Homeostasis - Online Tutor, Practice Problems & Exam Prep

Homeostasis is the maintenance of a stable internal environment, crucial for physiological balance. It involves regulating fluid levels, nutrient levels, body temperature, and waste management, ensuring these factors remain within a narrow range despite external changes. This dynamic equilibrium requires constant adjustments, and failure to maintain it can lead to disease states, known as pathology. Understanding homeostasis is essential for grasping the complexities of physiology and the body's adaptive mechanisms.

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. Right? 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 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 3 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 3 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 and 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.

blood pH range : 7.35 to 7.45

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 diseases that you get on their own. They're usually symptoms of another physiological condition, but they can be pretty severe symptoms.

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 to 37.5. If your body temperature falls too low, we call that hypothermia.

Body temperature range : 36 °C to 37.5 °C

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 hyperthermia. 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 is 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.

Blood glucose range : 70 mg/dL to 90 mg/dL

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.

Here’s what students ask on this topic:

What is homeostasis and why is it important in physiology?

Homeostasis is the maintenance of a stable internal environment within the body, crucial for physiological balance. It involves regulating factors such as fluid levels, nutrient levels, body temperature, and waste management, ensuring these factors remain within a narrow range despite external changes. This dynamic equilibrium requires constant adjustments by the body. Homeostasis is essential because it allows the body to function optimally and adapt to external changes. Failure to maintain homeostasis can lead to disease states, known as pathology. Understanding homeostasis is fundamental for grasping the complexities of physiology and the body's adaptive mechanisms.

How does the body maintain homeostasis?

The body maintains homeostasis through various feedback mechanisms, primarily negative feedback loops. These mechanisms involve sensors that detect changes in the internal environment, control centers (usually the brain) that process this information, and effectors that enact the necessary adjustments. For example, to regulate body temperature, thermoreceptors detect changes, the hypothalamus processes this information, and effectors like sweat glands or muscles (shivering) adjust the temperature. This constant monitoring and adjustment ensure that internal conditions remain within a narrow, optimal range despite external fluctuations.

What are some examples of homeostatic processes in the human body?

Several homeostatic processes are crucial for maintaining a stable internal environment. Examples include thermoregulation (maintaining body temperature), osmoregulation (regulating fluid balance and concentration of solutes), blood glucose regulation (maintaining blood sugar levels), and acid-base balance (maintaining pH levels). Each of these processes involves specific feedback mechanisms that detect deviations from the set point and initiate responses to restore balance. For instance, insulin and glucagon regulate blood glucose levels, while the kidneys play a key role in osmoregulation and acid-base balance.

What happens when homeostasis is not maintained?

When homeostasis is not maintained, the body can enter a state of imbalance, leading to various disease states or pathologies. For example, failure to regulate blood glucose levels can result in diabetes, while an inability to maintain body temperature can lead to hyperthermia or hypothermia. Chronic imbalances can cause long-term health issues, such as hypertension from poor blood pressure regulation or acidosis/alkalosis from disrupted acid-base balance. Understanding these consequences highlights the importance of homeostasis in maintaining overall health and preventing disease.

What role does the hypothalamus play in homeostasis?

The hypothalamus is a critical brain region involved in maintaining homeostasis. It acts as a control center, processing information from various sensors throughout the body and initiating appropriate responses to maintain balance. The hypothalamus regulates body temperature, hunger, thirst, sleep, and circadian rhythms. For instance, it detects changes in body temperature and triggers responses like sweating or shivering to restore normal temperature. It also regulates the release of hormones from the pituitary gland, influencing processes like growth, metabolism, and stress response.