Chapter 14 - Hormonal Coordination Flashcards
What does endocrine system use and for what?
- uses the blood circulatory systems to transport hormones as signalling molecules for communication
What are hormones?
- molecules (proteins/steroids) that are released by endocrine glands directly into the blood
- act as messengers, carrying a signal from the endocrine gland to a specific target organ/tissue
What are the 2 types of hormones?
- steroid hormones (eg. oestrogen and testosterone)
- non steroid hormones - protein and peptide hormones, and derivatives of amino acids (eg. adrenaline, insulin and glucagon)
What is the difference between the 2 types of hormones?
- steroid hormones can pass through the membrane + enter the cell and the nucleus, to have a direct effect on the DNA in the nucleus
- non steroid hormones - proteins are not soluble in (lipids) the phospholipid membrane + do not enter the cell. Non steroid hormones bind to the cell surface membrane that triggers a cascade of responses with cell (release a second messenger inside the cell)
What are endocrine glands?
- ductless glands which have groups of cells that make + release hormone directly into blood in capillaries running through the gland
What are target cells?
- cells receiving an endocrine signal
What must non- steroid hormones target cells possess?
- they must have a complementary shaped receptor on cell surface membrane of target cell
- hormone binds to this receptor + initiates changes in the cell
What are first messengers?
- non-steroid hormones
- signalling molecules outside the cell that bind to the cell surface membrane + initiate an effect inside the cell
Second messengers
- first messengers cause the release of another signalling molecule in the cell
- it stimulates a change in the activity of the cell
- cAMP is the second messenger
What is the adrenal gland?
- endocrine glands
- humans have 2 (above each kidney)
- made up of adrenal cortex and adrenal medulla surrounded by a capsule
What is the adrenal cortex?
- outer layer of the adrenal gland
- controlled by hormones secreted by pituitary gland
What is adrenal medulla?
- inner layer of adrenal gland
- controlled by the nervous system
What does the Adrenal cortex secrete?
- Glucocorticoids
- Mineralocorticoids
- Androgens
What does the Adrenal medulla secrete?
- Adrenaline - increases heart rate and raises blood glucose conc (for energy if u need to fight or flight)
- Noradrenaline - increases heart rate, causes pupils to dilate and widens airways in the lungs and narrows blood vessels in non essential organs to create a higher blood pressure
What is adrenaline?
- hormone released from the adrenal glands, which stimulates the body to prepare for fight/flight
- a polar molecule derived from tyrosine
- means it can’t enter cells through the plasma membrane like a steroid hormone
- must be detected by specialised receptors on the plasma membrane of the target cells
What are the 3 layers within the adrenal cortex?
- zona glomerulosa - outermost
(secretes mineralocorticoids such as aldosterone) - zona fasciculata - middle
(secretes glucocorticoids such as cortisol) - zona reticularis - innermost
(secrete precursor molecules that are used to make sex hormones)
What does the adrenal cortex use cholesterol for?
- produce a range of hormones:
- steroid based + able to enter cells directly by dissolving into the cell surface membrane
- steroid hormones enter nucleus + have direct effect on the DNA to cause protein synthesis
What do steroid hormones do? (4)
- pass through the cell membrane of the target cell
- binds with a specific receptor with a complementary shape in the cytoplasm
- receptor-steroid hormone complex enters nucleus of target cell + binds to another specific receptor on the chromosomal material
- binding stimulates the production of mRNA molecules, which code for the production of proteins
What does mineralocorticoids from the zona glomerulosa do?
- help control the conc of Na and K in the blood
- therefore they contribute to maintaining blood pressure
- aldosterone acts on the cells of the DT + collecting ducts in the kidney
- increases absportion of Na+, decreases absorption of K+ and increases water retention = increases blood pressure
What does glucocorticoids from the zona fasciculata do?
- control the metabolism of carbs, fats and proteins in the liver
- cortisol is released in response to stress/ result of a low blood glucose concentration
- stimulates the production of glucose from stored compounds
What is released by the zona reticularis when incorrect enzymes present to release cortisol ?
- precursor androgens into the blood
- taken up by the ovaries/testes + converted to sex hormones
- sex hormones help development of the secondary sexual characteristics + regulate the production of gametes
Where is adrenaline released from and to? and How?
- adrenal medulla into the blood + transported around the body
- it attaches to receptors on surface of target cells and causes protein G to be activated
- therefore ATP converted into cAMP
- cAMP activates enzyme to hydrolyse glycogen into glucose (PROCESS OF GLYCOGENOLYSIS)
What effects does adrenaline have on the body?
- relax smooth muscle in bronchioles
- ↟stroke volume of the heart
- ↟ heart rate
- causing general vasoconstriction to ↟ blood pressure
- stimulates conversion of glycogen -> glucose via hydrolysis in liver
- dilating the pupils
- increasing mental awarenes
- inhibiting the action of the gut
- causing body hair to stand erect
The pancreas and what is it?
- gland located behind the stomach
- releases hormones to control blood glucose levels (functioning as an ENDOcrine gland)
- also release enzymes for digestion (functioning as an EXOcrine gland)
- mostly made up of exocrine tissue (secreting amylase, proteases and lipases)
What are the 2 main secretions of the pancreas?
- exo = Most of the cells of the pancreas secrete digestive enzymes found in pancreatic juices secreted into small intestine
- endo = hormones which are secreted from the islets of Langerhans into the blood (insulin and glucagon)
What do exocrine glands do ?
- secrete substances into a duct
What is the exocrine function of the pancreas?
- cells in the pancreas synthesise + release digestive enzymes
- to produce pancreatic juice (containing digestive enzymes) to be delivered to the small intestine
acini and that
group of cells = acinus
- acini grouped together into small lobules separated by connective tissue
- exocrine part of pancreas
- secretes digestive enzymes into duct
- tubules from the acini join = intralobular ducts that combine = pancreatic duct
What enzymes are within the fluid from the pancreatic duct?
- pancreatic amylase = carbohydrase which digests amylose to maltose
- trypsinogen = inactive protease which’ll be converted to the active form trypsin when it enters the duodenum
- lipase = which digests lipid molecules
What does the fluid from pancreatic duct contain?
- sodium hydrogen carbonate which makes it alkaline
- helps neutralise contents of the digestive system
Where are the islets of Langerhans?
- dispersed in small patches among the lobules of acini
- they are an endocrine tissue
What do the islets of Langerhans contain?
- alpha + beta cells that make up the endocrine tissue in the pancreas
alpha cells secrete glucagon
beta cells secrete insulin
What happens when insulin is secreted from the beta cells in the islets of Langerhans?
- effects that reduce blood glucose concentration
- BGC is too ↟, insulin is released from the beta cells
- liver cells become more permeable to glucose and enzymes are activated to convert glucose to glycogen
- BGC is too ↡, insulin secretion stops
- glucose is stored as glycogen in cells
What happens when glucagon is secreted from the alpha cells in the islets of Langerhans?
- effects that increase blood glucose concentration
- BGC is too low, glucagon is released from the alpha cells
- adrenal gland also releases adrenaline
- second messenger model occurs to activate enzymes to hydrolyse glycogen
- BGC is too high, glucagon release stops
How is insulin released from the beta cells when glucose is too high?
- high glucose is detected by the β cells in the pancreas
- the conc. of glucose is high = glucose molecules enter the β cells by facilitated diffusion (via glucose transporter)
- cells respire this glucose and produce ATP which bind to potassium ion channels
- K+ channels are normally opened and Ca+ channels are normally closed.
- high conc. of ATP causes the K+ channels in the β cells to close (at rest the potential difference across the cell membrane is about -70mV) producing a change in the membrane potential as K can no longer diffuse out and this means it becomes less -ve
- depolarisation occurs as K+ can’t diffuse out
- change in the membrane potential causes the voltage-gated Ca channels to open
- response to influx of calcium ions, the β cells secrete insulin
- secretory vesicles carry insulin and move towards the cell-surface membrane and fuse with it where they release insulin into the capillaries via exocytosis
- once in the bloodstream, insulin circulates around the body + stimulates the uptake of glucose by muscles cells, fat cells and the liver
What are the effects insulin has on the cell?
- attaching to receptors on surface of target cells changes tertiary structure of channel proteins so more glucose is absorbed via faciliated diffusion
- more protein carriers are incorporated into cell membranes so more glucose absorbed into cell
- more active enzymes involved in conversion of glucose to glycogen for storage - results in glycogenesis in liver
- more glucose is converted to fats
- more glucose used in respiration
What is hypoglycaemia?
- BGC drops below 4mmoldm-^3 + remains too low for long periods
What is the main problem caused by hypoglycaemia?
- inadequate delivery of glucose to the body tissues, and in particular, to the brain
- cause tiredness + irritability to impairment of brain function + confusion -> lead to seizures, unconsciousness + death
What is hyperglycaemia?
When BGC rises too ↟ for long periods of time
- permanently high -> significant organ damage
What is used as the diagnosis for diabetes mellitus?
- BGC consistently ↟ than 7mmol dm^-3
How is low blood glucose dealt with?
glycogenolysis
- glucagon attaches to the complimentary receptors on the surface of target cells (liver cells (hepatocytes)) when blood passes these cells
- activates a G protein that activates the enzyme adenylyl cyclase (this is cuz the shape of enzyme adenylyl cyclase changes so its activated)
- which catalyses the conversion of ATP to the second messenger, cyclic AMP (cAMP)
- cAMP binds to protein kinase A enzymes to activate them
- Active protein kinase A enzymes activate phosphorylase kinase enzymes by adding phosphate groups to them
- Active phosphorylase kinase enzymes activate glycogen phosphorylase enzymes
- they then catalyse breakdown of glycogen to glucose
What are the effects of glucagon?
- more fatty acids are used in respiration
- amino acids + fats are converted into additional glucose, by gluconeogenesis
Glycogenesis
- converting glucose into glycogen
- occurs in liver and catalysed by enzymes there
Glycogenolysis
- hydrolysis of glycogen to glucose
- occurs in liver due to second messenger model
Gluconeogenesis
- creating glucose from other molecules
- eg aminoacids/glycerol from liver
What is the conc of blood glucose controlled by?
- negative feedback mechanism incl. both insulin and glucagon
What are glucagon and insulin referred to as?
- antagonistic - they have opp effects on BGC
- inhibit the effect of the opposing hormone
What is diabetes mellitus?
- type 2
- a condition in which body is no longer able to produce sufficient insulin to control its BGC
What can diabetes mellitus lead to ?
- prolonged ↟ conc of glucose (hyperglycaemia) after a meal rich in sugars + carbohydrates
- can also lead to conc dropping too low (hypoglycaemia) after exercise or fasting
What are the other 2 names Type 1 diabetes is referred to as?
- insulin-dependent diabetes
- juvenile-onset diabetes (starts in childhood)
What is Type 1 Diabetes thought to be the result of?
- autoimmune response in which the body’s immune system attacks + destroys the beta cells
- may also result from a viral attack
What is a person with Type 1 no longer able to do ?
- synthesise sufficient insulin + cannot store excess glucose as glycogen
- excess glucose in the blood isn’t removed quickly, leaving high conc
- when blood glucose falls, there is no store of glycogen so it falls even lower
What is Type 2 diabetes known as?
- non-insulin-dependent diabetes
What is Type 2 diabetes?
hereditary
- person can produce insulin but not enough to control their glucose levels
- BGC is almost permanently raised, which can damage major organs
Why do people’s responsiveness to insulin decline as they age?
- specific receptors on the surface of the liver and muscle cells become less responsive + cells lose ability to respond to insulin in the blood
Which 5 factors bring an earlier onset of Type 2 diabetes?
- obesity
- lack of regular exercise
- diet high in sugars, particularly refined sugar
- Asian/Afro-Caribbean origin
- family history
How is Type 1 diabetes treated?
- insulin injection
- diet - lots of fruit and veg
- BGC must be monitored+correct dose of insulin administered to keep GC stable
What are 3 alternatives to insulin injections?
- insulin pump therapy - small device constantly pumps insulin into bloodstream through permanently inserted needle under skin
- islet cell transplantation - healthy beta cells from the pancreas of a deceased donor implanted into the pancreas
- complete pancreas transplant
What does recent research show that might be possible to treat Type 1 diabetes?
using stem cells to grow new islets of Langerhans in the pancreas
- stem cells are not differentiated yet + can be induced to develop into variety of cell types
What have scientists found in pancreas of adult mice?
- precursor cells
- capable of developing into variety of cell types + may be true stem cells
- if similar can be found in human pancreas, it could be used to produce new beta cell
How can Type 2 diabetes be treated?
- changes in lifestyle
- lose weight, exercise regularly + monitor diet
- medication reduces glucose the liver releases to blood/ amount of insulin released from the pancreas
What are the 7 advantages of using insulin from genetically modified bacteria?
- exact copy of human insulin - faster acting + more effective
- less chance of developing tolerance to insulin
- less chance of rejection due to immune response
- lower risk of infection
- cheaper to manufacture the insulin than extract from animals
- manufacturing process is more adaptable to demand
- people are less likely to have moral objections to using insulin produced from bacteria than to use those extracted from animals
COMMON EXAM QUESTION !!!
Explain why the protein insulin must be administered intravenously rather than orally.
Insulin is a protein, if it was taken orally it would be digested by the enzyme protease found in the gut before entering the bloodstream.
