Homeostasis - Online Tutor, Practice Problems & Exam Prep

Introduction to Homeostasis

We're now going to spend some time talking about homeostasis, and homeostasis is probably the key physiological concept that you need to understand for this course. It's going to be the underpinnings of so much of physiology. Homeostasis is the maintenance of a stable internal environment, and we can break that word down. We see that "homeo" comes from the Greek for "similar" or "the same," and "stasis" comes from the Greek for "standing still." So, inside your body is standing still, unchanging. That's going to refer to things like fluid levels, nutrient levels, your body chemistry, waste levels, oxygen levels, body temperature. Over here to help you remember homeostasis, we have this picture of a woman out on a cold day and a man out on a real hot sunny day, and I know even though the external conditions that they're in, I know their body temperatures, at least within a few degrees, because they're alive and they're human. Internal conditions are going to be always kept at a set point or at least within a narrow range. Now, it's important to think though, homeostasis doesn't mean that your body is just a lump that never does anything. Your body is dynamic, and so sometimes you want to think of this instead as a dynamic equilibrium. Your body is always changing. Your body is not at a fixed state. Your external conditions are always changing around you. Your body needs to do constant work to maintain all those factors that I was talking about earlier. Now, when we say your body cannot maintain homeostasis, a failure to do so, we call a disease state. Or in anatomy and physiology sometimes we refer to that as pathology. So again, we're going to get into the details of homeostasis and how it's maintained going forward. Let's get to it.

Homeostasis Example 1

This example wants us to name three variables that are under homeostatic control. Now, don't worry at this point in the course; you don't need to know a whole bunch of homeostatic mechanisms in detail. We're going to go over one mechanism in some detail in a future video, but for now, you just want to know generally what's the type of stuff that's maintained by homeostasis, and what does it generally look like? So for this example, we have three columns. We have variable, range, and pathology. Remember, pathology is when something's in a disease state, and for homeostasis, that means that it is out of the normal range. So first up, we have blood, and this is going to be blood pH. So blood pH is maintained between 7.35–7.45. That's a really tight range. If you're a chemist and you're able to buffer a reaction in that tighter range, you're going to be pretty happy. Alright. If it goes outside of that range, we call it either acidosis or alkalosis. Acidosis, if the blood is too acidic or the pH falls too low, or alkalosis, if the blood is too alkaline or basic or if the pH is too high. Now acidosis or alkalosis, those aren't like diseases that you get on their own. They're usually a symptom of another physiological condition, but it can be a pretty severe symptom. Next up, we have internal body temperature. And I'm sure you know your internal body temperature is very stable. It's maintained between about 97 degrees Fahrenheit to 99.5 degrees Fahrenheit. In Celsius, that's 36–37.5. If your body temperature falls too low, we call that hypothermia. If it gets too high, we call it hyperthermia. And it doesn't have to change a lot to be really serious. If your body temperature changes 10 degrees in either direction, you're in a lot of trouble. If your body temperature falls 10 degrees, that's hypothermia; you could die if it stays there very long. If it goes up to 107 degrees Fahrenheit, well, if it's there again for very long, you risk some serious lasting damage. Now, just notice we are not saying this is a fever. A fever is something different. A fever is a response where your body, in a very controlled way, raises body temperature a certain amount. So this is when it is uncontrolled and therefore pathology. Finally, we have blood glucose. Blood glucose or blood sugar is maintained between 70 milligrams per deciliter to 90 milligrams per deciliter and importantly, that's post fasting. So, when they measure your blood glucose, you're not supposed to eat beforehand because if you're eating, it's absorbing sugar into the blood and your blood glucose could go up and down some. But just think about that post fasting; if you don't eat for a while, the amount of glucose in your blood stays the same. Now you're using glucose all the time. So that means your body is constantly regulating this and amazingly, it's going to stay in that range for a good long while. I'm not exactly sure how long, but at least for days. I'd guess even longer than that. Now if it falls outside of that range, we call it hypoglycemia or hyperglycemia. Hyperglycemia and hypoglycemia, again, you know, those aren't diseases that you get, but they are symptoms of other things, the main one being diabetes. Okay. So again, the information here, all the specific terms and numbers, you do not need to know exactly. But hopefully, this gives you a better idea of how homeostasis works and the type of things under homeostatic control. We have a few practice problems below, and we're going to go into homeostasis in more detail in a few more videos. I'll see you there.

Which example most clearly describes a system maintained by homeostasis?

• A. A growing child will deposit new bone rapidly until the endocrine system signals the end of puberty.
• B. During the 'fight-or-flight' response, the sympathetic nervous system causes a change in many physiological factors from increased blood pressure to decreased pain response.
• C. Humans typically have 52 total chromosomes, 26 from inherited from their biological mother and 26 from their biological father.
• D. Blood osmolality is maintained by the kidneys in a range from about 290 to 300 mOsm/kg.

Which example below describes a system that is NOT able to maintain homeostasis?

• A. A person who is running breathes more rapidly in response to changing in O₂ and CO₂ levels.
• B. A person with diabetes will experience large spikes and crashes of blood glucose without proper monitoring. 
• C. A person moving from the cold to inside a warm house, but their body temperature does not change.
• D. When fluid levels in the body are high, the kidneys will remove more water from the blood.