5.1.1 - Homeostasis Flashcards
What is homeostasis?
The maintenance of a dynamic equilibrium of conditions in the body
What do most of the feedback systems in the body involve?
Negative feedback
What happens in a negative feedback system?
A small change in one direction is detected by sensory receptors, and as a result, effectors work to reverse the change and restore conditions to their base level
What happens in a positive feedback system?
A change in the internal environment is detected by sensory receptors, and effectors are stimulated to reinforce the change and increase the response
Give an example of a positive feedback system
When a blood vessel is damaged, platelets stick to the damaged region and they release factor that initiate clotting and attract more platelets. These platelets also add to the positive feedback cycle and it continues until a clot is formed
Describe the positive feedback during childbirth
The head of the baby presses against the cervix, stimulating oxytocin production. Oxytocin stimulates the uterus to contract, pushing the head of the baby even harder against the cervix, releasing more oxytocin
What is thermoregulation?
The maintenance of a constant core body temperature
What physical processes cause changes in temperature?
Exothermic chemical reactions
Latent heat of evaporation
Radiation
Convection
Conduction
What is radiation?
The transmission of EM waves to and from the air, water, or ground
What is convection?
The heating and cooling by currents of air or water, warm air or water rises and cooler air or water sinks, setting up convection currents around an organism
What is conduction?
Heating as a result of the collision of molecules.
What are ectotherms?
Animals that use their surroundings to warm their body, and so their core body temperature is heavily dependent on their environment
What are endotherms?
Animals that rely on their metabolic processes to warm up and usually maintain a very stable core body temperature regardless of environmental temperature
Give examples of behavioural responses of ectotherms to increase temperature
- Basking in the sun when cold, and orientate their bodies so the max SA is exposed to the sun
- Pressing their bodies against warm ground to heat up by conduction
- Exothermic metabolic reactions
Give examples of behavioural responses of ectotherms to decrease temperature
- Seek shade
- Press their bodies against cool earth or stones
- Orientate bodies so minimum SA is exposed to sun
- Minimise movements
Give examples of physiological responses to warming
Dark colours absorb more radiation than light, and lizards living in colder climates tend to be darker coloured
How do endotherms detect temperature changes?
Peripheral temperature receptors in the skin detect changes in surface temperature. Temperature receptors in the hypothalamus detect the temperature of the blood deep in the body. The combination gives great sensitivity and allows it to respond to changes, but also preempt possible problems
Describe how endotherms may cool down
Vasodilation, increased sweating, and reducing the insulating effect of hair or feathers
Describe how vasodilation cools the body down
The arterioles near the surface of the skin dilate when the temperature rises. The vessels connecting the arterioles and the venules constrict, so blood is forced through the capillary networks close to the surface. The skin flushes, and cools due to increased radiation
How does sweating cool the body down?
As sweat evaporates from the surface of the skin, heat is lost, cooling the blood below the surface
How does reducing the insulating effect of hair cool the body down?
The erector pili muscles in the skin relax, so the hair of feathers lie flat, avoiding the trapping of an insulating layer of air. It has little impact in humans
Describe how endotherms increase their body temperature
Vasoconstriction, decreased sweating, and raising the body hair or feathers
How does vasoconstriction heat the body up?
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. This prevents radiation
How does decreased sweating heat the body up?
When core temperature is lower, the rate of sweating decreases. This reduces cooling by the evaporation of water from the surface of the skin
How does raising the body hair or feathers heat the body up?
As the body temperature falls, the 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 through the skin.
How does shivering heat the body up?
Shivering is rapid, involuntary contraction and relaxation of the large voluntary muscles in the body. The metabolic heat from the exothermic reactions warm up the body instead of moving it
