5.1.4 - Hormonal Communication

Question 1

What is the endocrine system?

Answer 1

A communication and control system in the body

Question 2

How does the endocrine system work?

Answer 2

It is made up of endocrine glands that synthesise and secrete hormones directly into blood vessels flowing through the glands

Question 3

What are hormones?

Answer 3

They are chemical messengers that are secreted into the blood, transported in the bloodstream and detected by target cells and tissues

Question 4

How do steroid hormones cause a response?

Answer 4

They are lipid soluble and can diffuse across the cell surface membrane into their target cells to bind to a receptor often located within the cytoplasm

Question 5

How do non-steroid hormones cause a response?

Answer 5

They are insoluble in lipids so they cannot diffuse across the cell surface membrane. Instead, they bind to complementary shaped receptors on the cell surface membrane of the target cell. This causes a cascade of responses within the cell creating a response.

Question 6

Where are the adrenal glands located in humans?

Answer 6

Just above each kidney

Question 7

What is the structure of adrenal glands?

Answer 7

They are made up of the adrenal cortex and the adrenal medulla surrounded by a capsule

Question 8

What hormones are secreted by the adrenal cortex and what effects do they have?

Answer 8

• Mineralocorticoids - help control potassium and sodium ion concentration in blood
• Glucocorticoids - help control metabolism of proteins and carbohydrates in the liver
• Androgens - impact development of sex organs and secondary sexual characteristics

Question 9

What hormones are secreted by the adrenal medulla and what effects do they have?

Answer 9

• Adrenaline - increases heart rate, raises blood glucose concentration, increases sweat production and increases breathing rate
• Noradrenaline - increases heart rate, causes pupils to dilate, widens airways in lungs and narrows blood vessels in non-essential organs

Question 10

Where is the pancreas located in humans?

Answer 10

Just below the stomach

Question 11

What is the function of the pancreas?

Answer 11

It releases hormones to control blood glucose levels and enzymes for digestion

Question 12

What is most of the pancreas made up of?

Answer 12

Exocrine tissue secreting amylases, proteases and lipases

Question 13

How are the hormone secreting cells arranged?

Answer 13

In the islets of Langerhans which are made up of alpha and beta cells

Question 14

What do alpha cells secrete?

Answer 14

Glucagon

Question 15

What do beta cells secrete?

Answer 15

Insulin

Question 16

How would your blood glucose concentration increase?

Answer 16

Ingestion of food or drink containing carbohydrates

Question 17

How would your blood glucose concentration decrease?

Answer 17

Following exercise or if you have not eaten

Question 18

What is the response to low blood glucose concentration?

Answer 18

• A fall in blood glucose concentration below the normal level is detected by alpha cells in the islets of Langerhans
• Alpha cells secrete glucagon and adrenal glands release adrenaline
• Glucagon binds to receptors on the cell surface membranes of liver cells to increase blood glucose concentration
• Blood glucose concentration returns to normal

Question 19

What is the response to high blood glucose concentration?

Answer 19

• A rise in blood glucose concentration above the normal level is detected by beta cells in the islets of Langerhans
• Beta cells secrete insulin
• Insulin acts on target cells particularly muscle and liver cells to reduce blood glucose concentration
• Blood glucose concentration returns to normal

Question 20

How does glucagon raise blood glucose concentration?

Answer 20

• Converts glycogen to glucose - glycogenolysis
• Converts glycerol and amino acids into glucose - gluconeogenesis
• Causes the body to use more fatty acids in respiration

Question 21

How does insulin reduce blood glucose concentration?

Answer 21

• Causes more glucose channels to be inserted into the cell surface membrane so increasing the uptake of glucose especially by muscle cells
• Attaches to receptors on the surfaces of target cells which changes the tertiary structure of the channel proteins resulting in more glucose being absorbed by facilitated diffusion
• Increases rate of respiration so more glucose is used
• Activates enzymes involved in conversion of glucose to glycogen (glycogenesis) in muscle and liver cells
• Causes excess glucose to be converted into fat

Question 22

How is the secretion of insulin controlled?

Answer 22

• Beta cell surface membranes contain calcium ion channels which are closed
• There are also potassium ion channels in the beta cell surface membranes which are open. These allow potassium ions to diffuse out of the cell. The inside of the cell becomes more negative and sets up a potential difference of -70mV across the membrane
• Under high blood glucose concentrations glucose molecules diffuse into the cell and are quickly respired to release ATP
• The increase in ATP causes the potassium ion channels to close which means they cannot move out of the cell and the potential difference across the membrane becomes less negative
• The depolarisation opens the voltage gated calcium ion channels to allow calcium ions to diffuse into the cell down their concentration gradient
• The calcium ions cause vesicles containing insulin to move to and fuse with the cell surface membrane releasing insulin by exocytosis

Question 23

What is the second messenger model?

Answer 23

• Glucagon/adrenaline binds to glucagon receptors which causes a change in shape to the enzyme adenyl cyclase activating it
• Activated adenyl cyclase enzymes convert ATP into cyclic AMP (cAMP) which is the second messenger
• cAMP activates protein kinase which hydrolyses glycogen into glucose

Question 24

Which 3 processes take place in the liver?

Answer 24

• Glycogenesis - conversion of glucose to glycogen under the influence of insulin
• Glycogenolysis - conversion of glycogen to glucose under the influence of glucagon
• Gluconeogenesis - conversion of non-carbohydrates to glucose under the influence of glucagon

Question 25

What is the cause of type 1 diabetes?

Answer 25

The pancreas stops producing insulin usually in childhood.

Question 26

What is the cause of type 2 diabetes?

Answer 26

Glycoprotein receptors on cell membranes lose their sensitivity to insulin usually in adulthood due to obesity and poor diet

Question 27

What is the treatment for type 1 diabetes?

Answer 27

Injections of insulin 2-4 times a day

Question 28

What is the treatment for type 2 diabetes?

Answer 28

Regulate dietary carbohydrates especially refined sugars

Question 29

How is insulin produced for treatment?

Answer 29

By genetically modified bacteria

Question 30

What are the benefits of the way insulin is now produced for treatment?

Answer 30

• Less chance of a diabetic developing tolerance so it’s no longer effective and lower risk of infection
• Cheaper to manufacture
• Fewer ethical objections
• Exact copy of human insulin so more effective

Question 31

How could stem cells be used as a treatment in the future?

Answer 31

Scientists have found precursor cells in pancreatic tissue of adult mice. If similar cells could be found in human pancreatic tissue they could be used to produce new beta cells for type 1 diabetics.