Hormonal Communication Flashcards
Define hormone
- Chemical messenger that triggers response in target cells
- Sends information about changes in environment around body
Define endocrine gland
- Group of specialised cells
- Secrete hormones into bloodstream
Define endocrine system
Series of endocrine glands around the body
Describe the difference between an endocrine gland and an exocrine gland
- Endocrine gland secretes hormones directly into bloodstream
- Exocrine gland secretes chemicals through ducts into organs
Where is insulin secreted from and what is its function?
- Insulin is secreted from the beta cells of the pancreas.
- It decreases blood glucose concentration.
Where is glucagon secreted from and what is its function?
- Glucagon is secreted from the alpha cells of the pancreas.
- It increases blood glucose concentration.
Where is adrenaline secreted from and what is its function?
- Adrenaline is secreted from the adrenal medulla.
- Adrenaline increases heart and breathing rate, and raises blood glucose level.
Where is ADH secreted from and what is its function?
- ADH is secreted from the pituitary gland.
- It increases water reabsorption in the kidneys.
Describe how hormones travel around the body to target cells
- Secreted into blood stream by endocrine gland
- Travel in blood plasma to target cell
- Bind to specific receptors on target cell
- Trigger target cells to produce response
Describe how steroid hormones trigger an effect in target cells
- Lipid soluble
- Diffuse through phospholipid bilayer
- Bind to steroid hormone receptors inside cell
- e.g. in cytoplasm, in nucleus
- Hormone-receptor complex forms
- Acts as transcription factor
- Facilitates or inhibits transcription of specific gene
- e.g. oestrogen
Describe how non-steroid hormones trigger an effect in target cells
- Hydrophilic so cannot pass through phospholipid bilayer
- Bind to specific receptors on cell surface membrane of target cell
- Triggers cascade reaction mediated by secondary messengers
- e.g. adrenaline
Where are the adrenal glands located?
On top of each kidney
Describe the structure of the adrenal glands
Medulla
- Inner region of gland
- Produces adrenaline, noradrenaline
Cortex
- Outer region of gland
- Produces cortisol, aldosterone
How is the production of hormones in the adrenal cortex controlled?
By hormones released from pituitary gland
Outline the three main types of hormone produced by the adrenal cortex
Glucocorticoids
- e.g. cortisol - helps regulate metabolism and blood pressure
- e.g. corticosterone - regulates immune response
Mineralocorticoids
- e.g. aldosterone - controls blood pressure
Androgens
- Male and female sex hormones
Outline the hormones secreted by the adrenal medulla
Adrenaline
- Increases heart rate
- Raises blood glucose concentration
Noradrenaline
- Works with adrenaline in response to stress
- Increases heart rate, widens pupil, widens air passages
Both released when sympathetic nervous system is stimulated
Outline the main roles of the pancreas
- Produces and secretes enzymes for digestion
- Produces hormones to control blood glucose concentrations
Which endocrine tissue is responsible for producing and secreting insulin and glucagon?
Islets of Langerhans
Which cells in the islets of Langerhans produce glucagon?
Alpha (⍺) cells
Which cells in the islets of Langerhans produce insulin?
Beta (β) cells
What is the role of the pancreatic acini?
- Acts as exocrine glandular tissue
- Produces digestive enzymes and pancreatic juice
- Enzymes and pancreatic juice secreted into ducts
- Travel through ducts to small intestine
Explain how the pancreas acts as both an endocrine and exocrine gland
Endocrine
- Produces insulin and glucagon hormones
- ⍺ cells secrete glucagon
- β cells secrete insulin
- Hormones secreted directly into bloodstream
Exocrine
- Produces enzymes for digestion (amylase, protease, lipase)
- Releases enzymes via a duct into the small intestine
Define glycogenolysis
- Glycogen stored in liver and muscle cells broken down into glucose
- Glucose released into blood stream
Define gluconeogenesis
- Production of glucose from non-carbohydrate sources
- e.g. from glycerol and amino acids in the liver
Outline how blood glucose concentration can be increased
- Diet - eating carbohydrate-rich food
- Glycogenolysis
- Gluconeogenesis
Define glycogenesis
- Production of glycogen from glucose
- Glycogen stored in liver
Outline how blood glucose concentration can be decreased
- Respiration - glucose used to produce ATP
- Glycogenesis
Describe the effect of insulin on other cells
- All cells (except red blood cells) have receptors for insulin on cell surface membrane
- Binding of insulin to receptor causes change in tertiary structure of glucose protein channels
- Channels open so more glucose enters cell
- Insulin activates enzymes that convert glucose to glycogen
Explain how insulin lowers blood glucose levels once secreted
- Causes glucose channel proteins to open - Increases rate of absorption of glucose by cells
- Increases respiratory rate
- Increases cells’ requirement for glucose so increases uptake
- Increases rate of glycogenesis in liver
- Increases rate of glucose to fat conversion
- Inhibits release of glucagon from ⍺ cells
Where is insulin broken down?
Liver
When is most insulin secreted?
Soon after eating
What happens when high blood glucose concentration returns to normal?
- Detected by β cells in pancreas
- Secretion of insulin reduced
- Example of negative feedback
Describe the effect of glucagon on other cells
- Produced by alpha cells in pancreas
- If blood glucose concentration too low, ⍺ cells in islet of Langerhans detect fall and secrete
glucagon into bloodstream - Only liver and fat cells have receptors for glucagon on cell surface membrane
- Binding of glucagon to receptor causes cascade of reactions inside liver and fat cells
Explain how glucagon raises blood glucose levels once secreted
- Promotes glycogenolysis - Liver breaks down glycogen into glucose
- Reduces amount of glucose absorbed by liver cells
- Increases gluconeogenesis - Increases conversion of amino acids and glycerol into glucose - Takes place in liver
- Inhibits release of insulin from β cells
What happens when low blood glucose concentration returns to normal?
- Detected by ⍺ cells in pancreas
- Secretion of glucagon reduced
- Example of negative feedback
Describe how negative feedback is used to control blood glucose concentration
- β cells and ⍺ cells detect change in blood glucose concentration
If higher glucose concentration, β cells release insulin
- Causes increased uptake of glucose by effector cells
- Glucose converted to glycogen via glycogenesis
- Use of glucose in respiration increased
- Blood glucose concentration falls, less insulin released
If lower glucose concentration ⍺ cells release glucagon
- Causes increased conversion of glycogen to glucose via glycogenolysis
- Increased conversion of amino acids and lipids to glucose via gluconeogenesis
- Glucose leaves cells by facilitated diffusion through glucose channels
- Blood glucose concentration increases, less glucagon released
Explain the mechanism by which insulin is released from β cells
When blood glucose concentration increases:
- Glucose moves into cell through glucose transporter protein
- Glucose metabolised inside mitochondria
- Produces ATP (via aerobic respiration)
- ATP binds to ATP-sensitive potassium channels
- Causes potassium channels to close
- K+ ions cannot diffuse out of cell
- Potential difference falls
- Depolarisation occurs
- Depolarisation causes voltage-gated calcium channels to open
- Ca2+ ions enter cell
- Cause vesicles to release insulin by exocytosis
Explain how insulin is stored in β cells when blood glucose concentration is normal
Normal blood glucose concentration:
- Potassium channel in plasma membrane of β cells are open
- K+ ions diffuse out of cell
- Resting potential of -70mV maintained
- Insulin stored within vesicles
Explain why β cells continue to secrete insulin even when there is no further glucose intake
- Continues to be secreted as long as blood glucose concentration remains high
- Sufficient ATP still present and so K+ channels remain closed
- Exocytosis still being triggered by Ca2+
What is diabetes?
Inability to control blood glucose levels properly
What are the two types of diabetes?
- Type I - early-onset
- Type II - late-onset
Describe the cause of Type 1 diabetes
- Immune system destroys beta cells of pancreas
- Insulin no longer secreted
- Can be hereditary or triggered by environmental factor (e.g. infection, cancer)
Describe the treatment of Type 1 diabetes
- Regular insulin injections
- Blood glucose levels monitored
Define hyperglycaemic
Blood glucose concentration too high
Define hypoglycaemic
Blood glucose concentration too low
Why is careful monitoring of blood glucose concentration necessary with Type I diabetes?
- Blood glucose concentration varies throughout the day
- e.g. increased exercise will cause blood glucose concentration to decrease
- Knowing exact blood glucose concentration ensures correct dose of insulin given
- If too low a dose they will remain hyperglycaemic
- Can result in death if left untreated
- If too high a dose they can become hypoglycaemic
- Can result in a coma/unconsciousness
Describe the cause of Type II diabetes
- Insulin continues to be produced
- Target cells in liver are unable to respond to insulin
Describe the treatment of Type II diabetes
Careful control of diet
List features that would increase a person’s risk of developing Type II diabetes
- Obesity
- Sedentary lifestyle
- High intake of sugar
- Genetic predisposition
- Increasing age
- High blood pressure
List the symptoms of Type II diabetes
- Decreasing responsiveness to insulin
- High blood glucose
- Glucose in urine
- Loss of weight / tiredness
- Increased production of urine
- Dehydration and thirst
Explain the dietary advice that should be given to a patient who has developed Type II diabetes
- Regulate diet/total calorie intake and exercise
- Ensures a balanced energy budget
- Low fat diet
- Avoid weight gain
- Consume complex carbohydrates
- Ensure gradual release of glucose into blood
- Eat regular small meals
- Ensure a steady supply of glucose
- Do not go for long periods without meals
- Avoid large drop in blood glucose
- Consume foods with low glycemic index
- Avoid abrupt changes in blood glucose
How was insulin originally obtained for medical use?
From pancreas of slaughtered pigs and cows
How is insulin produced today?
Genetic modification of bacteria
Why is insulin from genetically modified bacteria more effective than pig/cow insulin?
- Bacteria produce human insulin
- Cow/pig insulin may have different structure
- Receptors for insulin in human not fully complementary to pig/cow insulin
State the advantages of treating Type I diabetes by using insulin that has been produced by
genetically modified bacteria rather than insulin that has been extracted from pigs
- Plentiful and dependable supply
- Cheap to manufacture
- Not cruel to pigs
- No religious objections
- Reliable quality
- Human insulin produced so no allergic reaction
What type of stem cells are required for stem cell therapy of Type I diabetes?
Totipotent stem cells
Where are totipotent stem cells extracted from?
- Human embryos
- From infertility treatments or terminated pregnancies
Why is stem cell therapy still not widely used?
- Technology still being developed
- Ethical concerns over use of embryos
- Unknown whether uncontrolled cell growth could occur
- Causing tumour formation
