control of blood glucose concentration

-glycogenolysis

-glycogenesis

-gluconeogenesis

glycogenolysis- converting glycogen to glucose

glycogenesis- converting glucose to glycogen

gluconeogenesis- converting amino acids and glycerol to glucose

[liver does these conversions]

blood glucose concentration can be increased by

-carbohydrate-rich food → broken down →release glucose→ absorbed into blood

-glycogenolysis

-gluconeogenesis

blood glucose concentration can be decreased by

-respiration→ glucose used to release energy [exercise→ more glucose needed] [glucose is used]

-glycogenesis [glucose is stored]

blood glucose concentration is high

-Beta cells in the Islets of Langerhans detect high blood glucose concentration

-beta cells release insulin into the blood

-insulin binds to receptors on the plasma membrane of liver cells [/muscle cells]

-this causes more glucose transport proteins to be inserted in plasma membrane

-more glucose enters cells from the blood

-insulin increases uptake of glucose by liver cells [/muscle cells]

-insulin stimulates glycogenesis in the liver (the conversion of glucose to glycogen) [glucose stored as glycogen in cells]

-more glucose is used in respiration [increased respiration]

-insulin increases the rate of glucose to fat conversion

-when the blood glucose concentration returns to normal, insulin secretion decreases. [negative feedback]

This is negative feedback because the response reverses the original change.

what does insulin inhibit?

inhibits release of glucagon from alpha cells

consequence of high blood glucose concentration

-this lowers the water potential of the blood

-this causes water to leave the cells by osmosis

-this causes cells to be damaged

[use when asked why glucose concentration has to be maintained]

blood glucose concentration is low

-alpha cells in the Islets of Langerhans detect low blood glucose concentration

-alpha cells release glucagon into the blood

-glucagon stimulates the breakdown of glycogen to glucose (glycogenolysis)

-glucose is released into the blood

-glucagon stimulates gluconeogenesis

-glucagon stimulates increased respiration of fats

-when the blood glucose concentration returns to normal, glucagon secretion decreases.

[negative feedback]

what does glucagon inhibit?

inhibits release of insulin from beta cells

consequence of low blood glucose concentration

-reduces the availability of glucose for respiration

-reduces rate of respiration

-Less ATP produced

[can lead to dizziness]

what channels do beta cells have?

potassium ion channels

calcium ion channels

beta cell during resting state

-potassium ion channels are open and calcium ion channels are closed [like synapse when at rest]

-potassium ions diffuse out of the cell, making the inside of the cell more negative relative to the outside (-70mV)

how is the secretion of insulin controlled?

-when blood glucose concentration is high, glucose enters the beta cell through the glucose transporter protein (1) [facilitated diffusion]

-glucose is metabolised in mitochondria to produce ATP (2) [more glucose→increased respiration]

-ATP binds to potassium ion channels, causing them to close (3)

-potassium ions cannot diffuse out of cell

-the concentration of potassium ions increases inside beta cell

-plasma membrane becomes depolarised (becomes less negative →as theres more positive K+ ions)

-calcium ion channels open (4)

-calcium ions enters the beta cell and causes the vesicles containing insulin to fuse with plasma membrane

-insulin is released by exocytosis (5)