place = Negative feedback // removal of glucose reduced the secretion of insulin from 𝛽 cells. 

Glucagon and the ɑ cells of the pancreas 

ɑ cells detect the fall in blood glucose concentrations releasing the hormone glycogen directly into the blood plasma. 

Glycogen action include: 

- Attaching to specific protein receptors on cell-surface membrane of liver cells 

- Activating enzymes convert glycogen to glucose 

- Activating enzymes involved in conversion of amino acids and glycerol into glucose = glyconeogenesis 

This returns the blood glucose concentration to the optimum. 

Role of adrenaline in regulating the blood glucose level 

Adrenaline raises the blood glucose concentration by:

- Attaching to protein receptors on the cell-surface membrane of target cells 

- Activating enzymes that causes the breakdown of glycogen to glucose in the liver. 

Adrenaline is produced when there is a period of excitement or stress. 

Hormone interaction in regulating the blood glucose

Insulin and glycagon act in opposite directions = antagonistically 

These two hormones are sensitive to control of the blood glucose concentration // blood glucose concentration is not constant there are fluctuations around the optimum temperature. 

When writing about negative feedback its important to mention that the secretion of a hormone - insulin - would result in the reduction of its own secretion.