topic 6- homeostasis and response Flashcards
what is a stimulus
a detectible change in the environment
what is a tropism
plants response in growth to a stimuli
describe phototropism in shoots
1) shoot tip cells produce IAA causing cell elongation
2) if there is unilateral light IAA diffuses to shady side of plant
3) cells elongate on shady side allowing plant to bend towards light source
describe phototropism in roots
1) IAA diffuses to shaded side of root
2) this inhibits cell elongation on shady side so the root cells elongate more on the lighter side allowing the roots to bend away from light
why is negative phototropism beneficial for plant roots
-anchors plant into ground
-as roots grow deeper into soil they can access more water sources
describe gravitropism in shoots
1) IAA will diffuse from the upper side to the lower side of a shoot
2) if plant is vertical, cells elongate so plant grows upwards
3) if plant is horizontal, it will cause the shoot to bend upwards - negative
describe gravitropism in roots
1) IAA diffuses to lower side of roots
2) upper side elongates so plant roots anchor downwards
what is a reflex
a rapid, automatic response to protect you from danger
steps of reflex arc
stimulus - receptor - sensory neurone - intermediate neurone - motor neurone - effector - response
what is a taxes
organism will move it’s entire body towards a favourable stimulus / away from unfavourable stimulus (directional)
what is a kinesis
organism changes the speed of movement and the rate it changes direction (non-directional)
what are receptors
cells that detect a stimuli
what is Pacinian corpuscle receptors
detect a change in pressure on skin
sensory neurone wrapped in many layers of plasma membrane which contain special channel proteins
steps of how Pacinian corpuscle works
1) pressure detected deforms the plasma membrane so the stretch mediated sodium channels widen
2) Na+ diffuses into sensory neurone
3) establishes generator potential
what do Rod cells do
process images in black and white
1) rhodopsin pigment must be broken down by light energy
2) can detect light at low intensities as many rod cells connect to one sensory neurone so high visual sensitivity as just enough neurotransmitters to overcome threshold
3) brain cannot distinguish between the seperate sources of light that stimulated it - low visual acuity
what do Cone cells do
produce images in colour, 3 different types for red green and blue that absorb different wavelengths of light
1) iodopsin pigment broken down by light energy but only at high intensities
2) only one cone cell connects to a sensory neurone - why you can’t see colour in the dark
3) brain can distinguish between different sources of light as cone cells send seperate impulses to brain - high visual acuity
where are rod and cone cells found
cone cells located near fovea
rod cells further away
what does myogenic mean
the cardiac muscle contracts of its own accord, but the rate of contraction is controlled by a wave of electrical activity
where is the SAN
right atrium wall (pacemaker)
where is the AVN
near the border of right and left ventricles
where is the Bundle of His
runs through the septum
where are the Purkyne fibres
walls of ventricles
steps for control of the heart
1) SAN releases a wave of depolarisation across the atria, causing it to contract
2) AVN releases another wave of depolarisation when the first reaches it, a non conductive layer prevents wave of depolarisation travelling down to ventricles
3) Bundle of His conducts wave of depolarisation down the septum and Purkyne fibres
4) apex and walls of ventricles contract, causing a delay - advantage as gives time for atria to contract and release max blood to ventricles
what are the 2 types of nervous system involved in controlling the heart
sympathetic - linked to sinoatrial node to increase heart rate (medulla oblongata)
parasympathetic - decreases heart rate
what stimuli change the heart rate
pH - detected by chemoreceptors in carotid artery
blood pressure- detected by pressure receptors in carotid artery
response to change in blood pH by heart
pH of blood decreases when you respire due to carbonic acid - must be removed so enzymes don’t denature
increase heart rate, more impulses via sympathetic neurone to SAN so carbon dioxide can diffuse into the alveoli more rapidly
response to differs in blood pressure by heart
too high- cause damage to artery walls - more impulses via parasympathetic neurone to decrease heart rate
too low - insufficient supply of oxygenated blood to cells
a woman takes moderate exercise. explain the steps that cause her heart rate to increase while she exercises
1) increased CO2 conc detected by chemoreceptors due to the change in pH
2) chemoreceptors send impulses to medulla oblongata via sensory neurone
3) medulla oblongata increases frequency of impulses along the sympathetic motor neurone to the sinoatrial node
4) sinoatrial node increases heart rate so there is increased blood flow around body to provide more O2 to respiring tissues
where are neurotransmitters made
cell body of neurone
what do dendrites do
carry action potentials to surrounding cells
what is the axon
conductive long fibre that carries nervous impulse across motor neurone
what are Shcwann cells
wrap around the axon to form the myelin sheath which is a lipid and therefore does not allow charged ions to pass through it, gaps in myelin sheath are nodes of Ranvier
what is resting potential of an axon
-70mv
when a neurone is not conducting an electrical impulse, there is a difference of electrical charge inside and outside the neurone
how is resting potential established
sodium potassium pump- pumps 2K+ in and 3Na+ out in active transport using ATP
this creates an electrochemical gradient causing K+ to diffuse out and Na+ to diffuse in
membrane has more K+ leak channels so more permeable to K+ so K+ diffuses out than Na+ in, making negative resting potential
what is an action potential
when the neurone’s voltage increases beyond a set point from the resting potential, generating a nervous impulse
describe action potential
1) stimulus activates the voltage gated sodium ion channels to open
2) Na+ diffuse in depolarising membrane to +40
3) voltage gated Na+ channels close and K+ channels open
4) K+ diffuse out of membrane hyperpolarising it past its resting potential eg -75
5) sodium potassium pump restores RP
why do some stimuli not generate an action potential
all or Nothing principle - did not reach threshold of depolarisation as not enough Na+ diffused in
if stimuli reaches threshold it will always peak at the same maximum voltage - bigger stimuli have increased frequency of action potentials
which action potential can move faster, myelinated or unmyelinated neurones
myelinated as action potential jumps from nodes of Ranvier
what is the importance of the All or Nothing principle
to make sure animals only respond to large enough stimuli in the environment and not every change
what is the refractory period
after an action potential is generated, there is a period of time where membrane cannot be stimulated, because Na+ channels are recovering and cannot be opened
importance of refractory period
- ensures discrete impulses are produced (seperate)
-ensures action potentials travel in one direction
-limits number of impulse transmissions
factors affecting speed of conductance of action potential
1) myelination and saltatory conduction
2) axon diameter
3) temperature
what is saltatory conduction
action potential jumps from node to node, making it travel along the axon faster
how does diameter increase conductance of action potential
wider diameter increases speed of conductance as there is less leakage of ions
how does temp increase conductance of action potential
high temp increases as
1) ions diffuse faster
2) enzymes involved in respiration work faster, there is more ATP for active transport
what is a synapse
gaps between the end of an axon of one neurone and the dendrites of another neurone
steps of function of an excitatory synapse
1) action potential arrives depolarising membrane
2) voltage gated Ca2+ channels open and they diffuse in, acting as an internal signal
3) synaptic vesicles migrate to presynaptic membrane and fuse with it
4) neurotransmitters released by exocytosis and diffuse across synaptic cleft
5) protein receptors on post synaptic knob bind with neurotransmitters, allowing Na+ to diffuse into membrane
6) action potential propagates
cholinergic synapse steps
acetyl choline neurotransmitter binds to protein receptors
enzyme breaks down acetylcholine into choline and acetate which can be reabsorbed by pre synaptic neurone
what is summation
rapid build-up of neurotransmitters in the synapse to help generate an action potential
what is spatial summation
many different neurones collectively trigger a new action potential by combining the neurotransmitter they release to exceed threshold value
what is temporal summation
one neurone releases neurotransmitter repeatedly over a short period of time to add up to enough to exceed the threshold value
what happens in inhibitory synapse as opposed to excitatory
when neurotransmitters bind Cl- channels open and they diffuse in and K+ ions move out, hyperpolarising membrane
similarity of synapses and neuromuscular junction
both are unidirectional
differences of synapse and neuromuscular junction
neuromuscular- excitatory synapse- both
don’t connect to another neurone
at the end point of action potential
neurotransmitter binds to muscle fibres
how do 2 muscles work together
in antagonistic pairs, when one contracts the other relaxes
description of myofibrils
made up of fused cells that share nuclei and cytoplasm, known as sarcoplasm, and there is a high number of mitochondria
what is a sarcomere
myofibrils formed from 2 different proteins, myosin and actin
describe bands in a sarcomere
A band - myosin and actin
H zone - myosin
I band - actin
Z line - end of sacromere
how do the bands change when a muscle contracts
A band - stays same
H zone - shorter
I band - shorter
Z lines - closer together
describe steps to the sliding filament theory
1) when AP reaches muscle it stimulates a response
2) calcium ions released from sarcoplasmic reticulum to sarcoplasm
3) Ca2+ bind to troponin pulling the tropomyosin aside and exposing myosin binding sites on actin
4) while ADP is attached to the myosin head, it binds to myosin binding sites forming a cross bridge
5) creating tension, actin filament is pulled and slides over myosin in power stroke releasing ADP and Pi
6) ATP binds to myosin head and myosin head cocks back to original position, ATPase converts ATP-> ADP + Pi which provides energy for this to occur
what does phosphocreatine do
providing phosphate to regenerate ATP from ADP
properties of slow twitch muscles
dark red colour
high myoglobin conc (o2 storage)
high capillary density
low force of contraction, shorter duration
many mitochondria
aerobic respiration
make ATP from oxygen
low reliance on PC
low ease of fatigue
properties of fast twitch muscles
pale in colour
low myoglobin conc
low capillary density
higher force of contraction, long duration
not many mitochondria
anaerobic respiration
glucose used to make ATP
high reliance on PC
high ease of fatigue
what is homeostasis
process of regulating an organisms internal conditions in response to internal/external changes
maintains body temp and blood pH
what is negative feedback
when any deviations from normal values are restored to their original level
pancreas role in restoring blood glucose conc
detects changes in blood glucose levels
Islets of Langerhans cells release insulin and glucagon to bring blood glucose levels back to normal
insulin function
released when blood glucose levels are too high to decrease them
glucagon function
released when blood glucose levels are too low to increase them
adrenaline function
released by adrenal glands when your body anticipates danger resulting in more glucose being released to blood
mechanism if blood glucose levels increase
detected by Beta cells in pancreas
beta cells release insulin
liver cells become more permeable to glucose and enzymes are activated to convert glucose to glycogen
glucose is removed from blood
mechanism if blood glucose levels decrease
detected by Alpha cells in pancreas
alpha cells release glucagon / adrenal gland releases adrenaline
second messenger model occurs to activate enzyme to hydrolyse glycogen to glucose
how does insulin decrease blood glucose
-attaches to receptors on target cells, changing tertiary structure of channel proteins so more glucose being absorbed
-more protein channels are incorporated into membranes to increase glucose absorption
-activating enzymes involved in conversion of glucose to glycogen (glycogenesis)
how does insulin cause more channel proteins to be incorporated
vesicles with channel proteins fuse with membrane
how does glucagon increase blood glucose
-attaches to receptors on Liver cells
-activates adenylate cyclase which converts ATP into cyclic AMP , cAMP activates enzyme protein kinase
-hydrolyses glycogen to glucose
-activates enzymes that convert glycerol and amino acids into glucose
what is glycogenesis
converts glucose to glycogen, occurs in liver
what is glycogenolysis
hydrolyses glycogen to glucose, occurs in liver
what is gluconeogenesis
creation of glucose from other molecules eg amino acids/glycerol
what is type 1 diabetes
unable to produce insulin
starts in childhood
could be a result of autoimmune disease that attacks beta cells in liver
what is type 2 diabetes
receptors on target cells lose their responsiveness to insulin
develops in adults due to obesity/poor diet
what could give you hypertonic blood
too much sweating
not drinking enough water
lots of ions in diet eg salt
steps of ultrafiltration in kidneys
1) blood enters glomerulus from afferent arteriole
2) has high HP due to afferent arteriole being wider than efferent
3) pressure outweighs HP and OP in renal Bowmans capsule so small solutes and water are filtered out
4) pass through fenestra, basement membrane and podocytes
5) plasma proteins too large to pass through
6) filtrate goes through to proximal convoluted tubule
steps of selective reabsorption in kidneys
Na+ actively transported from epithelial cells into blood, setting up an Na+ conc gradient
Na+ diffuses from PCT lumen into epithelial cells, carrying glucose with it in a cotransport protein
sets up glucose conc gradient so glucose can be selectively reabsorbed into the blood by facilitated diffusion
how does the Loop of Henle concentrate urine
1) Na+ and Cl- actively transported out of ascending limb which is impermeable to water
2) raises conc of Na+ and Cl- in tissue fluid
3) water diffuses by osmosis out of the descending limb down water potential gradient
4) loss of water concentrates Na+ and Cl- in descending limb
5) Na+ and Cl- diffuse out of conc solution in descending limb, sets up an increasing salt conc deeper into the medulla
6) water moves out of the collecting duct by osmosis down gradient down whole length of collecting duct due to the maintained water potential gradient
why is their glucose in the urine of someone with untreated diabetes
high blood glucose
not all glucose can be reabsorbed from proximal convoluted tubule
as carrier proteins are saturated for facilitated diffusion
role of glucose in gluconeogenesis
activates enzymes that convert glycerol/amino acids to glucose
where is ADH released into blood
posterior pituitary gland
what happens if the blood water potential is too low to restore it
detected by osmoreceptors in the hypothalamus
water leaves osmoreceptors by osmosis and they shrivel, causing hypothalamus to produce more ADH
where is ADH produced
hypothalamus
what is the role of ADH in the kidney
makes distal convoluted tubule and collecting duct more permeable to water so more water is reabsorbed into the blood
ADH binds to receptors on DCT and collecting duct
activates phosphorylase enzyme in cells
causes vesicles containing aquaporins to fuse with cell membrane
water diffuses through by osmosis back into blood
