5.1.4: Hormonal communication

Question 1

What is endocrine communication?

Answer 1

Specialised glands secrete hormones into bloodstream.
Circulatory system carries hormone to target cell/ tissue.
Lipid-soluble steroid hormones diffuse into cell & bind to
complementary receptor in cytoplasm. Peptide hormones bind to complementary receptor on cell-surface membrane

Question 2

Describe the structure of the adrenal glands.

Answer 2

cortex, medulla, blood vessels

located above kidneys

Question 3

What hormone does the medulla secrete?

Answer 3

Adrenaline in response to danger, stress or excitement as part of the fight or flight response.

Question 4

Which hormones does the cortex secrete?

Answer 4

● Mineralocorticoids e.g. aldosterone, which targets kidney & gut to control concentration of Na+ & K+ ions in blood.
● Glucocorticoids e.g. cortisol & corticosterone, which stimulate an increase in blood glucose concentration.

Question 5

Why is it important that blood glucose concentration

remains stable?

Answer 5

● Maintain constant blood water potential: prevent osmotic lysis/ crenation of cells.
● Maintain constant concentration of respiratory substrate: organism maintains constant level of activity regardless of environmental conditions.

Question 6

Define negative feedback.

Answer 6

Self-regulatory mechanisms return internal environment to optimum when there is a fluctuation.
Different mechanisms are responsible for dealing
with an increase/ decrease in normal level for
greater control.

Question 7

Define glycogenesis, glycogenolysis and gluconeogenesis.

Answer 7

Glycogenesis: liver converts glucose into the storage
polymer glycogen.
Glycogenolysis: liver hydrolyses glycogen into glucose
which can diffuse into blood.
Gluconeogenesis: liver converts glycerol & amino acids into glucose.

Question 8

Outline the role of glucagon when blood glucose

concentration decreases.

Answer 8

1. 𝞪 cells in Islets of Langerhans in pancreas detect decrease & secrete glucagon into bloodstream.
2. Glucagon binds to surface receptors on liver cells & activates enzymes for glycogenolysis & gluconeogenesis.
3. Glucose diffuses from liver into bloodstream.
4. 𝛼 cells detect that blood glucose concentration has returned to optimum & stop producing glucagon. (negative feedback).

Question 9

Use the secondary messenger model to explain how

glucagon works.

Answer 9

1. Hormone-receptor complex forms.
2. Conformational change to receptor activates G protein.
3. Activates adenylate cyclase, which converts ATP to
   cyclic AMP (cAMP).
4. cAMP activates protein kinase A pathway.
5. Results in glycogenolysis.

Question 10

Outline what happens when blood glucose concentration increases.

Answer 10

1. 𝝱 cells in Islets of Langerhans in pancreas detect increase & secrete insulin into bloodstream.
2. Insulin binds to surface receptors on target cells to:
   a. increase cellular glucose uptake.
   b. activate enzymes for glycogenesis (liver & muscles).
   c. stimulate adipose tissue to synthesise fat

Question 11

Describe how insulin leads to a decrease in blood

glucose concentration.

Answer 11

● Increases permeability of cells to glucose.
● Increases glucose concentration gradient.
● Triggers inhibition of enzymes for glycogenolysis.

Question 12

How is insulin secretion controlled?

Answer 12

1. 𝛽 cells have K+ & Ca2+ ion channels to maintain p.d.
   -70mV.
2. As glucose concentration increases, glucose enters 𝛽
   cells via facilitated diffusion.
3. Respiration of glucose produces ATP. ATP-gated K+ ion
   channels close, so K+ ions no longer diffuse out of cell.
4. P.d. in cell becomes more positive = depolarisation. Ca2+ ion channels open. Ca2+ triggers exocytosis of insulin.

Question 13

Describe the exocrine function of the pancreas.

Answer 13

Secretes digestive enzymes e.g. amylase, trypsin & lipase to the duodenum via the pancreatic tract.

Question 14

Explain the causes of Type 1 diabetes mellitus and

how it can be controlled.

Answer 14

Body cannot produce insulin e.g. due to autoimmune
response which attacks 𝛽 cells of Islets of Langerhans
Treat by injecting insulin from animal source or genetically modified bacteria. Possible future treatment: use stem cells to produce new 𝛽 cells.

Question 15

Explain the causes of Type 2 diabetes mellitus and

how it can be controlled.

Answer 15

● Glycoprotein receptors are damaged or become less responsive to insulin.
● Strong positive correlation with poor diet /obesity.
● Treat by controlling diet and exercise regime.