5.4 Hormonal communication Flashcards
What do endocrine glands do?
Secrete hormones directly into the blood
What do exocrine glands do?
Secrete molecules into a duct, which carries the secretion to another place e.g. salivary gland
Which glands make up the endocrine system?
Pituitary -
Thyroid -
Adrenal -
Pancreas -
Testes -
Ovaries -
Define a hormone
a chemical messenger which is transported in the bloodstream to target organs/tissues
What are the two types of hormone?
- Protein:
—> e.g. Adrenaline
—> non-steroid hormones act via a G-protein in the plasma membrane - Steroid:
—> e.g. oestrogen
Explain what is meant by first and second messengers
- The first messenger is the hormone that brings the “information or signal” from the endocrine gland
- A second messenger inside the cell causes the effect
Where are the adrenal glands found?
Above each kidney
What are the two main areas of the adrenal glands?
Adrenal cortex
Adrenal medulla
What is the adrenal medulla under the control of?
Sympathetic nervous system
what type of hormones does the adrenal cortex produce?
Glucocorticoids
Mineralocorticoids
Androgens
What hormones are Glucocorticoids?
- Cortisol
- Corticosterone
What is the function of cortisol?
- the primary stress hormone which regulates metabolism of glucose, proteins and fats to release usable energy.
- reduces sensitivity to pain
What hormone is a mineralocorticoid?
Aldosterone
What is the function of aldosterone?
- Regulates levels of salts (sodium and potassium)
- Regulates water balance in the blood
Which hormone does the adrenal medulla produce?
Adrenaline
Noradrenaline
What is the function of adrenaline?
- increases heart rate
- converts glycogen to glucose
What is the function of noradrenaline?
- increases heart rate
- widens pupils
- widens air passages
- narrows blood vessels in non-essential organs
What is the function of the hypothalamus?
- Controls homeostasis in the body
- Controls secretion of hormones from the pituitary gland
Explain the stages in the function of adrenaline
- Adrenaline - the primary messenger, binds to specific receptor on cell surface membrane
- Activates adenylyl cyclase, on inside of cell surface membrane
- Catalyses production of second messenger - cAMP
- cAMP causes a cascade of enzyme controlled reactions
- leads to more glucose available
What is CRF? Where is it released?
Corticotropin Releasing Factor
released from hypothalamus
What is the function of CRF?
Stimulates production of ACTH from anterior pituitary gland
What is the function of ACTH?
Stimulates production of cortisol from adrenal cortex
How does the G-protein work?
- The hormone binds to a receptor of the target cell
- The G-protein activates the effector molecule
- The effector converts inactive ATP into a second messenger cAMP
- The secondary messenger can then act directly on another protein, altering the activity of the cell through a cascade of enzyme-controlled reactions
How do steroidal hormones work?
- Steroid hormone diffuses into cell
- Binds to receptor protein
- Hormone-receptor complex enters nucleus
- Triggers transcription
- MRNA formed leaves the nucleus to reach ribosomes
- Translation of new proteins
What are androgens
Sex hormones
Which cells make up the Islets of Langerhans?
α cells
β cells
What is the function of α cells?
Manufacture and release glucagon
What is the function of β cells
Manufacture and release insulin
How are blood glucose levels controlled?
Negative feedback
What factors affect blood glucose concentration?
- Absorption in the gut following carbohydrate digestion
- Hydrolysis of glycogen stores
- Non-carbohydrates such as lipids, lactate and amino acids that have been converted to glucose
What happens if there is a decrease in blood glucose concentration?
- Detection by α and β cells
- Alpha cells secrete glucagon and beta cells stop the secretion of insulin
- reduced uptake of glucose by hepatocytes
- Glycogenolysis - glycogen is converted to glucose
- Fatty acids are used a respiratory substrate instead of glucose
- Gluconeogenesis - Glycerol and amino acids combine to form glucose
- Blood glucose levels rise
What happens if there is an increase in blood glucose levels?
- Alpha cells stop producing glucagon and beta cells start producing insulin
Explain the stages of insulin production and secretion from the b cells:
- at normal BGC, K+ channels open and K+ions diffuse out - the cell has a PD of -70mv
- When BGC increases, glucose enters cell by glucose transporter
- Glucose metabolised by mitochondria –> produces ATP
- ATP binds to K+ion channels, causing them to close
- K+ can no longer diffuse out of cell, PD decreases to -30mv and cell is depolarised
- This causes voltage-gated Ca channels to open
- Ca2+ ions enter cell and cause secretory vesicles to release insulin by exocytosis
Which factors lead to an increase in blood glucose concentration?
Eating carbohydrates
Glycogenolysis
Gluconeogenesis
Which factors leads to a decrease in blood glucose concentration?
Exercise - increased respiration
Glycogenesis
Which changes happen when insulin is released?
- Increase in glucose transporter proteins on cell membrane - increased glucose uptake from blood
- Increased glycogenesis in liver + muscle cells as glucose converted to glycogen to be stored
- increased conversion of glucose to fats
- increased metabolism of glucose for respiration
- inhibiting release of glucose
Explain how the release of insulin to inhibit glucose production is an example of negative feedback
- glucose enters cell by facilitated diffusion through transport protein channels embedded in the cell membrane
- Insulin binds to its receptor, sets off a chain of reactions, which results in more glucose transporter proteins being released and moving to the plasma membrane
- this leads to an increased uptake of glucose from the blood
- As BG levels fall, the production of insulin is inhibited - negative feedback
Which changes happen when low blood glucose is detected?
- Glucagon released by A-cells in pancreas
–> reduced uptake of glucose by hepatocytes
–> Glycogenolysis - glycogen split to produce glucose - fatty acids used as respiratory substrate
- Gluconeogenesis - glycerol and amino acids form glucose
What is diabetes mellitus?
a condition where the body can no longer produce sufficient amounts of insulin to control its blood glucose concentration
What are the causes of type 1 diabetes?
- autoimmune response - the bodies immune system destroys b cells in pancreas
- virus
What are the causes of type 2 diabetes?
- insulin is still produced but insulin receptors on the cell surface membrane lose their ability to respond to insulin
What are risk factors for type 2 diabetes?
- obesity
- lack of exercise
- diet high in sugar
- family history
What problems does not enough/no insulin cause?
- excess glucose cannot be stored as glycogen - blood glucose concentration increases too much
—> this damages cells - osmosis - blood has a lower WP so cells crenate
How can type 1 diabetes be treated?
- insulin injections
—> insulin levels monitored and then dosage given - Insulin pump
—> insulin pumped directly into blood by permanent needle under skin - Islet cell transplantation
—> healthy b cells transplanted from deceased to patient - Pancreas transplant
How can type 2 diabetes be treated - lifestyle?
- losing weight
- regular exercise
- monitored diet
- stop smoking
How can type 2 diabetes be treated - medication?
- recuse amount of glucose released from the liver
- boost insulin levels
What are the sources of insulin to treat diabetes?
- Pancreas of animals - pigs
- Genetically modified e.coli bacteria to produce human insulin
What are the advantages of using insulin from bacteria?
- Exact copy of human insulin - faster and more effective
- less chance of rejection from immune system
- lower risk of infection
- cheaper to manufacture
- less ethical issues than using animals
What will happen to the body if it gets hyperglycaemic
- Water potential of blood lowers
- water moves by osmosis, down WP gradient, from body cells to the blood
- cells become dehydrated / crenate
What will happen to the body if it gets hypoglycaemic
- brain starved of glucose
- respiration decreases
- fainting / coma
