Organisms Respond To Chnages In Their Internal And External Environments Flashcards
1
Q
What do receptors do?
A
They detect stimuli, they can be cells or proteins on cell surface membranes
2
Q
What do effectors do?
A
Bring out a response to a stimulus, to produce an effect
They include muscle cells and cells found in glands like the pancreas
3
Q
What are the three main types of neurones?
A
Sensory = transmit electrical impulses from receptors to the central nervous system (brain and spinal cord)
Motor = transmit electrical impulses from the CNS to the effectors
Relay = transmit electrical impulses between sensory and motor neurones
4
Q
What happens when a stimulus is detected by a receptor cell?
A
An electrical impulse is sent along a sensory neurone
When an electrical impulse reaches the end of a neurone, chemical called neurotransmitters take the information across to the next neurone and so on
5
Q
What is a typical response to a stimulus?
A
Sensory Motor
Stimulus —> Receptors ————> CNS ————> Effectors —> Response
6
Q
What is the central nervous system?
A
The CNS made up of the brain and the spinal cord
7
Q
What is the peripheral nervous system?
A
Made up of the neurones that connect the CNS to the rest of the body
8
Q
What is the somatic nervous system?
A
Controls conscious activities e.g. running and playing video games
9
Q
What is the autonomic nervous system?
A
Controls unconscious activities e.g. digestion
(It has two divisions that have opposite affects on the body
10
Q
What is the sympathetic nervous system?
A
Fight or flight getting the body ready for action
11
Q
What is the parasympathetic nervous system?
A
Calms the body down to rest and digest
12
Q
What are reflexes?
A
Where the body responds to a stimulus without making a conscious decision to respond, because you don’t have to spend time deciding how to respond, they protect the body as they are rapid
Uses a relay neurone instead of going to the CNS
13
Q
What is an example of a typical reflex arc?
A
Hand-withdrawal in response to heat:
- thermoreceptorsdetect heat stimulus
- sensory neuron carries impulse to the relay neurone
- relay neurone connects the the motor neurone
- motor neurone sends impulses to the effect (muscles in arm)
- muscles contract and you with-draw your hand
14
Q
How is nervous system communication localised, short-lived and rapid?
A
Localised = when an impulse reaches the end of a neurone, neurotransmitters are secreted directly onto targets cells
Short-lived = neurotransmitters are quickly removed once they have done their job
Rapid = electoral impulses are really fast
15
Q
What is positive tropism?
A
Where growth is towards the stimulus
16
Q
What is negative tropism?
A
Where growth is away from as stimulus
17
Q
What is phototropism?
A
Response to light:
- shoots are positively phototropic and grow towards light
- roots are negatively phototropic and grow away from light
18
Q
What is gravitropism?
A
Response to gravity:
- shoots are negatively gravitropic and grow upwards
- roots are positively gravitropic and grow downwards
19
Q
What effects on growth does auxin have?
A
Growth factors called auxins stimulate the growth of shoots by cell elongation
However high concentrations of auxins can inhibit growth in roots
20
Q
What is Indoleacetic Acid?
A
IAA is a type of auxin that is produced in the tips of the roots and shoots of plants, it is moved around the plant to control tropisms
It moves by diffusion and active transport for short distances and via the phloem for long distances
Resulting in different parts of the plant having different concentrations of IAA, resulting in uneven growth either towards or away from a stimulus
21
Q
What does IAA do in phototropism?
A
IAA moves to the more shaded parts of the roots and shoots so there is uneven growth
Shoots = concentration of IAA increases on the shaded side and elongates the cells and the shoots bend towards the light
Roots = concentration of IAA increases on the shaded side but it inhibits the growth of these cells so the root bends away from light
22
Q
What does IAA do in gravitropism?
A
IAA moves to the underside of shoots and roots so there is uneven growth
Shoots = concentration increases on the underside where cells elongate so the shoot grows upwards
Roots = cocnentraion increases on the underside where cell growth is inhibited and so the root grows downwards
23
Q
What is taxis in animals?
A
The organisms move towards her away from a directional stimulus e.g. light
For example, phototaxis organisms will move away from a light source if it helps them survive
24
Q
What is kinesis in animals?
A
Organisms movement is affected by non-directional stimulus E.G.humidity
Is the random movement in order to get to better conditions for example in high humidity would move slow slowly and turn less so they stay in the correct conditions, in drier areas they will move more quickly in order to find better conditions quicker
25
How do receptor cells communicate information via the nervous system?
- when a receptor is in resting state there is a difference in charge between inside and outside the cell, generated by ion pumps and ion channels, meaning that there’s a voltage across the membrane aka potential difference
- P.D. At rest is the resting potential, when a stimulus is detected the cell membrane is excreted and becomes more permeable, allowing more ions to move in and out of the cell - altering the potential difference, change in p.d. due to a stimulus is called the generator potential
- bigger stimulus = bigger movement of ions and a bigger change in p.d. So bigger generator protein all is produced
- generator potential is big enough it will trigger an action potential = electrical impulse along a neurone, it is only triggered if the generator potential reaches the threshold value
- strength of the stimulus is measured by the frequency of action potentials
- if the stimulus is too weak = wont reach the threshold value = no action potential
26
What is the pacinian corpuscle?
- mechanoreceptors = detect mechanical stimuli e.g. pressure and vibrations, they are found in your skin
- they contain a sensory neurone called a sensory nerve ending, which is then wrapped in loads of layers of connective tissue called lamellae
- when a pacinian corpuscle is stimulated, the lamellae are deformed and press on the sensory nerve ending
- causing the sensory neurones cell membrane to stretch, deforming the stretch-mediated sodium ion channels to open and allow sodium ions to diffuse into the cell creating a generator potential
- if the generator potential reaches the threshold it triggers an action potential
27
What are photoreceptors in the eye?
- light receptors
- light enters through the eye through the pupil, the amount of light is controlled by the muscles of the iris
- light rays are focused by the lens onto the retina, which lines the inside of the eye, this is where the photoreceptor cells are
- the fovea is an area where there are lots of photoreceptors
- nerves impulses from the photoreceptor cells are carried from the retina to the optic nerve which is a bundle of neurones
- where the optic nerve is there is a blind spot
28
How do photoreceptors convert light into an electrical impulse?
- light enters the eye and hits the photoreceptors and is absorbed by light-sensitive optical pigments
- light bleaches the pigments causing a chemical change and altering the membrane permeability to sodium ions
- a generator potential is created and if it reaches the threshold, a nerve impulse is sent along a bipolar neurone
- bipolar neurones connect photoreceptors to the optic nerve, which takes the impulses to the brain
29
What’s the difference between rod and cone cells generally?
Rods = found over all the retina, only give black and white images
Cones = mostly concentrated on the fovea, contain red-sensitive pigments, blue-sensitive pigments, and green-sensitive pigments
30
What is the defence between the sensitivity of rod and cone cells?
Rods = very sensitive to light, work well in dim light mainly because many rod cells join to one neurone, so many weak generator potentials to reach the threshold and trigger an action potential
Cones = less sensitive to light, work best in bright light because one cone cell joins to one neurone so it take more light to reach the threshold and trigger an action potential
31
What is the difference in visual acuity between rod and cone cells?
- rods give low visual acuity because many rods join to the same neurone, which means light from two points close together can’t be told apart
- cones give high visual acuity as cones are close together and one cone joins to one neurone, when light form two points hits two cones, two action potentials go to the brain - so you can distinguish two points that are close together as two separate points
32
What is meant by the heart muscle being myogenic?
It can contract and relax without receving signals from nerves
33
How does the cardiac muscle contrail the regular beating of the heart?
- the sinoatrial node (SAN) which is in the wall of the right atrium sets the rhythm of the heartbeat by sending out regular waves of electrical activity to the atrial walls, causing the right and left atria to contract at the same time
- a band of non-conducting collagen tissue prevent the waves from being passed from the atrial to the ventricles
- the waves from the SAN are transferred to the atrioventricular node (AVN), which passes the waves of electrical activity to the bundle of His, there is a slight delay however before the AVN reacts to make sure the atria have emptied before the ventricles contract
- bundle of His is a group of muscle fibres that conduct the waves of electrical activity between the ventricular to the apex if the heart, the bundle splits into fibre muscle fibres called the Purkyne tissue
- the Purkyne tissue carries the waves of electrical activity into the muscle walls of the right and left ventricles casing them to contract simultaneously from the bottom up
34
How is heart rate controlled by the brain and autonomic nervous system?
- SAN generates electrical impulses that cause the cardiac muscles to contract
- the rate at which SAN fires is unconsciously controlled by a part of the brain called the medulla oblongata
- animals need to alter their heart rate to respond to internal stimuli
- electrical impulses from receptors are sent to the medulla along sensory neurones, where it is processed and sends impulses to the SAN along sympathetic or parasympathetic neurones
35
What are pressure receptors called?
Baroreceptors in the aorta and carotid arteries, stimulated by high and low blood pressure
36
What are chemical receptors called?
Chemoreceptors in the aorta, carotid arteries and the medulla
Monitor oxygen, co2 and pH of the blood
37
How does the heart respond to high blood pressure?
- Baroreceptors detect high blood pressure, impulses are sent to the medulla, which sends impulses along parasympathetic neurones, which secrete acetylcholine, which binds to receptors on the SAN
- heart rate slows down to reduce blood pressure back to normal
38
How does the heart respond to low blood pressure?
- baroreceptors detect low blood pressure, then impulses are sent to the medulla, which sends impulses along the sympathetic neurones which secrete noradrenaline which binds the receptors on the SAN
- heart rate speeds up to increase blood pressure back to normal
39
How does the heart respond to high blood oxygen, low carbon dioxide or high pH?
- chemorecptoers detect chemical changes in the blood, causing impulse to be sent to the medulla, which sends impulses along parasympathetic neurones, which secrete acetylcholine which binds to receptors on the SAN
- heart rate decreases to return O2, CO2 and pH levelss back to normal
40
How dies the heart respond to low blood oxygen, high carbon dioxide and low pH?
- chemoreceptors detect chemical changes in the blood, causing impulses to be dent to the medulla, which sends impulses along the sympathetic neurones, and secrete noradrenaline which binds to the receptors on the SAN
- heart rate increases to return O2, CO2 and pH back to normal
41
How does myelination affect the speed if conduction of action potentials?
- some neurones have a myelin sheath which is an electrical insulator made up of Schwann cells
- between the Schwann cells there ate patches if bare membrane called the nodes of ranvier, sodium ion channels are concentrated at the nodes
- on a myelinated neurone, depolarisation only happens at the nodes of ranvier, the neurones cytoplasm conducts enough electrical charge to depolarise the next node so the impulse jumps from node to node
- this is called saltatory conduction and its really fast
- non-myelinated neurones, the impulse travels along the entire axon depolarising the whole length of the membrane which takes longer
42
How does axon diameter affect the speed of condition of action potentials?
- action potentials are conducted quicker along axons with bigger diameters because there is less resistance to the flow of ions than in the cytoplasm of a smaller axon
- with less resistance, depolarisation reaches other parts of the neurone cell membrane quicker
43
How does temperature affect the speed of conduction of action potentials?
Speed of conduction increases as the temperature increase, as ions diffuse faster, speed only increases up to around 40°C as after that the proteins begin to denature
44
What happens during a synapse?
- the tiny gap between the two cells is called the synaptic cleft
- presynaptic neurone has a swelling called a synaptic knob, which contains synaptic vesicles filled with chemicals called neurotransmitters
- when an action potential reaches the end of a neurone it causes neurotransmitters to be released into the synaptic cleft
- they diffuse across to the postsynaptic membrane and bind to specific receptors
- where they might trigger an action potential and cause a muscle contraction or hormone to be secreted
- impulses are unidirectional = the impulse can only travel in one direction
- neurotransmitters are removed from the cleft so the response doesn’t keep happening
45
What is a cholinergic synapse?
- an action potentials arrives at the presynatic knob
- the action potentials stimulates voltage-gated calcium ion channels in the presynaptic neurone to open
- calcium ions diffuse into the synaptic knob
- the influx of calcium ions into the synaptic knob causes the synaptic vesicles to move to the presynaptic membrane
- they then fuse with the membrane
- vesicles release the neurotransmitter acetylcholine into the synaptic cleft = exocytosis
- ACh diffuses across synaptic cleft and binds to specific cholinergic receptors on the postsynaptic membrane
- causing sodium ion channels to open
- the influx of sodium ions causes depolarisation and an action potential is generated if the threshold is reached
- ACh is removed from the synaptic cleft so the response doesn’t keep happening
- ACh is broken down by an enzyme called acetylcholinerase and the products are re-absorbed by the presynaptic neurone and used to make more ACh
46
How can neurotransmitters be excitatory, inhibitory or both?
Excitatory neurotransmitters depolarise the postsynaptic membrane, ,asking it fire an action potential if the threshold is reached
Inhibitory neurotransmitters hyper-polarise the postsynaptic membrane preventing it from firing an action potential
47
What is spatial summation?
- many neurones connect to one neurone
- small amount of neurotransmitter released from each of these neurones can be enough altogether to reach the threshold in the postsynaptic neurone and trigger an action potential
- if some neurones release an inhibitory neurotransmitter then the total effect of all the neurotransmitters might be no action potential
48
What is temporal summation?
Where two or more nerve impulses arrive in quick succession from the same presynaptic neurone
- making an action potential more likely because more neurotransmitters is released into the synaptic cleft
49
What is a neuromuscular junction?
- a synapse between a motor neurone and a muscle cell
- using acetylcholine, which binds to cholinergic receptors called nicotinic cholinergic receptors
- similar to normal cholinergic synapses, there are some differences though:
- the postsynaptic membrane has lots of folds that form clefts, these clefts store the enzyme that breaks down ACh
- more receptors than other synapses
- ACh is always excitatory at a neuromuscular junction, so when a motor neurone fires an action potential, it normally triggers a response
50
How can drugs affect the action of neurotransmitters at synapses?
- if drugs are the same shape as the neurotransmitter, called agonists, causing more receptors to be activated
- some drugs block receptors so they can’t be activated by neurotransmitters, called antagonists, meaning fewer receptors can be activated, can result in a muscle being paralysed
- some drugs inhibit the enzyme that breaks down neurotransmitters, meaning there are more neurotransmitters in the synaptic cleft to bind to receptors and they are there for longer, leading to loss of muscle control
- some drugs stimulate the release of neurotransmitters from the presynaptic neurone so more receptors are activated
- some drugs inhibit the release of neurotransmitters from the presynaptic neurone so fewer receptors are activated
51
What is meant by muscles acting in antagonistic pairs?
- skeletal muscle is the type of muscle used to move, they attached to bones by tendons and ligaments attach bones to other bones
- Pairs of skeletal muscles contract and relax to move bones at a joint the bones of the skeleton are incompressible so they act as levers giving the muscle something to pull against
- Muscles working together to move a boat antagonistic pairs the contracting muscle is the agonist and the relaxing muscle is the antagonist
For example, the bones of your lower arm are attached to a bicep muscle and a tricep muscle by tendon, when the bicep contracts your tricep relaxes, pulling the bone so your arm bends at the elbow hear the biceps of the agonist and the triceps of the antagonist
52
How is skeletal muscle made up of long muscle fibres?
- skeletal muscle was made up of large bundles of long cells called muscle fibres
- Cell membrane of muscle fibre cells is called sarcolemma
- parts of the sarcolemma fold inwards across the muscle fibre and stick into the sarcoplasm, these folds are called transverse T tubules and they helped to spread electrical impulses throughout the sarcoplasm so they reach all parts of the muscle fibre
- A network of Internet internal membranes called the sarcoplasmic reticulum runs through the psycho plasm, which stores and releases calcium ions
- Muscle fibres have lots of mitochondria to provide ATP, and they are multinucleate
- Muscle fibres have lots of long cylindrical organelles called myofibrils they are made up of proteins and highly specialised for contraction
53
Why does myofibrils contain thick myosin filaments?
- made of the protein myosin
- dark bands of a myofibril contain the thick myosin filaments and some overlapping thin actin filaments called A-bands
- in the middle of each sarcomeres there is a M-line which is the middle of the myosin filaments
- z-line = sarcomeres
- around the m-line there is a h-zone which only contains myosin filaments
54
Why do myofibrils contain thin actin filaments?
- thin myofilaments are made of the protein actin
- light bands in the myofibril contain thin actin filaments which are called I-bands
55
What is the sliding filament theory and how does explain muscle contraction?
- myosin and active filament slide over one another to make the sarcomeres contract (the microfilaments themselves don’t contract)
- This stimulates contraction of lots of sarcomeres meaning the myofibrils and muscle fibres contract
- sarcomeres returned their original length as the muscle relaxes
56
Why do myosin filaments have globular heads and binding sites?
Myosin filaments have globular heads that are hinged so they can’t move back and forth
- each myosin head has a binding site for actin and a binding site for ATP
- actin filaments have binding sites for myosin heads, called actin-myosin binding sites
- another protein called tropomyosin is found between actin filaments, it helps myofilaments move past each other
57
How are binding sites in resting muscles blocked by tropomyosin?
- in a resting muscle the actin-myosin binding site is blocked by tropomyosin
- so myofilaments can’t slide past each other because the myosin heads can’t bind to the actin-myosin binding sites on the actin filaments
58
How is muscle contraction triggered by an influx of calcium ions?
- an action potential causes Ca+ channel proteins in the ER to open
- Ca+ floods into the sarcoplasm and binds to the tropomyosin binding sites causing it shape to change
- tropomyosin moves away from the binding sites on actin
- adp attached to the myosin heads allows it to bind to the actin to form a cross-bridge
- as it binds it causes adp and a phosphate ion to be released causing the myosin heads to change its angle by approx.45’
- this pulls the actin filaments along
- atp binds to the myosin heads allows causing its shape to change and it detaches from the actin binding site
- atp is hydrolysed by the Ca+ hydrolyse atp to adp and a phosphate group, providing energy to return the myosin heads allows to its original position
- the process repeats while the concentration of Ca+ remains high in sarcoplasm
59
Why does excitation stop when calcium ions leave?
- muscle stops being stimulated, so calcium ions leave their binding sites and are moved by active transport back into the sarcoplasm if reticulum
- causing the tropomyosin to move back so they block the actin myosin binding sites again
- muscles aren’t contacted because no myosin heads are attached to actin filaments
- actin filaments slide back to their relaxed position, which lengthens the sarcomere
60
How do ATP and phosphocreatine provide energy for muscle contraction?
1) Aerobic respiration
- most atp is generated via oxidative phosphorylation in the cells mitochondria
- aerobic respiration only works when there’s oxygen = good for long periods of low intensity exercise
2) Anaerobic respiration
- atp is made rapidly by glycolysis
- end product of glycolysis is pyruvate, which is converted to lactate by lactate fermentation, which can build up quickly and cause muscle fatigue = good for short periods of hard exercise
3) ATP-Phosphocreatine PCr system
- ATP is made by phosphorylating ADP adding a phosphate group from PCr
- PCr is stored inside cells and the ATP-PCr system generates ATP very quickly
- PCr runs out after a few seconds so good for short bursts of vigorous exercise
- anaerobic and alactic
61
What’s the difference between slow twitch and fast which muscle fibres?
Slow twitch:
- contract slowly
- muscles used for posture for example
- good for endurance activities
- can work for a long time
- energy releases through aerobic respiration, lots of mitochondria and blood vessels supply the muscles with oxygen
- reddish in colour because they a re rich in myoglobin = stores oxygen
Fast twitch:
- contract quickly
- used for fast movement
- good for short bursts of speed and power
- energy releases through anaerobic respiration, few mitochondria or blood vessels
- whitish colour because they do not have much myoglobin
62
How are neurone cell membranes polarised at rest?
- in resting state, the outside of the membrane is positively charged compared to the inside, because there are more positive ions outside the cell
- so the membrane is polarised - there’s a difference in charge across it
63
What is a resting potential and how is it created?
- the voltage across the membrane when its at rest is called the resting potential about -70mV
- created and maintained by sodium-potassium pumps and potassium ion channels
- sodium potassium pumps move sodium ions out of the neurone, but the membrane isn’t permeable to sodium ions, so they can’t diffuse back in, creating a sodium ions electrochemical gradient because there are more positive sodium ions outside the cell
- they also move potassium ions in the neurone, but the membrane is permeable to potassium ions so they diffuse back out through potassium ion channels
- making the outside of the cell positively charged compared to the inside
64
How do neurone cells become depolarised when they are stimulated?
1) stimulus - excites the neurone cell membranes, causing sodium ions electrochemical gradient channels to open, membrane becomes more permeable to sodium so sodium ions diffuse into the neurone down the sodium ion electrochemical gradient making the inside less negative
2) depolarisation - if the P.D. Reaches the threshold, more sodium ion channels open, more sodium ions diffuse rapidly into the neurone
3) re polarisation - at a p.d. Around +30mV the sodium ion channels close and potassium ion channels open, the membrane is more permeable to potassium so potassium ions diffuse out of the neurone down the potassium ion concentration gradient, this starts to get the membrane back to its resting potential
4) hyperpolarisation - potassium ion channels are slow to close so there’s a slight overshoot where too many potassium ions diffuse out of the neurone, the p.d. Becomes more negative than the resting potential
5) resting potential - ion channels are reset, the sodium-potassium pumps move sodium returns the membrane to its resting potential and maintains it until the membranes excited by another stimulus
65
What is the refractory period?
When the neurone cell membrane can’t be excited again straight away
- this is because the ion channels are recovering and they can’t be made to open, sodium ion channels are closed during re polarisation and the potassium ion channels are closed during hyperpolaisation
66
How does the action potential move along as a wave of depolarisation?
- action potential happens, some of the sodium ions that enter the neurone, diffuse sideways
- causing sodium ions channels in the next region of the neurone to open and sodium ions diffuse into that part
- causing a wave of depolarisation, the waves move away from the parts of the membrane in the refractory period because these parts can’t fire an action potential
67
How does the refractory period produce discrete impulses?
Ion channels can’t be opened, so the refractory period acts as a time delay between one action potential and the next:
- action potentials don’t overlap, but pass along as discrete impulses
- there’s a limit to the frequency at which the nerve impulses can be transmitted
- action potentials are unidirectional
68
What is the all or nothing principle in terms of action potentials?
- once the threshold is reached, an action potential will always fire with the same change in voltage, no matter how big the stimulus is
- if the threshold values isn’t reached no action potential will fire
- a bigger stimulus wont cause a bigger action potential but it will cause them to fire more frequently
69
What is homeostasis?
Involves control systems that keep your internal environment roughly constant, keeping your internal environment stable, which is vital from cells to function normally and to stop them being damaged
70
Why is it particularly important to maintain pH, blood glucose and temperature?
Temperature = if temp is too high enzymes may become denatured , if too low enzyme activity is reduced, lowing the rate of metabolic reactions
The highest rate of enzyme activity happens at their optimum temperature
pH = too high or too low enzymes can denature
The highest rate of enzyme activity happens at their optimum pH usually around 7
Glucose = too high, the water potential of blood is reduced to a point where water molecules diffuse out of cells into the blood by osmosis, which can cause the cells to shrivel up and die
Too low and the cells are unable to carry out normal activities because there isn’t enough glucose for respiration to provide energy
71
How do homeostatic systems detect a change and respond to it by negative feedback?
Homeostatic systems involve receptors, a communication system and effectors
- receptors detect when a level is too high or too low
- effectors respond to counteract the change = bringing the level back to normal = negative feedback mechanism
72
How do multiple negative feedback mechanism give more control?
Homeostasis involves multiple negative feedback mechanisms for each thing being controlled
- as having more then one mechanism gives more control over changes in your internal environment
- multiple mechanisms means you can actively increase or decrease a level so it returns to normal
- with only one all you would be able to do is turn it on and off, it would be a slower response with less control
73
How do positive feedback mechanisms amplify a change from the normal level?
Some changes trigger a positive feedback mechanisms, which amplifies the change
- the effectors respond to further increase the level away from the normal level
- positive feedback is useful to rapidly activate something e.g. blood clot after an injury
- it can also occur when a homeostatic system breaks down e.g. hypothermia where heat is lost from the body faster then it is produced, as body temp falls the brain doesn’t work and the shivering stops, making the body temp fall even further
74
How do eating and exercise change the concentration of glucose in your blood?
- all cells need a constant energy supply to work - so blood glucose concentration needs controlling
- concentration of glucose in the blood is normally around 90 mg per 100 cm3 of blood, its monitored by the pancreas
- blood glucose rises after eating food containing carbohydrate
- blood glucose falls after exercise, as more glucose is used in respiration to release energy
75
What clusters of cells secrete insulin?
Beta cells secrete insulin
- found in the pancreas called islets of Langerhans
76
What clusters of cells secrete glucagon?
Alpha cells
77
How does insulin control blood glucose?
Insulin lowers blood glucose concentration when it’s too high:
- insulin binds to specific receptors on the cell membranes of liver cells and muscle cells
- it increases the permeability of muscle cell membranes to glucose, so the cells take up more glucose, this involves increasing the number of channel proteins in the cell membranes
- insulin also activates enzymes in liver and muscle cells that convert glucose into glycogen
- the cells are able to store glycogen in their cytoplasm, as an energy source
- this process of forming glycogen from glucose is called glycigenisis
- insulin also increases rhe rate of respiration of glucose, especially in muscle cells
78
How does glucagon control blood glucose concentration?
Glucagon raises blood glucose concentration when its too low:
- glucagon binds to specific receptors on the cell membranes of liver cells
- glucagon activates enzymes in liver cells that break down glycogen into glucose
- the process of breaking down glycogen is called glycogenolysis
- glucagon also activates enzymes that are involved in the formation of glucose from glycerol and amino acids
- the process of forming glucose form non-carbohydrates is called gluconeogenesis
- glucagon decreases the rate of respiration of glucose cells
79
How do negative feedback mechanisms respond to a rise in blood glucose concentration?
Rise in blood glucose concentration —> pancreas detects glucose conc is too high —> B cells spectre insulin and A cells stop secreting glucagon —> insulin binds to receptors on liver and muscle cells —> cells take up more glucose/glycogensis is activated/cells respire more glucose —> less glucose in blood —> back to normal
80
How do negative feedback mechanisms respond to a fall in blood glucose concentration?
Pancreas detects fall in blood glucose concentration —> A cells secrete glucagon and B cells stop secreting insulin —> glucagon binds to receptors on liver cells —> glycogenolysis is activated/ gluconeogenesis is activated/cells respire less glucose —> cells release glucose into the blood —> back to normal
81
How does insulin make glucose transporters available for facilitated diffusion?
- skeletal and cardiac muscle cells contain a channel protein called GLUT4 which is a glucose transporter
- when insulin levels are low, GLUT4 is stored in vesicles in the cytoplasm of cells
- when insulin binds to receptors on the cell-surface membrane, it triggers the movement of GLUT4 to the membrane
- glucose can then be transported onto the cell through GLUT4 protein by facilitated diffusion
82
How does adrenaline increase blood glucose concentration?
- adrenaline is secreted from your adrenal glands
- when there is a low concentration of glucose in you blood when you are stressed or exercising
- adrenaline binds to receptors in the cell membrane of liver cells, where it activates glycogenolysis and inhibits glycogensis
- it activates glucagon secretion and inhibits insulin secretion which increases glucose concentration
- adrenaline gets the body ready for action by making more glucose available for muscles to respire
83
How do both adrenaline and glucagon activate glycogenolysis inside a cell even though they bind to receptors on the outside?
- receptors have specific tertiary structures, they bind to their receptors and activate an enzyme called adenylate cyclase
- activated adenylate cyclase converts ATP into a chemical signal called a second messenger
- the second messenger is called cyclic AMP
- cAMP activates an enzyme called protein kinase A which activates a cascade that breaks down glycogen into glucose
84
What is type 1 diabetes?
The immune system attacks the B cells in the islets of Langerhams so they can’t produce any insulin
- after eating, the blood glucose levels rise and stays high = hyperglycaemia and can result in death if untreated, the kidneys can’t reabsorb all this glucose
- treated with insulin therapy, but too much insulin can produce a dangerous drop in blood glucose levels = hypoglycaemia
- eating regularly and controlling simp;e carbohydrate intake helps to avoid a sudden rise in glucose
85
What is type 2 diabetes?
Linked with obesity and more likely in people with a family history of the condition, can also be caused by lack of exercise, age and poor diet
B cells don’t produce enough insinuation or when the body cells don’t respond properly to insulin, as their receptors don’t work, so blood glucose concentration is higher
Can be treated with lifestyle, diet and regular exercise, but in severe cases insulin injections may be needed
86
Why is type 2 diabetes a growing health problem?
Increasingly common in the UK, it has been linked to increasing levels of obesity, a move towards more unhealthy diets and low levels of physical activity
- it can cause additional health problems such as visual impairment and kidney failure so health advisors want to educate people, and think the food industry has a role to play
87
How can the risk of type 2 diabetes be reduced?
- east a diet low in fat, sugar and salt, with plenty of whole grains, fruit and vegetables
- take regular exercise
- lose weight if necessary
- change4life
- food industry to be reducing the advertising of junk food, improving the nutritional value of their products and use clearer labelling on products
Some food industry’s have:
- use sugar alternatives
- reducing sugar fat and salt concentration
88
How can colorimetry be used to determine the concentration of a glucose solution?
- quantitive Benedict’s reagent is different to normal Benedict’s reagent as when heated with glucose the initial blue colour is lost but a brick red precipitate is not produced
- you can use a colorimeter to measure the light absorbance of the solution after the quantitive Benedict’s test gas been carried out
- the higher the concentration of glucose, the more blue colour with be lost, decreasing the absorbance of the solution after
89
How do the kidneys excrete waste and regulate blood water potential?
- quantitive Benedict’s reagent is different to normal Benedict’s reagent as when heated with glucose the initial blue colour is lost but a brick red precipitate is not produced
- you can use a colorimeter to measure the light absorbance of the solution after the quantitive Benedict’s test gas been carried out
- the higher the concentration of glucose, the more blue colour with be lost, decreasing the absorbance of the solution
90
How is blood filtered through the kidneys?
1) blood from the renal artery enters the smaller arterioles in the cortex of the kidney
2) each arteriole splits into a structure called a glomerulus — a bundle of capillaries looped inside a hollow ball called a Bowman’s capsule = where ultrafiltration takes place
3) arteriole that takes blood into each glomerulus is called the afferent arteriole, and the arteriole that takes the blood away from the glomerulus is called the efferent arteriole
4) efferent arteriole is smaller in diameter than the afferent arteriole, so the blood in the glomerulus is under high pressure
5) the high pressure forces liquid and small molecules in the blood out of the capillary and into the Bowman’s capsule
6) liquid and small molecules pass through three layers to get into the Bowman’s capsule and enter the nephron tubules - the capillary wall, a membrane and the epithelium of the bowman’s capsule
7) larger molecules like proteins and blood cells can’t pass through so stay in the blood, substances in the bowman’s capsule are known as the glomerular filtrate
8) the glomerular filtrate passes along the rest of the nephron and useful substances are reabsorbed along the way
9) finally the filtrate flows through thr collecting duct and passes out of the kidney along the ureter
91
How are useful substances reabsorbed along the nephron tubule?
- selective re absorption takes place as the glomerular filtrate flows along the proximal convoluted tubule (PCT), through the loops of hence and the distal convoluted tubule
- useful substances leave the tubules and enter the capillaries
- the epithelial of the wall of the PCT has microvilli to provide a large surface area for the reabsorption of useful materials from the glomerular filtrate into the blood
- glucose is reabsorbed along the PCT by active transport and facilitated diffusion
- water enters the blood by osmosis because the water potential of the blood is lower then that of the filtrate, water is reabsorbed from the PCT, loop of henle, DCT and the collecting duct
- the remaining filtrate is urine (water, dissolved salts, urea etc…) not proteins, blood cells or glucose
92
How do the kidneys regulate the water potential of the blood?
The kidneys regulate the water potential of the blood so the body has the right amount of water = osmoregulation
- if the water potential is too low, more water is reabsorbed by osmosis into the blood form the tubules, so urine ism more concentrated
- vice versa
93
How does the loops of henle maintain a sodium ion gradient?
1) near the top of the ascending limb, Na+ ions are pumped out into the medulla using active transport, the ascending limb is impermeable to water, so the water stays inside the tubule, creating a low water potential in the medulla, because there’s a high concentration of ions
2) because there’s a lower water potential in the medulla than in the descending limb, water moves out of the d limb into the medulla by osmosis, making the filtrate more concentrated, so the water in the medulla is reabsorbed into the blood through capillaries
3) near the bottom of the ascending limb Na+ ions diffuse out into the medulla, further lowering the water potential in the medulla, the ascending limb is impermeable to water, so it stays in the tubule
4) water moves out of the distal convoluted tubule DCT by osmosis and is reabsorbed into the blood
5) the first three stages massively increase the ion concentration in the medulla which lowers the water potential, causing water to move out of the collecting duct by osmosis, as before the water in the medulla is reabsorbed into the blood through the capillary network
94
How is water reabsorption controlled by hormones?
Water potential of the blood is monitored by cells called osmoreceptors in the hypothalamus in the brain
- when water potential of the blood decreases, water will move out of the osmoreceptor cells by osmosis, which causes rhe cells to decrease in volume, sending a signal to the hypothalamus which sends a signal to the posterior pituitary gland, which causes the gland to release anti diuretic hormones ADH into blood
- ADH makes the walls of the DCT and collecting duct ,ore permeable to water
- meaning more water is reabsorbed from these tubules into the medulla and into eh blood by osmosis, a small amount of concentrated urine is produced, which means less water is lost from the body
95
How does ADH change the water content of the blood when it’s too low or too high?
Too low = water content drops, so water potential drops —> detected by osmoreceotors in the hypothalamus —> P pituitary gland is stimulated to releases more ADH which means the DCT and collecting duct become more permeable, so more water is reabsorbed into the blood by osmosis —> a small amount of highly concentrated urine is produced and less water is lost
Too high = water content rises, so water potential rises —> detected —> PPG releases less ADH —> DCT and collecting duct become less permeable so less water is reabsorbed —> large amount of dilute ur line is produced and more water is lost
