Hormonal communication 5.4 Flashcards
What is the endocrine system?
A communication system using hormones as signalling molecules
What are hormones?
Molecules released by the endocrine gland directly into the blood that act as messangers carrying a signal to target cells/ organs
What are the two types of hormones?
- protein hormones (adrenaline, insulin)
- steroid hormones (oestrogen, testosterone)
How are hormones released?
They are released directly into the blood by the endocrine glands
What are the cells recieving the endocrine signal called?
Target cells
How are steroid hormones detected by target cells?
They diffuse directly into the cell as they are lipid soluble so can move through the phospholipid bilayer
How are non-steroid hormones detected by target cells?
Target cells must possessspecific receptors made of glycoproteins on their plasmam membrane that is complimentary in shape
Are steroid-hormones primary or secondary messangers?
Primary messangers
What do non-steroid hormones do to the inside of the cell?
- by binding on the outside they cause the release of the secondary messanger
- the SM stimulates a change in the activity of the cell
- it does so by causing a cascade of enzyme controlled reactions that alter the activity of the cell
How is a secondary messanger caused by the binding of a primary messanger?
- a protein in the plasma membrane is activated when the hormone binds to the receptor
- the protein activates an effector molecule which is an enzyme that converts an inactive molecule into the active secondary ,essanger
- effector molecule is usually adenyl cyclase which converts ATP into cyclic AMP (cAMP)
Where are the adrenal glands found?
Anterior to the kidneys (just above)
What is the structure of the adrenal glands?
- outer adrenal cortex
- inner adrenal medulla
What hormones does the adrenal cortex secrete?
- mineralocorticoids such as aldosterone
- glucocorticoids such as cortisol
(steroid based hormones)
What hormones does the adrenal medulla secrete?
- adrenaline
- noradrenaline
What are the functions of the hormones from the adrenal cortex?
- aldosterone = control conc. of Na+ and K+ in the blood, maintaining blood pressure (increases)
- cortisol = control metabolism of carbohydrates, fats and proteins in the liver, released in response to stress
What are the actions of the hormones produced in the adrenal cortex?
Steroid hormones diffuse into the nucleus and have a direct effect on the DNA to cause protein synthesis
What are the functions of the hormones from the adrenal medulla?
- adrenaline = relax smooth muscle in bronchioles, increase heart rate, dialate pupils, cause body hair to stand erect, vasoconstriction to increase BP
What are the actions of of the hormones from the adrenal medulla?
It is a polar molecule so it is detected by receptors (many tissues have adrenaline receptors so it has a widespread effect)
What are the two main secretions of the pacrease?
- pancreatic juices containing enzymes secreted into small intestines
- horomones which are secreted from the islets of langerhans into the blood
What is the difference between exocrine glands and endocrine glands?
- exocrine glands secrete substances into a duct
- endcrine glands secrete substances directly into the blood
What is the exocrine function of the pancreas?
- to synthesise and release digestive enzymes
- exocrine glands are found in groups called acinus
- releases pancreatic amylase, trypsinogen and lipase
What is the endocrine function of the pancreas?
- islets of langerhans contain alpha and beta cells which make up the endocrine tissue
- secrete glucagon and insulin
What do alpha cells release?
Glucagon
What do beta cells release?
Insulin
What is the process for releasing insulin?
- plasma membrane of beta cells contains K+ and Ca2+ ion channels
- K+ ion channels are usually open so K+ ions flow out
- this makes the inside of the cellmore negative
- when glucose conc. is high glucose moves into the cell
- glucose is metabolised to produce ATP
- the production of ATP causes the K+ ion channels to close
- K+ ions accumulate inside the cell and make it less negative
- change in potential difference opens Ca+ ion channels
- Ca+ ions moving into the cell causes vesicles containing insulin to fuse with the plasma membrane to release insulin by exocytosis
How is blood glucose conc. regulated?
What structure in the pancreas monitors blood glucose conc.?
Islets of langerhans
What cells do insulin and glucagon have an effect on?
liver cells (hepatocytes)
What is hypoglycemia?
When a person’s blood glucose conc. is too low (below 4mmol dm-3) for long periods of time
What is hyperglycemia?
When a person’s blood glucose conc. is too high (above 6mmol dm-3) for long periods of time
What does a permanently high blood glucose conc. mean?
Can be used as a diagnosis for diabetes mellitus
What happens if blood glucose levels rise too high?
- high blood glucose conc. is detected by beta cells
- they respond by secreting insulin into the blood
- insulin travels through the body in the circulatory system to the target cells
How does insulin decrease blood glucose conc.?
- insulin binds to specific insulin receptors on the target cells plasma membrane as it is a protein so cannot pass through
- the binding activates the enzyme tyrosine kinase
- tyrosine kinase causes phosphorylationof inactive enzymes
- this activates the enymes
- leads to a cascade of enzyme controlled reactions
What effect does insulin have on target cells?
- more glucose specific transport proteins are places in plasma membrane (caused by vesicles fusing to plasma membrane)
- more glucose enters cell
- glycogenesis
- more glucose converted to fats
- more glucose used in respiration
What happens if blood glucose levels fall too low?
- low blood glucose conc. is detected by alpha cells
- alpha cells secrete glucagon into the blood
- glucagon travels through the body in the circulatory system to the target cells
How does glucagon increase blood glucose conc.?
- glucagon binds to specific glucagon receptors on the target cells plasma membrane as it is a protein so cannot pass through
- this stimulates a G protein
- ATP is converted to cAMP which activates a series of enzyme controlled reactions
What effect does glucagon have on target cells?
- glycogenolysis
- more fatty acids used in respiration
- gluconeogenisis
How is negative feedback loop involved in the control of blood glucose concentration?
- hormones regulating blood glucose conc. have opposing effects on the conc.
- one of their effects is to inhibit the effects of the other hormone
- when a change in the conc. is detected one of the hormones is released to reverse the effect and bring the conc. back to the optimum lever
- this pushes the conc. too far in the opposite direction so the opposing hormone is released to reverse the effect
What is type 1 diabetes?
An autoimmune disease where the immune system attacks and destroys beta cells so the pancreas can no longer synthesis or secrete insulin
What is type 2 diabetes?
When specific insulin receptors on target tissues become less responsive
What is the cause of type 1 diabetes?
Autoimmune disease or viral attack
What is the cause of type 2 diabetes?
- obesity
- lack of regular exercise
- high sugar diets
- family history
How do you treat type 1 diabetes?
- insulin injections
- insulin pump therapy
- islet cell transplantation
- pancreas transplantation
How do you treat type 2 diabetes?
- changes in lifestyle (lose weight, exercise regularly, monitor diet)
- insulin injections
- medication that reduces the amount of glucose the liver releases into the bloodstream/ boosts the amount of insulin released
What are the advantages of using genetically modiefied bacteria as an insulin source?
- exact copy of human insulin so faster acting and more efective
- less chance of rejection
- lower risk of infection
- cheaper to manufacture
- manufacturing is adaptable to demand
- less moral objections
What hormone stores glucose as a fat?
Insulin
What hormone converts glucose to pyruvate and what is the process called?
- insulin
- glycolysis
What hormone converts fats and proteins to glucose and what is the process called?
- glucagon
- gluconeogenesis
What hormone converts glucose to glycogen and what is the process called?
- insulin
- glycogenesis
What hormone converts glycogen to glucose and what is the process called?
- glucagon
- glycogenolysis
