Module 5.1 - Homeostasis and Communication Flashcards
What is homeostasis? (2)
- Maintenance of constant internal environment
- Metabolic processes that respond to changes in an organism’s external and internal environment
Why does homeostasis occur? (1)
- To increase the chances of survival by avoiding harmful environments
What is the change in the internal/ external environment called? (1)
- Stimulus
Receptors? (3)
- Detect stimuli
- Specific to one type of stimulus
- Can be cells or cell membrane proteins
Effectors? (2)
- Cells that respond to stimulus
- Muscles or glands
What is cell signalling? (4)
- Cells communicated with other cells to produce a response
- Nervous system communicate via secreting neurotransmitters
- Hormonal system release hormones
- Cell-surface receptors recognise these chemicals secreted
Why is homeostasis important? (2)
- Controls internal environment to allow optimum functioning for cells
- Controls temperature, pH and concentration of ions
Why is homeostasis important for enzyme control? (3)
- Enzymes control the rate of metabolic reactions
- If body temperature is too high, enzymes can become denatured leading to low metabolic activity
- If body temperature is too low, metabolic rate & activity becomes slow
How do enzymes become denatured? (4)
- Enzyme’s molecules vibrate too much
- Hydrogen bonds break changing tertiary structure
- Enzyme can no longer work as an efficient catalyst
- Metabolic reactions are less efficient
What is negative feedback? (4)
- Effectors responding to stimulus
- To counteract a change where internal environment has been shifted away from the norm
- Negative feedback may not work if change is too big
- e.g. Huge drop in body temperature due to prolonged exposure to the cold
What is positive feedback? (4)
- Effectors responding to stimulus to rapidly activate something
- e.g. blood clot
- To amplify a change to push internal environment away from its norm
- Positive feedback isn’t apart of homeostasis
Describe the feedback process of a blood clot (4)
- Platelets activated and chemical cascade begin
- The increase in activating platelets is the positive feedback
- Blood clot forms
- Negative feedback begins to stop
What are the types of neurones? (3)
- Sensory
- Relay
- Motor
Structure of a neurone generally? (3)
- Cell body with nucleus
- Dendrites and dendrons
- Axon
Structure of myelin sheath? (2)
- Made of Schwann cells
- Between Schwann cells are nodes of Ranvier
Sensory neurone? (5)
- Transmit impulses from receptors to CNS
- Myelinated
- Short dendrites
- One long dendron
- Short axon
Relay neurone? (3)
- Transmit impulses between sensory and motor neurones
- Non-myelinated
- Many short dendrites
Motor neurone? (4)
- Transmit impulses from CNS to effectors
- Myelinated
- Many short dendrites
- Long axon
Steps in neuronal communications: (6)
- Stimulus
- Receptors detect
- Impulses sent through the sensory neurone to CNS
- CNS processes information and coordinates response
- Impulses sent through the motor neurone to effectors
- Effectors respond to stimulus
Why are sensory receptors known as transducers? (2)
- They convert different forms of energy into electrical energy
- Electrical energy = nerve impulses
Resting potential? (4)
- Potential difference at rest = resting potential
- Membrane is polarised at -70mV
- Outside of membrane is relatively positively charged compared to inside membrane
- As there are more positive ions outside of cell
Generator potential? (3)
- Stimulus detected
- Cell membrane excited
- Difference in charge inside and outside cell = change in potential difference = generator potential
Action potential? (3)
- The bigger the stimulus; the bigger the movement of ions; the bigger the change in potential difference
- If potential difference is big enough it’ll trigger an action potential
- Weak stimulus = weak generator potential = no action potential
Threshold level (1)
- Level of generator potential needed for action potential
How is resting potential maintained? (2)
- Membrane permeability
- Sodium-potassium pumps
Membrane permeability: (4)
- Membrane isn’t permeable to Na+
- Na+ can’t diffuse back in
- Creates sodium ion electrochemical gradient
- Membrane is permeable to K+
Sodium-potassium pumps? (3)
- 3 Na+ ions move out of neurone for every 2 K+ that move in
- K+ move through K+ channels on membranes
- ATP is used for this process
What is the cell membrane when it is stimulated? (1)
- Depolarised
Sequence in action potential: (5)
- Stimulus
- Depolarisation
- Repolarisation
- Hyperpolarisation
- Resting potential
What happens to the cell membrane when a stimulus is detected? (5)
- Stimulus excites membrane
- Na+ channels open
- Membrane become permeable to Na+
- Na+ diffuse in down Na+ electrochemical gradient
- Inside of neurone becomes less negative
What happens to the cell membrane at depolarisation? (3)
- Potential difference raised from -70mV to -55mV
- More Na+ ions diffuse in
- Positive feedback
What happens to the cell membrane at repolarisation? (5)
- Potential difference raised from -55mV to +30mV
- Na+ channels close
- Voltage-gated K+ channels open
- K+ diffuse out down K+ electrochemical gradient
- Negative feedback as restoration to resting potential begins
What happens to the cell membrane at hyperpolarisation? (3)
- K+ channels are slow to close
- Overshoot of K+ diffusing out of membrane
- Potential difference becomes more negative than resting potential
What happens to the cell membrane at resting potential? (2)
- Ion channels are reset
- Refractory period finishes
Refractory period? (3)
- Period of cell membrane recovery
- Na+ channels close during repolarisation
- K+ channels close during hyperpolarisation
How does action potential move down the neurone? (4)
- As a wave of depolarisation
- Cell 1 depolarises and initiates cell 2 to depolarise
- Cell 2 depolarises
- Cell 1 enters refractory period
The “all or nothing” principle? (4)
- When threshold is reached an action potential will fire
- With the same change in voltage
- No matter how big the stimulus is
- Bigger stimulus do increase frequency of action potentials
Action potential in myelinated neurones? (6)
- Saltatory conduction
- Myelin sheath = electrical insulator
- Schwann cells prevent impulse passing
- Impulse needs to jump at node of Ranvier
- Node of Ranvier can become depolarised
- Faster
Action potential in non-myelinated neurones? (2)
- Impulses travel down whole length of axon membrane
- Slower than saltatory conduction
What is a synapse? (1)
- A junction between a neurone and another neurone or a cell
What happens at the presynaptic neurone? (6)
- Action potential reaches synaptic knob
- Triggers Ca2+ influx
- Causes voltage-gates Ca2+ channels to open
- Ca2+ diffuse into synaptic knob
- Cause neurotransmitters vesicles to fuse with presynaptic membrane
- Neurotransmitters leave via exocytosis
What happens at the synaptic cleft? (4)
- Neurotransmitters released into synaptic cleft
- Diffuse across to postsynaptic membrane
- Bind to specific receptors
- Triggers action potential in the postsynaptic neurone
What happens at the postsynaptic neurone? (2)
- Action potential triggers opening of sodium channels
- Influx in Na+ causes depolarisation
What happens to the neurotransmitters after an impulse passes through the synapse? (2)
- Neurotransmitters are removed from cleft and broken down by enzyme
- They return to the synaptic knob to be reused
What is an excitatory synapse? (1)
- Depolarises postsynaptic neurone to trigger action potential
What is an inhibitory synapse? (2)
- Hyperpolarised postsynaptic neurone
- Prevents an action potential
What is an synaptic divergence? (2)
- One neurone connect to many neurones
- Information can be dispersed to many parts of the body
What is an synaptic convergence? (2)
- Many neurones connect to one neurone
- Information can be amplified
What is summation? (2)
- Neurotransmitters combine to excite the postsynaptic neurone to meet the action potential threshold
- Happens when the stimulus is weak
Types of summation? (2)
- Spatial
- Temporal
Spatial summation? (3)
- Synaptic convergence
- Many impulses can be coordinated into one amplified impulse
- Increases chance of action potential threshold to be met
Temporal summation? (3)
- Two or more impulses arrive in quick succession from the same presynaptic neurone
- Shortens frequency of impulses arriving
- Increases chance of action potential threshold to be met
Why are receptors only on the postsynaptic neurone? (1)
- To ensure impulse only moves in one direction
Hormonal system? (1)
- Made of endocrine glands and hormones
Endocrine glands? (1)
- Secretes hormones
Hormones? (3)
- First messengers
- Chemical messengers that travel through the bloodstream
- Bind to specific receptors called target cells
What happens when a first messenger binds to a target cell? (2)
- Triggers an enzyme in the cell membrane
- Which catalyse the production of second messengers
What are second messengers? (2)
- Signalling molecules
- Activate a cascade inside cell
Adrenaline? (3)
- First messengers that binds to receptors and activate enzyme adenylyl cyclase
- Activated adenylyl cyclase catalyses the production of cyclic AMP (cAMP) from ATP
- cAMP activates a cascade for Glycogenolysis
How can glands be stimulated? (2)
- Change in concentration of a substance
- Electrical impulses
Structure of adrenal gland? (3)
- Outer part called cortex
- Inner part called medulla
- Both structures are involved in the response to stress
Cortex? (2)
- Secrete steroid hormones
- Cortisol and aldosterone
Roles of cortisol and aldosterone? (3)
- Triggers gluconeogenesis to increase amount of energy available so body can respond to situation
- Increasing blood volume and pressure by up taking sodium ions and water by kidneys
- Supress the immune system
Medulla? (2)
- Secretes catecholamine hormones (modified amino acids)
- Secretes adrenaline and noradrenaline
Roles of adrenaline and noradrenaline? (3)
- Make energy by increasing heart and breathing rate
- Glycogenolysis
- Constricts blood vessels so that blood is diverted to the brain and muscle
Ectotherms? (5)
- Internal temperature is dependent on external temperature
- Cannot regulate internal temperature through homeostasis
- Rely on changing their behaviour
- Metabolic rates are higher at higher temperatures
- Generate little heat
Endotherms? (3)
- Internal temperature is not dependent on external temperature
- Regulate internal temperature through homeostasis
- Have high metabolic rates and generate a lot of heat
Mechanisms to reduce body temperature: (3)
- Sweating
- Hair lie flat
- Vasodilation
Sweating? (1)
- Water in sweat evaporates from the surface of the hot skin cooling the body down
Hair lie flat? (3)
- Erector pili muscles relax and hair lie flat
- Less air is trapped in hairy insulating layer
- Heat can be lost easier
Vasodilation? (2)
- Arterioles near skin dilate for more blood in the capillary
- More heat is loss through radiation
Mechanisms to increase body temperature: (5)
- Shivering
- Less sweat
- Hair stands up
- Vasoconstriction
- Hormones
Shivering? (2)
- Muscles contract in spasms
- Makes body shiver to produce more heat through increased respiration
Less sweat? (1)
- Less sweat is secreted to reduce heat loss via evaporation
Hairs stand up? (3)
- Erector pili muscles contract
- Trapping more air within the hairy insulating layer
- Reduces heat loss
Vasoconstriction? (2)
- Arterioles near skin constrict for less blood in the capillary
- Less heat is loss through radiation
Hormones? (2)
- Adrenaline and thyroxine are released
- Increase metabolism so more heat is produces
What is role of the hypothalamus in controlling body temperature? (1)
- Hypothalamus receives information from thermoreceptors and coordinates a response to increase or reduce temperature
Types of thermoreceptors: (2)
- Thermoreceptors in hypothalamus detects change in internal temperature (through blood temperature)
- Thermoreceptors in the skin (peripheral temperature receptors) detect external temperature
How are the levels of glucose controlled? (1)
- Through the hormonal system with the help of insulin and glucagon
From where are insulin and glucagon secreted from? (3)
- From a cluster of cells called the Islets of Langerhans
- Alpha cells secrete glucagon
- Beta cells secrete insulin
Role of insulin and glucagon: (2)
- Insulin lowers blood-glucose concentration
- Glucagon increases blood-glucose concentration
How does insulin work? (3)
- Binds to receptors on liver and muscles cell membranes which increases its permeability to glucose so that more glucose is taken up by cells
- Activates enzymes involved in glycogenesis
- Increases the rate of respiration of glucose
How does glucagon work? (2)
- Binds to receptors on liver cell membranes and activates enzymes involved in glycogenolysis and gluconeogenesis
- Decreases the rate of respiration of glucose
When do beta cells secrete insulin? (1)
- When cells are depolarised
How do beta cells secrete insulin? (5)
- Glucose enters cell by facilitated diffusion
- More glucose in beta cell causes the rate of respiration to increase
- More ATP is produced which triggers K+ ion channels to close
- This causes a build-up of K+ ions inside the cell and the cell become depolarised
- Depolarisation triggers Ca2+ channels to aid insulin-stored-vesicles to leave the cell via exocytosis
When does diabetes occur? (1)
- When blood glucose concentration is not controlled
Type 1 diabetes? (6)
- Auto-immune disease where body attacks beta cells
- No insulin is produced
- So when blood glucose concentrations rises it remains high
- Glucose can’t be absorbed by the kidney and is excreted through urine
- Develops in children or young adults
- Can be hereditary
How do you treat Type 1 diabetes? (3)
- Insulin therapy through insulin injections or insulin pumps
- Islet cell transplantation
- Lifestyle changes such as monitoring diet and increased physical activity
Type 2 diabetes? (3)
- Beta cells don’t produce enough insulin or insulin receptors are faulty
- Develops later on in life
- Linked to obesity
How do you treat Type 2 diabetes? (3)
- Lifestyle changes such as eating a balanced diet, regular exercise and loosing weight
- Medication such as metformin, sulfonylureas and thiazolidinediones
- Insulin therapy
Why is using genetically modified bacteria to produce insulin a good alternative to animal pancreas extractions? (5)
- Cheaper
- Larger quantities
- GM bacteria makes human insulin which more effective than using pig or cattle insulin
- Less likely to trigger and immune response
- May be ethically and religiously preferred
How can stem cells be used to cure diabetes? (1)
- Can be grown in beta cells for transplantation
