Section 3: Thermoregulatory Responses
Section 3 Task 2: Do some or all of the following activities.
Watch this video on thermoregulation by muscles (equivalent to Sun
Reading 1: Sky level text
Reading 2: Sun level text
Section 3 Task 2: Do some or all of the following activities.
Simple worksheet that covers a lot of ideas (Grass level)
Annotate these two diagrams with what you've learned from the readings (Sky level).
Retrieval grid (Sun level)
Section 4: Biological Ideas for Excellence
Breakdown in Thermoregulation
I can comprehensively analyse how an extreme environmental influence results in a breakdown of thermoregulation.
Prolonged exposure to high temperatures can lead to hyperthermia. This is where the body temperature increases well beyond normal/optimum conditions.
If the body's core temperature rises:
Normal negative feedback mechanisms break down, as it's not able to lower body temperature.
Sweating too much has caused other issues dehydration lack of salts
Positive feedback occurs and certain physiological responses now make the issue worse. The person's body temperature can spiral out of control.
High temperatures now start affecting enzyme and other metabolic activity.
A core body temperature of >42°C usually causes death.
If the body's core temperature falls below 35°C, a person may suffer from hypothermia. Again, the body's thermoregulatory mechanisms fail and positive feedback occurs leading to a further decrease in temperature.
If the body's core temperature decreases:
Negative feedback mechanisms break down, as it's not able to increase body temperature.
Lots of energy has been spent creating heat through shivering, energy begins being diverted to vital organs.
Positive feedback now occurring making the issue worse (slows down in metabolic activity means less heat produced
Low temperatures now start affecting enzyme and other metabolic activity.
Read the stories on heat transfer, written on small pieces of paper by my Year 9 Science class.
Which of their ideas apply to athletes competing at the Coast to Coast Race South Island?
Biochemical and/or Biophysical Processes
I can comprehensively discuss the biochemical and/or biophysical processes underpinning the mechanism.
Biophysical and biochemical process of sweating and evaporative cooling:
How is sweating initiated by the hypothalamic control centre?
Role of sympathetic nervous system and acetylecholine neutrotransmitter.
Role of muscarinic receptors on the sweat glands.
How does the secretory coil portion of the eccrine gland produce primary sweat?
How does the duct portion of the eccrine gland reabsorb Na+ and Cl- ions?
How does evaporative cooling actually take heat away from the skin?
Biochemical process of thyroid hormone function and control:
How is thyroid hormone (T3 and T4) produced?
Hypothalamus as a control centre as well as an effector.
Along with other effectors: anterior pituitary gland and thyroid gland.
What does T3 do?
Activation of transcription of many genes.
Increases BMR, number and size of mitochondria, and aerobic respiration/chemiosmosis.
I can comprehensively discuss the significance of thermoregulation in terms of its adaptive advantage.
What is the difference between an endotherm and an ectotherm?
What are Endotherms?
Endo = inside, therm = heat
An endotherm is an animal that is dependent on or capable of the internal generation of heat. They keep warm using heat generated inside the body (thermogenesis). They regulate their heat loss by physiological mechanisms in the skin.
Most mammals have body temperatures between 37-39ºC. Our body temperatures varies slightly for a number of reasons.
In healthy humans the average is about 35.8ºC in the early morning and about 37.3ºC in the evening (for precise comparisons temp should be taken at the same time each day).
Temperature varies with level of activity, and may rise to 40ºC in vigorous exercise.
Body temperature varies from person to person suggesting that there may be genetic factors involved.
Temperature also varies from one part of the body to another. Though the core temperature in deeper parts of the body does not fluctuate much, in the outer shell (especially the limbs) it varies considerably.
Different organs have slight differences, reflecting variation in heat production.
To maintain homeostasis, internal thermoregulatory processes are activated to correct the core temperature. Since endotherms regulate their own body temperature (thermoregulation), we are not dependent on our environment for heat.
What are Ectotherms?
Ecto = outside, therm = heat
An ectotherm is an animal that is dependent on external sources of body heat.
Amphibians, lizards, snakes, turtles, many fishes, and most invertebrates are mainly ectothermic, because they gain most of their heat from external resources.
How do Ectotherms thermoregulate?
Ectotherms generate a little bit of heat from respiration. However, not enough for thermoregulation. Although ectotherms do not generate enough heat for thermoregulation, many adjust body temperature by simple behavioural means, such as seeking out shade or basking in the sun.
When exposed to air, most amphibians lose heat rapidly by evaporation from their moist body surfaces, making it difficult to keep sufficiently warm.
However, an amphibian can maintain a satisfactory body temperature simply by moving to a location where solar heat is available. When the surroundings are too warm, amphibians seek shady spots or other cooler microenvironments.
Like amphibians, reptiles like snakes use behaviour as their dominant means of thermoregulation.
When cold, they seek warm places, orienting themselves toward heat sources and expanding the portion of their body surface exposed to the heat source (to increase surface area for heat transfer).
When hot, they move to cool areas or turn in another direction. Many reptiles keep their body temperatures very stable over the course of the day by shuttling back and forth between warm and cool spots.
Many terrestrial invertebrates can adjust internal temperatures by the same behavioural mechanisms used by vertebrate ectotherms.
For example, the desert locust, for example, must reach a certain temperature to become active, and on cold days, it orients in a direction that maximises the absorption of sunlight.
Other terrestrial invertebrates have certain postures that enable them to maximise or minimise their absorption of heat from the sun.
For example, dragonflies have an "obelisk" posture that minimises the amount of body surfafce exposed to the sun. This posture helps reduce heat gain by radiation.
Adaptive advantages of Endothermy:
Generally speaking, endotherms have the ability to maintain a constant internal body temperature, regardless of external conditions(although extreme changes may not be able to be regulated).
Activity is possible when the external temperature is quite cool, such as at night, early in the morning, or during winter.
The ability to inhabit colder parts of the planet due to their ability to maintain that internal temperature. The adaptive advantage of this is that we can survive in (nearly) all environments on Earth, can occupy a wide range of niches for food and shelter, leading to greater reproductive success.
Disadvantages of Endothermy:
A sufficient proportion of energy intake is required to regulate internal body temperature in the cold.
More food is required for this contributing factor to homeostasis (for example, a shrew has to eat its own body mass in food each day to prevent itself from starving).
Less energy obtained from food is used for growth (or at least more food is needed for growth).
Adaptive advantage of Ectothermy:
Because their heat source is largely environmental, ectotherms generally need to consume much less food than endotherms of equivalent size - an advantage if food supplies are limited.
Less energy intake is required from food for maintaining temperature (thermoregulation), so less food overall is needed, as expense of energy on metabolism is far lower.
Ectotherms do not need to eat as often and can survive greater periods of starvation than endotherms.
Greater portions of energy from food can be used for growth.
Ectotherms also usually tolerate larger fluctuations in their internal temperatures.
Disadvantages of Ectothermy
Are only able to survive in certain climates, and cannot survive in very cold climates.
The need to hibernate (remain inactive) during the winter as organisms cannot be active at that time.
Vulnerability to predation when basking in the sun.
The need to rely on ambush predation, rather than sprint predation, as they cannot chase prey as quickly and for as great distance as endotherms can.
Overall, ectothermy is an effective and successful strategy in most environments, as shown by the abundance and diversity of ectothermic animals.