communication and homeostasis Flashcards
features of a good communication system
cover the whole body so the action of all cells and tissues can be co-ordinated
enable localised communication between cells
enable long distance communication between cells (widespread)
enable specific communication (targets specific cells to respond only)
be rapid (allowing fast response to rapid changes)
enable long term responses (more hormonal)
enable short term responses (more neuronal)
how do cells communicate with each other
cell signalling
2 communication systems: neuronal and hormonal
communicate to create a co-ordinated response
identify/recognise each other via cell signalling
cell signalling neuronal vs hormonal
both involve cell signalling molecules which are complementary to the shape of their receptor molecules on the cell surface membrane
neuronal often short term
hormonal long term
what may a cell signalling molecule be
protein
amino acid
lipid
glycoprotein
another organic chemical
examples of cell signalling molecules
hormones
antibodies
histamines
cytokines like interleukins
example of cell signalling from communicable diseases
in immune response, T helper cells bind to specific APCs (clonal selection) before clonal expansion is triggered by cytokine interleukin 1
T helper cells then bind to specific B lymphocytes stimulating plasma cell production by cytokine interleukin 2
what is the nervous system
interconnected network of neurones that signal to each other across synapses via neurotransmitters
what are neurones
specialised cells which can conduct electrical impulses very quickly to enable rapid responses e.g. reflexes
what do cells within endocrine glands release
hormones directly into the blood
what is a hormone
a chemical messenger which has a specific shape that is recognised by specific target cells
hormonal system: long or short term responses?
both
example of LT hormone response
LT stress response e.g. illness or injury. body cannot sustain bursts of energy mediated by adrenaline and noradrenaline so other hormones e.g. cortisol are important.
cortisol affects cellular metabolism leading to stimulation of glucose synthesis
nervous control vs hormonal control:
transmission
N: elec and chem transmission (nerve impulses and chemicals across synapses)
H: chem transmission (hormones) through blood system
nervous control vs hormonal control:
speed
N: rapid transmission and response
H: slower transmission and relatively slow-acting (adrenaline is an exception)
nervous control vs hormonal control:
ST/LT
N: often short term changes
H: often long term changes
nervous control vs hormonal control:
pathway
N: pathway is specific (through nerve cells)
H: pathway not specific (blood around whole body) but is target specific
nervous control vs hormonal control:
size of response
N: responses often v localised e.g. one muscle
H: response may be very widespread e.g. growth
nervous control vs hormonal control:
cell signalling molecules
both involve cell signalling molecules which are complementary to the shape of the receptor they interact w
both work together for the co-ordinated responses in the body e.g. in fight/flight response, sympathetic nervous system stimulates adrenal gland to release adrenaline
cell signalling definition
the process bay which cells communicate with each other for co-ordination of bodily functions
cell recognition
cells work together
trigger reaction inside of target cell
e.g. hormone
explain how a glycoprotein can act as a receptor
cell signalling molecule binds to a complementary receptor (complementary to shape of ligand) e.g. hormones/ neurotransmitters to trigger a response
may be involved in endocytosis
has a specific shape
outline 3 roles of glycoproteins in membranes
allow for recognition of ‘self’ by the immune system
act as antigens
stabilises membrane forming H bonds w/ H2O molecules
act as receptors for cell-signalling molecules
binding sites for hormones
examples of changes to the internal environment
blood glucose concentration
water potential of blood
internal temperature
pH of blood
blood pressure
examples of changes to the external environment
humidity
light intensity
external temperature
new/sudden sound
pressure on skin
what’s another word for an environmental change
stimulus
what’s another word for a change in behaviour
response
examples of responses to external stimuli
seasonal change in temperature causes thick fur development of rabbits (white and brown)
appearance of predator/prey causes fight/flight and hormone release
give 2 reasons why both plants and animals need to be able to respond to changes in their environment
to avoid being eaten and to obtain access to resources
state an organ that is associated with maintaining the internal environment of a mammal and state the role it plays
pancreas releases insulin to regulate and maintain blood glucose levels
definition of homeostasis
maintenance of a stable internal environment around a set point despite internal/ external environmental changes
what does homeostasis include
thermoregulation
blood glucose concentration
blood salt concentration
water potential of blood
blood pressure
blood pH (conc of CO2)
what is the thermoregulation important for
enzyme activity
why is controlling blood glucose level necessary
needed for respiration
affects water potential
why is controlling blood salt concentration necessary
affects the water potential
affects blood pressure
why is controlling water potential of the blood necessary
it affects blood pressure
why is controlling blood pressure necessary
ensures blood delivered efficiently and without damage to walls of blood vessels/ heart
why is controlling blood pH necessary
decreases pH which affects enzymes
what is feedback
when effectors bring about a response they change the condition in the body and this new condition will be detected by receptors (i.e. the input has changed) which in turn will affect the response
what is negative feedback
a change initiates a series of events and negative feedback is a mechanism that reverse the change bringing the system back to optimum
what is overshoot in a homeostatic mechanism
it takes time to respond to a stimulus and the response may cause an overshoot and so homeostasis involves fluctuations around the optimum
what does negative feedback ensure
conditions inside a living organism remain within a relatively narrow range
what is overshoot minimised by
gradually cutting off corrective mechanisms
quick response
antagonistic control
positive feedback details
the mechanism that increases a change, taking the system further away from the optimum
tends to be harmful, but not always
not involved in homeostasis
examples of positive feedback
opening of channels in neurones
blood clotting
during hypothermia
during birth
examples of positive feedback: opening of channels in neurones
Na+ enters the axon due to stimulus
potential difference becomes less negative
voltage gated Na+ channels open
more Na+ enters
action potential fired
examples of positive feedback: blood clotting
platelets attract more platelets which accelerates clotting
examples of positive feedback: during hypothermia
body temp drops
enzymes become less active
exergonic metabolic reactions slower
less heat released
temp drops further
enzyme activity decreases further
temp decreases further
examples of positive feedback: during birth
cervix dilates
pituitary gland releases oxytocin
oxytocin increases uterine contractions
this stretches the cervix further
causes more oxytocin release
causing more contractions
inflammation response involving cell signalling
mast cells release histamines and cytokines
these attract neutrophils and macrophages and T helper cells
histamines make blood vessels more permeable and make arterioles vasodilator
more tissue fluid formed
pain, heat, redness and swelling occur
heat prevents pathogen reproduction
how could rhodniin (prevents action of thrombin) enable an insect to continuously feed on the blood of its prey
thrombin is involved in the cascade activation for blood clotting, so inhibiting it will mean fibrinogen is not converted to fibrin, so blood remains liquid and wound exposed
what are plasmodesmata
adhesion between plant cells is mediated by their cell walls- in particular a specialised pectin-rich region of the cell wall called the middle lamella which acts asa. flue to hold adjacent cell walls together
how do adjacent plant cells communicate with each other
via cytoplasmic connections called plasmodesmata
plasmodesmata are dynamic structures and they can open or close in response to specific stimuli allowing regulated passage of macromolecules between cells
plasmodesmata diameter
40nm
number of plasmodesmata between a pair of neighbouring cells
between 1000 and 100000
when and how do plasmodesmata form
during cell division
parts of the endoplasmic reticulum of the parent cell get trapped in the new cell wall that is produced to create new daughter cells
role of cells by plasmodesmata
control the permeability/diameter of plasmodesmata
types of junctions between adjacent animal cells
tight
gap
adherens
desmosomes
what type of junction is this
gap junction
what type of junction is this
tight junction
what type of junction is this
adherens
what type of junction is this
desmosomes
description of tight junction
cells are tightly held against each other by many individual groups of tight junction proteins called claudins, each of which interacts with a partner group on the opposite cell membrane
description gap junction
develop when a set of 6 membrane proteins called connexions form an elongated, donut-like structure called a connexon
when they align w those of adjacent animal cells, a channel forms between the cells
description adherens
built from cadherins (transmembrane proteins) and catenins (connected to actin filaments)
desmosomes description
cadherins (specialised adhesion proteins) are found on the membranes of both cells and hold the membranes together
tight junction function
create a watertight seal between 2 adjacent animal cells (keep liquid from escaping between cells)
gap junction function
allow for transport of ions, water and other substances between animal cells
important in cardiac muscle for synchronised contraction
adherens function
provide strong mechanical attachments between adjacent cells
hold cardiac muscle cells together as heart expands and contracts repsonsible for contract inhibition
desmosomes function
act like spot welds between adjacent epithelial cells
involves a complex of proteins
pin adjacent cells together ensuring cells in organs and tissues that stretch e.g. skin and cardiac muscle , remain connected in an unbroken sheet
why is it necessary to control body temperature?
optimum temp for enzyme activity
molecules have more kinetic energy so increased frequency of successful collisions so increased rate of reaction (Q10=2)
what does increasing body temperature do
(hyperthermia etc)
if temperature increases too much, enzymes denature so rate falls
too high- hyperthermia: cellular respiration fails to work, leading to organ failure. initially, patient may have hot dry skin and reduction in BP, increased HR and nausea, vomiting and headaches
what does decreasing body temp do (hypothermia etc)
too low=hypothermia (pale blue, cold skin and shivering)
Q10=2 so if temp drops 10 degrees, enzymatic reactions fall by 1/2
POSITIVE FEEDBACK LOOP so get colder
core temperature definition
operating temperature inside the body
peripheral temperature definition
temperature of skin
core vs peripheral temperature
core temp maintained close to set point
peripheral temp is more variable and influenced by the environment
conduction definition
transfer of heat from hotter to cooler objects in contact
heat energy can also be conducted to surrounding medium eg air
convection definition
warmer air is less dense and so will rise through surrounding cooler air, creating air currents
convection speeds up loss of energy from objects by conduction and evaporation
radiation definition
transfer of heat energy from a body to colder objects that are not in contact with each other
heat energy is transferred by infrared waves
evaporation definition
change of a liquid to a vapour which is accompanied by a cooling e.g. sweating, wallowing, respiratory surfaces
can only lose heat by this method
what is an endotherm
organism that uses heat from metabolic reactions to maintain body temperature so have a higher metabolic rate
what is an ectotherm
organism that relies on external source of heart to maintain body temperature
endotherm example
mammals
ectotherm examples
fish
reptiles
amphibians
some insects
endotherm vs ectotherms temp range
endotherms control body temp within strict limits
ectotherms are not able to control body temp internally so cannot increase metabolism to increase temperature
endotherm controlling body temp mechanisms
use a variety of mechanisms: physiological and behavioural
ectotherm controlling body temp
fluctuates with external temperature
endotherms activity level impacting temp
activity level is largely independent of external temperature
ectotherms activity level impact on body temp / vice versa
activity level depends on external temp: more active at higher temps as enzymes at optimum
ectotherms niche?
often exploit a narrower niche
what do ectotherms do if they are too cold
try to absorb more heat from environment:
move to sunny area and bask in the sun
lie on a warm surface e.g. a rock
expose a larger SA to sun/warm surface
move around to generate some heat
what do ectotherms do if they are too hot
try to avoid gaining more heat or increase heat loss to the environment:
move out of sun and seek shade
move underground into burrow
decrease SA exposed to sun/warm surface
increase rate and depth of breathing so more water evaporates (open buccal cavity to expose moist surface)
advantages of being an ectotherm
lower respiratory rate required
less food required
more of their food converted to growth
can survive longer without food
disadvantages of being an ectotherm
can be more vulnerable to large fluctuations in environmental temp
cannot exploit as many locations
more susceptible to predation if less active
less active at colder temps: limits their activity level
why do lizards bask in the sun w their mouths open
buccal cavity open so more water evaporates so more heat loss
lizard doesn’t overheat
(temp control)
suggest why aquatic organisms have relatively few problems in maintaining a stable body temp
water has a high SHC so its temp remains relatively constant, providing a stable habitat where ectotherms remain at a relatively stable temp
role of peripheral temperature receptors
detect changes in temp of skin and send impulses to hypothalamus
give early warning that body temp may be about to change
how does the hypothalamus work as a thermoregulatory centre?
monitors temp of blood flowing through it using thermoreceptors
receives impulses from peripheral thermoreceptors in the skin
send impulses via motor neurones to sweat glands, muscles in arterioles, skeletal muscles and hair erector muscles
increase metabolism to increase exergonic reactions so more heat released (increase TRH->TSH->thyroid gland->thyroxine)
what is the blood supply in sweat glands for
supplies the fluid for making sweat
why do sweat glands have a sympathetic nerve
part of autonomic nervous system (motor neurones)
why is there smooth muscle in the walls of arterioles supplying capillaries in the skin
contract to cause vasoconstriction (less blood flow to skin so less heat loss by radiation)
relax to cause vasodilation (more blood flow to skin so more heat loss by radiation)
what are shunt vessels and their role in heat loss
allow blood to bypass capillaries in the surface of the skin so less heat is lost
role of erector muscles in thermoregulation
contract and pull on the base of hair follicle to stand up and trap air, acting as an insulator so less heat lost
(air trapped between hairs, a poor conductor of heat so insulates the body)
role of shivering in thermoregulation
muscles contract, respiring which is an exergonic reaction so releases heat
vasodilation mechanism
if core temp starts to increase, smooth muscle in arteriole walls relaxes and arteriole dilates
more blood flows through the capillaries near the surface of the skin
this increases the rate of heat loss from the body
vasoconstriction mechanism
if core temp of body starts to decrease, smooth muscle in the arteriole walls contracts which constricts the arteriole
less blood flows through the capillaries close to the surface of the skin bc blood is redirected through the shunt vessels (deeper layers of skin)
reduces rate of heat loss from the body
suggest why the ear provides a more accurate measurement of body temperature than the skin surface
ear is close to/shares blood supply with hypothalamus, so measures a temp closer to your core temp than the peripheral temp at the skin
general features of a neg feedback loop
maintaining internal environment around a set point
receptors detect change from a set point
effectors produce change to return to set point via response
why does someone w hypothermia need to be warmed up gently rather than fast
sudden heating causes vasodilation of arteries to extremities, so cold blood flows to the heart and can cause heart failure
more blood flow to capillary bed so more heat loss
why does core temp drop initially when person w hypothermia is placed in bath of warm water
heat energy lost from periphery
warm blood diverted from core to skin
why is core re-warming better than other methods of rewarming
w/o core rewarming, other methods lead to vasodilation and cold blood to heart so lower BP
temp of medulla oblongata restored faster and this controls HR, BR and shivering via autonomic NS
cerebrum temp restored faster, which controls cognitive function
cerebellum temp restored faster, which restores co-ordination
endotherm behavioural responses to being too cold
orientate body towards sun to increase SA exposed to sun
lie in sun
move about to generate heat in muscles (in extreme conditions roll into a ball shape to reduce SA and heat loss)
remain dry
endotherm behavioural responses if too hot
orientate body to reduce SA exposed to sun
hide away from sun in shade/burrow
remain inactive and spread limbs out to enable greater heat loss
wet skin to use evaporation to help cool down (cats lick themselves, elephants spray water over body)
endotherm physiological responses if too hot
vasodilation
panting (more vaporisation of water from surface of lungs and airways)
less skeletal muscle contraction
erector muscles relax
sweating
less response in liver so less heat released
endotherm physiological responses if too cold
vasoconstriction
less panting
shivering
erector muscles contrat
less sweating
more resp in liver cells so more energy form food converted to heat
why is it important to maintain the core temperature at a set point (norm) of 37C?
metabolic/chemical reactions are heat sensitive
enzymes have an optimum temperature
high temperatures lead to enzymes denaturing
ESCs fail to form
