Neuronal and Hormonal Communication Flashcards
1
Q
Define sensory receptor
A
cells/sensory nerve endings that respond to a stimulus in the internal or external environment of an organism and can create action potentials
2
Q
Define transducer
A
cell that converts one form of energy into another
3
Q
Describe what sensory receptors are
A
-specialised cells that can detect change in surroundings
-most are energy transducers that convert one form of energy to another
-most are adapted to detect changes in particular form of energy
-each change in environment is called a stimulus
-sensory receptors respond to stimulus by creating a signal in the form of electrical energy- nerve impulse
4
Q
Change in pressure leads to
A
-pacinian corpuscle in skin
-movement to electrical
5
Q
Change in light intensity leads to
A
-light sensitive cells (rods and cones) in retina
-light to electrical
6
Q
Change in temperature leads to
A
-temperature receptors in skin and hypothalamus
-heat to electrical
7
Q
Change in chemicals in air leads to
A
-offactory cells in epithelium lining nose
-receptors detect presence of chemical and create electrical nerve impulse
8
Q
Describe the pacinian corpuscle
A
-pressure sensory on skin that detects pressure changes
-oval shape structure that has series of concentric rings of connective tissue wrapped around end of nerve cell
-when pressure on skin changes, rings of connective tissue deform and push against nerve ending
-sensitive only to changes in pressure; therefore when pressure is constant, they stop responding
9
Q
PERMEABILITY: describe channels of the nervous system
A
-cells associated with nervous system have specialised channel proteins
-some of these, called sodium channels, are specific to sodium ions
-others called potassium channels, specific to potassium ions
-these channels also possess gate that can open of close channel
-the sodium channels sensitive to smell movements of membrane, so when deformed by changing pressure, sodium channels open
-this allows sodium ions to diffuse into cell, producing generator potential
10
Q
Describe how permeability of nervous system cells changed
A
-membranes also contain sodium/potassium pumps that actively pump sodium ions out of cell and potassium ions into cell
-when channel proteins all closed, the sodium/potassium pumps work to create concentration gradient
-concentration of sodium outside cell increases whilst concentration of potassium ions inside cell increases
-3NA+ OUT / 2K+ IN
-membrane is more permeable to potassium so some leak out of cell
-less permeable to sodium so few able to leak into cell
-result of this is potential gradient across cell
-cell negatively charged cross inside compared with outside
-negative potential enhanced by presence of negatively charged anions in cell
11
Q
Describe how nerve impulse generated
A
-when cell is inactive, cell membrane said to be polarised that is negatively charged inside compared with outside
-nerve impulse created by altering permeability of nerve cell membrane to sodium ions
-achieved by sodium ion channels opening
-as sodium ion channels open, membrane permeability is increased and sodium ions move across membrane down concentration gradient into cell
-movement of ions across membrane creates change in potential difference across membrane
-inside cell less negative than usual - called depolarisation
-change in potential across receptor membrane called generator potential
-below threshold (-50mV)
12
Q
Describe how action potential created
A
-if small stimulus detected, only few sodium channels will open
-the larger the stimulus, the more gated channels will open
-if enough gates opened and enough sodium ions enter cell, the potential difference across cell membrane changes significantly and will initiate action potential
-threshold potential is above -50mV
13
Q
Define motor neurone
A
neurones that carry action potential from CNS to effector, such as muscle or gland
14
Q
Define relay neurone
A
join sensory neurones to motor neurones
15
Q
Define sensory neurones
A
neurones that carry action potential from sensory receptor to CNS
16
Q
What is the function of neurones
A
-once stimulus detected and its energy ben converted to depolarisation of receptor cell membrane, impulse must be transmitted to other parts of body
-the impulse transmitted along neurones as an action potential
-the action potential carried as rapid depolarisation of membrane caused by influx of sodium ions
17
Q
What are the differences between types of neurones
A
-motor neurones have cell body in CNS and have long action potential out to effector
-sensory neurones have long dendron carrying action potential from sensory receptor to cell body which is positioned outside CNS
-they have short axon carrying action potential in CNS
-relay neurones connect sensory and motor neurones together
-they have many short dendrites and short axon
-number of dendrites and number of divisions of axon is variable
-relay neurones essential part of nervous system which conduct impulses in coordinated pathways
18
Q
Location of myelinated and non myelinated neurones
A
-around one third of peripheral neurones in vertebrates are myelinated neurones - insulated by individual myelin sheath
-remainder of peripheral neurones and neurones in CNS are not myelinated
19
Q
Describe the composition of myelinated neurones
A
-most sensory and motor neurones are associated with Schwann cells which make up fatty sheath called myelin
-these schwann cells wrapped tightly around neurone so sheath actually consists of several layers of membrane and thin cytoplasm from scwann cell
-at intervals of 1-3mm along neurone there are gaps in myelin sheath - called nodes of Ranvier
-each node very short - about 2-3um
20
Q
What does the myelin sheath do
A
-because myelin sheath tightly wrapped around neurone, it prevents movement of ions across neurone membranes
-therefore movement of ions across membrane can only occur at nodes of Ranvier
-this means the impulse or action potential, jumps from one node to next
-makes conduction more rapid
21
Q
Describe non myelinated neurones
A
-also associated with Schwann cells but several neurones may be enshrouded in one loosely wrapped Schwann cell
-means action potential moves along neurone in wave rather then jumping from node to node
22
Q
What are the advantages of myelination
A
-can transmit action potential much quicker than non myelinated neurones
-typical speed of myelinated is 100-120ms-1 however non myelinated is just 2-20ms-1
-carry action potentials over long distances from sensory receptors to CNS then to effectors
-increased speed of transmission means action potential reaches end of neurone much more quickly allowing for a rapid response to a stimulus
-non myelinated neurones tend to be shorter and carry action potentials only over short distance
-often used in coordinating body functions such as breathing and action of digestive system
-therefore, increased speed of transmission not so important
23
Q
Describe neurotransmitter
A
-chemical signals across synapse
-synthesised in ribosomes on RER
-stored in terminal branch
24
Q
Define action potential
A
-brief reversal of potential across membrane of neurone causing peak of +40kV compared to resting potential of -60mV
25
Define resting potential
-potential difference across membrane while neurone at rest
26
Describe neurones at rest
-while neurone not transmitting action potential, said to be at rest
-sodium/potassium ion pumps use ATP to pump 3 sodium ions out of cell for every 2 potassium ions pumped in
-gated sodium channels kept closed
-however, some potassium ion channels open, therefore plasma membrane more permeable to potassium ions than to sodium ions
-potassium ions tend to diffuse out of cell
-cell cytoplasm also contains anions
-hence interior cell maintained at negative potential compared with outside
-cell membrane said to be polarised
-potential across cell membrane about -60mV- called resting potential
27
How is resting potential maintained
1) Na+/K+ pump - 3Na+ out/2K+ IN
2) Na+ channels closed
3) Some K+ channels open
4) Anions inside cell e.g chloride, hydrogen carbonated
28
How is depolarisation caused
-Na+ diffuse in cell
29
Define voltage gated
respond to changes in voltage rather than environmental stimuli
30
Why is the action potential a positive feedback
-action potential is self-perpetuating - once it starts at one point in the neurone it will continue along to end of neurone
-all action potentials are same magnitude (+40mV)
-therefore referred to as all or nothing response
-if it does not reach threshold, it will not be generated
31
Describe the stages of an action potential
1) membrane starts in its resting state - polarised with inside of cell being -60mV compared to outside. There is higher concentration of sodium ions outside than inside and higher concentration of potassium inside than outside
2) sodium ion channels open and some sodium diffuse into cell
3) membrane depolarises - becomes less negative with respect to outside and reaches threshold value of -50mV
4) positive feedback causes nearby voltage-gated sodium ion channels to open and many sodium ions flood in. As more sodium ions enter, cell becomes positively charged inside compared outside
5) potential difference across plasma membrane reaches +40mV. Inside of cell positive compared with outside
6) sodium ion channels close and potassium channels open
7) potassium ions diffuse out of cell bringing potential difference back to negative compared with outside - called repolarisation
8) potential difference overshoots slightly, making cell hyperpolarised
9) original potential difference restored so cell returns it to its resting states
32
Describe the refractory period
-after action potential, sodium and potassium ions in wrong places
-concentrations of these ions inside and outside cell must be restored by action of sodium/potassium pumps
-for short time after each action potential to its importance to stimulate cell membrane to reach another action potential - known as refractory period to allow for recovery
-ensures action potential transmitted in one direction only
33
How does a local current form
1) when action potential occurs, sodium ion channels open at that point in neurone
2) open sodium ion channels allow sodium ions to diffuse across membrane from region of higher concentration outside neurone, into neurone. The concentration of sodium ions inside neurone rises at point where sodium ion channels open
3) sodium ions continue to diffuse sideways along neurone, away from region of increased concentration. This movement of charged particles is called a local current
4) the local current causes slight depolarisation further along the neurone which affects voltage gated sodium ion channels, causing them to open. The open channels allow rapid influx of sodium ions causing a full depolarisation (action potential) further along the neurone. The action potential has therefore moved along neurone.
34
Describe saltatory conduction
-where action potential jumps from one node to next
-myelin sheath is insulating layer composed of schwann cells wrapped tightly around the neurone
-sodium and potassium ions cannot diffuse through this layer
-therefore the ionic movement that creates action potential cannot occur over much of length of neurone - only a nodes of Ranvier
-in myelinated neurones, local currents therefore elongated and sodium ions diffuse along neurone from one node to next
35
Advantages of saltatory conduction
-a myelinated neurone can conduct an action potential at up to 120ms-1 - which is quicker than a non myelinated neurone
-this speeds up transmission of action potential along the neurone
36
What is the all or nothing rule
-all action potentials produce a depolarisation of +40mV
-for this to occur, they must reach threshold potential of -50mV else only a generator potential will be produced
37
How is the intensity of a stimulus determined
-the frequency at which the action potentials in the sensory region of the brain arrive
-higher frequency=more intense stimulus
-when stimulus is at higher intensity, more sodium ions opened in sensory receptor
-this produces more generator potentials
-as a result there are more frequent action potentials in sensory neurone then in CNS
38
What is a synapse
-a synapse is a junction between two or more neurones where one neurone can communicate with or signal to another neurone
-between the two neurones there is small gap, approximately 20nm wide called synaptic cleft
-the action potential in presynaptic neurone causes release of chemical called neurotransmitters that diffuse across synaptic cleft and generate new action potential in postsynaptic neurone
39
What is a cholinergic synapse
-a synapse that uses acetylcholine as its neurotransmitters
40
What are specialised features of the presynaptic bulb
-many mitochondria - indicating active process requiring ATP involved
-large amount of smooth endoplasmic reticulum which packages neurotransmitters into vesicles
-large number of vesicles containing molecules of chemical called acetylcholine that will diffuse across synaptic cleft
-number of voltage gated calcium ion channels on cell surface membrane
41
What is the postsynaptic membrane
-contains specialised sodium ion channels that can respond to the neurotransmitters
-these channels consist of five polypeptide molecules
-two of these have special receptor site that is specific and complementary to acetylcholine
-when acetylcholine molecule is present in synaptic cleft, binds to the receptor sites and causes sodium ion channels to open
42
Describe the transmission across a synapse
1) action potential arrives at synaptic bulb
2) voltage-gated calcium ion channels open
3) calcium ions diffuse into synaptic bulb
4)calcium ions cause synaptic vesicles to move and fuse with presynaptic membrane
5) acetylcholine released by exocytosis
6) acetylcholine molecules diffuse across cleft
7) acetylcholine molecules bind to receptor sites on sodium ion channels in postsynaptic membrane
8) sodium ion channels open
9) sodium ions diffuse across postsynaptic membrane into postsynaptic neurone
10)generator potential or excitatory post synaptic potential EPSP created
11) if sufficient generator potentials combine then potential across post synaptic membrane reaches threshold potential
12) a new action potential is generated in postsynaptic neurone
43
What is the role of acetylcholinesterase
-if acetylcholine left in synaptic cleft it will continue to open sodium ion channels in postsynaptic membrane and continue to cause action potentials
-acetylcholinesterase is enzyme found in synaptic cleft
-it hydrolyses acetylcholine to ethanoic acid and choline
-this stops transmission of signals
44
What happens to ethanoic acid and choline
-they are recycled
-re-enter the synaptic bulb by diffusion and recombined to acetylcholine using ATP from respiration in mitochondria
-recycled acetylcholine stored in synaptic vesicles for future use
45
Define summation
occurs when effects of several excitatory post synaptic potentials added together
46
How are action potentials example of cell signalling
-action potential all or nothing response
-once action potential starts, it will be conducted along entire length of neurone
-the action potential does not vary in size or intensity
-at end of neurone pre synaptic membrane releases neurotransmitter molecules into synaptic cleft
-the post synaptic neurone responds to these molecules - an example of cell signalling
47
What happens when EPSP is not sufficient to cause action potential
-one action potential passes down axon to synapse and cause few vesicles to move and fuse to pre synaptic membrane
-the relatively small number of acetylcholine molecules diffuse across cleft, producing small depolarisation
-this is an excitatory post synaptic potential
-this on its own, isn't sufficient to cause action potential in post synaptic neurone
-summation can result from several action potentials in pre synaptic neurone (temporal summation) or from action potentials arriving from several different pre synaptic neurones (spatial summation)
48
Difference between temporal and spatial summation
TEMPORAL
-series of action potentials in same pre synaptic neurone
SPATIAL
-several pre synaptic neurones may each contribute to producing an action potential in post synaptic neurone
49
Describe an inhibitory post synaptic potential
-GABA and glycine (neurotransmitter)
-can reduce effect of summation and prevent action potential in post synaptic neurone
-work either by opening chloride channels or opening potassium channels to cause hyperpolarisation
50
ROLE OF SYNAPSES: Convergence
-several pre synaptic neurones converge on one post synaptic neurone
-several EPSPs could be prevented from sending from one IPSP
51
ROLE OF SYNAPSES: Divergence
-one presynaptic neurone diverges to post synaptic neurones
52
ROLE OF SYNAPSES: one way transmission
-they ensure one way transmission occurs
-because there are only complementary receptors found on post synaptic membrane
53
ROLE OF SYNAPSES: Summation
-low level action potentials can be amplified by summation
54
ROLE OF SYNAPSES: Habituated
-repeated stimulation
-run out of vesicles of acetylcholine (ACh)
-synapses in fatigue
-e.g. background noise
55
ROLE OF SYNAPSES: Memory and conscious thought
-creation and strengthening neural pathways
-post synaptic membrane more sensitive to ACh
-addition of ACh receptors
56
ROLE OF SYNAPSES: Connect 2 neurones
-so signal passed from one to other - may be more complex and involve more than 2 synapses
57
Describe signalling using hormones
-the endocrine system is used for communication around body
-uses blood circulatory system to transport its signals
-signals release by endocrine system are molecules called hormones
-the blood system transports materials all over body, therefore any hormone released in blood will be transported throughout body
58
What are the types of hormone
-non steroid, protein and peptide hormones, derivatives of amino acids - e..g adrenaline, insulin, glucagon
-do not enter cell as are not soluble in phospholipid bilayer
-they need to bind to the cell surface membrane and release a second messenger inside cell
-steroid hormones e.g. oestrogen, testosterone, can pass through membrane and enter cell and nucleus
-have direct effect on DNA
-non polar
59
Describe endocrine glands
-hormones released into blood directly from endocrine glands
-the endocrine glands are ductless glands - consist of groups of cells that manufacture and release hormone directly into blood
-endocrine glands have groups of cells with associated capillaries but no visible ducts
-endocrine glands include pituitary, thyroid, thymus, adrenal, pancreas ovaries and testes
60
How are the signals detected
-hormones always have specific function
-cells receiving endocrine signal are called target cells
-these cells may be grouped together in target tissue such as epithelium of collecting ducts
-alternatively, may be more widely dispersed in number of tissues such as receptors for adrenaline found in CNS
-for non steroid hormones, target cells must possess specific receptor on plasma membrane that is complementary to shape of hormone
-this hormone binds to receptor and initiates changes in cell
-each hormone is different to another therefore they only affect cells that possess correct, specific receptor
61
Describe first and second messengers
-non steroid hormones are known as first messengers
-they are cell signalling molecules outside cell that bind to cell surface membrane and initiate effect inside cell
-usually cause release of another signalling molecule in cell called second messenger
-the second messenger stimulates change in activity of cell - set off cascade of enzyme controlled reactions
62
How is the second messenger activated
-many non steroid hormones act via G. protein in membrane
-the G protein is activated when hormone binds to receptor
-the G protein in turn activates an effector molecule - usually an enzyme that converts an inactive molecule to activate second messenger
-in many cells, effector molecule is the enzyme adenyl cyclase which converts ATP to cyclic AMP (cAMP)
-cAMP is the second messenger - may initiate cascade of enzyme controlled reactions that alter activity of cell
63
Describe the structure of adrenal glands
-adrenal glands are an example of endocrine gland
-found lying anterior (just above) kidneys - one on each side
-each gland is divided to outer adrenal cortex and inner adrenal medulla
-both regions are well supplied with blood vessels and produce hormones which are secreted directly into blood vessels
64
Describe the layers of the adrenal cortex
-the adrenal gland has outer capsule surrounding three distinct layers of cells
-zona glomerulosa - outermost layer; secretes mineralocorticoids such as aldosterone
-zona fasciculata - middle layer; secretes glucocorticoids such as cortisol
-zona reticularis - innermost layer; thought to secrete precursor molecules used to make sex hormones
65
Describe the adrenal medulla
-found at centre of adrenal gland and secretes adrenaline and noradrenaline
66
What are the functions of the hormones from the adrenal cortex
-the adrenal cortex uses cholesterol to produce a range of hormones
-these hormones are steroid based and able to enter cells directly by dissolving into cell surface membrane
-steroid hormones enter nucleus and have direct effect on DNA to cause protein synthesis
67
Summarise the action of steroid hormones
1) steroid hormones passes through cell membrane of target cell
2) steroid hormone binds with specific receptor (with complementary shape) 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 messenger RNA (mRNA) molecules which code for production of proteins
68
Role of mineralocorticoids
-e.g. aldosterone
-from zona glomerulosa help control concentrations of sodium and potassium in blood
-as result also contribute to maintaining blood pressure
-aldosterone acts on cells of distal tubules and collecting ducts in kidney
-it increases absorption of sodium ions, decreases absorption of potassium ions and increases water retention so increases blood pressure
69
Role of glucocorticoids
-e.g. cortisol
-from zona fasciculata help control metabolism of carbohydrates, fats and proteins in liver
-cortisol is released in response to stress of as a result of a low blood glucose concentration
-it stimulates production of glucose from stored compounds, especially glycogen, fats and proteins, in the liver
70
Role of cortisol
-may also be released by zona reticularis
-however, if correct enzymes not present for release of cortisol, then the zona reticularis releases precursor androgens into the blood
-these are taken up by ovaries or testes and converted to sex hormones (e.g. testosterone in males and oestrogen in females)
-sex hormones help development of secondary sexual characteristics and regulate production of gametes
71
Describe the mechanism of adrenaline from the adrenal medulla
-adrenaline released from adrenal medulla into blood and transported throughout body
-adrenaline polar molecule derived from amino acid tyrosine
-this means it cannot enter cells through plasma membrane like steroid hormone can
-therefore must be detected by specialised receptors on plasma membrane on target cells
-many cells and tissues have adrenaline receptors
-therefore effects of adrenaline are widespread
72
Describe the role of adrenaline and effects
-to prepare body for activity
-relax smooth muscle in bronchioles
-dilate pupils
-increase stroke volume of heart
-increase heart rate
-cause general vasoconstriction to raise blood pressure
-stimulate conversion of glycogen to glucose
-increase mental awareness
-inhibiting gut action
-body hair stand erect
73
Role of pancreas
-pancreas has both exocrine and endocrine functions
-two main secretions of pancreas are pancreatic juices containing enzymes which are secreted into small intestine
-and hormones which are secreted from islets of Langerhans into blood
74
Describe the exocrine function of pancreas
-exocrine glands secrete substances into a duct
-most cells in pancreas synthesise and release digestive enzymes
-exocrine cells are in small groups surrounding tiny tubules
-each group of cells is called an acinus (plural acini)
-acini are grouped together into small lobules separated by connective tissue
-cells of acini secrete enzymes they synthesise into tubule at centre of group
-tubules from acini join to form intralobular ducts that eventually combine to make up pancreatic duct
-pancreatic duct carries fluid containing enzymes into first part of small intestine, duodenum
75
Describe what enzymes make up the fluid from the pancreatic duct
-pancreatic amylase - carbohydrase which digests amylose to maltose. Maltose to glucose by maltase
-trypsinogen - inactive protease which will be converted to active form trypsin when enters duodenum. Converts proteins to peptides
-lipase - digests lipid molecules
-also contains sodium hydrogencarbonate which makes it alkaline
-helps to neutralise contents of digestive system that have just left acidic environment of stomach
76
Describe the endocrine function of the pancreas
-dispersed in small patches among lobules of acini are islets of Langerhans
-islets of Langerhan contain alpha and beta cells that make up endocrine tissue in pancreas
-the alpha cells secrete glucagon and beta cells secrete insulin
77
When is insulin released
-insulin is secreted from beta cells in islets of Langerhans, and brings about effects that reduce blood glucose concentrations
-if blood glucose concentration too high, then important that insulin released from beta cells
-however, if blood glucose concentration drops too low, important insulin secretion stops
78
How is insulin released from beta cells
1) cell membrane of beta cells contain both calcium ion channels and potassium ion channels
2) the potassium ion channels are normally open and calcium ion channels are normally closed. Potassium ions diffuse out of cell making inside more negative; at rest, potential difference across cell membrane about -70mV
3) when glucose concentrations outside cell are high, glucose molecules move into cell
4) glucose quickly used in metabolism to produce ATP. This involves enzymes glucokinase
5) extra ATP causes potassium channels to close
6) potassium can no longer diffuse out and this alters potential difference across cell membrane - becomes less negative inside
7) change in potential difference opens calcium ion channels
8) calcium ions enter cell and cause secretion of insulin by making the vesicles containing insulin to move to cell surface membrane and fuse with it, releasing insulin by exocytosis
79
What is normal blood concentration of glucose
4-6 mmol dm3
80
Describe hypoglycaemia
-if persons blood glucose concentration allowed to drop below 4mmol dm3 and remain too low for long periods, person said to be hypoglycaemic
-main problem caused by hypoglycaemia is inadequate delivery of glucose to body tissues and in particular to brain
-mild hypoglycaemia may simply caused tiredness and irritability
-however, in severe causes, may be impairment of brain function and confusion, which may lead to seizures, unconsciousness and even death
81
Describe hyperglycaemia
-if blood glucose concentrations is allowed to rise too high for long periods this is known as hyperglycaemia
-permanently high blood glucose concentrations can lead to significant organ damage
-a blood glucose concentration that is consistently higher than 7mmol dm3 is used as diagnosis for diabetes mellitus
82
How is glucose monitored
-the cells in islets of Langerhans constantly monitor the concentration of glucose in the blood
-if concentration rises or falls away from acceptable concentration then alpha and beta cells in islets of Langerhans detect change and respond by releasing relevant hormone
-insulin = blood glucose high
-glucagon= blood glucose low
83
What happens when concentrations change
-these hormones act on the cells in the liver (hepatocytes) which can store glucose in form of glycogen
-where there is excess glucose in blood it is converted to glycogen
-if glucose needed to raise blood concentration then glycogen converted back to glucose
84
Describe what happens when blood glucose too high
-a high blood glucose concentration is detected by beta cells in islets of Langerhans
-the beta cells respond by secreting insulin into blood
-insulin travels throughout body in circulatory system
-the target cells are the liver, muscle and other body cells including those in the brain
85
Describe the molecule insulin
-human insulin is a small protein of 51 amino acids, therefore unable to pass through cell surface membrane
-the target cells possess the specific membrane-bound receptors for insulin
-when insulin binds to insulin receptor, the activates the enzyme tyrosine kinase which is associated with receptor on inside of membrane
-tyrosine kinase causes phosphorylation of inactive enzymes in the cell
-this activates enzymes leading to cascade of enzyme-controlled reactions inside the cell
86
Describe the effects of insulin on the cell
-more transporter proteins specific to glucose placed into cell surface membrane. Achieved by causing vesicles containing these transporter proteins to fuse with membrane
-more glucose enters cell
-glucose in cell converted to glycogen for storage - glycogenesis
-more glucose converted to fats
-more glucose used in respiration
-the increased uptake of glucose, through the specific transported proteins, reduces blood glucose concentrations
87
Describe what happens in blood glucose too low
-a low blood glucose concentration detected by alpha cells in islets of Langerhans
-the alpha cells then secrete hormone glucagon into blood
-glucagon is small protein containing 29 amino acids
-its targets cells are hepatocytes which possess specific receptor for glucagon
-when blood passes these cells, glucagon binds to receptors
-this stimulates G protein inside membrane which activates adenyl cyclase inside each cell
-adenyl cyclase converts ATP to cAMP which activates series of enzyme controlled reactions in cell
88
What are the effects of glucagon
-glycogen converted to glucose - glycogenolysis- by phosphorylase A which is one of enzymes activated in cascade
-more fatty acids used in respiration
-amino acids and fats converted to additional glucose by gluconeogenesis
-overall effect is to increase blood concentration
89
Describe how glucose concentration involves negative feedback
-concentration of blood glucose is controlled by negative feedback mechanism involving both insulin and glucagon
-hormones are antagonistic - have opposite effects on blood glucose concentration
-one of their effects is to inhibit effects of opposing hormone
-blood concentration of glucose will not remain constant - will fluctuate around required concentration
-when too high, insulin release
-when too low, glucagon released
90
What is diabetes mellitus
-a condition in which body is no longer able to produce sufficient insulin to control its blood glucose concentration
-this can lead to prolonged very high concentrations of glucose (hyperglycaemia) after a meal rich in sugars and other carbohydrates
-it can also lead to concentration dropping too low (hypoglycaemia) after exercise or fasting
91
Describe type 1 diabetes
-also known as insulin dependent diabetes or juvenile onset diabetes because usually starts in childhood
-thought to result of autoimmune response in which bodys immune system attacks and destroys beta cells
-may also result from viral attack
-person no longer able to synthesise sufficient insulin and cannot store excess glucose as glycogen
-excess glucose in blood not removed quickly, leaving prolonged period of high concentration
-however, when blood glucose falls, no store of glycogen that can be used to release glucose
-therefore blood glucose concentration falls too low - period of hypoglycaemia
92
Describe type 2 diabetes
-also known as non insulin dependent diabetes
-person with type 2 diabetes can produce insulin, but not enough
-as people age, their responsiveness to insulin declines
-probably because specific receptors on surface of liver and muscle cells become less responsive and cells lose ability to respond to insulin in blood
-blood glucose concentration almost permanently raised which can damage major organs and circulation
93
What factors can bring on earlier onset of type 2 diabetes
-obesity
-diet high in sugars, especially refined
-afro-caribbean or asian origin
-family history
94
How is type 1 diabetes treated
-using insulin injections
-blood glucose concentration monitored and correct dose of insulin administered to keep glucose concentrations fairly stable
95
What are alternatives to insulin injections
-insulin pump therapy - small device constantly pumps insulin into bloodstream through needle permanently inserted under skin
-islet cell transplant - healthy beta cells from pancreas of deceased donor implanted into pancreas of type 1 patient
-complete pancreas transplant
96
Describe the stem cell possibility
-recent research has shown it may be possible to grow new islets on Langerhans in pancreas using stem cells
-stem cells are not yet differentiated and can be induced to develop into variety of cell types
-most common sources of stem cells are bone marrow and placenta
-would give patient freedom from daily insulin injections
97
How can type 2 diabetes be treated
-usually by changes in lifestyle
-advised to lose weight, exercise regularly and carefully monitor diet, taking care to match carbohydrate intake and use
-may be supplemented by medication that reduces amount of glucose the liver release to bloodstream or boosts amount of insulin released from pancreas
-in severe cases, may include insulin injections or use of other drugs that slow down absorption of glucose from digestive system
98
How is insulin sourced to treat diabetes
-extracted from pancreas of animals - usually from pigs as this matches human insulin most closely
-however, more recently, insulin produced by Escherichia coli bacteria that have undergone genetic modification to manufacture human insulin
99
What are the advantages of GM bacteria
-exact copy of human insulin, therefore faster acting and more effective
-less chance of developing tolerance to insulin
-less chance of rejection due to immune response
-lower risk of infection
-cheaper to manufacture and more adaptable to demands
-people less likely to have moral objections
100
What happens when glucose levels lowered
- B cells decrease insulin secretion
- A cells increase glucagon secretion
-hepatocytes are target cells
1) breakdown glycogen into glucose (glycogenolysis)
2) use of fatty acids in respiration
3) production of glucose from other compounds (such as fats and amino acids) - gluconeogenesis
101
What happens when blood glucose levels raised
-B cells increase insulin secretion
-detected by target cells (hepatocytes and muscle cells)
1) More glucose channels placed on membrane
2) More glucose enters cells
3) Glucose converted to glycogen (glycogenesis)
4)Glucose converted to fats
5) More glucose used in respiration
102
Define glycogenesis
glucose converted to glycogen
103
Define glycogenolysis
glycogen converted to glucose
104
Define gluconeogenesis
creation of new glucose when fats and proteins broken down (when blood sugars low)
105
Define phosphorylation
inactive enzymes converted to active enzymes via addition of phosphates
