C2. Control of Blood Glucose Concentration

Question 1

Glucose concentration in the blood
All cells need a constant _______supply to work-so blood glucose concentration must be carefully controlled. The concentration of glucose in the blood is normally around 90 mg per 100 cm³ of blood. It’s monitored by cells in the ______________. Blood glucose concentration rises after ________ ______ containing ________________. It falls after ____________, as more glucose is used in ______________to release energy.

Answer 1

All cells need a constant energy supply to work-so blood glucose concentration must be carefully controlled. The concentration of glucose in the blood is normally around 90 mg per 100 cm³ of blood. It’s monitored by cells in the pancreas. Blood glucose concentration rises after eating food containing carbohydrate. It falls after exercise, as more glucose is used in respiration to release energy.

Question 2

Hormonal control of blood glucose concentration
The hormonal system controls blood glucose concentration using two hormones called __________and __________. Like all hormones, _________and __________are chemical messengers that travel in the blood to their ________cells (___________). They’re both secreted by clusters of cells in the pancreas called the islets of Langerhans.

Answer 2

The hormonal system controls blood glucose concentration using two hormones called insulin and glucagon. Like all hormones, insulin and glucagon are chemical messengers that travel in the blood to their target cells (effectors). They’re both secreted by clusters of cells in the pancreas called the islets of Langerhans.

Question 3

The _______of ______________contain _____(B) cells and ________(a) cells. B cells secrete __________into the blood. a cells secrete ___________into the blood. Insulin and glucagon act on ___________, which respond to restore the blood glucose concentration to the normal level.

Answer 3

The islets of Langerhans contain beta (B) cells and alpha (c) cells. B cells secrete insulin into the blood. a cells secrete glucagon into the blood. Insulin and glucagon act on effectors, which respond to restore the blood glucose concentration to the normal level.

Question 4

Figure 1: The location of a and B cells in the islets of Langerhans.

Answer 4

Question 5

Insulin
Insulin _______blood glucose concentration when it’s too ____. It binds to __________ ___________on the cell membranes of _________cells and ______cells (_______________). It increases the _______________of muscle-cell membranes to glucose, so the cells take up more glucose. This involves increasing the number of channel __________in the cell membranes.
Insulin also activates ___________in _________and _________cells that convert ________into ___________. The cells are able to store _____________in their ___________, as an __________source. The process of forming glycogen from glucose is called _____________. Insulin also increases the rate of ___________of ________, especially in _________cells.

Answer 5

Insulin lowers blood glucose concentration when it’s too high. It binds to specific receptors on the cell membranes of muscle cells and liver cells (hepatocytes). It increases the permeability of muscle-cell membranes to glucose, so the cells take up more glucose. This involves increasing the number of channel proteins in the cell membranes.
Insulin also activates enzymes in muscle and liver cells that convert glucose into glycogen. The cells are able to store glycogen in their cytoplasm, as an energy source. The process of forming glycogen from glucose is called glycogenesis (see Figure 2). Insulin also increases the rate of respiration of glucose, especially in muscle cells.

Question 6

Figure 2: The process of glycogenesis.

Answer 6

Question 7

Glucagon
Glucagon _______ blood glucose concentration when it’s too ___. It binds to _________ ____________on the cell membranes of _____cells and ____________enzymes that break down _____________into ___________. The process of breaking down __________is called ________________.

Glucagon also ___________ enzymes that are involved in the formation of _________from ____________(a component of lipids) and ________ acids. The process of forming __________from non-carbohydrates is called ________________. Glucagon ____________the rate of _____________of glucose in cells.

Because they travel in the blood to their ________cells, the responses produced by hormones are ________than those produced by __________impulses (which are very quick). It also means that responses to hormones can occur all over the body if their _________cells are widespread, unlike nervous impulses that are localised to one area. Hormones are not broken down as quickly as ___________________ though, so their effects tend to last for _________.

Answer 7

Glucagon raises blood glucose concentration when it’s too low. It binds to specific receptors on the cell membranes of liver cells and activates enzymes that break down glycogen into glucose. The process of breaking down glycogen is called glycogenolysis.

Glucagon also activates enzymes that are involved in the formation of glucose from glycerol (a component of lipids) and amino acids. The process of forming glucose from non-carbohydrates is called gluconeogenesis. Glucagon decreases the rate of respiration of glucose in cells.

Because they travel in the blood to their target cells, the responses produced by hormones are slower than those produced by nervous impulses (which are very quick- It also means that responses to hormones can occur all over the body if their target cells are widespread, unlike nervous impulses that are localised to one area. Hormones are not broken down as quickly as neurotransmitters though, so their effects tend to last for longer.

Question 8

Figure 3: The processes of glycogenolysis and gluconeogenesis.

Answer 8

Question 9

Negative feedback mechanisms and
glucose concentration
can be for a ….

Answer 9

Rise in blood glucose concentration
or
Fall in blood glucose concentration

Question 10

Rise in blood glucose concentration

When the ___________detects blood glucose concentration is too ____, the _ ______secrete _________and the _ ______stop secreting ____________. Insulin then binds to _________on _____and _________cells (the effectors). The liver and muscle cells respond to ____________the blood __________concentration, e.g. glycogenesis is activated. ________ __________ _______________then _________to __________.

Answer 10

When the pancreas detects blood glucose concentration is too high, the B cells secrete insulin and the a cells stop secreting glucagon. Insulin then binds to receptors on liver and muscle cells (the effectors). The liver and muscle cells respond to decrease the blood glucose concentration, e.g. glycogenesis is activated (see previous page). Blood glucose concentration then returns to normal.

Question 11

Figure 5: Negative feedback mechanism activated by a rise in blood glucose.

Answer 11

Question 12

Fall in blood glucose concentration
When the __________detects blood glucose is too ___, the _cells secrete ___________and the _cells stop secreting __________. Glucagon then binds to __________on _______cells (the effectors). The _______cells respond to increase the blood __________concentration, e.g. ___________________is activated. ________ __________ _______________then _________to __________.

Answer 12

When the pancreas detects blood glucose is too low, the a cells secrete glucagon and the B cells stop secreting insulin. Glucagon then binds to receptors on liver cells (the effectors). The liver cells respond to increase the blood glucose concentration, e.g. glycogenolysis is activated. Blood glucose concentration then returns to normal.

Question 13

Figure 6: Negative feedback mechanism activated by a fall in blood glucose.

Answer 13

Question 14

Glucose transporters
Glucose transporters are _________ __________which allow _________to be transported across a ____ ___________. __________and _________ ____ contain a glucose transporter called _______. When insulin levels are low, _______is stored in ___________in the ___________of ____, but when ___________binds to ____________on the cell-surface membrane, it triggers the movement of ________to the membrane. Glucose can then be __________________into the cell through the _______protein by _____________ ___________.

Answer 14

Glucose transporters are channel proteins which allow glucose to be transported across a cell membrane. Skeletal and cardiac muscle cells contain a glucose transporter called GLUT4. When insulin levels are low, GLUT4 is stored in vesicles in the cytoplasm of cells, but when insulin binds to receptors on the cell-surface membrane, it triggers the movement of GLUT4 to the membrane. Glucose can then be transported into the cell through the GLUT4 protein by facilitated diffusion.

Question 15

Figure 7: The effect of insulin on the availability of GLUT4.

Answer 15

Question 16

Adrenaline
Adrenaline is a hormone that’s secreted from your adrenal glands (found just above your kidneys). It’s secreted when there’s a low concentration of glucose in your blood, when you’re stressed and when you’re exercising. Adrenaline binds to receptors in the cell membrane of liver cells and does these 2 things to increase blood glucose concentration:…

Adrenaline also activates __________ ____________and inhibits _________secretion, which ____________glucose concentration. Adrenaline gets the body ready for action by making more ___________available for muscles to __________.

Answer 16

• It activates glycogenolysis (the breakdown of glycogen to glucose).
• It inhibits glycogenesis (the synthesis of glycogen from glucose).

Adrenaline also activates glucagon secretion and inhibits insulin secretion, which increases glucose concentration. Adrenaline gets the body ready for action by making more glucose available for muscles to respire.

Question 17

Figure 8: The effect of adrenaline on glycogenesis and glycogenolysis.

Answer 17

Question 18

Second messengers pt1
Both ____________and ______________ can activate _________________inside a cell even though they _____to ______________on the ___________of the cell. They do this by the second messenger model - the _____________of the __________to ____ ______________activates an ________________on the inside of the cell membrane, which then produces a chemical known as a __________ ______________. The second messenger activates other ___________in the cell to bring about a ___________.

Answer 18

Both adrenaline and glucagon can activate glycogenolysis inside a cell even though they bind to receptors on the outside of the cell. They do this by the second messenger model - the binding of the hormone to cell receptors activates an enzyme on the inside of the cell membrane, which then produces a chemical known as a second messenger. The second messenger activates other enzymes in the cell to bring about a response.

Question 19

Second Messengers pt2
The receptors for adrenaline and glucagon have ___________ ____________structures that make them _________________in shape to their respective __________. To activate _________________, ____________and ____________bind to their _____________and activate an enzyme called _____________ __________. _____________ __________ _________converts ____into a chemical called _______ _____(______), which is a _________ ____________. ______activates an enzyme called __________ ___________ _. _________ _________ _ activates a __________(a chain of reactions) that breaks down ____________into ___________ (___________________)

Answer 19

The receptors for adrenaline and glucagon have specific tertiary structures that make them complementary in shape to their respective hormones. To activate glycogenolysis, adrenaline and glucagon bind to their receptors and activate an enzyme called adenylate cyclase. Activated adenylate cyclase converts ATP into a chemical called cyclic AMP (CAMP), which is a second messenger. cAMP activates an enzyme called protein kinase A. Protein kinase A activates a cascade (a chain of reactions) that breaks down glycogen into glucose (glycogenolysis)

Question 20

Tip: Remember,
adrenaline and glucagon bind to receptors on the cell membranes of …

Answer 20

liver cells.

Question 21

Figure 9: Seconder messenger model of adrenaline and glucagon action

Answer 21

Question 22

Summary of blood control - fill in blanks

Answer 22