5.4 Flashcards
What is endocrine system used for
Communication around the body using blood circulatory system to transport its signals (hormones)
What does blood system transport and what does this mean for hormones
Transports materials all over body, so hormones released into blood also transported throughout body
What are the 2 types of hormone
Peptide hormones (derive from amino acid, adrenaline, insulin, glucagon), steroid hormones (oestrogen, testosterone)
How do peptide hormones act on cell membrane
Proteins not soluble in phospholipid bilayer and don’t enter cell, peptide hormones bind to cell surface membrane and release 2nd messenger inside cell
How do steroid hormones act on cell membrane
Pass through membrane and enter cell and nucleus to have direct effect on DNA
How are hormones released into blood in endocrine system
Released directly into blood from endocrine glands, these are ductless glands that have a group of cells that manufacture hormones and release them directly into blood capillaries that run through glands
How do hormones effect cells when transported throughout body
Have specific functions so usually only act on 1 tissue type even if transported round whole body
What are target cells
Cells receiving endocrine signal which are either grouped together in target tissue like epithelium of collecting ducts or more widely dispersed in many tissues (adrenaline receptors in CNS and PNS)
What must non steroid hormones target cells have
Specific receptors on plasma membrane with complementary shape to hormone, hormone binds to this receptor and initiates changes in cell
What does it mean if all cells in body pass complementary hormone receptors
Then all cells can respond to signals but each hormone is different so some hormones carried in blood without effecting cells without complementary receptors, only specific target cells respond to hormone
What is a first messenger and why
Non-steroid hormones as they’re signalling molecules outside cell that bind to cell surface membrane and initiate effect inside cell, usually they cause release of signalling molecule in cell (second messenger) which stimulates change in cell activity
How do many peptide hormones act on cell membrane as first messenger
Via G protein in membrane, G protein activated when hormone binds to receptor and G protein activates an effector (usually an enzyme that converts inactive molecule into active 2nd messenger)
In many cells what is the effector molecule and what do it convert
Effector molecule is adenyl cyclase and converts ATP in cAMP (cyclicAMP)
What is cAMP
A second messenger that may act directly on another protein like an ion channel or may initiate cascade of enzyme controlled reactions that alter cell activity
From head to bottom how are glands involved with hormones positioned
Pituitary gland, thyroid gland, thymus, adrenal gland, pancreas, ovaries, testes
What are adrenal glands
Endocrine glands found anterior to kidneys (1 each side of body), each divided by outer region (adrenal cortex) and inner region (adrenal medulla), both regions supplied with blood vessels and produce hormones secreted directly into blood
What is the adrenal cortex structure
Adrenal gland has outer capsule and 3 distinct zones in cortex, zona glomerulosa, zona fasciculata, zona reticularis
What is zona glomerulosa
Outermost layer of adrenal cortex that secretes mineralocorticoids like aldosterone
What is zona fasciculata
Middle layer of adrenal cortex that secrets glucocorticoids like cortisol
What is zona reticularis
Innermost layer, secretes precursor molecules that make sex hormones
What is adrenal medulla
Found at centre of adrenal gland and secretes adrenaline and noradrenaline
What does adrenal cortex use cholesterol to produce
Steroid based hormones that can enter cell directly by dissolving into cell surface membrane, steroid hormones enter nucleus and have direct effect on DNA to cause protein synthesis
What is the action of steroid hormones
1.steroid hormone passes through cell membrane of target cell 2.steroid hormone binds to specific receptors in cytoplasm 3.receptor steroid hormone complex enters nucleus of target cell and binds to another specific receptor on chromosomal material 4.binding stimulates production of mRNA molecules which code for production of proteins
What is the role of mineralocorticoids from zona glomerulosa in the body
Help control Na+ and K+ in blood and contribute to maintaining blood pressure, aldosterone acts on cells of distal tubules and collecting ducts in kidneys, it increases absorption of Na+ and decreases absorption of K+ and increases water retention to increase BP
How do glucocorticoids from zona fasciculata act on body
Control metabolism of carbs, fats and proteins in liver, cortisol released in response to stress or due to low blood glucose concentration, it stimulates production of glucose from stored compounds (especially glycogen, fats, proteins) in liver
Although cortisol released form zona fasciculata what happens if correct hormones aren’t present to release it
Zona reticularis releases precursor androgens into blood, these are taken up by ovaries or testes and converted to sex hormones which help development and regulate gamete production
What is adrenaline
A polar molecule derived from amino acid tyrosine and released from adrenal medulla, means it can’t enter cell so detected by receptors on plasma membrane of target cells
Are adrenaline effects widespread
Yes as many cells have complementary adrenaline receptors
What is role of adrenaline
Prepare body for activity
What are examples of how adrenaline prepares body for activity
Relax smooth muscle in bronchioles, increase stroke volume in heart, increase heart rate, vasoconstriction to raise BP, converts glycogen to glucose, dilates pupils, increasing mental awareness, inhibits gut action, body hair stands erect
What is the pancreas
Small organ below stomach with endocrine and exocrine function
What are 2 main secretions from pancreas
Pancreatic juices containing enzymes which are secreted into small intestines, hormones secreted from islets of langerhans into blood
What do exocrine glands do
Secrete substances into ducts
What do most cells in pancreas synthesise and release
Digestive enzymes which has an exocrine function
What are acini cells
Exocrine cells in small groups around tiny tubules, acini cells grouped together in small tubules separated by connective tissue
What do acini cells do
Secrete enzymes that they synthesise into tubules at centre of the group of cells, tubules form acini join to form intralobuar ducts that eventually combine to make pancreatic duct
What does the pancreatic duct do
Carries fluid containing enzymes to first part of small intestines called duodenum
What does fluid from pancreatic duct contain
Pancreatic amylase, trypsinogen, lipase, fluid also has sodium hydrogencarbonate making it alkaline to neutralise content of digestive system after leaving acidic stomach environment
What is function of pancreatic amylase
A carbohydrate which digests amylose to maltose
What is trypsinogen function and lipase function
Try= An inactive protease which is converted to active trypsin when enters duodenum, lipase= digests lipid molecules
What is the Pancras endocrine function/structure
In small patches amount acini lobules are islets of langerhans, these have alpha and beta cells that make up endocrine system in pancreas
What do alpha cells secrete
Glucagon
What do beta cell secrete
Insulin
What happens when insulin secreted from beta cells in islets of langerhans
Brings about effect that reduces blood glucose concentration
What must happen when blood glucose goes too high and what must happen when it’s too low
Too high, insulin must be secreted from beta cells, and necessary that beta cells stop secreting insulin when blood glucose too low
What are the first 4 steps of beta cells releasing insulin
1.cell membrane of beta cells have Ca+ and K+ channels 2.K+ channels are normally open and Ca+ channels closed, so K+ diffuse out of cell making inside more negative (-70mV resting potential) 3.when glucose concentrations outside cell high glucose molecules move into cell 4.glucose is quickly used in metabolism to produce ATP, involving enzyme glucokinase
What are the last 4 steps of beta cells releasing insulin
5.extra ATP causes K+ channels to close 6.K+ can no longer diffuse out altering potential difference across cell membrane 7.this change in potential difference opens Ca+ channels 8.Ca+ enter cell and cause secretion of insulin by making vesicles containing insulin move to cell surface membrane and fuse with it releasing insulin by exocytosis
What is hypoglycaemia
When blood sugar drops and stays low for long period of time
What are symptoms of hypoglycaemia
Inadequate glucose delivered to tissues like brain, mild hypoglycaemia causes tiredness and irritability but severe cases can impair brain function and confusion leading to seizures and death
What is hyperglycaemia
Blood glucose too high and can lead to organ damage (high blood glucose diagnosis Diabetes mellitus)
What monitor blood glucose concentration and what happens when change detected
Cells in islets of langerhans detect change, depending on blood glucose rise/fall alpha or beta cells detect change and release correct hormones (insulin if too high, glucagon if too low)
What do hormones released from alpha and beta cells act on
Hepatocytes which store glucose as glycogen, excess glucose converted to glycogen, if blood glucose low, glycogen hydrolysed back to glucose
What happens when blood glucose too high
Beta cells in islets of langerhans detect it and secrete insulin into blood, target cells are in liver, muscle and brain
What is insulin made up of and what does this mean
Made up of 51 amino acids so can’t pass cell surface membrane, target cells have membrane bound insulin receptors, when it binds it activates enzyme tyrosine kinase associated with receptor inside membrane
WhT does tyrosine kinease cause as result of blood glucose too high
Causes phosphorylation of inactive enzymes in cell which activates enzymes leading to cascade of enzyme controlled reactions inside cell
What effects does insulin have on cell
More transporter proteins specific to glucose placed in cell surface membrane by vesicles containing these fusing with plasma membrane, so more glucose enters cell, glucose converted to glycogen for storage, more glucose converted to fats or used in respiration, increases uptake of glucose through specific transporter proteins reduces blood glucose concentration
What is glycogenesis
Glucose converted to glycogen for storage
What happens when blood glucose too low
Detected by alpha cells and glucagon released
What is glucagon and what does this mean
Derived from amino acids, target cells are hepatocytes which have specific glucagon receptors as it cannot enter cell
What happens when glucagon binds to complementary receptors
It stimulates G protein in membrane activating adenyl cyclase inside each cell which converts ATP to cAMP which activates enzyme controlled reactions inside cell
What are the effect of glucagon inside cell
Glycogen converted to glucose by phosphorylase A, 1 of enzymes activated in cascade, more fatty acids used in respiration, amino acids and fats converted to extra glucose, overall effect increases blood glucose
What is glycogenolysis
Glycogen converted to glucose
What is gluconeogenesis
Amino acids and fats converted to extra glucose
What is concentration of blood glucose controlled by
Negative feedback involving hormones insulin and glucagon, hormones are antagonistic (opposite effect), 1 effect inhibits the effect of the other
Do blood glucose always stay the same
No it fluctuates
How does negative feedback work if rise in blood glucose
Beta cells detect change-beta cells secrete insulin-insulin detected by receptors in liver and muscle cells-liver and muscle cells convert glucose to glycogen-blood glucose falls
How does negative feedback work if fall in blood glucose
Detected by alpha cell-alpha cells secrete glucagon-glucagon detected by receptors on liver cells-liver cells convert glycogen to glucose and release into blood-blood glucose rises
What is diabetes mellitus
Condition where body no longer produces sufficient insulin to control blood glucose concentration which can lead to hyperglycaemia after meals rich in sugars and other carbs, it can also lead to hypoglycaemia after exercise or fasting
What is type 1 diabetes
Insulin dependant diabetes, usually starts in childhood as result of autoimmune response where body’s immune system attacks and destroys beta cells or could be result of viral attack
In healthy person how is blood glucose regulated
Glucose absorbed into blood and ant excess converted to glycogen in liver and muscles, this glycogen can then be used to release glucose when blood glucose concentration falls
What happens to regulating blood glucose in someone with type 1 diabetes
No longer synthesise sufficient insulin and can’t store excess glucose as glycogen, excess glucose in blood not removed quickly, leading prolonged period of high concentration. But when blood glucose falls no store of glycogen used to release glucose so blood glucose concentration falls too low (hypoglycaemia)
What is type 2 diabetes
Non-insulin dependant diabetes, they can produce insulin but not enough, as people age responsiveness to insulin decreases as receptors on liver and muscle cells less responsive and cells lose ability to respond to insulin in blood
What happens in type 2 diabetes
Blood glucose concentration permeantly raised which can damage major organs and circulation
What factors endive early onset type 2 diabetes
Obesity, lack of exercise, high sugar diet, family history
How is type 1 diabetes treated
Insulin injections, blood glucose concentration must be monitored and correct dose of insulin administered to keep glucose concentration stable
What are 3 alternatives to insulin injections in type 1 diabetes treatment
Insulin pump therapy-small device constantly pumps insulin into bloodstream through needle that’s permanently inserted under skin, islet cell transplant-healthy beta cells from pancreas of deceased donor implanted in pancreas, complete pancreas transplant
What is a developing treatment for type 1 diabetes
Using stem cells to grow new islets of langerhans in pancreas
Where are stem cells obtained for treating type 1 diabetes
Mostly bone marrow or placenta stem cells, but, also precursor cells in pancreas of adult mice are capable of developing into many cells, if this is the same for humans then could be used to produce new beta cells
How is type 2 diabetes treated
Changes in lifestyle, lose weight, exercise regularly and monitor diet, may take supplementary medicine to reduce amount of glucose in liver released into blood or boost insulin released form pancreas, severe cases may use insulin injection
How did insulin use to be extracted for treating diabetes
Pancreas of animals like pigs as matches human insulin closely
How is insulin now extracted for treating diabetes
Bacteria have undergone genetic modification to manufacture human insulin
What are advantages of using insulin from genetically modified bacteria
Exact cope of human insulin so faster and more effective, less chance of developing insulin tolerance, less chance of rejection due to immune response, lower risk of infection, cheaper to manufacture and more can be made, less moral objections to using bacteria rather than extracting it from animals
