For the Matrics: Homeostasis 1 – constant internal environment

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This video was made for Matric revision, covering the topic
Human homeostasis: part 1 – Negative feedback, Glucose regulation Thermoregulation 
Hopefully this is helpful in your revision.







Hello, I am Dr Derek Keats, a former professor of biology, and I have a new topic today, and it is homeostasis. This is an awesome topic because it is all about how we maintain the optimal state of things in our bodies despite considerable pressure to change. In this video we are going to cover the notion of homeostasis – maintaining a constant, optimal internal environment. We will look at the role played by negative feedback by reviewing glucose regulation, and then talking about thermoregulation.


I like hiking, and >> I love hiking where there is a nice hill to climb. I also love the snow, and in my younger days I used to cross country ski a lot, and sit around on the ice doing ice fishing. I have even gone SCUBA diving under the ice, and >> played ice breaker with my butt. I have been dropped off by a >> helicopter in the middle of the Arctic pack ice, and live to talk about it. I still love swimming, even if the water is a little chilly. Right now, a June morning in Johannesburg, it is cold, probably 3 degrees Celsius. I am shivering.

I am at the tail end of a winter flu or cold, and last week, my body temperature increased by 1.5 degrees. It was a panic, I had to get an injection, take antibiotics and steroids, vitamins and to all sorts of nasty things to get better. But 1.5 degrees is not much, and despite playing in the snow or diving under ice and shivering like a jackhammer in an East Rand gold mine, and climbing mountains in 30 degree heat and sweating like the fountains in Pretoria, my body temperature has not fluctuated by that amount from those activities. Ever. If it did, I would be sick, and would have to stop.

Can you imagine yourself in all those or similar situations, and think if your body temperature changed. It didn’t did it? It remained as static.

Have you ever wondered how the body can do that?

That is homeostasis, and that is what we are going to look at here.


We can think of >> homeostasis as a tendency of an organism or a cell to >> regulate its internal conditions, usually by a system of feedback controls, so as to stabilize health and functioning, regardless of the outside changing conditions.

>> The word homeostasis is derived from the Greek, >> homeo or “same”, >> and stasis or “stable” and its literal meaning is something like ‘remaining stable’ or ‘remaining the same’. Of course, if you write that down as the meaning of homeostasis on a test, you won’t get ANY marks, because you would need to give the real, practical meaning – the first definition we have used.

>> we are going to be looking at thermoregulation, >> water and salts, >> carbon dioxide and oxygen, and >> glucose >> which of course is review for you.


To understand homeostasis, you need to understand the concept of negative feedback. If you have ever been in >> an air conditioned room on a hot day, you have seen an example of negative feedback in action. >> Imagine the temperature being below normal room temperature because the air conditioner was on. >> The thermostat senses this, and >> switches the air conditioner off. The temperature rises due to the surrounding heat, and restores the temperature back to normal room temperature. >> But maybe it is hot outside and the temperature continues to rise. Again the thermostat senses this, and switches the air conditioner back on to cool it down. >> Thus temperature is maintained within a narrow range of the temperature that we have set it to.


We have seen the way the glucose levels in the blood are maintained by the interaction of insulin and glucagon, this is an example of a homeostatic mechanism in action. And it involves feedback, remember our review video on this under the endocrine system >> TALK FROM THE SLIDE


Now we are going to look at thermoregulation in our own bodies, not in a room with an airconditioner and a thermostat. The principles are similar, but the mechanisms for adjusting temperature obviously differ. You should recall from pervious grades that there are two ways in which body temperature in animals is controlled: >> ectothermy and >> endothermy. >> We are endo thermic.


Recall that an ectotherm is an organism whose internal heat production is relatively small. >> Hence, body temperature is determined by the temperature of the surrounding environment and access to sunlight. >> Such organisms are also referred to as poikilotherms, meaning their temperature fluctuates, but actually some ectotherms are able to maintain a fairly constant body temperature through behaviour, so this word is falling into disuse due to its inaccuracy in some cases. All >> invertebrates, >> fish, and >> reptiles and amphibians are ectotherms.


An endotherm is an organism that produces heat internally through various mechanisms. >> Because they produce their own heat and usually also have cooling mechanisms, >> they are able to maintain a constant body temperature in spite of temperature fluctuations in the surrounding environment. >> For this reason, they are also called homeotherms. >> Birds and >> mammals are endotherms, and us being mammals are endotherms.




If the mechanisms of thermoregulation fail for some reason we can have an >> increase in body temperature, called hyperthermia. >> In this case the body produces or absorbd more heat than it can dissipate. >> This can be caused heat stroke (for example, exercising too much in the sun on a very hot day), as well as adverse reaction to some drugs. >> Hyperthermia is not the same as a fever, although both involve elevated body temperature. A fever is actually caused by a physiological increase in the body’s temperature set point – it is like someone turned up the thermostat on our air conditioner. >> Hyperthermia is sometimes induced using drugs for the the treatment of certain illnesses, such as cancer.


The opposite of hyperthermia is hypothermia, something we are perhaps more familiar with. >> Hypothermia is a condition in which the core body temperature drops below the required temperature for normal metabolism, around 35 degrees Celsius. >> It can happen when you are exposed to cold and the internal mechanisms are unable to replenish the heat that is being lost. For example, if you are immersed in cold water, or if you are outside in cold conditions with inadequate clothing. >> Hypothermia is characterized by mental confusion, uncoordinated movements, decreased heartrate, and decreased respiratory and metabolic rates.

>> Hypothermia is also sometimes induced medically for certain treatments, for example during complex surgery where there is a need to reduce the body’s demand for oxygen.


We have pretty much covered what you need to know for the South African grade 12 life science syllabus on this subject.

>> If you want to take it further, and have a deeper understanding, you could search Google or another search engine using terms such as homeostasis, negative feedback, glucose regulation, human homeostasis, thermoregulation or any of the other terms we have used in this video.

>> You can look for videos on this and related subjects on YouTube or other online sources of video material.

>> You can visit the local or school library, and read up on the topics there.

>> If you want to get creative, you can interview a family member, family friend, or acquaintance about stressful situations that they got out of because of adrenaline.

>> And remember, if you find something good, put it on the wiki.

SLIDE 13 (final)

I am Derek Keats, and this resource is licensed under a Creative Commons, Attribution license.