6) Organisms respond to changes in their environment Flashcards
1
Q
Stimulus definition
A
Any change in the internal or external environment
2
Q
Receptor definition
A
Cells or proteins on the cell surface membrane that detect stimuli
3
Q
Effectors definition
A
Cells that bring about a response to a stimulus, to produce an effect
4
Q
Indoleacetic acid (IAA):
A
- Hormone which affects cell elongation to control tropisms
- Produced in tips of shoots (growing regions)
- IAA moved around plant by active transport + diffusion via phloem
5
Q
Tropism definition
A
The response of a plant to a directional stimulus
6
Q
Phototropism:
A
- Growth of a plant in response to light
- Shoots- positively phototrophic + grow towards light. IAA concentration increases on shaded side- cells elongate + the shoot bends towards light
- Roots- negatively phototrophic + grow away from light. IAA concentration increases on the shaded side- growth is inhibited so root bends away from the light
7
Q
Gravitropism:
A
- Growth of a plant in response to gravity
- Shoots- negatively gravitrophic + grow upwards. IAA concentration increases on lower side- cells elongate so shoot grows upwards
- Roots- positively gravitrophic + grow downwards. IAA concentration increases on lower side- growth is inhibited so the root grows downwards
8
Q
Taxes:
A
Organism move towards or away from a directional stimulus
eg movement towards light (positive phototaxis), movement towards a chemical (positive chemotaxis)
9
Q
Kinesis:
A
Organism’s movement is affected by a non-directional stimulus (eg humidity)
Organism changes the speed at which it moves and the rate it changes direction. This increases its chance of a quick return to a favourable environment
If it moves a considerable distance into an unfavourable environment, its rate of turning may decrease so that it moves in straight lines before it turns
Brings organism into a new region with favourable conditions
10
Q
Reflex arc definition
A
Pathway of neurones involved in a reflex
Response is rapid, short lived, localised, involuntary
11
Q
Route of an impulse in a reflex arc:
A
1) Stimulus
2) Receptor- detect stimulus + generates nerve impulses to sensory neurone
3) Sensory neurone- passes nerve impulses to spinal cord
4) Intermediate neurone- links the sensory neurone to motor neurone
5) Motor neurone- carries nerve impulses from spinal cord to an effector
6) Effector- muscle or gland which brings about a response
7) Response
12
Q
Importance of reflex arcs
A
- Involuntary- allow brain to carry out more complex responses + means response is rapid
- Fast- neurone pathway is short- few synapses
- Protects body from harm
13
Q
What are pacinian corpuscles?
A
Type of receptor found in skin. Only respond to mechanical stimuli
14
Q
Features of receptors:
A
- Respond only to a specific stimuli
- Stimulation leads to the establishment of a generator potential
15
Q
How do pacinian corpuscles detect a stimulus?
A
1) Pacinian corpuscles contain end of neurone- neurone wrapped in layers of connective tissue (lamellae)
2) Pacinian corpuscle stimulated- lamellae deformed + press on sensory nerve ending
3) Causes sensory neurone’s cell membrane to stretch, deforming the stretch mediated sodium ion channels
4) Channels open + sodium ions diffuse into neurone, creating a generator potential
5) If the generator potential reaches the threshold, it triggers an action potential
16
Q
Structure of pacinian corpuscle
A
- End of neurone
- Surounded by layers of connective tissue with viscous gel between
17
Q
Receptors in the eye:
A
Found on the retina
- Rod cells and cone cells
- Both types act as transducers by conserving light energy into the electrical energy of a nerve impulse
18
Q
Rod cells:
A
- Many rod cells connected to a single sensory neurone in the optic nerve
- Sensitive to light- used to detect light at low intensity
- To create generator potential- pigment in rod cells (rhodopsin) must be broken down. There is enough energy from low intensity light to cause this breakdown
- Many weak generator potentials in bipolar cells, to which rod cells are connected to, combine to reach the threshold and trigger an action potential
- Low visual acuity- as many rod cells join same neurone
- Black and white- cannot distinguish different wavelengths of light
- 1 type only
- More numerous than cone cells
19
Q
Cone cells:
A
- Each cone cell connected to a single sensory neurone
- Less sensitive to light- takes more light to reach the threshold + trigger action potential
- Pigment (iodopsin)- requires higher light intensity for its breakdown
- Higher visual acuity
- Images in colour
- 3 types- each contains a different type of iodopsin
20
Q
Visual acuity definition
A
The ability to distinguish between points that are close together
21
Q
Autonomic nervous system definition
A
Controls the involuntary activities of internal muscles and glands
Divided into the sympathetic and parasympathetic nervous system
22
Q
Myogenic muscle definition
A
Muscle that can contract or relax without receiving signals from nerves
This pattern of contraction controls the regular heartbeat
23
Q
How does myogenic stimulation of the heart transmit a wave of electrical activity and cause the heart to contract?
A
1) Sinoatrial node (SAN) sends out regular waves of electrical activity to the atrial walls
2) This causes the atria to contract
3) A layer of non-conductive tissue (atrioventricular septum) prevents the wave crossing the ventricles
4) The waves of electrical activity are transferred from the SAN to the atrioventricular node (AVN)
5) After a short delay, to make sure the atria have emptied before the ventricles contract, the AVN passes the waves of electrical energy along a series of muscle fibres (Purkyne tissue) - collectively makes up bundle of His
6) Bundle of His splits into smaller fibres of Purkyne tissue- carries waves of electrical activity into muscular walls of the right and left ventricles- causing them to contract simultaneously from bottom up
24
Q
Sinoatrial node (SAN):
A
Distinct group of cells found in the walls of the right atrium
Generates electrical impulses that cause cardiac muscle to contract
Controlled by part of brain- medulla oblongata
25
Atrioventricular node (AVN):
Distinct group of cells found in walls of right atrium
AVN passes waves of electrical energy, from the SAN, along a series of muscle fibres called Purkyne tissue, which collectively make up the Bundle of His
26
Purkyne tissue:
A series of muscle fibres in the muscular wall of the heart
Carry waves of electrical activity from the bundle of His, into the muscular walls of the right and left ventricles, causing them to contract simultaneously, from bottom up
27
Sympathetic nervous system definition
Makes up part of the autonomic nervous system
Stimulates effectors and so speeds up activity
28
Parasympathetic nervous system definition
Part of the autonomic nervous system
Inhibits effectors and so slows down activity
29
Medulla oblongata:
Controls changes to heart rate so varying demands of oxygen can be met
Has 2 centres
- A centre that increases heart rate- linked to SAN by sympathetic nervous system
- A centre that decreases heart rate- linked to SAN by parasympathetic nervous system
30
Chemoreceptors- where found? What sensitive to?
- Found: walls of carotid arteries, aorta, medulla
| - SENSITIVE TO CHANGES IN pH of blood that result from changes in carbon dioxide concentration
31
The role of chemoreceptors in changing heart rate to alter carbon dioxide concentrations in the blood
- High carbon dioxide = pH blood low
- Chemoreceptors detect this + increase frequency of nervous impulses to centre of nervous oblongata
- Centre increases frequency of impulses via sympathetic nervous system to the SAN
- Increases rate of production of electrical waves by SAN- increases heart rate
- Increase blood flow- more carbon dioxide removed by lungs
- pH rise back to normal- receptors + aorta reduce frequency of nervous impulses to the medulla oblongata
- Medulla oblongata reduces frequency of impulses to SAN- reduction in heart rate
32
Pressure receptors: Where found? What sensitive to?
- Found: carotid arteries + aorta
| - SENSITIVE TO CHANGES IN BLOOD PRESSURE
33
Role of pressure receptors in changing heart rate to alter blood pressure
- Higher blood pressure- pressure receptors transmit more nervous impulses to the centre in the medulla oblongata that decreases heart rate
- Centre sends impulses via the parasympathetic nervous system to the SAN - decrease in heart rate
- Lower blood pressure- pressure receptors transmit more nervous impulses to the centre in the medulla oblongata that increases heart rate
- Centre sends impulses via the sympathetic nervous system to SAN- increases heart rate
34
Neurone definition
Specialised cells adapted to rapidly carry nerve impulses from one part of the body to another
35
Motor neurone definition
Transmit nerve impulses from an intermediate (relay) neurome to an effector,such as a gland or muscle
Have a long axon + many short dendrites
36
What is a myelinated motor neurone?
A motor neurone that has a myelin sheath
37
Structure of a myelinated motor neurone:
CELL BODY- contains all usual cell organelles + large amounts of RER- associated with protein + neurotransmitter production
DENDRONS- extensions of the cell body which subdivide into smaller branched fibres (dendrites) that carry nerve impulses towards the cell body
AXON- single long fibre that carries nerve impulses away from cell body
SCHWANN CELLS- surround axon- protect it + provide electrical insulation. Wrap themselves around axon many times, so layers of membrane build up around axon
MYELIN SHEATH- covers axon, made up of membranes of schwann cells. Rich is myelin (lipid)- acts as an electrical insulator
Nodes of Ranvier- tiny patches of bare membrane between schwann cells. Sodium ion channels are concentrated at the nodes- where depolarisation occurs
38
Establishment of a resting potential in a neurone:
- Resting state- outside of membrane is positively charged compared to inside- membrane=polarised, there is a potential difference across the membrane
- Resting potential created + maintained by sodium potassium pumps and potassium ion channels in neurone's membrane
- Na-K pump moves sodium ions out of neurone- not permeable to Na ions so they can not diffuse back in- electrochemical gradient
- Na-K pump also move K ions into neurone- but membrane is permeable to K ions so can diffuse back out of K ion channels
39
Action potential definition
A sequence of events which causes a change in potential difference across part of the membrane of the axon
Energy of the stimulus causes a temporary reversal of the charges either side of the part of the axon membrane (inside of membrane now becomes positively charged)
40
Generation of an action potential in a neurone:
1) STIMULUS- energy causes Na ion channels to open in axon membrane- more permeable to Na ions- diffuse into neurone down sodium ion electrochemical gradient (inside membrane less negative)
2) DEPOLARISATION- if potential difference reaches threshold, more Na ion channels open
3) REPOLARISATION- at PD about +30mV, Na ion channels close + K channels open. Membrane more permeable to K- so K diffuse out neurone- (starts to get neurone back to its resting potential)
4) HYPERPOLARISATION- K ion channels slow to close- slight 'overshoot'- too many K ions diffuse out neurone. PD become more negative than resting potential
5) RESTING POTENTIAL- ion channels reset
41
All or nothing principle (generation of action potential in nerves)
- Weak stimulus- PD threshold not exceeded- no depolarisation or action potential occurs
- Strong stimulus- more energy- threshold reached
- A stimulus providing energy above the threshold value will produce an action potential with the same change in voltage, no matter how big the stimulus is
- Bigger stimulus won't create a bigger action potential- BUT will cause more frequent action potentials
42
Refractory period definition:
The period after an action potential has been created where an inwards movement of Na ions is prevented because sodium channels are closed
During period- impossible for a further action potential to be generated
Acts as a time delay between one action potential to the next
43
3 purposes of the refractory period when generating an action potential
- Ensures action potentials don't overlap, but pass along as discrete impulses
- Ensures action potentials are unidirectional
- Limits the number of action potentials + frequency at which the nerve impulses can be transmitted
44
The passage of an action potential along a non-myelinated axon
non-myelinated = neurone does not have a myelin sheath
- When action potential occurs- Na ions enter neurone
- Causes wave of depolarisation to travel along neurone
- Wave moves away from parts of the membrane in the refractory period as these parts can't fire an action potential
45
Passage of an action potential along a myelinated axon (+ name the process)
- Fatty sheath of myelin around axon acts as an electrical insulator- prevent action potentials forming
- Breaks in myelin = nodes of Ranvier- only place where action potentials can occur
- Action potentials move from node to node- SALTATORY CONDUCTION
- Pass along myelinated neurone faster than along axon of a non-myelinated neurone of the same diameter- as in non-myelinated, impulse travels as a wave along the whole length of the axon
46
Nerve impulse definition
The transmission of an action potential along the axon of a neurone
47
Factors affecting the speed of conductance of an action potential along the axon of a neurone:
- MYELINATION- myelinated axon---- saltatory conduction= faster
- AXON DIAMETER- bigger diameter= faster conduction as less resistance to flow of ions
- TEMPERATURE- higher temp- faster conduction (up to about 40 degrees- after that point proteins begin to denature + speed decreases)
48
Structure of a synapse:
SYNAPTIC CLEFT- tiny gap between the cells at a synapse
PRESYNAPTIC NEURONE- neurone which releases the neurotransmitter
SYNAPTIC KNOB- swollen portion of the presynaptic neurone- contains many mitochondria + ER- both required in manufacture of neurotransmitter
SYNAPTIC VESICLES- where neurotransmitter is stored
49
Synapse definition
The junction between a neurone + another neurone or between a neurone and an effector cell
Transmit information from one neurone to another by means of chemicals called neurotransmitters
50
Neuromuscular junction definition
A synapse between a motor neurone and a muscle cell
51
Structure of a neuromuscular junction:
SYNAPTIC CLEFT
PRESYNAPTIC NEURONE ----------------- muscle cell
Lots of mitochondria + ER to manufacture the neurotransmitter acetylcholine
52
Cholinergic synapse definition:=
A type of synapse in which the neurotransmitter is acetylcholine (ACh)
53
Transmission across a cholinergic synapse:
1) Action potential arrives at synaptic knob of presynaptic neurone
2) Action potential stimulates voltage-gated Ca ion channels in presynaptic neurone to open + Ca ions enter synaptic knob by facilitated diffusion
3) Influx of Ca ions causes synaptic vesicles to move to presynaptic membrane- fuse with it. Causes vesicles to release acetylcholine into synaptic cleft (exocytosis)
4) Ach diffuses across synaptic cleft + binds to specific receptor sites on Na ion protein channels on postsynaptic membrane
5) Causes Na ion channels to open- allows influx of Na ions into postsynaptic neurone
6) Causes depolarisation + action potential in postsynaptic neurone is generated is threshold reached
7) ACh is removed from synaptic cleft so response doesn't keep happening --- Hydrolysed by acetyl cholinesterase (AChE) + products are re-absorbed by presynaptic neurone to make more ACh
54
Inhibitory synapse definition
Synapses which make it less likely that a new action potential will be created on the postsynaptic neurone
55
Transmission across an inhibitory synapse
1) Presynaptic neurone releases a neurotransmitter that binds to chloride ion protein channels on the postsynaptic neurone - causes chloride ion protein channels to open
2) Cl ions move into postsynaptic neurone by facilitated diffusion
3) Binding of neurotransmitter causes opening of nearby K protein channels
4) K ions move out of postsynaptic neurone into the synapse
5) Combined effect of negatively charged chloride ions moving in + positively charged K ions moving out makes the inside of the postsynaptic membrane more negative + outside more positive
6) Membrane potential increases (HYPERPOLARISATION)- makes it less likely that a new action potential will be created as a larger influx of sodium ions is needed to produce one
56
Unidirectionality of synapses:
- Transmission across a cholinergic synapse is unidirectional
- Impulse can only travel in 1 direction as receptors are only on the postsynaptic membranes
Always: Presynaptic neurone---------------------------------Postsynaptic neurone
57
Summation definition
When the effect of neurotransmitters released from many neurones is added together
2 types of summation:
- Spatial
- Temporal
58
Spatial summation of synapses:
- When a number of presynaptic neurones connect together + release enough neurotransmitter to exceed the threshold value of the postsynaptic neurone
- Together they trigger an action potential
59
Temporal summation of synapses:
- A single presynaptic neurone releases neurotransmitters many times over a very short period
- Makes an action potential more likely as more neurotransmitter is released into the synaptic cleft
60
Similarities between a cholinergic synapse + neuromuscular joint:
- Both have neurotransmitters transported by diffusion
- Both have receptors, that on binding with the neurotransmitter, cause an influx of Na ions
- Both use Na-K pump to repolarise axon
- Both use enzymes to break down neurotransmitter
61
Differences between a cholinergic synapse (CS) + neuromuscular joint (NJ) :
- CS- excitatory or inhibitory but NJ only excitatory
- CS links neurones to neurones, or neurones to an effector organ. NJ only links neurones to muscles
- CS- motor, sensory + intermediate neurones may be involved. NJ- only motor neurone involved
- CS- action potential may be produced along another neurone. NJ- action potential ends here
- CS- acetylcholine binds to receptors on membrane of post-synaptic neurone. NJ- acetylcholine binds to receptors on membrane of muscle fibre
62
Effect of drug action of synapses:
- Agonist- same shape as neurotransmitter- so mimic their action at receptors
- Antagonists- block receptors so they can't be activated by neurotransmitters
- Inhibition of enzyme which breaks down neurotransmitters- means more neurotransmitter binds to receptors
- Inhibition of release of neurotransmitter from presynaptic neurone- so fewer receptors activated
- Stimulation of release of neurotransmitter from presynaptic neurone- so more receptors activated
63
Skeletal muscle definition
A type of muscle, attached to bones by tendons, that are used to move
64
Antagonistic muscle pairs definition
Muscles that work together to move a bone
Contacting muscle = agonist
Relaxing muscle = antagonist
65
Overall structure of skeletal muscle:
- Made up of large bundles of long cells called muscle fibre
- Muscle fibre cells contain myofibrils (long cylindrical organelles)
- Myofibrils made up of myofilaments- Myosin + Actin
66
Structure of a muscle fibre cell:
- SARCOLEMMA- cell membrane. Bits of sarcolemma fold inwards across the muscle fibre + stick into the sarcoplasm- form tranverse T tubules- help spread electrical impulses throughout the sarcoplasm so they reach all parts of muscle fibre
- SARCOPLASM- cytoplasm
- SARCOPLASMIC RETICULUM- network of interanl membranes, run through sarcoplasm. Stores + releases Ca ions
- MITOCHONDRIA- lots- provide ATP needed for muscle contraction
- MYOFIBRILS- long cylindrical organelles
Multinucleated- contain many nuclei
67
Myofibril definition
Long cylindrical organelles found in a muscle fibre cell
68
Structure of a myofibril
- Contain myofilaments
- MYOSIN- Thick myofilament. Forms dark bands which also contain some overlapping actin filaments. (A-bands)
- ACTIN- Thin filaments. Forms light bands which contain only actin filaments (I-bands)
- SARCOMERE- many short units of myofilament
- Z-LINE- mark the ends of each sarcomere
- M-LINE- marks the middle of each sarcomere
- H- ZONE- surrounds the m-line- only contains myosin filaments
69
Myofibril contraction (Sliding filament mechanism):
- Contraction caused when myosin + actin filaments slide over one another to make sarcomeres contract
- Simultaneous contraction of lots of sarcomere means myofibrils + mucles fibres contract
- A-bands stay same length
- I-bands get shorter
- H- zones get shorter
70
Myosin and actin interaction:
- Myosin has globular heads- hinged
- Myosin head has binding site for actin + a binding site for ATP
- Actin has a binding site for myosin heads
- Tropomyosin- protein found between actin filaments which helps myofilaments move past each other
- Resting muscle- actin-myosin binding site is blocked by tropomyosin- myofilaments can't slide past each other as myosin heads can't bind to the actin-myosin binding site on the actin filaments
71
Muscle contraction process:
1) Action potential from motor neurone stimulates muscle fibre - depolarises sarcolemma
2) Depolarisation spreads down -T-tubules to sarcoplasmic reticulum- causes it to release stored Ca ions into the sarcoplasm
3) Ca ions bind to a protein attached to tropomyosin, causing the protein to change shape. Pulls attached tropomyosin out of the actin-myosin binding site on the actin filament
4) Exposes binding site- allows myosin head to bind to form ACTINOMYOSIN bridge
5) Ca ions also activate ATP hydrolase- hydrolyses ATP to provide energy
6) Energy from ATP causes myosin head to bend- pulls actin filament along
7) Another ATP molecule provides energy to BREAK actinomyosin bridge
8) Myosin head reattches to a different binding site further along actin filament (cycle is repeated)
ATTACH, MOVE, DETACH, REATTACH to new binding site
72
Actinomyosin bridge definition
The bond formed when a myosin head binds to actin filament
Many actinomyosin bridges form + break very rapidly, pulling the actin filament along- shortens sarcomere, causing the muscle to contract
73
Muscle relaxation:
- When muscle stoped being stimulated- Ca ions leave binding site + are moved by active transport back to sarcoplasmic reticulum
- Causes tropomyosin molecules to move back- block actin-myosin binding site
- Actin filaments slide back to their relaxed position- lengthens sarcomere
74
Role of ATP in muscle contraction:
Hydrolysis of ATP provides energy for:
- The movement of myosin heads
- The reabsorpton of Ca ions into endoplasmic reticulum
75
Role of phosphocreatine in muscle contraction:
Very active muscle- demand for ATP is greater than the rate at which blood can supply oxygen
Means generating ATP anaerobically is required
- Phosphocreatine- stored in muscle
- Acts as a reserve supply of phosphate- available to combine with ADP to reform ATP
- Store is replenished using phosphate from ATP when muscle relaxes
76
What are the 2 different types of muslce fibre that make up skeletal muscle?
Slow twitch muscle fibre
Fast twitch muscle fibre
77
Slow twitch muscle fibres:
- Contract slowly
- Muscles used for posture
- Good for endurance activities
- Can work for a long time without getting tired
- Energy's released slowly through aerobic respiration- lots of mitochondria + blood vessels
- Reddish in colour as rich in myoglobin (stores oxygen)
78
Fast twitch muscle fibres:
- Contract quickly
- Muscles used for fast movement
- Good for short bursts of speed + power
- Get tired quickly
- Energy's released quickly through anaerobic respiration using glycogen- few mitochondria or blood vessels
- Whitish in colour- don't have much myoglobin
79
Homeostasis definition
The maintenance of a constant internal environment
80
Importance of maintaining a stable blood pH:
- Too high- enzymes denatured, hydrogen bonds break, change tertiary structure, change active site, metabolic reactions less efficient
- Too low- enzyme activity reduced, slows rate of metabolic reactions
81
Importance of maintaining a stable blood pH
- pH too high or low- enzymes denatured
| - Breaks ionic + hydrogen bonds- tertiary structure changes, change in active site, metabolic reactions less efficient
82
Importance of maintaining a stable blood glucose concentration
- Affects water potential of blood- stable blood glucose = constant water potential
- Too high- water potential of blood reduced, water molecules diffuse out of cells by osmosis, cell shrivels up, dies
- Too low- not enough glucose to provide energy for respiration
83
Negative feedback definition
When a deviation from an optimum is detected + effectors counteract the change, bringing the level back to normal
84
Negative feedback mechanism definition
The mechanism that restores levels to normal
85
Why does homeostasis involve multiple negative feedback mechanisms for each thing being controlled?
- Gives more control over changes in internal environment
| - Faster response
86
Positive feedback definition
When a deviation from an optimum causes changes that result in an even greater deviation from the normal
eg- blood clots or when homeostatic system breaks down
87
What 3 sources does blood glucose come from?
- DIET- glucose absorbed following hydrolysis of carbohydrates
- GLYCOGENOLYSIS- hydrolysis of glycogen to glucose. Glycogen stored in muscle cells + liver
- GLUCONEOGENESIS- production of glucose from sources other than carbohydrate
88
Factors that influence blood glucose concentration:
- Rises after eating food containing carbohydrate
| - Falls after exercise- as more glucose used in respiration to release energy
89
Glycogenesis definition
Conversion of glucose into glycogen
| Occurs when blood glucose concentration is high- liver removes glucose from blood + converts it into glycogen
90
Glycogenolysis definition
Breakdown of glycogen into glucose
| Occurs when blood glucose concentration is low- liver converts stored glycogen back into glucose
91
Gluconeogenesis definition
Production of glucose from sources other than carbohydrate
| When liver's supply of glycogen is exhausted, it can produce glucose from glycerol and amino acids
92
Where is insulin secreted?
Beta (B) cells
Found in the islets of Langerhans in the pancreas
93
Where is glucagon secreted?
Alpha (a) cells
Found in the islets of Langerhans in the pancreas
94
Describe the events that occur when blood glucose concentration is too high:
- More insulin secreted by B cells
- Insulin binds to specific receptors on the cell membrane of liver and muscle cells (target cells)
- Increases the permeability of the muscle cell membranes to glucose- cell takes up more glucose, reducing concentration of glucose in the blood
- Insulin also activates enzymes in the liver + muscle cells that convert glucose into glycogen (glycogenesis)
- Insulin increases the rate of respiration of glucose in cells
95
Describe the events that occur when blood glucose concentration is too low:
- Glucagon binds to specific receptors on the cell membrane on the cell membrane of liver cells (target cells)
- Activates enzymes in liver cells that break down glycogen into glucose (glycogenolysis)
- Glucagon also activates enzymes that are involved in formation of glucose from glycerol and amino acids (gluconeogenesis)
- Glucagon decreases rate of respiration of glucose in cells
96
Role of adrenaline in controlling blood glucose concentrations:
Hormone which raises blood glucose concentration by attaching to receptors on the cell-surface membrane of target cells which:
- Activates glycogenolysis (breakdown of glycogen to glucose)
- Inhibits glycogenesis (synthesis of glycogen from glucose)
- Activates glucagon secretion + inhibits insulin secretion
97
Second messenger model in controlling blood glucose concentrations:
Adrenaline and glucagon both activate glycogenolysis (breakdown of glycogen to glucose) through the second messenger model
1) Receptors for adrenaline + glucagon on membrane of target cells, have specific tertiary structures that make them complementary in shape to their respective hormones
2) Adrenaline + glucagon bind to their receptors + activate the enzyme ADENYLATE CYCLASE
3) This converts ATP into chemical signals called CYCLIC AMP (cAMP)- acts as a second messenger
4) cAMP activates an enzyme called PROTEIN KINASE- catalyses conversion of glycogen to glucose
98
Type I diabetes- cause + treatment
- B cells can't produce insulin
- After eating, blood glucose levels rise + stay high- cells can't take up glucose so blood glucose concentration become too high
- Insulin therapy- regular insulin injections
- Eating regularly + controlling simple carbohydrate intake
99
Type II diabetes- cause + treatment
- B cells don't produce enough insulin or when receptors lose their responsiveness to insulin
- Usually acquired later in life + linked with obesity
- Cell don't take up enough glucose so blood glucose concentration- too high
- Treated by balanced diet, exercise, medication, insulin injections
100
Kidney definition
An organ with the function of regulating the water potential of the blood and excreting waste products, such as urea
101
Cortex definition
Outer region of the kidney
Made up of renal (Bowman's) capsule, convoluted tubes + blood vessels
102
Renal artery definition
Supplies kidney with blood from heart via aorta
103
Structure of the nephron
GLOMERULUS- mass of capillaries- where ultrafiltration occurs
RENAL (BOWMAN'S) CAPSULE- closed end at start of nephron, cup shaped + surrounds glomerulus. Inner layer - podocytes
AFFERENT ARTERIOLE- takes blood into each glomerulus
EFFERENT ARTERIOLE- takes filtered blood away from glomerulus (smaller than afferent arteriole)
PROXIMAL CONVOLUTED TUBULE- series of loops surrounded by blood capillaries
LOOP OF HENLE- long, hairpin loop- sets up sodium ion gradient
DISTAL CONVOLUTED TUBULE- series of loops surrounded by blood capillaries
COLLECTING DUCT- tube which a number of distal convoluted tubules from a number of nephrons empty
BLOOD CAPILLARIES
104
Ultrafiltration definition
Process where substances are filtered out of the blood and into the nephron
105
Role of nephron in filtering blood + producing glomerular filtrate
1) Blood enters glomerulus through afferent arteriole + efferent arteriole takes blood out of the glomerulus
2) Efferent arteriole is smaller in diameter than afferent arteriole so blood in glomerulus is under high pressure
3) High pressure forces water + small molecules in blood out of the capillary + into the renal (Bowman's) capsule forming glomerular filtrate
4) Inner layer of renal capsule is made up of specialised cells (podocytes) which have spaces between them- allows filtrate to pass beneath them
5) Larger molecules can't pass through so stay in blood
6) Water + small molecules enter nephron tubules
106
Role of nephron in the re-absorption of glucose and water by the proximal convoluted tuble
1) Na ions actively transported out of cells lining PCT into blood capillaries
2) Na ions diffuse from lumen of PCT into epithelial lining cells- another molecule is transported across with the sodium ion (co-transport)
3) These molecules that have been co-transported into epithelial cells then diffuse into the blood
4) Water is reabsorbed by osmosis as the water potential of the blood is lower than that of the filtrate
107
Selective re absorption definition
Process where useful substances (eg glucose and right amount of water) are reabsorbed, from the nephron, and enter the capillary network wrapped around nephron tubules
108
How are epithelial cells lining the proximal convoluted tubules in the nephron adapted to reabsorb substances into the blood?
MICROVILLI- large surface area to reabsorb useful molecules from globular filtrate
MANY MITOCHONDRIA- provide ATP for active transport
109
Osmoregulation definition
The control of the water potential of the blood
110
Structure + function of the loop of Henle in the nephron
- Located in medulla (inner layer) of the kidneys
- 2 limbs- descending + ascending
- Limbs control movement of Na ions so that water can be reabsorbed by the blood- acts as a counter current multiplier
- Counter current multiplier ensures there is always a water potential gradient drawing water out of the tubule
- Descending limb- narrower + thin wall, permeable to water
- Ascending limb- wider, thick wall, impermeable to water
111
Role of the nephron in maintaining a gradient of Na ions in the medulla by the loop of Henle
1) Near top of ascending limb, Na ions pumped out into medulla by active transport
2) Ascending limb is impermeable to water , so water stays in tubule
3) Lower water potential in medulla due to high concentration of ions
4) Water moves out of descending limb (which is permeable to water) by osmosis
5) Water in medulla is reabsorbed into blood through capillary network
6) Filtrate moves down descending limb, lowering its water potential- reaches lowest water potential at tip of loop
7) At base of ascending limb , Na ions diffuse out of filtrate, further lowering water potential of medulla
8) Water moves out of DCT and collecting duct by osmosis + is reabsorbed into capillary network
Process= counter current multiplier
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Where is antidiuretic hormone (ADH) produced?
Posterior pituitary gland
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What is the water potential of blood monitored by?
Cells called osmoreceptors in the hypothalamus
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Role of ADH when we are dehydrated:
- Water potential of blood decreases- water moves out of osmoreceptors by osmosis
- Cells decrease in volume- sends signals to other cells in hypothalamus- send signals to posterior pituitary gland
- Stimulates gland to release ADH into the blood
- ADH makes walls of DCT + collecting duct more permeable to water (increases number of aquaporins)
- Means more water is reabsorbed from these tubules into the medulla + into blood by osmosis
- Small amount of concentrated urine produced
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Role of ADH when we are overly hydrated:
- Water potential of blood increases- water moves into osmoreceptor cells by osmosis
- Causes cells to increase in volume- sends signals to other cells in hypothalamus- send signal to posterior pituitary gland
- Gland releases less ADH into blood
- Walls of DCT + collecting duct less permeable to water (fewer aqauporins)- so less water reabsorbed into blood by osmosis
- Large amount of dilute urine produced
