1
Q
What is an ectotherm?
A
An organism that regulates it body temperature largely by exchanging heat with its surroundings
2
Q
What is an endotherm?
A
An organism that generates heat to maintain its body temperature, typically above the temperature of its surroundings
3
Q
What are ectotherms also known as?
A
Poikilotherm species
4
Q
What are 2 examples of ectotherms?
A
- Fish
- Reptiles
5
Q
What are 2 examples of endotherms?
A
- Birds
- Mammals
6
Q
True or false: significant cost is associated with being an endotherm
A
True
7
Q
How does the mitochondrial membrane surface area differ between endotherms and ectotherms?
A
Greater in endotherms
8
Q
How does the total cytochome oxidase activity (involved in oxidative phosphorylation) differ between endotherms and ecotherms?
A
Greater in endotherms
9
Q
True or false: there is variation between the core body temperature and the peripheral body temperature
A
True
10
Q
True or false: all mammals are true endotherms
A
False; organisms like the platypus and echidna can show ectotherm behaviour at greater ambient temperatures
- But for the most part, they have stable core body temp
11
Q
What are homeotherms?
A
Same temperature everywhere in the body
12
Q
What are heterotherms?
A
Variation in body temperature (either temporal or regional)
13
Q
What is temporal heterothermy?
A
Certain endotherms (e.g. bats, hummingbirds and ground squirrels), when at rest (either short-term or longer duration during torpor or hibernation), reduce metabolism, and their body temperature drops close to the surrounding environment
- An organism switches between being warm and cool at different times (daily or seasonally).
14
Q
What is regional heterothermy
A
Certain endothermic and ectothermic animals are able to maintain different temperature “zones” in different regions of their body
- e.g. the core body tep of deer are warmer than their limbs in the winter
15
Q
Normal body temperature in mammals is close to 37°C (98.6 °F). To maintain a constant temperature, what needs to happen in general?
A
The amount of heat lost by the body must be balanced by the amount of heat produced (bodies have evolved mechanisms to predict changes in temp).
16
Q
Body temperature may increase to _____ during heavy exercise, or to as high as ____ during febrile illness.
A
38.3°C-40°C, 42°C
17
Q
Long exposure to cold may reduce the body temperature to ____
A
36.1°C
18
Q
How does the core temperature change with temperature fluctuations? What about skin temperature?
A
Core temperature (temperature of internal organs) remains constant at 36.7°C - 37°C, even when the environmental temperature fluctuates between 13-60°C for a short period at rest.
Skin temperature, however, changes with the temperature of the surroundings.
19
Q
What is the thermal neutral zone in general and specifically?
A
In general: the ambient temperature at which the body doesn’t have to work hard to generate heat or cool down
- About 20-22°C in humans, provided that you have normal clothing on
20
Q
Fluctuations in body temperature occur when…
A
The rate of heat loss does not balance the rate of heat gain
21
Q
What is metabolic rate?
A
The rate of energy expenditure (usually per hour)
22
Q
How can metabolic rate be measured, both directly and indirectly?
A
Directly by direct calorimetric methods (using a chamber), or indirectly by measuring oxygen consumption (and then calculating calorigenic activity or heat production)
23
Q
How many calories of heat does the body produce per liter of oxygen?
A
4.8
24
Q
What is basal metabolic rate (BMR)?
A
Rate of energy expenditure in a post-absorptive condition (has not eaten for ~12 hours), following a rest period (mentally and physically relaxed; usually after a good night’s sleep) at room temperature (22-23°C)
25
What does the BMR reflect?
The energy the body needs to perform its most essential activities, such as breathing and maintaining resting levels of neural, cardiac, liver and kidney function (i.e. it is the energy cost of living)
26
What is the BMR in a 70 kg adult?
60-72 Kcal/h (~1500 - 1700 Kcal (Cal)/Day)
27
What is the difference between Cal and cal?
Cal=kcal
cal=calorie
28
Describe how surface area/mass ratio affects basal metabolic rate (BMR)
As surface area:mass ratio decreases (in larger animals), the whole-animal metabolic rate increases while the mass-specific metabolic rate decreases
29
How does surface area:mass ratio differ between small and large animals?
Greater in small animals but lower in large animals
30
Small animals have a much greater mass-specific metabolic rate. What does this cause, in terms of their lifestile?
Animals like the shrew have to eat all the time, since they have to generate so much energy
31
How does O2 consumption per unit distance (ml x g^-1 x km^-1) relate to weight of animals?
As weight increases, O2 consumption per unit distance decreases
- per unit distance = how much oxygen an animal uses to travel a certain distance
- same relationship as mass-specific MR
32
How does mass-specific metabolic rate relate to running speed in different sized animals?
Small animals will need a high amount of energy, even at a small running rate due to high mass-specific metabolic rate
33
What 5 factors influence basal metabolic rate (BMR)?
1. Surface area/mass ratio
2. Age
3. Gender
4. Muscle vs. fatty content
5. Stress and hormones
34
How does age influence BMR?
BMR is higher in younger age and declines significantly with age
- Increases during first ~5 years of life due to increase in growth hormone, then declines when you stop linearly growing (around 15-17 years in humans)
35
How does gender influence BMR?
BMR is higher in males than in females (b/c of sex hormones and androgens)
36
How does muscle/fatty content impact BMR?
BMR is higher in muscular people than in fatty people because muscle can generate more mechanical thermogenesis
37
People who are physically fit can maintain a (lower/higher) BMR
Lower
38
What is total metabolic rate (TMR)?
Total rate of energy expenditure during ongoing involuntary and voluntary activities
39
What does total metabolic rate (TMR) depend on?
The type of activity. With no activity (i.e. no exercise), a 70 kg man would use approximately 2000 Cal per day (for females, ~1700 Cal per day).
- TMR would range between activities like sleeping (65 Calories per hour) vs. running 7.5 km/h (570 Calories per hour)
40
How does exercise affect TMR?
It can increase heat production to 20-50X normal for a few seconds or minutes, depending on physical fitness
41
What 4 hormones can affect total metabolic rate?
1. Thyroid hormones
2. Catecholamines (Epinephrine and Norepinephrine)
3. Sex hormones
4. Growth hormones and certain growth factors
42
The increase in TMR during exercise is (slower/faster) in people who are physically fit
Slower
43
How does thyroid hormone impact TMR? (2)
- Can increase TMR by 50-100% above the normal
- Low thyroid secretion reduces TMR by 40-60% below the normal (has a lethargic effect)
44
Thyroid secretions impact TMR on the (short/long)-term
Long
45
How does the sympathetic pathway impact TMR in many tissues?
Epinephrine and norepinephrine significantly increase TMR in many tissues, due to a chemical thermogenic effect
46
The sympathetic pathway impacts TMR on the (short/long)-term
Short
47
Where is calorigenic activity that contributes to TMR more significant? Why?
Brown fat that in other metabolically active tissues because brown fat contains a large number of mitochondria
48
True or false: brown fat is greater in babies and animals that fluctuate temperature
True
49
What 4 things cause heat production in the body?
1. Byproduct of metabolism primarily in the liver, muscle, heart, etc
2. Increased thyroid hormone (long-term)
- When you adapt to a colder environment over a long period of time
3. Increased sympathetic activity (short-term)
- chemical thermogenesis
4. Increased muscle activity, such as shivering
- mechanical thermogenesis
50
Where does heat loss occur primarily?
Through the skin
51
What 3 things increase heat loss?
1. Increased/decreased rate of conductance
- Increased in environment with colder ambient temp
- Decreased in environment with warmer ambient temp
2. Increased rate of heat transfer from the skin to the surroundings
3. Increased rate of sweating
52
What organ is known as your "furnace"?
Liver
53
What is the most important factor for short-term heat production?
Chemical thermogenesis through increased sympathetic activty
54
Explain how muscle contraction (mechanical thermogenesis) an effective means of heat production?
Muscle has an energy efficiency of ~25%
- for every 1 cal of chemical energy converted into mechanical work, 3 cal are degraded to heat
55
True or false: sweating is an effective mechanism of heat loss in all mammals
False; only in some
56
How does skin insulation impact core temperature?
Skin insulation is an effective means of maintaining normal core temperature (fur or blubber as well). Subcutaneous fat, in particular, is an important insulator as heat conductance of fat is ~1/3 of other tissues
57
Describe how fur helps with maintaining normal core temperature
It disrupts the temperature gradient between the environment and inside of the body, regardless of the temperature outside.
- i.e. decrease in temp from core to ambient temp is not as abrupt as it is without fur
58
Subcutaneous fat (decreases/increases) conductance
Decreases
59
The heat conductance of fat is about ____ of other tissues
1/3
60
The amount of blood flow to the skin can affect...
- Thus, regulating blood flow to the skin is...
The heat conductance from the core to the skin.
An effective way of controlling body temperature
61
What happens to subcutaneous blood vessels (capillaries) in high temperature?
High temp -> vasodilation -> increased blood flow -> increased conductance from core to the skin -> increased heat loss
- Why you look pink in greater temperatures
62
What happens to subcutaneous blood vessels (capillaries) in low temperature?
Low temp -> vasoconstriction -> decreased blood flow -> decreased conductance from core to the skin -> decreased heat loss
- Why you look pale in lower temperatures
63
How does the body ensure adequate blood flow for nutrients/oxygen during vasocontriction?
Shunt vessels exist in a lower layer beneath the skin. More blood flows through the shunt.
64
In humans, what are 3 body parts where conductance is particularly effective for regulating heat loss?
1. Ear
2. Face
3. Hands
65
True or false: in most mammals, there are certain areas of the body that allow for heat exchange
True; e.g. ears in a bunny
66
What 3 things is heat loss by skin affected by?
1. Radiation
2. Conductance
3. Evaporation
67
Describe how radiation affects heat loss by skin
~60% of the total heat is lost through infrared radiation released through our skin
68
How is the biggest proportion of heat loss through the skin?
Through radiation
69
Describe how conductance affects heat loss by skin
Conductance is influenced by the temperature gradient (cannot be controlled)
- i.e. loss of heat by the colder temperature of other things
70
Conductance of heat to (air/water) is greater than that to (air/water)
Water, air
71
What volume of fluid does the normal evaporation rate from the skin and lungs amount to in a day?
600 mL
72
What is our hourly heat loss through evaporation?
12-16 Cal/h
73
How is heat loss through evaporation from the skin and lungs increased?
Increased by greater air current (i.e. convection)
- Why standing in front of a fan allows for better cooling
74
How does the environment impact evaporation (beyond just air current)?
Evaporation is decreased in hot and humid environments because there would be a smaller gradient
75
Radiation and conduction are effective mechanisms of heat loss when ______, but the body will gain heat when _____
Skin temp > surrounding temp
Skin temp < surrounding temp
76
What is the only active mechanism we have to lose heat?
Sweating
77
Sweat is carried to the surface of the skin through...
The sweat duct
78
When produced, sweat is _____ to plasma, excluding ____
Isotonic, proteins
79
What happens to the surrounding ions as sweat travels through the duct?
Most of the ions (mainly sodium and chloride) are reabsorbed during passage through the duct
80
What are 3 important environmental factors influencing temperature control?
1. Movement of air
2. Moisture
3. Temperature gradient
81
Why do hikers take salt tablets?
When the rate of sweating is high, ~1/2 of constituents (e.g. 60 mEq/L of Na+) may be lost
82
How does aldosterone impact sweating?
It reduces the secretion of Na+ and Cl- in the sweat
83
How does acclimatization to hotter environments impact sweating?
Acclimatization for a few weeks increases the ability to sweat from 700 mL/Hr to ~2000 mL/hr
84
What pathway is sweating controlled by?
Cholinergic sympathetic pathway in the subdermal region of the sweat gland
- Still sympathetic, but uses acetylcholine as the neurotransmitter
85
Upon from the cholinergic sympathetic system, ______ can also increase sweating, but this ______
Circulating epinephrine (adrenaline)
is not related to the cooling mechanism
- this is if you're nervous
86
Other than the sympathetic fibre of the sweat gland, _______ are exceptionally cholinergic
The piloerector muscle and a few blood vessels
87
A number of mammals have their skin covered by thick fur and lack sweat glands. What is an alternative mechanism of heat loss?
Panting, which is shallow breathing that does not increase alveolar ventilation/ventilation rate
88
Where is the temperature-regulator center? What does it receive signals from?
Posterior hypothalamus, which receives nervous feedback signals from sensory thermoreceptors located peripherally and in the preoptic area of the Anterior hypothalamus
89
What 2 body parts feed info to the posterior hypothalamus?
1. Sensory thermoreceptors located peripherally
2. Sensory thermoreceptors in the preoptic area of the anterior hypothalamus
90
Where are thermal signals relayed before reaching the posterior hypothalamus?
Thermal signals are relayed to the brain stem, thalamus, and somatic sensory cortex and then relayed to the Poster hypothalamus, which results in an appropriate response
91
True or false: the thermoregulatory response is a reflex
False; it is not a reflex. The info goes through the brain steam and is relayed to the posterior hypothalamus
92
What 7 different temperatures can thermoreceptors distinguish between?
1. Freezing cold
2. Cold
3. Cool
4. Indifferent
5. Warm
6. Hot
7. Burning hot
93
What are the 4 types of sensory receptors?
1. Cold pain receptors
2. Cold receptors
3. Warm receptors
4. Heat pain receptors
94
At what temperature do cold pain receptors fire? When does it peak?
<15°C
- Peaks at 5°C, and then signal diminishes
95
At what temperature do cold receptors fire? When does it peak?
~10-43°C
- Peaks at 25°C
96
At what temperature do warm receptors fire? When does it peak?
~30°
- Peaks at 42°C
97
At what temperature do heat pain receptors fire?
>45°C
98
Where are cold and warm receptors located in general?
Immediately under the skin at discrete points and varying densities
99
Where are peripheral thermoreceptors mainly pesent?
Around the skin region, but there are also deep temperature receptors present around the spinal cord, in the abdominal viscera, and around the great veins in the upper abdomen and thorax
100
There are ~10 times more peripheral (cold/hot) receptors and (cold/hot) receptors
Cold, hot
101
Cold-pain and Hot-pain receptors are only stimulated by...
Extreme heat or cold
102
Describe adaptation of peripheral thermoreceptors
Temperature receptors are strongly stimulated when subjected to abrupt changes in temperature
- The response fades away gradually
- e.g. jumping into cold water at the pool is uncomfortable at first, but you get used to it over time
103
What is spatial summation in peripheral themroreceptors?
Thermal sensation is proportional to the number of thermoreceptors stimulated
- e.g. if you put your fist into hot water it won't affect you as much as if you were to change your entire body temperature by 2°C
104
True or false: a large temperature change over a small area and a greater effect than a small temperature change over a large area
False; a small temperature change over a large area has a greater effect than a large temperature change over a small area
105
The preoptic area of the hypothalamus is also known as what?
The anterior hypothalamus
106
What does the preoptic area of the hypothalamus (anterior hypothalamus) contain, and what does it serve as?
Contains thermoreceptors and serves as a temperature-sensing region
107
The number of (cold/heat)-sensitive receptors is three times greater than (cold/heat)-sensitive receptors in the Anterior hypothalamus
Heat, cold
- opposite to peripheral pattern
108
What is the critical temperature set-point determined by?
The degree of activity of temperature receptors in the hypothalamus
- Temperatures above the setpoint initiate a response to high temperature (evaporative heat loss), and temperatures below the set point initiate a response to cold temperature (heat production)
109
True or false: set points are the same between everyone
False; they're different between everyone, which is why some people may feel cold in the same room as others who feel hot
110
How does your set point change in response to an increase in skin temperature?
An increase in skin temperature results in a decrease in the set point in anticipation of a warming period (predicts how your body will change, so it can prevent shivering at a higher temperature and enable sweating)
111
Feedback from peripheral temperature receptors provides a _______ mechanism for altering the hypothalamic set point
Physiological
112
Draw the set-point diagram on pg. 38 of the thermoregulation 1 notes
113
How does your set point change in response to a decrease in skin temperature?
A decrease in skin temperature results in an increase in set point in anticipation of a cooling trend
114
Draw the set-point diagram on pg. 39 of the thermoregulation 1 notes
115
What is the relationship between skin temperature and set point?
Inverse
116
True or false: the human response of the body to increased or decreased internal temperature is very efficient
True
117
In humans, there is a ___°C change in the body temperature for each _____°C change in environmental temperature
1, 25-30
118
True or false: the heat production on a set-point graph goes to 0
False, due to BMR
119
Increased body temperature above the set points results in the (stimulation/inhibition) of thermoregulatory centers in the Posterior Hypothalamus
Inhibition
120
What 3 things does an increase in body temperature above the set point lead to?
1. Increased sweating
2. Increased vasodilation
3. Decreased body heat production (decreased shivering/mechanical thermogenesis and metabolism/chemical thermogenesis)
121
A temperature rise of ___°C results in a significant increase in sweating
~0.5
122
True or false: sweating is a very efficient mechanism of cooling
True
123
Describe vasodilation
Dilation of the blood vessels in almost all areas of the body, particularly skin, ears, hands, etc.
124
Decreased body temperature above the set points results in the (stimulation/inhibition) of thermoregulatory centers in the Posterior Hypothalamus
Stimulation
125
What 4 things does a decrease in body temperature below the set point lead to?
1.Increased vasoconstriction
2. Increased piloerection
3. Increased shivering
4. Increased chemical thermogenesis
126
How does vasoconstriction impact conductivity from the core to the skin?
Reduced conductivity
127
Describe the 4 steps of piloerection
1. Sympathetic stimulation (with ACh)
2. Contraction of the arrector pili muscle attached to hair follicles
3. Upright stance of hair
4. Insulation (important in animals with fur)
128
Describe the 3 steps of shivering
1. Excitation of the primary motor center for shivering in the posterior hypothalamus through the brain stem
2. Increased tone of skeletal muscle (different from full contraction)
3. Shivering (recall that work generated by muscle contraction is 25% efficient)
129
Describe the 4 steps of chemical thermogenesis
1. Increased sympathetic stimulation
2. Increased norepinephrine and epinephrine levels (does not include increasing circulatory adrenaline)
3. Increased metabolic rate
4. Increased chemical thermogenesis
130
What does acclimatization to the cold in some animals result in, in terms of chemical thermogenesis? What about in humans?
Acclimatization in some animals increases chemical thermogenesis by ~500% (10-15% in humans at the most, only for a long period of time)
131
How does prolonged exposure to cold impact thyroid hormone production?
Prolonged exposure to cold leads to increased thyroid hormone production, which increases overall BMR (this is prevalent in animals that undergo hibernation)
132
Describe the steps for how cold leads to an increase in thyroid hormone
1. Prolonged exposure to the Cold increases the brain pituitary thyroid axis
2. Causes increased TRH secretion
3. Causes increased TSH
4. Causes increased thyroid hormone secretion
5. Increased metabolic rate
(Chemical thermogenesis)
133
How does thyroid hormone-induced increase in BMR in prolonged exposure to cold impact the thyroid? What does this constitute?
May lead to an increase in the size of the thyroid gland (up to 40%). Not pathological this time, physiological
- Constitutes an adaptation
134
People normally living in the Arctic and military personnel stations in that region have...
Higher thyroid activity and increased metabolic rates
135
What are the subconscious mechanisms for body temperature control complemented by?
Behavioural aspects resulting from discomfort (either feeling to hot or too cold)
- e.g. when you're cold, you seek shelter or put on a jacket
136
Why can you never elicit a response to both heat and cold?
The circuitry is designed in a way that when it stimulates a response to one, it simultaneously inhibits the opposite pathways.
- e.g. if you stimulate panting or sweating due to heat, you inhibit thermogenesis at the same time
137
In the response to heat pathway, what is stimulated and what is inhibited?
Panting/sweating is stimulated while vasomotor tone and thermogenesis is inhibited
138
In the response to cold pathway, what is stimulated and what is inhibited?
Thermogenesis and vasomotor tone are stimulated while panting/sweating is inhibited
139
What is pyrexia?
A fever
140
Define fever/pyrexia
A state of increased body temperature beyond the normal range. It could result from infection, allergic reaction, CNS injuries and cancer.
141
What does pyrogen release cause?
White blood cells (leukocytes), such as macrophages and neutrophils release cytokines (Interleukins IL-1 and IL-6, as well as TNF - tumour necrosis factor) in response to certain compounds known as pyrogens
142
What are the most common pyrogens? (3)
1. Bacterial lipopolysaccharide toxins (LPS)
2. Viral polyribonucleotide pyrogen (Poly I: Poly C, which is a synthetic analog of double-stranded RNA that gets incorporated into your body)
3. Cytokines released from injured cells or stimulated leukocytes
143
What do pyrogens act through?
The Toll family of membrane receptors that initiate innate immune responses that lead to fever
144
True or false: Toll receptors are evolutionary conserved
True
145
What 2 common pyrogens are exogenous?
1. Bacterial lipopolysaccharide toxins (LPS)
2. Viral polyribonucleotide pyrogen (Poly I: Poly C)
146
Pyrogens such as cytokines (IL-I, IL-6, TNF) act through Toll family of membrane receptors, which results in...
The activation of inducible cyclo-oxgenase-II (COX-II) enzyme, which results in the productino of Prostaglandins (PG)
147
How do prostaglandins impact hypothalamic set-point?
Prostaglandins increase the hypothalamic set-point to a significant degree and increase body temperature (fever)
148
Draw the pathway on pg. 50 of the thermoregulation 1 notes
149
What impact do compounds like Aspirin/Endomethacin have on fever?
Compounds that block prostaglandin production, such as aspirin/Endomethacin, reduce the degree of fever
150
Draw the pathway on pg. 51 of the thermoregulation 1 notes
151
Pyrogens increase the hypothalamic set point. What responses are activated in response to this?
Usual responses to cold are activated, such as vasoconstriction, piloerection, increased epinephrine (E) secretion and shivering
- During this period, the person experiences chills and feels cold, even though the body temperature is above normal
152
What is pyresis?
The increase in body temperature in response to pyrogens
153
What is antipyresis, and what occurs during this period?
When the factor causing fever is removed, the set-point will be reduced to a lower level. This stimulates the hypothalamic preoptic area resulting in the onset of response to reduce body temperature, such as sweating, vasodilation, etc.
154
When may the thermoregulatory process be disrupted?
When the body temperature reaches the upper limit. It is rarely a problem, but can become a problem in a fever induced by some infections such as malaria
- About 42-43°C
155
What are 2 potential reasons as to why we have fevers?
1. Sign of disease (tells us that we're sick)
2. There is evidence that increased temperature can enhance the body's defense response.
156
What are 3 pieces of experimental evidence that support how increased temperature potentially enhances the body's defense response?
1. Neutrophil migration and movement (diapedesis) significantly increases when temperature is higher
2. A number of genes that are important for immunity are activated by various heat shock proteins
3. In lower vertebrates, survival from infection significantly increased at higher temperatures
157
Define hyperthermia (heat stroke)
The upper limit of survival that is reached if the cooling mechanism is not efficient, either because of high humidity or excessive heat gain
158
What happens in terms of thermoregulation beyond the upper limit?
A loss of ability to regulate temperature
159
True or false: the upper and lower limits of survival are variable between species
True
160
What are 9 symptoms of hyperthermia
1. Extreme weakness and exhaustion
2. Headache
3. Dizziness
4. Nausea
5. Confusion
6. Abdominal distress
7. Delirium
8. Collapse
9. Eventually unconsciousness
161
True or false: our cold tolerance is better than heat tolerance
True (unless we get freezing damage)
162
What 3 things does sustained hyperthermia result in?
1. Hemorrhages (endothelial membranes in blood vessels get damaged)
2. Degeneration of cells throughout the body, particularly in brain cells
3. Damage to the liver, kidney and brain cells (the usual cause of death in hyperthermia)
163
Beyond humidity and hot ambient temperature, what can else can significantly increase temperature and lead to heat stroke?
Sustained exercise
- May reach 40°C or higher
164
How can certain mammals (e.g. hooved mammals like sheep, goats, gazelles and carnivores like cats and dogs) manage sustained running without being affected by heat stroke in general?
Through anatomical adaptation
165
How do a number of hooved animals prevent overheating of the brain?
They have a counter-current heat exchanger that cools down the arterial blood supply into the brain.
- The head carotid artery supplying the brain passes through a venous blood sinus (cavernous blood, found in like a chamber) which contains blood returning from the nasal cavity and respiratory passages (which is 2-3°C cooler)
- Sinus cavernosus is cooler because these animals keep licking their nasal areas when the weather is hot
- So counter-current flow: one way for warm blood in external carotid artery, while cool blood in venous draining from nasal cavities
- This allows for cooling through increased latent heat of vaporization
- Therefore, brain temperature is cooler than core temperature when the animal is running
166
True or false: the counter-current heat exchanger in animals is enough to protect them from any damage
False; sustained running in these animals could lead to heat stroke so they still need to rest since other parts of their body may get damaged
167
True or false: certain animals including rodents and primates do not have the counter-current exchange system involving the sinus cavernosus
True
168
Define hypothermia
A lower limit that is reached if the heating mechanism is inefficient (i.e. there is a loss of ability to regulate temperature), during sustained exposure to extreme cold
- Decreases beyond the lower limit result in a loss of ability to regulate temperature, which results in a further decline in body temperature and the development of initial symptoms of hypothermia, including sleepiness, coma and eventually death (due to impaired brain function)
169
True or false: there is a definitive number for the lower limit of survival in hypothermia
False, but it's usually when core temp is <23-24°C
170
What do hikers do in the cold to avoid hypothermia?
They try to stay awake (generates mechanical thermogenesis)
171
How does hypothermia affect your cells?
Exposure to extreme cold results in frostbite (ice crystal formation) and tissue damage.
- Ice crystals that touch cell membranes, damage them and kill them
172
Why do you get red skin in the cold?
Fine smooth muscles of blood vessels present in the subdermal region of the face get paralyzed
- Decreased blood flow due to paralysis is compensated by vasodilation
- This is the last protection against hypothermia
173
How do wild animals survive the extreme cold in general?
By physiological and anatomical adaptation
174
What 2 adaptations do marine mammals use to enable heat conservation?
1. Blubber to increase insulation
2. Circulatory anatomical adaptation
- Blood flow to the extremities is through counter-current fashion to minimize heat loss
175
Describe counter-current blood flow in marine mammals
The arterial vessels allows blood to flow from the center, which passes down toward the tip of the fin. Heat is then trasnferred to returning blood, to heat up before reaching the core.
- Also there's a decreased temp gradient since the coldest temp is getting to the thinnest part of the fin
176
What biochemical adaptation is present in animals with regional heterothermy like deers, particularly those who maintain a lower temperature in their extremities?
Low-temperature lipids: cold-acclimatization results in a change in the lipids by becoming less saturated in the extremities: it becomes more oily and less viscous to allow adequate cell membrane functioning
- Caused by the activation of heat shock proteins at low temperatures that express genes that regulate lipid synthesis
177
How does the membrane viscosity of an animal acclimated at 20°C differ across ambient temperatures compared to the membrane of an animal acclimated at 5°C?
Membrane of an animal acclimated at 20°C has higher viscosity than one at 5°C overall, but viscosity of both still increase as it gets colder (which is why they're countered by less saturation)
178
How is the concept of low-temperature lipids economically important?
Neatsfoot oil is rendered and purified from the shin bones and feet (but not the hooves) of cattle for conditioning and softening leather
179
What anatomical adaptation is present in animals with regional heterothermy like deers, particularly those who maintain a lower temperature in their extremities?
Fur thickness/length of adult reindeer changes in the winter and summer
- Thicker in the winter, which disrupts the temp gradient between circulation and ambient temp.
180
What is the main/general adaptation for temporal heterotherms when dealing with extreme cold?
Dormancy: certain animals sleep through bad weather or lack of food
181
What are the 3 types of dormancy used by different temporal heterotherms?
1. Deep sleep
2. Torpor
3. Hibernation
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Why is dormancy advantageous?
It is advantageous to allow body temperature to drop to lower levels during periods of non-feeding to avoid energy loss and excessive catabolism
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Temperature can rise when animals wake up due to _____ metabolism, particularly in animals with ______
Increased, brown fat
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Not all animals can go through torpor or hibernation. What two animals are unable to do so?
Large animals, because of their mass (takes much longer to reach normal temp. during arousal periods), and very small animals because of their high metabolic rates (they can't afford to not eat to survive)
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What are the only types of animals that can hibernate/undergo torpor?
Medium-sized animals
186
True or false: bears hibernate
False; bears and large mammals deep sleep during the winter
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How does "winter sleep" differ from hibernation?
The "winter sleep" differs from deep hibernation in smaller mammals as body temperature falls only by 3-5°C rather than by 25-35°C
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What is torpor?
A short-term change in body temperature for a few hours to help animals survive in a cold climate (these animals reduce their set point)
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What stimulates torpor?
Photoperiod (shorter days) and to a larger extent, drop in temperature, cause physiological changes and characteristics of torpor
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What are the 3 effects of torpor?
1. Reduction in core temperature
2. Decrease in metabolic rate, heart rate, breathing rate and O2 consumption
3. Low blood supply to limbs, mainly restricted to the vital organs
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What are 2 examples of animals that undergo torpor on a daily basis?
1. Bats
2. Small birds like hummingbirds
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There is a (lesser/greater) reduction in body temperature seen in hibernation compared to torpor
Greater
193
How does minimum body temperature differ with respect to body mass for daily torpor compared to hibernation?
Its much more constant (less fluctuation) in hibernation compared to daily torpor
- So hibernation is a far more efficient way of surviving the winter
- minimum body temperature in hibernation is almost independent of size
194
What types of animals tend to hibernate?
Some mammals, particularly rodents and insectivores
- These animals store enough energy to hibernate
195
What happens to the hypothalamic thermostat during hibernation?
It is reset to a very low level
196
At an ambient temperature of 5-15°C, many hibernators keep as little as ____ above the ambient
1°C
197
True or false: thermoregulation is suspended during hibernation
False; if ambient temp falls below freezing, metabolism increases to maintain the body temperature above freezing
198
Why do some hibernators keep a stash of stored food?
From time to time they go through arousal when they come out of hibernation and can consume some of the food before going back into hibernation
199
How does the mass-specific metabolic rate differ between hibernating and non-hibernating conditions for the same set of animals?
There's a decrease in mass-specific metabolic rate with respect to increasing body weight in non-hibernating animals, but it remains constant for the same animals during hibernation. This is because during hibernation, they maintain a low metabolic rate regardless of differences in size (due to decreased temp gradient; so they don't lose as much heat)
200
What happens to the decrease in metabolic rate brought about by entering hibernation as body weight increases?
The difference diminishes as mammals increase in body size
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How long does hibernation usually last?
May last up to weeks or months
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True or false: during hibernation, animals stay asleep the entire time
False; they periodically arouse (e.g. to empty their bladders)
- arousal is uncomfortable
203
What's faster, onset of hibernation or onset of arousal? What does this result in?
Much faster for onset of arousal
- Why bears and other large animals can't hibernate: it takes much longer to reach normal temperature during arousal due to so much mass
204
During hibernation, animals reduce their metabolism by __%
93
205
What happens to blood flow during hibernation?
Cardiac output is slowed, resulting in reduced blood flow to 10% of normal
- Blood flow is mainly directed towards vital organs
206
Basal metabolic rate in ground squirrels drops to __% of normal during hibernation
7
207
What happens to the thyroid gland during hibernation?
There's evidence that it decreases in size due to decreased BMR
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What happens to respiration during hibernation
Reduce
209
Why do hibernating animals have to urinate if they're not drinking water?
Body metabolism still generates water
210
True or false: ectotherm vertebrates undergo the same type of hibernation in endotherms
False; a number of ectotherm vertebrates remain dormaant and inactive in the winter (e.g. snakes and frogs)
- BUT this is not the same as endotherm hibernation
- It is analogous to hibernation and temporal heterothermy in mammals and birds
211
Describe how snakes "hibernate"
Snakes find relatively warmer dens with hundreds of other snakes
- They become dormant in terms of activity
212
How do poikilotherms thermoregulate in general?
They thermoregulate and use physiological and anatomical adaptations to cope with extreme temperatures
213
Why is poikilothermy an energy-efficient way of life?
Because it does not require maintaining a constant body temperature, which reduces dependence on a steady energy source
214
True or false: the metabolic rate in poikiliotherms is maintained passively
False; the rate of metabolism in Poikilotherms depends on environmental temperature, developmental stage and species
- for example in fish, the metabolic rate decreases as the fish gets older, even if the metabolic rate increases with temperature
- increase in temp causes increased enzyme activity, but this isn't passive because there's other strategies to maintain metabolism
215
True or false: heterothermy is present in poikilotherms
True; some poikilotherms are able to increase the temperature of different parts of their body when necessary
216
What are two problems with low temperature for poikilotherms?
1. Enzymes are less effective at low temperatures
2. Membranes become more viscous as temp lowers
217
What changes occur in the membrane composition of poikilotherms?
Decrease in membrane saturation throughout entire body to increase viscosity
- form of acclimatization
218
What happens to enzymes in poikilotherms at lower temperatures?
Enzymes have to acclimate to increase metabolic rate at lower temperature
219
Describe an example of control of temperature conductance as an energy-efficient way of thermoregulation
During warming periods, Iguanas bask in the sun and have a higher body temperature (they're absorbing heat by radiation). They also have a rapid heartbeat and vasodilation which increases conductance through skin.
During cooling periods, Iguanas have a lower body temperature which causes a slowed heartbeat and vasoconstriction to decrease conductance through skin.
220
How does the time to heat/cool differ in Iguanas in the air and water?
Faster for both in water compared to air, and it's faster to heat up and than to cool down in both environments
221
True or false: behavioural adaptation also plays a role in iguana (poikilotherm) thermoregulation
True
222
What happens to hemoglobin affinity for O2 at higher temperatures?
It is significantly less (~50% at 50°C)
223
What is an upper critical temperature (UCT)?
All ectotherms have an upper critical temperature (UCT) beyond which the physiological processes break down
224
True or false: long-term exposure to temperatures beyond UCT would lethal
True
225
True or false: there is lots of variability in the UCT of poikilotherms
True
226
What is the ectotherm with the most variability in UCT?
Fish (can range from 6-35°C, depending on the ambient temp/location)
227
Describe the behavioural regulation in honeybee flies in response to heat and cold
In cold, they densely swam.
- These bees move from the center to the periphery and move back and forth constantly.
- Due to mechanical thermogenesis of flight muscles that heat up these bees.
In heat, they spread.
228
Describe regional heterothermy in flying insects/poikilotherms(e.g. beetles, bumble bees, locusts)
Shivering and chemical thermogenesis increases thoracic muscle temperature prior to flight (flight muscles ned high enzyme activity and fast contraction speed, which requires warming)
- The abdomen remains cooler though.
During flight, the thorax is always warmer than other parts of the body.
- Circulation in the abdomen assists in cooling to prevent
229
Describe the regional heterothermy in female pythons (poikilotherms)
When temperature is colder, they need to worm up their eggs form them to develop properly.
- They go through mechanical thermogenesis (shivering and muscle contraction) to help brood their eggs (in areas surrounding the eggs)
230
Describe regional heterothermy in Tuna (poikilotherms)
Tuna have muscle that contains lots of mitochondria, that appears red (darker muscle tissue). They're able to increase metabolism in these areas, so temperature goes up.
- Water respiration is through water movement through gills.
- Blood becomes equilibriated between gills and ambient temperature.
- They evolved an aorta that delivers this cold blood coming back from the gills straight to the red muscle, where warm blood leaving flows side by side
- Heat moves from warm venous blood to cold arterial blood (aorta)
- By the time the blood leaves the aorta and it reaches muscles, it's already warmed up
231
How does circulation in Tuna (a heterothermic ectotherm) differ from Trout (a homeothermic ectotherm)?
In Trout, the aorta carries the cold blood toward the body surface, so the blood becomes the same temperature as the water
- So the whole body = same temperature as environment
Aorta in the Tuna brings blood through a heat exchanger
232
Poikilotherms can survive extreme cold temperatures by what two things?
1. Freeze avoidance:
- Freeze avoidance by Super Cooling
- Freeze avoidance by Production of Antifreeze
2. Partial freeze tolerance:
- Freezing of extra cellular fluid compartment (ECF)
- Production of cryoprotectants
233
Describe freezing avoidace by super cooling
Super cooling is a state in which body fluids are cooled below their freezing temperatures, yet remain unfrozen because ice crystals fail to form by preventing the presence of ice nucleating centers
- Certain fish at the bottom of Arctic waters avoid the surface and areas containing ice crystals to prevent the mechanical seeding of ice (ice nuclei). This animals stay motionless
234
What are 2 examples of animals that avoid freezing through super cooling?
1. Arctic fjords
- Fish that live in a continuously super-cooled state
2. Antarctic mite
- Survive unfrozen at -10 to -20°C. Some species may remain active at these temperatures
235
Describe freeze avoidance by production of antifreeze
Certain fish and insects produce specific antifreeze molecules that lower their freezing point.
- Antifreeze molecules adhere to growing ice crystals and prevent the crystals from growing to hazardous sizes, thereby preventing tissue damage and allowing the free flow of the blood
236
What antifreeze compound do Flounder and Arctic cod produce?
Flounder and Arctic cod blood contain a specific Glycoprotein antifreeze protein that lowers the freezing point by several degrees
237
Apart from Glycoprotein antifreeze protein, what are 4 other compounds produced by insects that allow for antifreeze properties?
1. Sorbitol
2. Glycerol
3. Nonglycosylated proteins
4. Glycolipids
238
Certain insects (e.g. mites) increase the concentration of sorbitol, glycerol, nonglycosylated proteins or glycolipids in their body fluids (which may reach 30% of body weight). What effect does this have?
This will significantly raise the osmotic pressure and lower the freezing point (freezing point varies between -17 to -43°C)
- Since increased osmolarity = doesn't freeze at normal temperature (lower freezing point)
239
Describe how freezing of the extra cellular fluid compartment (ECF) influences freeze tolerance
Certain beetles produce compounds (nucleating proteins) that accelerate and regulate the freezing in ECF outside the cells (i.e. increases the freezing point)
- Freezing of the ECF increases osmotic pressure in the ECF and results in the dehydration of cells (body gets partially dessicated)
- Loss of water from cells increases the intracellular concentration and lowers the freezing point. This prevents cell freezing.
240
Describe how cryoprotectants allow for freeze tolerance
Many invertebrates, including insects, bivalves, gastropods, annelids and nematodes can survive partially frozen at -25 or -35°C for many weeks (some arctic species tolerate -55 to -70°C)
- The process is assisted by the production of cryoprotectants, such as Trehalose (sugar) and Proline in insects, which form a gel phase as cells dehydrate and prevent disruption of internal cell organelles by stabilizing the membrane
- This strategy is rare in vertebrates, but a few amphibians and reptiles use this method to survive (e.g. wood frog survives freezing of almost 65% of its body water).
