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 and bind to complementary receptor in cytoplasm. Peptide hormones bind to complementary receptor on cell surface membrane

Question 2

Describe the structure of the adrenal gland

Answer 2

Located above kidneys
They have an outer cortex and an inner medulla which contains blood vessels

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 hormone does the cortex secrete

Answer 4

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

Question 5

Why is it important the 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 and amino acids into glucose

Question 8

Outline the role of glucagon when blood glucose concentration decreases

Answer 8

1. Alpha cells in islets of langerhans in the pancreas detect decrease and secrete glucagon into the bloodstream
2. Glucagon binds to surface receptors on liver cells and activates enzymes for glycogenolysis and gluconeogenesis
3. Glucose diffuses from the liver into bloodstream
4. Alpha cells detect that blood glucose concentration has returned to optimum and 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. Beta cells in Islets of Langerhans in pancreas detect increase and 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 and muscles)
   c) stimulate adipose tissue to synthesis fat

Question 11

Describe how insulin leads to a decrease in blood glucose concentration

Answer 11

Increase permeability of cells to glucose
Increase glucose concentration gradient
Triggers inhibition of enzymes for glycogenolysis

Question 12

How is insulin secretion controlled

Answer 12

1. beta cells have K+ and Ca2+ ion channels to maintain p.d. -70mV
2. As glucose concentration increases, glucose enters Beta cells via facilitated diffusion
3. Respiration of glucose produces ATP. ATP gated K+ ion channels close so K+ ions no longer diffuse out of cells
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 and 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 attack Beta 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 Beta cells

Question 15

Explain the causes of Type 2 diabetes mellitus

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