Module 5: Section 4 - Hormonal Communication

• Steroid hormones eg. oestrogen and testosterone can pass through the membrane and enter the cell to the nucleus, to have a direct effect on the DNA in the nucleus 
• Protein and peptide hormones eg. adrenaline and insulin are not soluble in the phospholipid membrane and do not enter the cell:

1. Adrenaline in the blood binds to its specific and complementary receptor on the cell surface membrane - the adrenaline molecule is the first messenger

2. Activates a G protein

3. G protein activates an effector molecule, in this case the enzyme adenyl cyclase, which converts ATP to cyclic AMP (cAMP – a second messenger)

4. The cAMP can then either act directly on another protein (eg. an ion channel) or cause an effect inside the cell by activating a cascade of enzyme-controlled reaction

The cortex

• Secretes steroid hormones eg. cortisol and aldosterone when you're stressed
• These hormones have role both in the short term and long term responses to stress, their effects include:
  • Stimulating the breakdown of proteins and fats into glucose, increasing the amount of energy avaliable so the brain and muscles can repond to the situation
  • Increasing blood volume and pressure by increasing the uptake of sodium ions in the kidneys
  • Suppressing the immune system

The medulla

• Secretes catecholamine eg. adrenaline and noradrenaline when you're stressed
• These act to make more energy avaliable in the short term by:
  • Increasing heart and breathing rate
  • Causing cells to break down glycogen into glucose
  • Constricting some blood vessels so blood is diverted to the brain and muscles

Beta cells secrete insulin into the blood when blood glucose concentration is too high:

• Insulin binds to specific receptors on the cell membranes of liver and muscle cells
• It increases the permeability of the cells to take up more glucose
• Insulin also activates enzymes that covert glucose to glycogen (glycogenisis) - can be stored in the liver

Alpha cells secrete glucagon into the blood when blood glucose concentration is too high:

• Glucagon binds to specific receptors on the membranes of liver cells
• It activates enzymes that break down glycogen into glucose (glycogenolysis)
• Also promotes the formaiton of glucose from fatty acids and amino acids (gluconeogenisis)

1. When blood glucose concentration is high, more glucose enters the beta cells by facilitated diffusion

2. More glucose in a beta cell causes the rate of respiration to increase, making more ATP

3. The rise in ATP triggers the potassium ion channels in the beta cell plasma membrane to close

4. This means potassium ions can't get through the membrane so they build up inside the cell

5. This makes the inside of the beta cell less negative because there are more positively charged potassium ions inside the cell, so the plasma membrane is depolarised

6. Depolarisation triggers calcium ion channels in the membrane to open so calcium ions diffuse into the beta cell

7. This causes the vesicles to fuse with the beta cell membrane, releasing insulin (by exocytosis)

An auto immune disease - the body attacks and destroys the beta cells, so no insulin is produced

After eating, blood glucose concentration rises and stays high - can result in death if left untreated

The kidneys can't reabsorb all this glucose, so some of it is excreted in urine

Treating type 1 diabetes:

• Insulin therapy
• Islet cell transplantation
• Monitering blood glucose concentration - have to think about their diet and activity levels

Occurs when the beta cells don't produce enough insulin or when the body's cells don't respond as the insulin receptors don't work properly - blood glucose concentration is higher than normal

Usually acquired later in life than type 1, often linked with obesity. The risk of developing type 2 diabetes is increased in people from certain ethnic groups eg. African or Asian, and in people with a close family history of the disease

Treating type 2 diabetes:

• Initially managed through lifestyle changes - having a balanced diet, getting regular exxercise and losing weight can help prevent the onset of type 2 diabetes as well as control the effects
• Medication can be prescribed eg. that makes the receptor cells more sensitive to insulin
• Some people may require insulin therapy

Used to be extracted from animal pancreases but nowadays insulin can be made by GM bateria

(+) Cheaper than extracting it from animal pancreases

(+) Larger quantities can be made

(+) GM bacteria make human insulin - more effective than using animal insulin and its less likely to trigger an allergic response

(+) Some people may prefer insulin from GM bacteria for ethical or religious reasons eg. vegetarians may object to the use of animals, and some religios people may object to using pigs

Stem cells would be grown into beta cells

The beta cells would then be implanted into the pancreas of someone with type 1 diabetes

This means the person would be able to make insulin as normal