Module 5.4 - Hormonal Communication Flashcards
Define endocrine glands
Produce and secrete hormones directly into the blood
No ducts
Define exocrine glands
Do not produce hormones
Secrete molecules into a duct which carries them to where they are needed
What does adrenaline stimulate?
Relax smooth muscle in bronchioles Increased stroke volume Increased heart rate Vasoconstriction Converts glycogen to glucose Dilates pupils Increased mental awareness Inhibits actions of digestive system Body hair erects
What is a non-steroid hormone?
Protein/amino acid based hormone
Adrenal medulla
In the centre of the gland
Makes and secretes adrenaline and noradrenaline
Adrenal cortex
Uses cholesterol to produce steroid hormones
Zona Glomerulosa: nearest outside; secretes mineralocorticoids; helps control sodium and potassium levels in blood and blood pressure
Zona Fasciculata: secretes glucocorticoids (e.g. cortisol); helps control metabolism of carbs, fats and proteins in liver
Zona Reticularis: nearest medulla; secretes precursors to the sex hormones
How non-steroid hormones enter target cells
Non-steroid hormones are first messengers as they transmit the signal around the body and cause an effect on the cell when they bind to a complementary receptors on the plasma membrane
The binding causes a G-protein to activate adenyl cyclase
This converts ATP into cAMP which is the second messenger because it transmits the signal inside the cell and initiates a change in the cell
How steroid hormones enter target cells
Dissolve in cell surface membrane
Binds with a receptor in the cytoplasm
Receptor-hormone complex enters nucleus and binds to another receptor on the chromosome
Causes mRNA to be made and proteins produced
Contents of the pancreatic ‘juice’
Amylase
Trypsinogen
Lipase
Sodium hydrogen carbonate (neutralises pH of substances entering small intestine)
Acini
Groups of cells in pancreas which produce and secrete digestive enzymes (pancreatic ‘juice’)
Secrete enzymes into tubules which lead to pancreatic duct
This takes them to the small intestine
Islets of Langerhans
Contain alpha and beta cells
These cells detect changes in blood glucose levels
Alpha cells produce and secrete glucagon
Beta cells produce and secret insulin
Secrete hormones directly into closely associated capillaries
Blood glucose too high
Beta cells detect rise in blood glucose level
Stimulates production of insulin by beta cells
Glucagon production by alpha cells inhibited
Insulin secreted into blood
Insulin binds to receptors on target cells (hepatocytes and muscle cells)
More glucose channel inserts into plasma membrane
More glucose enters cells
Glucose converted to glycogen (glycogenesis)
Glucose converted to fats
Increased rate of glucose used in respiration
Results in less glucose in the blood
Example of negative feedback
Blood glucose too low
Alpha cells detect fall in blood glucose level
Stimulates production of glucagon by alpha cells
Insulin production by beta cells inhibited
Glucagon secreted into blood
Glucagon binds to receptors on target cells (heptocytes)
Causes hydrolysis of glycogen to glucose (glycogenolysis)
Conversion of fats and amino acids to glucose (gluconeogenesis)
Use of more fatty acids in respiration
Glucose is released into blood meaning more glucose in blood
How do beta cells control insulin production?
Cell membrane has potassium and calcium ion channels
Potassium channels are normally open so potassium ions flow out
When blood glucose concentration is high, the glucose moves into the cell
Glucose is metabolised to make ATP
The ATP closes the potassium ion channels
The accumulation of potassium ions alters the p.d. across the plasma membrane - the inside becomes less negative
The change in p.d. opens the calcium ion channels
Calcium ions causes vesicles of insulin to fuse with the plasma membrane, releasing insulin by exocytosis
Benefits of storing glucose as glycogen
Insoluble Unreactive Can’t diffuse out of cell Compact Easy to convert to glucose Lots of branches for enzymes to work on in hydrolysis
