A2 - Unit 1 - Communication and homeostasis Flashcards
Give 4 ways organisms can change their internal environment in order to survive
Blood glucose concentration
Internal temperature
Water potential
Cell pH
Give 4 ways organisms can change their external environment in order to survive
Humidity
External temperature
Light intensity
New or sudden sound
Why is coordination needed in an organism
Organisms have become specialised to perform specific functions, and different cells perform different functions
In order for the organism to work effectively these different functions need to be in coordination
What is homeostasis?
Coordination in order to maintain a relatively constant internal environment
What can cells do during cell signalling??
Transfer signals locally e.g. Between neurones at synapses (signal used is called a neurotransmitter)
Transfer signals across large distances, using hormones e.g. Cells of pituitary glad secrete ADH which acts on the kidneys
How do plants coordinate?
Plant stems grow towards a light source to maximise photosynthesis rate
Achieved through use of plant hormones
Describe the cell body in a neurone
Contains the nucleus surrounded by cytoplasm
Large amounts of ER and mitochondria involved in the production of neurotransmitters
These are chemicals used to pass signals from one neutrons to the next
Describe the dendrons in a neurone
Short extensions which comes from the cell body
Extensions divide into smaller and smaller branches known as dendrites
Responsible for transmitting electrical impulses towards the cell body
Describe the axons in a neuron
Singular elongated nerve fibres that transmit impulses away from the cell body
Fibres can be very long
Transmit impulses from the tips of the toes and fingers to the spinal cord
Cylindrical in shape
Very narrow region of cytoplasm surrounded by a plasma membrane
What are the three types of neurone?
Sensory
Relay
Motor
What is a sensory neurone?
Transmit impulses from a sensory receptor cell to a relay neurone, motor neurone, or the brain
They have one dendron
Carries the impulse to the cell body and one axon which carries the impulse away from the cell body
What is a relay neurone?
Transmit impulses between neurones e.g. Between sensory neurones and motor neurones
Have many short axons and dendrons
What are motor neurones?
Transmit impulses from a relay neurone or sensory neurone to an effector, such as a muscle or a glad
They have a long axon and many short dendrites
What route does the typical nervous response impulse travel?
Receptor- sensory neurone - relay neurone - motor neurone - effector cell
Describe the structure of myelinated neurones
Neurones are covered in a myelin sheath, made of many layers of plasma membrane
Schwann cells produce the thin layers of membrane, growing around the axon many times
Schwann cells stop growing when there’s 20 layers of membrane
Insulating layer
What is the node of Ranvier?
The gaps in the myelin sheath
Allows the electrical impulse to ‘jump’ from one node to the next
Allows the impulse to be transmitted much faster
How does an electrical impulse travelling through an non myelinated neurone differ to a myelinated neurone?
Myelinated, the impulse jumps across the neurone from one node of Ranvier to the other
Non myelinated impulse travels continuously along the nerve fibre much slower
What are the 4 different types of receptor??
Mechanoreceptor
Chemoreceptor
Thermoreceptor
Photoreceptor
Where are mechanoreceptors on the body?
Skin
Where are chemoreceptors on the body?
Nose
Where are thermoreceptor on the body?
Tongue
Where are photoreceptors in the body?
Eye
What is a transducer?
It converts a stimulus into a nerve impulse
What are pacinian corpuscles?
Specific sensory receptors that detect mechanical pressure
Located deep in the skin
Abundant in fingers and soles of the feet
What is a stimulus?
Any change in the environment that causes a response
What is a response?
A change in behaviour or physiology as a result of a change in the environment
What condition can affect how enzymes efficiently work?
Temperature
pH
An aqueous environment
Freedom from toxin and excess inhibitors
What are the two major systems of communication that work by cell signalling?
The neuronal system
The hormonal system
How does the neuronal system work?
Interconnected network of neurons that signal to each other across synapse junctions
The neurones can conduct a signal very quickly and enable rapid responses to stimuli that may be changing quickly
How does the hormonal system work?
Uses the blood to transport its signals
Cells in an endocrine organ release the signal directly into the blood
Carried all over the body but is only recognised by specific target cells
Hormonal system enables longer-term responses to be coordinated
What is negative feedback?
A process that brings about a reversal of any change in conditions
It ensures that an optimum steady state can be maintained, as the internal environment is returned to its original set of conditions after any change
Give 6 conditions that the body needs to keep constant
Body temperature Blood glucose concentration Blood salt concentration Water potential of the blood Blood pressure Carbon dioxide concentration
What three processes must occur in order to maintain a constant internal environment?
Any change to the internal environment must be detected
The change must be signalled to other cells
There must be a response that reverses the change
What pathway has to happen for negative feedback to work effectively?
Stimulus —> receptor —> communication pathway (cell signalling —> effector —> response
What structures are needed for the negative feedback pathway to work?
Sensory receptors e.g. temperature receptors, glucose concentration receptors
Communication system e.g. nervous system, hormonal system
Effector cells e.g. liver cells or muscle cells
What is positive feedback?
A process that increases any change detected by the receptors. It tends to be harmful and does not lead to homeostasis
How does the Pacinian corpuscule convert mechanical pressure into a nervous impulse
In normal state, sodium ion channels in the sensory neurones membrane are too narrow to allow sodium ions to pass through
Neurone of the Pacinian corpuscule has a resting potential
When pressure is applied to the Pc it changes shape. Causes the membrane surrounding its neurone to stretch
When membrane stretches, sodium ion channels widen. Sodium can now diffuse into the neurone
Influx of sodium ions changes the potential of the membrane
Becomes depolarised
Results in a generator potential
In turn, generator potential creates an action potential (a nerve impulse) that passes along the sensory neurone
Give 4 features of the synaptic knob
Many mitochondria
Large amount of smooth endoplasmic reticulum
Vesicles of a chemical called acetylcholine
Voltage-gated calcium ion channels in the membrane
What happens in the transmission of an action potential across a synapse
Action potential arrives
Voltage-gated calcium ion channels open
Calcium ions diffuse into synaptic knob
Calcium ions cause synaptic vesicles to move to and fuse with the presynaptic membrane
Acetylcholine is released by exocytosis
AcH molecules diffuse across the cleft
AcH binds to receptor sites on the sodium ions channels in the postsynaptic membrane
Sodium ion channels open
Sodium ions diffuse across the postsynaptic membrane into the postsynaptic neurone
Generator potential or excitatory postsynaptic potential (EPSP) is created
If sufficient generator potentials combine then the potential across the postsynaptic membrane reaches the threshold potential
New action potential is created in the postsynaptic neurone
What is acetlycholinesterase
An enzyme in the synaptic cleft
It breaks down the transmitter substance acetlycholine into ethanoic acid and choline
Stops the transmission of signals so that the synapse does not continue to produce action potentials
What happens to ethanol and choline after they have been broken down by acetlycholinesterase?
They are recycled
Re-enter the synaptic knob by diffusion and are recombined to acetylcholine using ATP from respiration
What is summation?
A term that refers to the way that several small potential changes can combine to produce one larger change in the potential difference across the membrane
Why might several presynaptic neurones cover one postsynaptic neurone?
Allows signals from different parts of the nervous system to create the same response
Useful where several different stimuli are warning us of danger
Why might one presynaptic neurone diverge into several postsynaptic neurones?
Allows one signal to be transmitted to several parts of the nervous system
Useful in a reflex arc
One postsynaptic neurone elicits the response while another informs the brain
How do neurones ensure that signals are transmitted in one direction?
Only the presynaptic knob contains vesicles of acetylcholine
What is acclimatisation?
After repeated stimulation a synapse may run out of vesicles containing the transmitter substance
Synapse is said to be fatigued
Means nervous system no longer responds to the stimulus
Helps to avoid overstimulation
What are hormones??
Molecules that are released by endocrine glands directly in the blood
Act as messengers carrying a signal from the endocrine glad to a specific target organ or tissue
What is an endocrine gland? Yeah
A gland that secretes hormones directly into the blood
What is an exocrine gland?
A gland that secretes molecules into a duct that carries the molecules to where they are used
What are target cells?
Those that possess a specific receptor on their plasma membrane
The shape of the receptor is complimentary to the shape of the hormone molecule
Many similar cells together form a tissue
That is adenyl cyclase?
An enzyme associated with the receptor for many hormones including adrenaline
Found on the inside of the cell surface membrane
What is an ectotherm?
An organism that relies on external sources of heat to regulate its body temperature
Why is it important to maintain and regulate body temperature?
Temperature can have a dramatic effect on the structure of your proteins including enzymes
Without the proper function of these enzymes in your body, it wouldn’t be able to work at all!
What is an endotherm?
Organism that can use internal sources of heat, such as heat generated from metabolism in the liver, to maintain its body temperature
Give three advantages of being an ectotherm
Use less of their food in respiration
Need to find less food and may be able to survive for long periods of time without eating
Greater proportion of energy obtained can be used for growth
Give two disadvantages of being an ectotherm
Less active in cooler temperatures
Will have to warm up in the morning before they can be active
Greater risk of predation
May not be capable for activity during winter
cant warm up sufficiently
So they must ensure they have sufficient stores of energy to survive over the winter, without eating
How do ectotherms regulate their body temperature?
Too cold: They bask in the sun or lie on a warm surface to heat up
Too hot: Stay underground or in the shade to cool down
How do ectotherms regulate their body temperature by exposing their body to the sun?
It enables more heat to be absorbed
How do ectotherms regulate their body temperature by orientating their body to and away from the sun?
To: Exposes larger surface area for more heat absorption
Away: Exposes lower surface area so that less heat is absorbed
How do ectotherms regulate their body temperature by hiding in a burrow?
Reduces heat absorption by keeping out of the sun
How do ectotherms regulate their body temperature by altering their body shape?
Exposes more or less surface area to the sun
How do ectotherms regulate their body temperature by increasing their breathing movements?
It evaporates more water and cools them down
Give three advantages of being an endotherm
Fairly constant body temperature whatever the temperature is externally
Activity possible when external temperatures are cool - such as at night
Ability to inhabit colder parts of the planet
Give three disadvantages of being an endotherm
Significant amount of energy intake is used to maintain body temperature in the cold
More food required
Less of the energy from food is used for growth
How do sweat glands in the skin help to maintain the body temperature of an endotherm
temp too high: secrete more sweat onto skin, water in sweat evaporates, using heat from blood to supply latent heat of vaporisation
temp too low: less sweat is secreted, less evaporation of water, less loss of latent heat
How do the lungs, mouth and nose help to maintain the body temperature of an endotherm
Too hot: Panting increases evaporation of water from lungs, tongue and other moist surfaces, using latent heat
Too cold: Animal does not pant, so less water evaporates
How do hairs on the skin help to maintain the body temperature of an endotherm?
Too hot: Hairs lie flat, providing little insulation, and thus more heat can be lost by convection and radiation
Too cold: Hairs are raised to trap a layer of insulating air, reducing the loss of heat from the skin
How do the arterioles leading to capillaries in the skin help to maintain the body temperature of an endotherm
Too hot: Vasodilation allows more blood into capillaries near the skin surface, more heat can be radiated from the skin which in pale skinned people may look red
Too cold: Vasoconstriction reduces the flow of blood through capillaries near the surface of skin, less heat is radiated
How do liver cells help to maintain the body temperature of an endotherm
Too hot: Rate of metabolism is reduced, less heat is generated from exergonic reactions such as respiration
Too cold: Rate of metabolism is increased, therefore respiration generates more heat, which is transferred to the blood
How do skeletal muscles help to maintain the body temperature of an endotherm?
Too hot: No spontaneous contractions
Too cold: Spontaneous contractions (shivering) generate heat as muscles cells respire more
What behavioural mechanisms do endotherms do if the external temperature is too hot?
Move into shade or hide in burrow
Orientate body to decrease surface area exposed to sun
Remain inactive and spread out the limbs to increase surface area
What behavioural mechanisms do endotherms to if the external temperature is too cold?
Move into sunlight
Orientate body to increase surface area exposed to sun
Move about to generate heat in muscles (except in extreme cold when it is better to keep still and roll into a ball to reduce surface area)
How do endotherms monitor the temperature of their blood?
In the hypothalamus of the brain
If the temperature drops below optimum the hypothalamus sends signals to reverse the change:
Increase rate of metabolism in order to release more heat from exergonic reactions
Release of heat through extra muscular contraction
Decreased loss of heat to the environment
What is the resting potential?
The potential difference or voltage across the neurone cell membrane while the neurone is at rest. It is about -60mV inside the cell compared with the outside
Other cells may also maintain a resting potential that might change under certain circumstances
What are voltage-gated channels?
Channels in the cell membrane that allow the passage of charged particles or ions. They have a mechanism called a gate which can open and close the channel. In these channels the gates respond to changes in the potential difference across the membrane
What is threshold potential?
A potential difference across the membrane of about -50mV. If the depolarisation of the membrane does not reach the threshold potential then no action potential is created
If the depolarisation reaches the threshold potential then an action potential is created
What is an action potential?
A depolarisation of the cell membrane so that the inside is more positive than the outside, with a potential difference across the membrane of +40mV. This can be transmitted along the axon or Dendron plasma membrane
What happens in a resting neurone?
Actively transporting ions across its cell surface membrane.
Sodium/potassium ion pumps are used to pump three sodium ions out of the cell for every two potassium ions that are pumped in
Plasma membrane more permeable to potassium ions than to sodium ions and many diffuse out again.
Cell cytoplasm contains large organic anions, help to maintain the interior of the cell at a negative potential
Cell membrane is said to be polarised
What is the all or nothing response?
Generator potentials in the sensory receptor are depolarisations of the cell membrane
A small depolarisation will have no effect on the voltage-gated channels
If the depolarisation is large enough to reach threshold potential it will open some nearby voltage-gated channels
Causes a large influx of sodium ions and the depolarisation reaches +40mV, which is an action potential!
Once this value is reached the neurone will transmit an action potential
But it will only do this if the value is reached, it is either ‘on’ or ‘off’
What are the 9 stages of an action potential?
- Membrane in resting state - polarised (inside of the cell being -60mV)
- Sodium ion channels open, some sodium ions diffuse into the cell
- Membrane depolarises - becomes less negative with respect to the outside (-50mV)
- Voltage-gated sodium ion channels open and many sodium ions flood in. As more sodium ions enter the cell becomes more positively charged inside compared to outside
- Potential difference across membrane reaches +40mV
- Sodium ion channels close and potassium channels open
- Potassium ions diffuse out of the cell bringing the potential difference back to negative - called repolarisation
- Potential difference overshoots slightly - hyperpolarisation
- Original potential difference restored so that the cell returns to its resting state
What is the refractory period?
It allows the cell to recover after an action potential
Ensures that action potentials are transmitted in only one direction
What are local currents?
The movements of ions along the neurone. The flow of ions is caused by an increase in concentration at one point, which causes diffusion away from the region of higher concentration
What is saltatory conduction?
Means ‘jumping conduction’, Refers to the way that the action potential appears to jump from one node of Ranvier to the next
What are the advantages of saltatory conduction?
Myelin sheath means that action potentials can only occur at the gaps between the Schwann cells that make up the myelin sheath
Speeds up the transmission of the action potential
Myelinated neurones conduct action potentials more quickly than non-myelinated neurones
What is a neurotransmitter?
A chemical that diffuses across the cleft of the synapse to transmit a signal to the postsynaptic neurone
What are cholinergic synapses?
Those that use acetylcholine as their transmitter substance
What is a synaptic knob?
A swelling at the end of the presynaptic neurone
How does the endocrine system transport its signals?
It uses blood circulation
NO DUCTS
How does the exocrine system transport its signals?
It contains ducts that carry their secretion to another place.
e.g. the saliva glands secrete saliva into a duct, the saliva flows along the duct into the mouth
What are the two types of hormone?
- Protein and peptide hormones and derivatives of amino acids (e.g. adrenaline, insulin and glucagon)
- Steroid hormones (e.g. sex hormones)
How do the two different hormones work in the endocrine system?
Proteins are insoluble in the phospholipid membrane and do not enter the cell
Steroids can pass through the membrane and enter the cell to have a direct effect on the DNA in the nucleus
How does adrenaline have an effect on the body?
Adrenaline (first messenger) is a protein and therefore cant enter the cell. It must have an effect some other way
It binds to the receptor on the outside of the cell surface membrane which is complimentary to its shape. Receptor is associated with an enzyme adenyl cyclase on the inner cell surface membrane
Enzyme converts ATP to cyclic AMP (cAMP). The cAMP is a second messenger inside the cell
cAMP then causes effect inside the cell by activating enzyme action
Where are the adrenal glands found in the body?
Just above the kidneys
one on each side of the body
Each gland can be divided into a medulla region and a cortex region
What do the cells in the medulla of the adrenal glad do?
Manufacture and release the hormone adrenaline in response to stress such as pain or shock
What effect does adrenaline have on the body?
Relax smooth muscle in the bronchioles Increase stroke volume of the heart Increase heart rate Cause general vasoconstriction to raise blood pressure Stimulate conversion of glycogen to glucose Dilate pupils Increase mental awareness Inhibit the action of the gut Cause body hair to erect
What does the adrenal cortex do?
Uses cholesterol to produce certain steroid hormones
What roles do steroid hormones made in the adrenal cortex have in the body?
Aldosterone helps to control the concentrations of sodium and potassium in the blood
Cortisol helps to control the metabolism of carbohydrates and proteins in the liver
What is the first messenger?
The hormone that transmits a signal around the body
What is the second messenger?
cAMP, which transmits a signal inside the cell
What is the pancreas?
A small organ lying below the stomach. It is an unusual organ in that it has both exocrine and endocrine functions
What three enzymes are manufactured in the pancreas?
Amylase - a carbohydrase
Trypsinogen - an inactive protease
Lipase
What is the pancreatic duct?
A tube that collects all the secretions from the exocrine cells in the pancreas and carries the fluid to the small intestine
What are the Islets of Langerhans?
Small patches of tissue in the pancreas that have an endocrine function
What cells are found in the islet of Langerhans?
alpha and beta cells
What do alpha cells secrete?
The hormone glucagon
What do beta cells secrete?
The hormone insulin
What is insulin?
The hormone released from the pancreas that causes blood glucose levels to go down
What is glucagon?
The hormone that causes blood glucose levels to rise
What are hepatocytes?
Liver cells
They are specialised to perform a range of metabolic functions
What happens in the liver if the blood glucose rises too high?
Detected by the beta cells
Beta cells secrete insulin into the blood
target cells such as hepatocytes, muscles cells and brain cells have receptors for insulin
insulin binds to the receptors
Activates adenyl cyclase which converts ATP into cAMP
which activates a series of enzyme-controlled reactions in the cell
Increased entry of glucose in through certain channels, reduces the blood glucose concentration
What effects does insulin have on the cell?
More glucose channels are placed into the cell surface membrane
More glucose enters the cell
Glucose in the cell is converted to glycogen for storage
More glucose is converted to fats
More glucose is used in respiration
Increased entry of glucose in through certain channels reduces the blood glucose concentration
What happens in the liver when the blood concentration is too low?
Detected by alpha cells
Alpha cells secrete the hormone glucagon
What are the effects of glucagon on the body?
Conversion of glycogen to glucose (glycogenesis)
Use of more fatty acids in respiration
The production of glucose by conversion from amino acids and fats
How does the body control insulin secretion?
Cell membranes of the Beta cells contain both calcium ion channels and potassium ion channels
Potassium ion channels are normally open and the calcium ion channels are normally closed. Potassium ions diffuse out of the cell making the inside of the cell more negative; at rest the potential difference across the cell membrane is about -70mV
When glucose concentrations outside the cell are high, glucose molecules diffuse into the cell
Glucose is quickly used in metabolism to produce ATP
Extra ATP causes the potassium channels to close
The potassium can no longer diffuse out and this alters the potential difference across the cell membrane - it becomes less negative inside
This change in potential different opens up the calcium ion channels
Calcium ions enter the cell and cause the secretion of insulin by making the vesicles containing insulin move to the cell surface membrane and fuse with it, releasing insulin by exocytosis
What is diabetes mellitus?
A disease in which blood glucose concentrations cannot be controlled effectively
What is hyperglycaemia?
The state in which the blood glucose concentration is too high
What is type 1 diabetes?
Known as insulin-dependent diabetes
Usually starts in childhood
Result of an autoimmune response in which the body’s own immune system attacks the beta cells and destroys them
May also result from a viral attack
Body is no longer able to manufacture sufficient insulin and cannot store excess glucose as glycogen
What is type 2 diabetes?
Non-insulin dependent diabetes
Can produce insulin
As people age their responsiveness to insulin declines
Level of insulin secreted by the beta cells may also decline
What factors can cause type 2 diabetes?
Obesity
Diet high in sugars, particularly refined sugars
Being of Asian or Afro-Caribbean origin
Family history
How is type 2 diabetes treated?
Careful monitoring and control of the diet
May be substituted with insulin injections or use of other drugs which slow down the absorption of glucose from the digestive system
How is type 1 diabetes treated?
Using insulin injections
Blood glucose concentration must be monitored and the correct dose of insulin must be administered to ensure that the glucose concentration remains fairly stable
What is hypoglycaemia?
The state in which the blood glucose concentration is too low
What are genetically engineered bacteria?
Bacteria are those in which the DNA has been altered. In this case a gene coding for human insulin has been altered into the DNA of the bacteria
What are stem cells?
Unspecialised cells that have the potential to develop into any type of cell
Give three advantages of using insulin from genetically engineered bacteria?
Exact copy of human insulin, faster acting and more effective
Less chance of developing tolerance to the insulin
Lower risk of infection
What is cell metabolism?
The result of all the chemical reaction taking place in the cytoplasm
What is myogenic muscle?
Tissue that can initiate its own contractions
What is a pacemaker?
A region of tissue in the right atrium wall that can generate an impulse and initiates the contraction of the chambers
What is the medulla oblongata?
Found at the base of the brain
The region of the brain that coordinates the unconscious functions of the body such as breathing rate and heart rate
What nerves run from the medulla oblongata to the heart?
Accelerator nerve
Vagus nerve
What is the cardiovascular centre?
A specific region of the medulla oblongata that receives sensory inputs about levels of physical activity, blood carbon dioxide concentration and blood pressure. It sends nerve impulse to the SAN in the heart to alter the frequency of excitation waves
Give three ways the heart has adapted to supply more oxygen and glucose
Increase in the number of beats per minute (increased heart rate)
Increase strength of contractions
Increase the volume of blood pumped per beat (stroke volume
What four factors control the rate of a heart beat?
Heart muscle is myogenic
Heart contains its own pacemaker - called the sinoatrial node (SAN), can initiate an action potential. AP travels as a wave of excitation over the atria walls, through the AVN and down the Purkyne fibres to the ventricles causing them to contract
Heart supplied by nerves from the medulla oblongata of the brain, these nerves connect to the SAN, do not initiate contraction but they can affect the frequency of the contractions
Heart muscle responds to the presence of the hormone adrenaline in the blood
What 5 factors affect heart rate?
Movement of the limbs
Production of CO2 and therefore pH of the blood
Concentration of CO2 after stopping exercising
Adrenaline in the blood
Blood pressure
