LECTURER:
Homeostasis is fundamental to anatomy and physiology. It's a fundamental concept that you must understand to do well in this unit. Homeostasis is a significant component of the assessment task of the case-based learning assessment that you will do. You need to understand homeostasis. You need to understand how the body systems are responding in order to maintain homeostasis. So in order to do that, we need to understand what homeostasis is. Now, if you break the word down, homeo stasis, homeo means the same, stasis means state, so homeostasis means the same state, and it's the body's attempt to maintain a normal optimal level of functioning. So what do we try and maintain? We try and maintain a body temperature. We try and maintain a stable body temperature. Now, that's stable body temperature for humans is around about 37 degrees. If we go above or below that, it's termed hypothermia or hypothermia. It means we're getting too hot and too cold. We need to maintain that body temperature of around 37 degrees.
Now, you can see here that a spider, for example, is not a warm-blooded animal. It doesn't maintain a constant body temperature within all cells and tissues of the body. And you can quite clearly say from the thermal image that the rear end of this spider is a lot warmer than the head and the extremities. That's different to a warm-blooded animal like us, where we maintain that normal body temperature even at the extremities. Obviously, when we get hot and cold, we have ways to deal with those fluctuations and changes. And this is what homeostasis is really about, maintaining that constant internal, stable environment. Another classic example that we're going to see is the body fluid composition of the nutrients, for example, glucose. If we can't maintain our blood glucose levels, we go into hyperglycaemia or hypoglycaemia. And this is a real problem for diabetics. We also need to maintain our oxygen levels and our oxygen levels stay really highly saturated with haemoglobin on our red blood cells.
We maintain our body fluid volume and this is interrelated with our blood pressure. If we ingest too much water, we increase our blood pressure and our body gets rid of it. If we ingest too many drugs or toxins or salt or anything like that, our body gets rid of it. We want to maintain this stable internal environment. In this internal stable environment, everything works optimally. How does homeostasis happen? What is homeostatic regulation? Well, it's all systems really working together to preserve that environment. You will very rarely see physiological systems working on their own, and they're constantly adjusting to stimuli. We will never see the muscular system work without the skeletal system. We'll never see the cardiovascular system and respiratory system not working together. And this is an important concept to understand when you go into your assessment task, you need to understand how one body system is affecting another. You need to understand how changing the internal environment within one body system really influences that next body system.
And this is a major focus of your case-based learning assessment that you will do. So what happens if we disturb homeostasis and we can't maintain this normal, stable internal environment? All disease happens. Most disturbances are resolved through this homeostatic mechanism. So infection, injury, stress, we get back to a normal internal environment, but sometimes we can have an injury or an infection or a genetic abnormality that can overwhelm this homeostatic mechanism and we can't fix. When this happens, it results in the malfunction of that organ system, and disease and illness occurs quite often being chronic. So there's two general mechanisms of autoregulation now. There's auto regulation at the local level, which includes the cells, tissues, organs and the organ system itself. Or we have intrinsic regulation. Intrinsic regulation involves the nervous system and the endocrine system. Now, these are the two systems which talk to every other system. Changing something in the body quite often involves the nervous system or the endocrine system in order to bring about homeostasis.
But you can also have that local auto-regulation or the intrinsic regulation that happens within the cells and tissues. And this might be due to difference in chemical concentrations across the membrane, where we see fluctuations in osmosis or movement of one salt across a membrane to fix that equilibrium that is happening within that system. So what must happen in homeostatic regulation? We must have three things involved. We must have a receptor. That receptor is sensitive to that change in the environment. So, for example, body temperature, it's a classic example. We're going to go through how the body maintains a constant internal environment in terms of its body temperature. But the receptor here is thermo receptors, which are sensitive to changes in temperature. That change is sensed by these thermal receptors, and it sends that information to the control centre. Now, the control centre is the brain, and in particular the hypothalamus. The hypothalamus is where we have these thermal receptors that are detecting the change.
Once that change is detected, we need an effector. Now, the effect of responds to that command of that control centre. So the three things that need to happen to maintain a constant internal environment or homeostatic regulation is we need a receptor to sense the change. We need the control centre to tell the body what to do, and it sends that information to the effector. So what type of receptors do we have in the body? And we're gonna learn more about these as we get into the different body systems. But we have thermal receptors. Thermal receptors located in the skin that really respond to the external environment. We have thermal receptors a little bit deeper in the skeletal muscle, the liver, the hypothalamus. So they're detecting changes in core temperature. We have thermal receptors located in the skin so they can detect environmental changes and start responding to what's going to happen immediately. If the body warms up or cools down too much. We have these deeper-lying thermal receptors that sense the change and bring about further change.
We have McKenna receptors. We can our receptors are responsive to compression, stretching, twisting, etc. So the mechanics of what's happening within the body, we can further break this down to tactile baroreceptors and proprioceptors. And probably the two most important here are baroreceptors and proprioceptors. So proprioceptors being about knowing where your arms and limbs are at any one time. Baroreceptors about detecting changes in pressure. So detecting changes in pressure, blood pressure, for example, baroreceptors respond to that change. Then chemoreceptors. You will need to understand chemoreceptors when we get to certain topics. Chemoreceptors are sensitive to changes in chemical concentration in the body. They're important for monitoring pH of the body, which we've already learnt about the pH. If the hydrogen ion concentration increases, these chemoreceptors detect that. What do the chemoreceptors do with that? They start making changes in the body to try and get rid of this hydrogen.
How do we do that? We create more buffers or we create bicarbonate buffering molecules or we start eliminating hydrogen ions and the kidneys. So it's really about detecting that change. We send that information to the brain, which is the command centre, and then we make the change at the effector. The effector here for camera receptors might be the kidney in terms of eliminating things. What is the control centre for Homeostasis? Well, the two systems that really maintain homeostasis are the nervous system and the endocrine system. We've learnt about the nervous system in the endocrine system briefly. The nervous system is fast specific short neural impulses sent to the effect or straight away. Something needs to happen fast. It does. If we cut ourselves, we start losing blood. The response is to constrict the blood vessels so that blood doesn't flow out of those veins or arteries too quickly. The endocrine system is a little bit longer lasting. It's with hormones. The hormones need to be synthesised or released into the blood and make their way to the effector.
So they're a little bit longer lasting in terms of maintaining homeostasis. What are the effectors? Well, that really depends on what's happened. We have the integument system, the muscle, cardiovascular system, respiratory, digestive and the urinary system. They might be all affected depending on what's happened. If the body is too cold, we get constriction, vasoconstriction, we stop blood going to the skin. We get our muscles to start shivering and contracting, generating energy. When we generate energy, we generate heat. All these systems might be involved in homeostatic regulation depending on what's happened. Now, as I said, when you come to do your case-based learning assessment, this is a fundamental component understanding what's happening within the system and more specifically what's happening within different components of that system. So you might only talk about the heart rather than the whole cardiovascular system. You might only talk about the spleen or the liver rather than the whole digestive system or the whole system that's involved with that disease.