Homeostasis Flashcards
1
Q
What is homoeostasis?
A
It means keeping things constant.
Comes from two Ancient Greekwords:
‘homeo,’meaning’similar,‘
‘stasis,’ meaning’stable.’
2
Q
Homeostasis definition:
A
The condition of a relatively stable internal environment, maintained within narrow limits. When deviations (increases or decreases) occur in the internal environment of a healthy organism, mechanisms act to restore values to the normal (optimum) state.
3
Q
What internal conditions need to be controlled?
A
Carbon dioxide, oxygen, wastes, temperature, salts, water, pH & glucose
4
Q
What does SR MERF (Steady State Control Systems) stand for?
A
Stimulus- change in internal environment
Receptor- detects the change
Modulator- control centre (processes info from receptors, compares info to optimum, sends message to effector)
Effector- carries out the response (muscle or gland)
Response- counteracts the stimulus
Feedback- original stimulus changed
5
Q
What is a negative feedback loop?
A
An increase in one thing leads to a decrease in another. Eg increased insulin production leads to decreased glucose in the blood
6
Q
What is a positive feedback loop?
A
An increase in one thing leads to an increase in another. Eg increased eostrogen secretion leads to increased LH secretion
7
Q
What does the human body do when it gets cold to decrease heat loss?
A
Constriction of blood vessels in the skin, reduction in sweating, conscious behaviour such as putting on a jumper or sheltering from the wind and reduction of surface area such as by curling into a ball.
8
Q
What does the human body do when it gets cold to increase heat production?
A
Shivering, increase in voluntary activity and increased metabolic rate (long term response).
9
Q
What does the human body do when it gets too hot to increase heat loss?
A
Dilation of blood vessels in the skin, sweating, conscious behaviour such as removing clothing or turning on a fan and increase surface area by spreading out.
10
Q
What does the human body do when it gets too hot to decrease heat production?
A
Decrease in voluntary activity and decreased metabolic rate (long term response).
11
Q
SR MERF for when the human body gets hot:
A
S- ↑Temp of blood
R- Thermoreceptors in hypothalamus
M- Hypothalamus
E - sweat glands, blood vessels, Skeletal muscle, Thyroid
R - ↑ sweat production, vasodilation, seek shade/ ↑ surface area, ↓ thyroxine ↓MR
F- ↓temp of blood
An increase in body temperature brings about a range of responses that serve to decrease the body temperature (negative feedback)
12
Q
SR MERF for when the human body gets cold:
A
S- ↓Temp of blood
R- Thermoreceptors in hypothalamus
M- Hypothalamus
E - Blood vessels, Skeletal muscle, Thyroid
R - vasoconstriction, shivering/↓ surface area/seek warmth, ↑Thyroxine ↑MR
F- ↑temp of blood
A decrease in body temperature brings about a range of responses that serve to increase the body temperature (negative feedback)
13
Q
Why do body levels need to be maintained within limits?
A
- Carbon dioxide - when dissolved in water forms carbonic acid, lowering pH and affecting enzyme activity
- Oxygen - to supply energy (ATP) for cellular functioning
- Nitrogenous Wastes - toxic - high concentrations inhibit the reactions that form them, also raises pH
- Temp - affects enzyme activity (metabolism)
- Salts - Na+ from NaCl important in regulating fluid levels as well as nerve transmission and muscle contraction
- Water - maintains conc. of cell contents at correct level for cellular reactions. Solvent for metabolic reactions
14
Q
Heat lost through radiation:
A
- No physical contact
- Waves of energy
- The sun
- 65% of body heat lost this way
15
Q
Heat lost through conduction:
A
- Contact
- Passes from one molecule to another
- 2% of body heat lost this way in air
16
Q
Heat lost through convection:
A
- Cool air that comes into contact with a warm body is heated, expands, becomes less dense, so rises
- Approx 15% of body heat lost this way (in air)
17
Q
Heat lost through evaporation:
A
- To break their cohesive bonds (evaporate) water molecules must be 100oC
- Takes a relatively large amount of heat with it
- Water has a cooling power approx. 50x greater than air
- Approx 20% of body heat lost this way
85% of heat is lost this way during intense activity
18
Q
What is an ectotherm?
A
- Gain heat from external environment (sun/warm rocks/water)
- Body temp fluctuates
- May regulate temp through behaviour
- Most invertebrates, reptiles, amphibians and fish
19
Q
Advantages of an ectotherm:
A
- Little energy required (low MR)
- Can feed less often
- Stay in shelter longer
20
Q
Disadvantages of an ectotherm:
A
- Inactive in cold, night
- More likely to get eaten
- Restricted geographic range
21
Q
What is an endotherm?
A
- Body heat from metabolic activity (internal)
- High metabolism
- Relatively constant temp
- Birds, mammals, some fast fish (tuna), some insects (bumble bees)
22
Q
Advantages of an endotherm:
A
- Body temp constant
- Active at any temp (24hrs/day, any geographic region)
- Able to avoid predators
- Makes them good predators
23
Q
Disadvantages of an endotherm:
A
- Large energy requirement (high MR)
- Need insulation and/or cooling mechanisms
24
Q
Ectotherm vs endotherm body temperature:
A
- Generally an endotherm’s body temperature remains relatively stable despite the environmental temperature whereas as ectotherms temperature varies with that of the environment
- Endotherms require less energy to maintain their body temperature as the temperature of their surroundings increases.
- Oxygen consumption is a measure of aerobic respiration (metabolism)
25
Losing Body Heat:
- Some heat lost through urine, faeces, lungs
- Most heat is lost through the skin
- Conduction, convection, radiation, evaporation
26
Physiological adaptations for a hot environment - Sweating or Panting:
- Sweating or panting: Water has 50x cooling effect of air, as water evaporates from a body surface it takes heat energy with it. Sweating- skin surface. Panting- lungs, mouth, throat. Coincides with vasodilation of blood vessels to skin.
27
Physiological adaptations for a hot environment - Coat thinning/fur flattening:
Some animals have a thick coat in the winter which they shed in the warm weather. Thick fur traps a layer of air close to the skin preventing heat loss via convection.
28
Physiological adaptations for a hot environment - Vasodilation:
Skin is in close contact with air. If blood flowing from body to skin is warmer than air. Then heat in blood can be lost to the environment by convection, conduction and radiation. Smooth muscle in the wall of the arteries flowing to the skin relaxes. Artery increases in diameter, increasing blood flow.
29
Physiological adaptations for a hot environment - Decrease metabolic rate:
Hormones control metabolic rate. Adrenalin, thyroxine. Heat is a by-product of metabolism.
30
Structural adaptations for a hot environment- Insulating fur:
- Shades the skin
- Prevents the skin surface absorbing heat by radiation
31
Structural adaptations in hot environments - SA:vol:
- Large extremities to aid heat loss
- Sphere is the shape with smallest SA:vol
- Long and thin greatest SA:vol
- For any one shape the larger the shape the smaller the SA:vol
- Large organisms counteract this by having structures sith a large SA:vol ratio
32
Behavioural adaptations in hot environments - Wallowing in water:
- The temperature of large water bodies doesn’t vary much throughout the day
- Water has 50x the cooling effect of air
- As long as the water is cooler than the animals body temperature it will lose heat to the water.
33
Behavioural adaptations in hot environments - burrowing or lying in shade:
Staying out of direct sunlight prevents heating by radiation.
34
Behavioural adaptations in hot environments - physical activity:
Decrease physical activity/movement in heat of day. Reduces metabolism and heat production
35
Behavioural adaptations in hot environments - Increase surface area:
- Increases heat loss
- Spreading out
- Flapping ears- creates air flow (wind)
- Ears highly vascularised (high blood flow- vasodilate)
36
Behavioural adaptations in hot environments - reduced conduction/radiation:
- Standing on two legs (not 4)
- Reduces conduction
- Lifting body off ground reduces conduction and radiation
37
What is heat transfer?
Heat is transferred from a warmer object to a cooler object until the objects are the same temperature
38
Physiological adaptations for a cold environment - Vasoconstriction:
- blood vessels in skin constrict
- restrict blood flow (to skin)
- reduce temperature of skin
- reduce heat loss through radiation
- most blood remains below insulating fat layer
39
Physiological adaptations for a cold environment - Increased MR:
- hormones increase metabolic rate
- adrenalin, thyroxine
- metabolic reactions are not 100% efficient
- heat is a by-product
40
Physiological adaptations for a cold environment - Decreased MR - Torpor (inactivity):
- Hibernation- long term reduction in MR and body temp (days)
- Diurnation- short term reduction in MR and body temp (hours)
- Reduces energy requirement when food is scarce
41
Physiological adaptations for a cold environment - Shivering:
Involuntary, repeated muscle contractions. Requires energy from metabolism, generates heat as a by-product.
42
Physiological adaptations for a cold environment - Piloerection:
- Involuntary raising of hairs
- Trap more air close to skin
- Air is a poor conductor of heat (provides insulation)
- Reduces heat loss by convection
43
Structural adaptations for a cold environment - Small SA:Vol (spherical):
- Spherical shapes smallest SA:vol
- For any shape the larger the shape the smaller the SA:vol
- rounded, stocky body
- Small extremities- ears/short limbs
- reduced surface area in contact with environment
- reduce area for heat transfer
44
Structural adaptations for a cold environment - Insulating fat:
- Surrounding layer of thick insulating fat
- Blubber is a good insulator (poor conductor of heat)
- Prevents conduction of heat from core to skin
- Allows skin to be cooler reducing the heat gradient between it and the water
- Fat (blubber) has very little blood flow as it has a low O2 requirement
45
Structural adaptations for a cold environment - Insulating fur (feathers):
- thick fur traps layer of air close to body
- air is a poor conductor (good insulator)
- stops air flow close to body
- reduces heat loss by convection
46
Behavioural adaptations for a cold environment - Huddling/clusters:
- Ectotherms- bumblebees huddle together and shiver
- Effectively reduces the surface area of the individual exposed to the cool air
- They share time on the outside of the huddle
- Even being on the outside is better than standing alone
47
Behavioural adaptations for a cold environment - Staying in burrows:
- Creates a warmer microclimate
- Reducing temperature gradient
48
Behavioural adaptations for a cold environment - Basking in the sun:
Absorb heat energy from the sun through radiation
49
Behavioural adaptations for a cold environment - Migration:
Moving to an area with a warmer climate removes the need for physiological and structural adaptations.
50
SA:Vol & Shape:
For any give surface area a sphere is the shape with the smallest sa:vol. Longer and thinner shapes have the highest sa:vol.
51
SA:Vol & Size :
If the shape is identical then the smaller it is the greater the sa:vol.
52
SA:Vol & Heat Loss:
Heat is lost at a set rate per unit of area regardless of the volume. Therefore organisms with a higher sa:vol will lose a greater proportion of their heat (or faster) than an organism with a smaller sa:vol.
53
SA:Vol & Metabolism:
The smaller the organism, the greater the sa:vol therefore the greater the heat loss to the environment and the greater the metabolism required to maintain homeostasis.
54
Why don’t marine mammals have fur?
Water compresses fur pushing the air out. Also not very hydrodynamic.
55
How does blubber prevent heat loss?
Poor conductor of heat
Fat (blubber) has very little blood flow as it has a low O2 requirement
Allows skin to be cooler reducing the heat gradient between it and the water
Reducing heat loss by conduction
56
Examples of counter-current heat exchange:
penguin legs (core temp- 390C)
flippers in seals, sea lions, and whales
Great White sharks
Arctic foxes & wolves
57
Blood flow without countercurrent heat exchange:
1. Artery and vein not touching
2. Arterial blood flowing to foot loses some heat to surrounding tissues
3. Large difference between foot temperature and ambient temperature means high rate of heat loss (19oC)
4. Venous blood returning to core loses some heat to surrounding tissue
5. Venous blood temp well below core temp therefore energy must be used to reheat blood to 37oC
58
Blood flow with countercurrent heat exchange:
1. Artery and vein touching
2. Arterial blood loses heat to venous blood
3. Cooler arterial blood means the difference between foot temp and ambient temp is less which means lower rate of heat loss (10oC)
4. Foot temp kept slightly above Ambient temp
5. Venous blood returning to core is warmed by the arterial blood
6. Venous blood almost back to core temp therefore little energy required to reheat blood to 37oC
59
What are nitrogenous wastes?
Are produced as a result of the breakdown of amino acids- deamination. Results in the production of ammonia. Ammonia may then be converted into uric acid or urea depending on the animal.
60
Components of Ammonia- NH3:
- extremely toxic (high pH)
- very soluble in H2O
- energy inexpensive to produce (small molecule)
- needs to be excreted in a very dilute urine
- excreted directly into surroundings
- only aquatic invertebrates and vertebrates such as fish (through gills) and larval amphibians which have a large water supply
- produce soft shelled eggs in water so the ammonia produced by the embryo can diffuse into the environment
61
Components of Urea- CO(NH2)2:
- mildly toxic (100 000x less than NH3)
- moderately soluble (excreted dissolved in H2O)
- energy expensive to produce (complex molecule)- organisms with a high MR
- Mammals and Amphibians- animals with access to water
- Allows internal development, as foetal urea can be passed across the placenta
62
Components of Uric Acid- C5H4N4O3:
- Virtually non-toxic
- Very low solubility
- Energy expensive (2x urea)- complex molecule
- Excreted without loss of H2O, allowing birds and reptiles to live in very dry areas.
- low toxicity and insolubility means it can be stored in hard shelled, dry eggs during development
- Allows birds to fly because they don’t have to carry heavy water with their nitrogenous wastes
63
How do you get water into your body?
Food (700mL)
Drink (1600mL)
Metabolism (200mL)
64
How do you lose water from your body?
lungs
skin
kidneys
faeces
65
What is the importance of water?
Excretion- The removal of the waste products of metabolism- Nitrogenous wastes
Temperature regulation
Gas exchange occurs through moisture on membranes
Component of blood- carries dissolved ions around the body
Some nutrients need water to be absorbed
66
Kidney reabsorption:
Urine is composed mainly of water, urea, ions, uric acid
Substances reabsorbed in kidney (Loop of Henle):
99% of the H2O
all glucose and amino acids
Most of the salts and urea.
Long loop of H = more water reabsorbed
67
Factors affecting water gain/loss:
Environment: availability of water, temp
Structure: SA:Vol, skin, scales, gills
Physiology: kidneys (loop of henle), large intestine
68
ADH- Anti-diuretic Hormone:
Diuretics increase urine production
Antidiuretics decrease urine production
69
SR MERF- Water Balance (low water):
S- Low H2O in blood
R- osmoreceptors in hypothalamus
M- Hypothalamus
E- posterior lobe of pituitary secretes ADH
R- collecting ducts more permeable (↑H2O absorption)
F- ↑ H2O in blood
70
SR MERF- Water Balance (high water):
S- High H2O in blood
R- osmoreceptors in hypothalamus
M- Hypothalamus
E- posterior lobe of pituitary stops ADH
R- collecting ducts less permeable (↓H2O absorption)
F- ↓H2O in blood
71
Adaptations- Camels
Sweating only at high temps (40oC)
Concentrated syrupy urine
Dry faeces
Metabolism of fat produces water
Can withstand large water loss- oval shaped blood cells
72
Adaptations- Kangaroo Rats
Water from metabolism of food (90%)
Respiratory moisture condenses in nasal passage
Long Loop of Henle produces conc urine
Dry faeces- long large intestine
Burrow during heat of day
73
Adaptations- Kangaroos
Metabolic water
Elongated large intestine- dry faeces
Concentrated urine
Efficient locomotion- stretchy tendons= less heat produced
Feed dawn and dusk- cooler, plants contain more water
74
Adaptations- Reptiles
Scaly skin impervious to water- ↓ evap
N excreted as uric acid paste- low in water
Nocturnal or shade during day- cooler, ↓ evap
75
Adaptations- Amphibians
Near water or humid environments
Some secrete waxy covering- ↓ evap
Some live underground during dry weather- cooler, humid microclimate
76
Adaptations- Invertebrates
Waxy cuticle- impervious to water
Uric acid paste- low in water
Seek shade- ↓ evaporation
Absorb water from air
77
Definition of isotonic:
Two solutions having the same concentration of dissolved ions
78
Difference between hypertonic and hypotonic:
When two solutions have different ion concentrations, the one with the higher concentration of ions is hypertonic, the one with the lower concentration is hypotonic. Water moves from where it is hypotonic to where it is hypertonic until it is isotonic (osmosis).
79
Definition of osmoconformers:
maintain ion and water levels to be isotonic with surroundings
80
Definition of osmoregulators:
maintain ion and water levels at an optimum level which is either hypertonic or hypotonic to their surroundings
81
Marine Organisms:
Sea Water (Marine) has high levels of dissolved ions in it
it is hypertonic to most organisms
water moves out of organisms (osmosis)
ions move into organism (diffusion)
82
Marine Organisms - Osmoconformers:
Body fluid composition varies with that of the water surrounding them (isotonic)
Intertidal species can tolerate large variations
Most marine invertebrates
Eg. Starfish, jellyfish, worms, molluscs
83
Marine Organisms - Osmoregulators:
Tissues are not isotonic to surroundings but hypotonic
Regulate their salt and water levels to maintain optimum levels regardless of the concentration of their surroundings
84
Marine Bony fish:
Fish are hypotonic
lose water (osmosis) Gain ions (diffusion)
Drink large amounts- salt water
excrete excess salt through secretory glands in gills (active transport)
small amounts of highly concentrated urine (very few nephrons- as most N is excreted via gills as NH3)
85
Cartilaginous fish (sharks and rays):
Kidneys reabsorb urea- maintain high urea levels- slightly hypertonic
Excrete water- large volume dilute urine
Excrete salt from salt gland in rectum (sharks)
86
Marine Organisms- Mammals:
Kidney produces urine high in both urea and salt
survive on metabolic water (carbs/fat)
food sources are high in water
highly efficient reabsorption of water from the rectum
87
Marine Birds:
Marine birds ingest high levels of salts in food and water
Excess salt excreted through nasal gland
Uses counter-current blood flow to remove large amounts of salt
Gland secretes solution with a higher salt concentration than seawater
88
Freshwater:
Has low levels of dissolved ions
it is hypotonic to the cells of organisms
water moves into organisms (osmosis)
ions move out of organism (diffusion)
All freshwater organisms are osmoregulators- the ion concentration in fresh water is lower than that of any living organism.
89
Freshwater Animals- Osmoregulators:
Adaptations
Amoeba- contractile vacuoles collect and expel excess water
Mammals- reabsorption of salts in the kidney
Invertebrates- nephridial organs (like kidney nephron)
90
Freshwater Fish:
large amounts of dilute urine
high filtration rate in kidneys
large number of glomeruli
reabsorption of ions in kidneys by active transport
active uptake of ions through the gills (active transport)
scales/mucus layer prevents water entering body
91
Freshwater problems:
higher water concentration in surroundings than cells
cells hypertonic to surroundings
water movement (osmosis)– into cells
Loss of salts by diffusion
92
Adaptations – freshwater:
large amounts of dilute urine/ high filtration rate in kidneys/large number of glomeruli (fish)
reabsorption of salts/ions in kidneys by active transport
active uptake of salts through the gills of fish
cells can actively pump salts into the cells
preventing water entering the cells so the water only enters the blood and is then excreted
scales/mucus layer prevents water entering body
93
Marine problems:
Lower water concentration in cells than in surroundings/cells hypotonic to surroundings
water movement out of cells
Movement of ions into cells
94
Adaptations – marine fish:
drink sea water
secretory cells in the gut actively absorb salts and transfer them to the blood
salts actively excreted by secretory glands in the gills
small amounts of highly concentrated urine
few nephrons
retaining high levels of urea (cartilaginous fish)
95
Adaptations – marine mammals:
survive on metabolic water by highly efficient reabsorbtion of water from the rectum (mammals).
96
Plant water balance:
Water gain = water loss
Water gain
Root hair cells
Water loss
Evaporation from surfaces
Transpiration through stomata
97
Water uptake in plants:
Water moves into root cell hairs by osmosis
From a low solute concentration to high solute concentration
Across cell membrane (semi permeable)
Passive process
Water moves along a concentration gradient
Concentration gradient is due to higher solute concentration in cells than in soil
Solutes move into root cells by active transport
98
Why do plants need water?
Photosynthesis
CO2 + H2O → C6H12O6 + O2
99
Transpiration in plants:
Evaporation of water from the cells of the leaves, through the stomata.
Helps keep leaves cool
Transport of minerals
Dissolving gases for exchange
Guard cells control water and gas exchange
100
Gas Exchange- Guard cells:
When turgid thin wall stretches more than thicker one causing them to bow out (open)
When they lose water they begin to close up, reducing gas exchange
Water, CO2, H2O
Need to take in CO2 for photosynthesis
Needs to get rid of O2
101
Factors affecting transpiration Rate:
Temperature
Wind
Surface area
Humidity
Light
Soil water
102
Adaptations of Xerophytes:
Xeros=dry, phyton=plant (ancient Greek)
Plants adapted to a dry habitat
103
Leaf Size:
Low surface area
Less stomata
Less evaporation
Large SA
More stomata
More evaporation
104
Xerophytes leaves:
Thick waxy cuticle
Stomata on lower leaf surface
Reduced number of stomata- less openings to lose water through
Stomata in pits, grooves or depressions, traps humidity
Leaf surface covered in hairs, trap humidity reflect light
Small, narrow or modified leaves (cacti spines, wattle phyllodes)= low SA
Leaves roll, curl or fold- trap humidity (microclimate)
Fleshy succulent leaves, stems or roots- store water
Deep root system to water table (Jarrah tree up to 40m)
Shallow root mat to absorb rainfall
Only open stomates at night
take up and store CO2 overnight
Cooler at night
Drop leaves in the dry season
Leaves hang vertically- less direct light
105
Water uptake in plants:
Water moves into root cell hairs by osmosis
From a low concentration of solute to a high concentration of solute
Across cell membrane (semi permeable)
Passive process
106
Halophytes (Salty Habitat):
Halan- salt phyton- plant (Ancient Greek)
107
Water uptake in salty environments:
Concentration of salt is higher in soil than root cells
Therefore water no longer moves into the cell by osmosis (water will move roots →soil)
Plants die from a lack of water
Build up of salt (in cells) can interfere with:
production of enzymes and hormones
metabolism/cell function
108
Halophytes - Managing salt (roots):
Returning salt to roots (vacuole)
salt conc in cell soil
water soil → root
Waxy cuticle on roots prevent salt entering
Prevent salt entering roots
Filtration mechanism at roots (casparian strip)
Water and minerals cannot cross the strip
109
Halophytes - Managing salt (Leaves):
Salt glands
Salt bladders
Accumulate salt in leaves and bark then drop
Store water in leaves- dilutes salt
Active transport to remove salt (into vacuoles)
Removes from cytoplasm
Stops interfering with cell function
110
Halophytes - Reducing water loss:
Reduced number and size of leaves
Few stomata
Sunken stomata
Silver hairs
Waxy cuticle
