16.3 Hormones and the regulation of blood glucose concentration

Question 1

What are the characteristics of hormones

Answer 1

1. Produced in glands, which secrete the hormone directly into the blood
2. Carried in the blood plasma to the cells on which they act - known as target cells - which have specific receptors on their membranes that are complementary to a specific hormone
3. Are effective in low concentrations, but often have widespread and long-lasting effects

Question 2

What is the name of the mechanisms hormones act by

Answer 2

The second messenger model

Question 3

What is the mechanism of adrenaline

Answer 3

1. Adrenaline binds to a transmembrane protein receptor within the cell membrane of a liver cell
2. The binding of adrenaline causes the protein to change shape on the inside of the membrane
3. This change of protein shape leads to the activation of adenyl cyclase. This activated adenyl cyclase converts ATP to cyclic AMP (cAMP)
4. cAMP acts as a second messenger that binds to protein kinase enzyme, changing its shape and therefore activating it
5. The active protein kinase enzyme catalyses the conversion of glycogen to glucose which moves out of the liver call by facilitated diffusion and into the blood, through channel proteins

Question 4

What is the pancreas

Answer 4

A large pale coloured gland situated behind the stomach

Question 5

What does the pancreas do

Answer 5

Produce enzymes (protease, amylase and lipase) for digestion and hormones (insulin and glucagon) for regulating blood glucose concentration

Question 6

What is the pancreas made up of

Answer 6

Cells that produce its digestive enzymes, and scattered throughout are hormone producing cells called the Islets of Langerhans.

Question 7

What are the two types of Islets of Langerhans and what do they secrete

Answer 7

Alpha cells - larger and produce glucagon

Beta cells - smaller and produce insulin

Question 8

What is the significance of the liver in blood glucose concentration

Answer 8

While the pancreas produces the hormones, it is inside the liver where the hormones act.

Question 9

What are the three processes that occur regarding blood glucose concentration within the liver

Answer 9

1. Glycogenesis
2. Gluconeogenesis
3. Glycogenolysis

Question 10

What is glycogenesis

Answer 10

The conversion of glucose into glycogen.

When blood glucose concentration is higher than normal the liver removes glucose and converts it to glycogen

Question 11

What is glycogenolysis

Answer 11

The breakdown of glycogen to glucose

When blood glucose concentration is lower than normal, the liver can convert stored glycogen into glucose which diffuses into the blood to restore the normal glucose concentration

Question 12

What is gluconeogenesis

Answer 12

The production of glucose from sources other than carbohydrate

Sources like amino acids and glycerol

Question 13

Where does blood glucose come from

Answer 13

1. Directly from the diet, in the form of glucose absorbed following hydrolysis of other carbohydrates like starch, maltose, lactose and sucrose
2. From the hydrolysis in the small intestine of glycogen (glycogenolysis)
3. From gluconeogenesis, which is the production of glucose from other sources than carbohydrates

Question 14

How do B cells detect the stimulus of a rise in blood glucose concentration

Answer 14

Because of receptors

Question 15

How do B cells respond to an increased glucose concentration

Answer 15

By secreting insulin directly into the blood plasma

Question 16

What cells have glycoprotein receptors

Answer 16

All except red blood cells

Question 17

What happens when insulin combines with glycoprotein receptors

Answer 17

1. 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
2. Activation of the enzymes that convert glucose to glycogen and fat

Question 18

How is blood glucose concentration lowered as a result of insulin

Answer 18

1. By increasing the rate of absorption of glucose into the cells
2. By increasing the respiratory rate of cells, which therefore use up more glucose, thus increasing their update of glucose from the blood
3. By increasing the rate of conversion of glucose to glycogen
4. By increasing the rate of conversion of glucose to fat

Question 19

How is the action of blood glucose negative feedback

Answer 19

Because the removal of glucose returns its concentration to the optimum. The lowering of the blood glucose reduces the secretion of B cells

Question 20

How do Alpha cells respond to a fall in blood glucose concentration

Answer 20

They secrete glucagon into the blood stream

Question 21

What is the action of glucagon

Answer 21

1. Attaching to specific protein receptors on the cell membrane of liver cells
2. Activating enzymes that convert glycogen to glucose
3. Activating enzymes involved in the conversion of amino acids and glycerol into glucose (gluconeogenesis)

Question 22

Why is the action of alpha cells negative feedback

Answer 22

Because the glucagon lowers the blood glucose concentration which in turn reduces the secretions of alpha cells

Question 23

How does adrenaline raise blood glucose concentration

Answer 23

1. Attaching to protein receptors on the membrane of target cells
2. Activating enzymes that cause the breakdown of glycogen to glucose in the liver