5.4 - Hormonal Communication

Question 1

Adrenal glands

Answer 1

Adrenal medulla

• Makes and secretes adrenaline which causes:
• Relax smooth muscle in bronchioles
• Increases heart rate and stroke volume of heart
• Causes glycogen to be hydrolysed to glucose
• Causes pupils to dilate
• Increases mental awareness

Adrenal cortex
- Produces steroid hormones e.g. glucocorticoids

Question 2

Adrenaline and cAMP

Answer 2

• Adrenaline is known as the first messenger because it transmits the signal around the body in
  the blood
• cAMP is the second messenger because it transmits the signal inside the cell and causes more
  enzyme controlled reactions to take place and cause an effect on the cell.

Question 3

Endocrine and exocrine and the pancreas

Answer 3

• Endocrine glands release hormones directly into the blood
• E.g. the pancreas – alpha cells release glucagon and beta cells release insulin
• Exocrine glands release molecules into ducts
• E.g. pancreas releases digestive enzymes into pancreatic duct which leads to small intestine

Question 4

Blood glucose is too high

Answer 4

• Beta cells detect rise in blood glucose level
• Rise inhibits glucagon secretion / production
  -Stimulates production of insulin (by beta cells)
• Insulin secreted into blood
• Insulin binds to receptors on hepatocytes (and muscle cells)
• More glucose channels inserted into plasma membranes of target cells so more glucose enters
  hepatocytes (and muscle cells)
• Glucose converted to glycogen (glycogenesis)
• Glucose converted to fats
• More glucose used in more respiration in target cells
• This results in less glucose in the blood

Question 5

Blood glucose is too low

Answer 5

• fall detected by alpha cells
• fall inhibits insulin secretion / production
• stimulates secretion / production of glucagon (by alpha cells)
• into blood
• binds to receptor on hepatocyte
• stimulates hydrolysis of glycogen to glucose / glycogenolysis
• gluconeogenesis / detail of gluconeogenesis
• glucose leaves hepatocytes by through glucose channels into blood stream

Question 6

How insulin release is controlled in a beta cell

Answer 6

• Glucose enters beta cell through carrier proteins
• Glucose is phosphorylated in glycolysis and ATP is produced
• ATP causes the potassium ion channels to close
• Cell membrane becomes depolarized/more positive (as potassium ions can no longer leave
  cell)
• This causes voltage-gated calcium ion channels to open and calcium ions enter the cell
• Calcium ions causes vesicles full of insulin to move towards the cell surface membrane, fuse
  with it and release the insulin
• Via exocytosis

Question 7

Diabetes mellitus – can’t control blood glucose levels

Answer 7

Type I – insulin dependent diabetes

• Insulin is no longer being produced by beta cells
• Beta cells have been damaged by body’s own immune system
• Can be inherited
• Treated with injections of insulin into subcutaneous fat

Type II – non insulin dependent diabetes
- Receptors on target cells for insulin become unresponsive to insulin (do still produce insulin)
- Treatment – diet low in carbohydrate and sugars, taking regular exercise
Risk factors:
*increasing age
*obesity more common in males and some ethnic groups
*high blood pressure
excessive alcohol intake

Question 8

Increasing heart rate in response to exercise

Answer 8

• produce more CO2 during exercise - dissolves to form carbonic acid - reduces blood pH
• lower pH detected by chemoreceptors in carotid arteries, aorta and brain
• increased action potential frequency in sensory neurone to cardiovascular centre in medulla
  oblongata
• cardiovascular centre sends nervous impulse to SAN via the accelerator nerve
• heart rate increases and increases stroke volume
• (impulse also sent to diaphragm and intercostals muscles to increase breathing rate and cause
  deeper breathing)
• Increases the speed carbon dioxide is removed
• Carbon dioxide levels returned to set point
• Example of negative feedback

Question 9

Decreasing heart rate in response to exercise

Answer 9

• stop exercise, conc of CO2 decreases - pH rises
• higher pH detected by chemoreceptors in carotid arteries, aorta and brain
• decreased action potential frequency in sensory neurone to cardiovascular centre in medulla oblongata
• cardiovascular centre sends nervous impulse to SAN via the vagus nerve
• heart rate decreases and so does stroke volume
• (impulse also sent to diaphragm and intercostal muscles to decrease breathing rate))
• Decreases the speed carbon dioxide is removed
• Carbon dioxide levels returned to set point
• Example of negative feedback

Question 10

Decreasing heart rate in response to increase in blood pressure

Answer 10

• monitored by baroreceptors (pressure receptors) in carotid sinus
• if b.p. is too high (e.g. exercise) sensory nerve carries signal to medulla oblongata
• cardiovascular centre sends nervous impulse to SAN via the vagus nerve
• heart rate decreases causing blood pressure to decrease