Hormones

How does endocrine communication work? Include the action of steroid and peptide hormones in your answer. [3]

1. Specialised glands secrete hormones into bloodstream

2. Circulatory system carries hormone to target cell/tissue

3. Hormones either diffuse into cell and bind to complementary receptor (steroid) or bind to complementary receptor on cell surface membrane (peptide)

Describe the structure of the adrenal glands [3]

• Located above the kidneys

• Centre of the gland is the adrenal medulla

• Surrounding the medulla is the adrenal cortex

What hormone does the adrenal medulla secrete?

• Adrenaline

Which hormones does the cortex secrete, include an example of each and their function [2]

• Mineralocorticoids-e.g aldosterone-targets kidney and gut to control concentration of Na⁺/K⁺ ions in the blood

• Glucocorticoids-e.g cortisol/corticosterone-stimulate an increase in blood glucose concentration

Describe the histology of the pancreas using this diagram.

A-Branch of Pancreatic Duct

B-Aciner Cells

C-α (alpha) cells

D-Capillaries

E-β Cells

F-Islet of Langehans

Why is it important that blood glucose concentration remains stable? [2]

• Maintains constant blood water potential which prevents osmotic lysis

• Maintain constant concentration of respiratory substrate ensuring the organism maintains a constant level of activity despite external factors

Define negative feedback

Self-regulatory mechanisms which return internal environment to optimum when there is a fluctuation

Define glycogenesis

Liver converts glucose into glycogen

Define Glycogenolysis

Liver hydrolyses glycogen into glucose

Define gluconeogenesis

Liver uses glycerol and amino acids to create new glucose

Outline the role of glucagon when blood glucose concentration decreases [4]

1. α cells in Islets of Langerhans in pancreas detect decrease and secrete glucagon into the bloodstream

2. Glucagon binds to surface receptors on hepatocytes and activates enzymes for glycogenolysis and gluconeogensis

3. Glucose diffuses from liver into bloodstream

4. α Cells detect that blood glucose concentration has returned to optimum and stops producing glucagon

Use the secondary messenger model to explain how glucagon works [5]

1. Hormone-receptor complex forms

2. Conformation change to receptor activates G-protein

3. Activates adenylate cyclase, which converts ATP to cyclic AMP (cAMP)

4. ⊂AMP activates protein kinase A pathway

5. Results in glycogenolysis

Outline what happens when blood glucose concentration increases [2]

1. β cells in Islets of Langerhans in pancreas detect increase and secrete insulin into the bloodstream

2. Insulin binds to surface receptors on target cells and causes a series of responses-including increasing cellular glucose uptake, activating enzymes for glycogenesis and stimulating synthesis of fat

Describe how insulin leads to decrease in blood glucose concentration [3]

• Increases permeability of cells to glucose

• Increase glucose concentration gradient

• Triggers inhibition of enzymes for glycogenolysis

How is insulin secretion controlled? [4]

1. As glucose moves into β cells via facilitated diffusion, it is used in respiration,producing lots of ATP

2. ATP sensitive K⁺ Channel shuts, depolarising the membrane as K⁺ can no longer diffuse out

3. Ca²⁺ Voltage gated channel protein opens, letting Ca²⁺ Ions into the cell to stimulate vesicles of insulin

4. Vesicles of insulin fuse to membrane via exocytosis

Describe the exocrine function of the pancreas

Secretes digestive enzymes like amylase, trypsin and lipase to the duodenum via the pancreatic duct

Explain the causes of Type 1 Diabetes

Body cannot produce insulin due to autoimmune responses which attack the β Cells in the Islets of Langerhans

Explain the cause of type 2 diabetes and the risk factorss. [2]

• Glycoprotein receptors are damaged or become less responsive to insulin

• Strong positive correlation with poor diet/obesity

How do you treat type 2 diabetes?

Treat by controlling diet and exercise regime

What are the two types of glands?

• Endocrine glands and exocrine glands

Describe endocrine glands’ function [2]

• Secrete hormones directly into bloodstream

• Produce chemical signalling molecules

Describe exocrine glands’ function and structure [2]

• Secrete chemicals to specific places

• These are carried by ducts to specific places

Describe peptide hormones [4]

• Not lipid soluble

• Cannot cross cell membrane

• Bind to complementary receptors on cell surface membrane

• Short term effects

Describe steroid hormones [4]

• Lipid soluble

• Bind to complementary receptors inside cell in cytoplasm

• Act on DNA transcription factors

• Long term effects

What happens at the synapse of an inhibitory Neurone, and why is the difference important?

• Instead of Na⁺ channels on the post-synaptic membrane, it is Cl⁻ channels

• This means that Cl⁻ diffuse into the cell, causing hyperpolarisation,making it harder to generate an action potential

D