Module 5- Homeostasis Flashcards
Define homeostasis
Maintenance of a constant internal environment in response to internal and external changes via physiological control systems
What do physiological control systems do in homeostasis?
-keep body temp, blood pH, blood glucose and blood w.p within its set limits
What is a negative feedback loop in homeostasis?
When a deviation from the set limits is detected in the body by a receptor, receptors send a signal to effectors, through the nervous system, which counteract the initial change
Describe positive feedback loops in homeostasis and give an example
-quite rare
-when a change from the set limits triggers a response to increase the change further
-e.g during child birth when the baby’s head presses on the cervix it causes the hormone oxytocin to be released, causing the uterus to contract which results in the release of even more oxytocin
Why is thermoregulation important?
-if body temp dropped too low there would be insufficient kinetic energy for enzyme controlled reactions
-if the body temp increased too high, enzymes would denature
-either way metabolic reactions could slow to the point that cells die
What are examples of ectotherms
Fish and reptiles
How do ectotherms (both aquatic and land) mainly control their body temp
-By behavioural responses such as warm up against conduction of hotter surfaces,orientate themselves to have an increased surface area exposed to the sun and cool down by moving to shade or into water, minimise movements to reduce metabolic heat generated by
-rarely use physiological responses but do sometimes alter their heart rate to increase or decrease their metabolic rate
-aquatic ectotherms don’t have much need to emulate their body temp as water has a high specific heat capacity and therefore temperatures remain relatively constant
-land ectotherms have a bigger challenge as the temperature of the air fluctuates
Compare thermoregulation in ectotherms and endotherms
-ectotherms are more vulnerable to changes in the environment
-endotherms can regulate their body temp within a very narrow range so is more specific
-ectotherms rely mainly on external heat sources to regulate their temperature
How do endotherms regulate their body temperature?
-through a nervous response
-peripheral thermoreceptors in the skin detect a change in the external temp and sends an impulse along a sensory neurone to the brain where the hypothalamus coordinates the impulse which triggers a response by glands in the skin and muscle
What do endotherms do to cool down?
-vasodilation-the arteriolar near the surface of the skin dilate due to the contraction of muscles near the blood vessels that connect the arteriolar. More blood flows through the arterioles near the skin surface so more heat radiates from the skin surface
-sweating-as sweat evaporates from the skin surface it takes heat energy with it
-erector pili muscles-relax so hairs lie flat to improve air circulation over the skin
What do endotherms do to warm up?
-vasoconstriction-arterioles near the surface of the skin constrict so very little blood flows through the capillary networks close to the surface of the skin so very little radiation takes place
-sweating-production of sweat will stop entirely
-insulation-erector pili muscles in the skin contract and stand erect to trap an insulating layer of air
-shivering-contracting and relaxing of muscles increase the rate of respiration and so more heat is produced
When might negative feedback not be possible?
When the change is too dramatic
