15 - homeostasis Flashcards
What is a positive feedback system?
A change in the internal environment of the body is detected by sensory receptors, and effectors are stimulated to reinforce that change and increase that response. e.g. when a blood vessel is damaged, platelets stick to the damaged region and they release factors that initiate clotting and attract more platelets.
What physical processes do changes in an organisms temperature depend on?
- Exothermic chemical reactions
- Latent heat of evaporation; objects cool down as water evaporates from a surface
- Radiation; the transmission of electromagnetic waves to and from the air, water or ground.
- Convection- heating as a result of the collision of molecules. Air is not a good conductor of heat by the ground and water are.
What are ectotherms?
- They use their surroundings to warm their bodies. Their core body temp is heavily dependent on their environments.
- Ectotherms include all invertebrate animals, along with fish, amphibians and reptiles.
- Many ectotherms living in water don’t need to thermoregulate. The high heat capacity of water means that the temp of their environment doesn’t change much.
- Ectotherms living on land have a bigger problem with temp regulation, as a result, they have evolved a range of strategies that enable them to cool down or warm up.
What are endotherms?
Rely on metabolic processes to warm up and they usually maintain a very stable core temp regardless of the environmental temp. Have adaptations which enable them to maintain their body temp and to take advantage of warmth from the environment. As a result, ectotherms survive in a wide range of environments. The metabolic rate of ectotherms is around 5X higher than that of ectotherms, so they need to consume more food to meet their metabolic needs than ectotherms of a similar size.
What behavioural responses so ectotherms use to overcome limitations imposed by the temp of their surroundings?
To warm up;
- bask in the sun
- orientate their bodies so that max SA is exposed to the sun
- extend their bodies to increase the SA exposed to the sun.
- pressing their bodies against the warm ground.
What physiological responses do ectotherms have to warming?
- Dark colours absorb more radiation thank light colours; Lizards living in colder climates tend to be darker coloured than those that live in hotter climates.
- Some ectotherms also alter their HR to increase or decrease the metabolic rate and sometimes to affect the warming or cooling across the body surfaces.
- They’re vulnerable to fluctuations in the environment compared to endotherms. However, by using a variety of behavioural and physiological responses many can maintain relatively stable core temp.
How do endotherms detect changes in temperature?
- The peripheral temp receptors are in the skin and detect changes in the surface temperature.
- Temp receptors in the hypothalamus detect temperature of the blood deep in the body.
- The temp of the skin is much more likely to be affected by external conditions than the temperature of the hypothalamus.
- The combination of the 2 gives the body great sensitivity and allows it to respond not only to actual changes in the temperature of the blood but to pre-empt possible problems that might result from changes in the external environment.
How do endotherms cool down?
Vasodilation
increased sweating
reducing the insulating effect of hairs or feathers.
How does vasodilation help to cool endotherms down?
- 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 constrict.
- This forces blood through the capillary networks close to the surface of the skin.
How does increased sweating help to cool down endotherms?
- Sweat spreads out across the surface of the skin.
- In some mammals, including humans and horses, there are sweat glands all over the body.
- As sweat evaporates from the surface of the skin, heat is lost, cooling down the blood below the surface.
- In some animals, the sweat glands are restricted to the less hairy areas of the body. These animals often open their mouths and pant when they get hot, again losing heat as the water evaporates.
How does reducing the insulating effect of hairs or feathers help to cool down endotherms?
- As the body temp increases, the erector pili muscles in the skin relax- as a result, the hair or the feathers of the animal lie flat to the skin. This avoids trapping an insulating layer of air. It has little effect in humans.
How do endotherms warm up?
Vasoconstriction
Decreased sweating
Rising the body hair or feathers
Shivering
How does vasoconstriction help an endotherm to increase their body temp?
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 warm blood is kept well below the surface.
How does raising the body hair of feathers help endotherms to warm up?
As temp falls, erector pili muscles in the skin contract, pulling the hair or feathers of the animal erect.
- This traps an insulating layer of air and so reduces cooling though the skin.
How does shivering help endotherms to warm up?
- Rapid involuntary contracting and relaxing of the large voluntary muscles in the body.
- The metabolic heat from the exothermic reactions warm up the body instead of moving it and is an effective way of raising the core temp.
