Chapter 15 - Homeostasis Flashcards
(96 cards)
1
Q
Negative feedback definition?
A
The result of a process inhibits the process from continuing to occur; it is the opposite of positive feedback.
2
Q
Why do multicellular organisms need communication systems?
A
Animals and plants need to respond to changes in their internal and external environment and coordinate the activities of different organs.
3
Q
How do these communication systems work?
`
A
- The systems involve cell signalling:
- In plants, the signalling is chemical, and involves plant hormones.
- In animals, the signalling can be chemical, involving hormones – the endocrine system or neurones can transmit electrical impulses in the nervous system (which also involves chemicals called neurotransmitters).
4
Q
cell signalling is?
A
cells communicating with other cells.
5
Q
Communication can be over?
A
- short distance between adjacent cells, for example at a synapse
- longer distance - between distant cells, for example the pituitary gland in the brain releasing the hormone ADH, which communicates with cells in the kidneys - nearly a metre away.
6
Q
cell signalling involves
A
a signal molecule being released by one cell, travelling to a target cell, binding to receptor molecules at the target cell, and having an effect.
7
Q
cell signalling between adjacent cells e.g.?
A
- An action potential arrives at the pre-synaptic cell.
- Neurotransmitter molecules are released by exocytosis.
- NT molecules bind to receptors on the post synaptic membrane.
- An AP is initiated in the post synaptic cell.
Enzymes clear the NT from the synaptic cleft
8
Q
cell signalling between distant cells e.g.?
A
- An endocrine cell secretes hormone molecules in response to a stimulus.
- The hormone (1st messenger) enters the bloodstream.
- The hormone binds to receptors on (or in) target cells.
- This binding causes an effect, often via a second messenger system
9
Q
what is a 2nd messenger ?
A
A second messenger is a molecule that is activated inside a cell by the binding of a 1st messenger (like a hormone) to a receptor in the target cell’s membrane.
The 2nd messenger can go on to have a cascade of complex effects in the cell.
A common 2nd messenger is Cyclic Adenosine Monophosphate - CAMP
10
Q
what is homeostasis?
A
The maintenance of a constant internal environment
11
Q
The nervous and endocrine systems work together to ?
A
maintain a constant internal environment.
12
Q
The internal environment means?
A
the conditions inside the body in which cells function.
13
Q
Variables of the internal environment that can dramatically affect cell’s activities?
A
- Temperature
- Water potential of blood and tissue fluid
- Concentration of blood glucose
Homeostatic mechanisms control these variables (and more) within very narrow ranges.
14
Q
How and why temp is controlled within a narrow range?
A
- Physiological mechanisms - sweating, vasodilation, vasoconstriction, shivering, piloerection.
- Behavioural mechanisms - curling up, spreading out, seeking cooler / warmer conditions
- To maintain an optimum temperature for enzyme activity. Too hot - enzymes denature; too cold - rate of metabolism slows.
15
Q
How and why Water potential of blood and tissue fluid is controlled within a narrow range?
A
- ADH secreted by pituitary gland ↑ water reabsorption in kidneys ∴ ↑ blood Ψ. Less ADH secretion ↓ blood Ψ.
- Water intake = water output. Thirst, drink, urine.
- Blood Ψ too low = water loss from cells, disrupting metabolism of esp. brain cells.
- Blood Ψ too high, cells gain water and swell - potentially v. serious in brain because of restricted volume.
16
Q
How and why Concentration of blood glucose is controlled within a narrow range?
A
- Hormones insulin and glucagon released by pancreas in response to low or high BG.
- Glucose input / production = glucose use.
- BG too low - cells run out of respiratory substrate (serious esp. for brain cells).
- BG too high affects blood Ψ - see above.
17
Q
n order to balance something, need a mechanism of?
A
negative feedback.
18
Q
There are 4 stages to each feedback ‘loop’:
A
- Normal range / set point
- Stimulus
- Receptor
- Response (caused by effectors)
19
Q
+ feedback is?
A
This is when a response is amplified, and moves away from a stable situation, often quite dramatically
20
Q
e.gs of + feedback?
A
- a stampede
- blood clotting
- lactation
- action potentials
- childbirth
21
Q
Blood clotting?
A
Activated platelets release signal molecules that activate more platelets,
22
Q
Lactation?
A
- milk production:
A suckling baby stimulates the brain to produce the hormone prolactin, which increases milk production, causing the baby to suckle more
23
Q
Action potentials?
A
An influx of sodium ions into a neurone depolarises the membrane so more sodium ions move in
24
Q
childbirth?
A
- Head of fetus pushes against cervix - stretch receptors in walls of cervix send action potentials to the brain.
- Brain causes release of hormone (oxytocin) into bloodstream.
- Oxytocin causes uterine smooth muscle to contract more forcefully
- therefore fetus’s head pushes against cervix harder, more stretch, more hormone, more contraction
- Cycle ends with birth of the baby & decrease in stretch
25
endotherms ?
maintain their body temperature independent of environmental temperature - at about 37℃ - so they are losing heat to their environment all the time.
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ectotherm?
its body temperature is the same as its environment
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Hypothermia can result in a fatal positive feedback loop -
metabolism is slowed by low temp - less heat generated - so metabolism slows even more
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Heat gain in endotherms?
- Metabolic thermogenesis - the production of heat by metabolic reactions in cells, eg respiration.
- Conduction, convection and radiation from the external environment eg. the sun, a hot radiator
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heat loss in endortherms?
Conduction, convection and radiation to the external environment, controlled physiologically by eg sweating, vasodilation, piloerection, and behaviourally by eg curling up, adding clothes
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thermoregulation is about?
balancing heat gain with heat loss, and maintaining the set point of 37℃
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what do we need for thermoregulation?
we need receptors to detect the rise or fall in temperature, and effectors that bring about responses, bringing the temperature back to the set point.
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Thermoregulation: receptors?
- Peripheral thermoreceptors are found mainly in the skin.
- generate action potentials when the temperature rises or falls.
- hypothalamus contains the thermoregulatory centre.
- In this are sensory receptors that detect core body temperature - the central thermoreceptors.
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thermoregulatory centre receives info from?
This area receives sensory input from both central and peripheral thermoreceptors, and sends action potentials (motor output) to effectors, causing the appropriate response.
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how do peripheral receptors communicate w thermoregulatory centre?
Sensory input - afferent action potentials move along sensory neurones from peripheral thermoreceptors to thermoregulatory centre.
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Note: capillaries do not
move. Blood flow through the capillaries changes.
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sweating?
- There are 2 types of sweat gland - eccrine and apocrine.
- Eccrine glands are most associated with thermoregulation.
- Stimulation by a motor neurone causes epithelial cells in the coiled section of the gland to secrete sweat into the duct.
- Sweat produced by eccrine glands is mainly water, containing low concentrations of ions like Na+ and HCO3-, as well as some organic molecules like glucose, lactate and cytokines.
- Sweating cools the body by evaporating from the surface of the skin. The high latent heat of vaporisation of water means this evaporation cools the skin sig
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Piloerection
- Arrector/ erector pili muscles contract, causing hair to stand up.
- This traps an insulating layer of air next to the skin, reducing heat loss.
- This response is not very effective in humans, as they don’t have much hair, but it other, especially smaller, mammals, it is highly effective.
- Arrector pili muscles contract because they are stimulated by neurones from the sympathetic nervous system
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(temp regulation) Longer term responses involve ?
the hormone thyroxine and a change in the basal metabolic rate
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endothermy +s?
+ Can be physically active at any time of day or night to feed or evade predation.
+ Can reproduce whenever opportunity presents itself.
+Ability to survive in a wide range of environments.
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endothermy -s?
- High rate of use of respiratory substrate to maintain temperature - metabolically expensive.
- Need to feed often due to high metabolic rates.
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ectothermy +s?
+ Need for food very low due to low metabolic rates.
+ Lizards for example, could go 2 weeks without a meal. + Metabolically ‘cheap’.
+ Higher proportion of food used for growth - can reach maturity to reproduce faster than endotherms.
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ectothermy -s?
- Only physically active for short periods of the day, for feeding and reproduction.
- Vulnerable to predation when body temp is low.
- Can only live in a narrow range of environments, eg the tropics.
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lt is impossible lo maintain a living mammal in a completely stable state bc?
everything causes minute changes. Instead, the body maintains a dynamic equilibrium, with small fluctuations over a narrow range of conditions. This is known as homeostasis.
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receptors, effectors
Information Iront the sensory receptors is transmitted to the brain and impulses are sent along the motor neurones to the effectors to bring about changes to restore the equilibrium in the body. Effectors are the muscles or glands that read to the motor stimulus lo bring about a change in response to a stimulus.
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what is thermoregulation?
maintenance of a relatively constant core body temp to maintain optimum enzyme activity
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behavioural mechanisms for temp regulation?
- bask in sun
- orientate bodies so the max SA is exposed to the sun, extend areas of the body to
-
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behavioural mechanisms for temp regulation? (for temp ⬆)
- bask in sun
- orientate bodies so the max SA is exposed to the sun, extend areas of the body to ⬆ the SA exposed to the sun
- pressing body against warm ground
- exothermic metabolic reactions
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behavioural mechanisms for temp regulation? (for temp ⬇)
- to cool down: shelter from the sun by seeking shade, hiding in cracks in rocks, digging burrows
- press bodies against cool, shady earth/stones or move into water or mud
- orientate bodies so that min SA is exposed to the sun & min their movements to reduce metabolic heat generated
49
Some ectothermes also
alter their heart rate to increase or decrease the metabolic rate and sometimes to affect the warming or cooling across the body surfaces.
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endothermes behavioural resposnes to temp change?
- Like ectotherms, endotherms have a range of behavioural responses : - basking in the Sun,
- pressing themselves to warm surfaces,
- wallowing in water and mud to cool down,
- and digging burrows to keep warm or cool.
- hibernation
- aestivation
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ectotherms rely mainly on?
behavioural responses by endotherms relu mainly on physiological adaptations
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physiological adaptations of endotherms?
These adaptations include the peripheral temperature receptors, the thermoregulatory centres of the hypothalamus, the skin, and muscles.
53
Vasodilation?
The arterioles near the surface of the skin dilate when the temperature rises. The vessels that provide a direct connection between the arterioles and the venules (the arteriovenous shunt vessels» constrict. This forces blood through the capillary networks close to the surface of the skin. The skin flushes, and cools as a result of increased radiation. If the skin is pressed against cool surfaces, then the cooling results from conduction.
54
endotherms in hot climates anatomical adaptations?
that live in hot climates often have anatomical adaptations as well as the behavioural and physiological adaptations. These minimise the effect of high temperatures and maximise the ability of the animal to cool down through the surface area of the body. They include a relatively large SA: V ratio to maximise cooling (e.g., include large ears and wrinkly skin), and pale fur or feathers to reflect radiation.`
55
Vasoconstriction?
The arterioles near the surface of the skin constrict. The arteriovenous shunt vessels dilate, so very little blood flows through the capillary networks close to the surface of the skin. The skin looks pale, and very little radiation takes place. The wann blood is kept well below the surface.
56
endotherms in cold climates anatomical adaptations?
endotherms living in cold climates often have additional anatomical adaptations to help them keep warm. Many have adaptations that minimise their SA: V ratio to reduce cooling (e.g., small ears). Another common adaptation is a thick layer of insulating fat underneath the skin
57
There are ? control centres:
2: The heat loss centre, The heat gain centre
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The heat loss centre
This is activated when the temperature of the blood flowing through the hypothalamus increases. It sends impulses through autonomic motor neurones to effectors in the skin and muscles, triggering responses that act to lower the core temperature.
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The heat gain centre
This is activated when the temperature of the blood flowing through the hypothalamus decreases. It sends impulses through the autonomic nervous system to effectors in the skin and the muscles, triggering responses that act to raise the core temperature
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how does increased HR in early morning when basking work + B or P?
P. Faster moving blood distributes heat to muscles, warming them up ready for contraction.
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How does Panting work + B OR P?
P. Increases rate of evaporation from tongue and inside mouth, cooling body - a bit like sweating
62
how does pressing body to sand in the morning work + B or P?
B. Increases conduction of heat from warm sand, raising body temperature.
63
e.g. of + feedback?
- digestion
- the stomach uses pepsin to digest proteins.
- it first secretes pepsinogen - an enzyme in an inactive form
- when food is taken into the body and needs o be digested, pepsinogen is converted into pepsin
- the conversion triggers a + feedback loop that changes other pepsinogen mols in the stomach to pepsin, so that the stomach accumulates enough for it to b able to digest proteins
64
brown fat?
- babies have large amounts
- contains mitochondria in which a hi prop pf the energy released from glucose in aerobic resp is released as heat, rather than being used to generate ATP - chemical thermogenesis
- babies have a rel. large SA:V so can lose heat rapidly if envir temp is low
- thfr imp in babies
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long term temp control?
- involves thyroxine, which is secreted by thyroid gland
- this increases metabolic rate & thermogenesis
- when the hypothalamus senses a frop in temp, secretes TRH into blood
- TRH is carried to the nearby anterior pituitary gland where it stimulates the secretion of TSH, which then stimulates the release of thryoxine by the thyroid gland
- thyroxine passes thru the CM of its arget cells & enters the nucleus where it switches on a no. of genes
- this causes ⬆ to be produced
66
long term temp control?
- involves thyroxine, which is secreted by thyroid gland
- this increases metabolic rate & thermogenesis
- when the hypothalamus senses a frop in temp, secretes TRH into blood
- TRH is carried to the nearby anterior pituitary gland where it stimulates the secretion of TSH, which then stimulates the release of thyroxine by the thyroid gland
- thyroxine passes thru the CM of its target cells & enters the nucleus where it switches on a no. of genes
- this causes ⬆ to be produced
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pH of blood and TF needs to be maintained so?
proteins in blood don’t denature
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glucose regulation importance?
- Glucose is a solute in the blood so glucose conc affects the water potential of the blood
- If there is a too low conc of glucose, then cells don’t have access to the energy they need, this can cause energy sensitive cells like neurons to die
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Importance of Homeostasis =
ensures cells in the body can function effectively , animals that can carry out homeostasis can live in a greater variety of habitats - bc animals that can keep an internal environment can survive a greater amount of external change
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Mechanism of - Feedback:
- The optimum point for the body (pH, Temperature, WP) is monitored by receptors
- When the receptors detect any change away from the optimum they send signals to a co-ordinator
- The co-ordinator then decides which response is appropriate and carries it out by sending signals to effectors
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order of feedback loop?
Receptors ➡ Co-ordinators ➡ Effectors (RCE)
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What do effectors do?
Effectors bring about the change that returns the internal conditions to their optimum, can usually be classed as either muscles or glands
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+ vs - negative feedback?
Positive feedback amplifies any change away from the set point - negative feedback decreases it
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positive feedback?
It brings about a large unstable change in the body, is usually harmful but there are some examples where it can be useful -e.g. Action potentials in neurons
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why do receptors and effectors need to be linked by efficient communication systems?
need to be linked by an efficient communication system bc they’re often in diff parts of the body - they communicate through cell signalling,
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In mammals there are 2 separate communication systems:
the neuronal and hormonal system
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The neuronal system responses ?
carries signals all around the body very rapidly, usually produces short term
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The hormonal system uses ?
blood to carry signals through the body, usually coordinates long term responses
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what do endocrine glands do?
Endocrine glands release hormones (cell signalling molecules) into the blood where they travel to cells that have receptors for the hormones
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Features of a good communication system:
- must cover all of the body so that all receptors can communicate with all effectors
- will allow specific communication
- needs to communicate rapidly so that a response can be coordinated immediately
- & needs to produce long and short term responses
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why does the modifies the heart rate ?
to respond to changing demands
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The heart rate can be modified by:
Changing HR, the contraction strength of the ventricles, or the V of blood transported in each stroke (heart beat)
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Innervation of the heart:
- The heart beats at a rate controlled by the sinoatrial node (the pacemaker)
- But the heart is myogenic - doesn’t need brain to beat
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To change the rate at which the heart beats?
- the heart is innervated by nerves from the sympathetic and parasympathetic nervous systems
- The nerves come from a part of the medulla oblongata called the cardiovascular centre
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the accelerans nerve?
The accelerans nerve is a sympathetic nerve contacting the SAN, this releases the neurotransmitter noradrenaline and increases the HR
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the vagus nerve?
The vagus nerve is a parasympathetic nerve contacting the heart, it releases acetylcholine and causes HR to slow
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Chemoreceptors...
in the carotid arteries and aorta measure the pH of the blood
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what happens when we exercise?
- When we exercise, the conc of CO2 in the blood rises which reacts with H2O to produce carbonic acid, lowering pH.
- This lowered pH is detected by chemoreceptors which then target the cardiovascular centre which causes the accelerans nerve to send more frequent impulses .
- This results in a faster heartbeat which causes more CO2 to pass through the lungs and be removed.
- This reduced the CO2 in the blood which means the chemoreceptors are stimulated less and the HR slows to normal.
- This is an e.g. of Negative Feedback
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stretch receptors in the carotid sinus?
detect changes in blood pressure which needs to be maintained at a set level. These receptors send signals to the cardiovascular centre of the medulla oblongata, the cardiovascular centre then sends signals to the heart to control the BP - sympathetic or parasympathetic.
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where else are there stretch receptors?
There are also stretch receptors in the limb muscles, these detect when exercise is occurring and increase the HR.
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Animals regulate their body temperature in 2 different ways:
ectothermy and endothermy
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Ectotherms =
rely on external sources of heat to regulate their body temperature (traditionally what ppl call cold blooded). They use their behaviour to regulate temperature, they include repti;es, amphibians, and most fish.
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Endotherms =
animals that use heat from metabolic reactions to maintain their body temperature. Most are birds and mammals.
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mechanism of thermoregulation?
- Changes in temperature are detected by temperature receptors in the thermoregulatory centre of the hypothalamus.
- This causes the nervous & hormonal systems to send signals to effectors, such as the skin.
- There are also temperature receptors in the skin which contact the hypothalamus.
- These peripheral receptors warn the hypothalamus of oncoming changes to temperature before the blood temperature has changed.
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Endotherms have an ?
internal source of heat - metabolic reactions release heat. They stay warm by insulating their internal source of heat. They have hair and feathers which can be used to keep warm.They can increase the rate of respiration in the liver, meaning more energy stores are converted into heat
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Animals that can’t sweat can ?
pant, which removes heat through evaporation of the saliva instead
