in our previous discussion we elaborated on the differences between equilibrium versus the dynamic steady state where in equilibrium we focus on both the rate and the concentration inside and outside being equal while in the dynamic steady state the rate in matches the rate out but there is a disequilibrium in terms of the chemical concentration of solutes and in order to achieve this there has to be an investment of outside energy into the system and so dynamic steady state was more akin to the balance that we see in the body the homeostasis that we see so in this video we're going to focus on the four main themes in physiology it ties into homeostasis at least the fourth theme does but the first theme has to do with energy usage so this will be a separate module in the beginning of unit one and we're gonna focus on aerobic respiration so how does the cell take molecules like sugars or protein breaks down and releases the energy that is in the chemical bonds in order to generate atp and then that atp in turn allows the cell to do work the second theme in physiology that we'll talk about and this will be specifically in the communication module is how do cells communicate with one another to form cohesive units like tissues or organs so we're going to talk about both chemical signals which are usually protein-based but not always and electrical signals especially in our discussion in neurophysiology lastly we'll talk about signal transduction that is how can we get a signal to cause a change inside the cell knowing full well that the plasma membrane is selectively permeable and the vast majority of these signals cannot cross the phospholipid bilayer in understanding communication we also need to take into consideration that you are composed of fluids within fluids within fluids so you have an aqueous environment inside the cell and we call that the intracellular fluid and this is also coincidentally called the cytosol now cytoplasm is a similar term and we're not going to make the distinction between cytosol and cytoplasm in this class but there is actually a distinction then we have the fluid that is outside the cell or the extracellular fluid the fluid that is adjacent to the cells this is co excuse me this is specifically known as the interstitial fluid and then the fluid that allows blood cells to properly move in blood vessels and it is sort of separated by the blood vessel walls from the interstitial fluid this is known as plasma when we look at the composition of these various fluids the extracellular fluids are virtually identical the only distinguishing feature between the plasma and the interstitial fluid everything being identical the only thing that is not is that the plasma has these proteins which we call plasma proteins that are secreted into the plasma through the liver the interstitial fluid does not have any significant amount of protein conversely the cytosol has the most protein because that's where proteins are made but when you look at the composition of electrolytes there's a huge difference so you look at potassium for example potassium levels are elevated inside the cell but they are very low inside the reciprocal is true with sodium and chloride sodium is elevated outside it is lower inside and so the rate in and out is the same but it's not at equilibrium because although the rate is the same the chemical concentration is going to be different and so that's because the cell inputs energy into the system and with these gradients that you have gradients are really just a form of energy which ties into our first theme of energy use so even though it requires energy to maintain a disequilibrium the gradient itself is a type of energy the third theme in physiology that we're going to cover is structure and how the structure relates to function so this was a discussion that we had in our first video where we compared anatomy the structure versus physiology the function and so this theme focuses on everything from proteins the structure that a protein has dictates its function you change the structure you change the function it applies to cells it applies to tissues okay we also examine mechanical properties of cells so for example the term compliance is the ability of cells to stretch so when you look at the cardiac muscle cells they have to stretch to accommodate blood volume to be engorged with blood and then they in turn in response to that stretching will contract okay the more you stretch the more you contract so compliance is your ability to stretch while elastance is the ability to go back to an unstretched state after being stretched so elastance is the same thing as recoil so keep in mind that these two terms are not exactly the same the ability to stretch is compliant the ability to spring back after being stretched that is elastance okay so we'll also focus on the interactions between various molecules so let's say a signal molecule with its receptor so there's a lot of tie in right structure function correlates to communication communication can correlate to energy use energy use correlates to communication and the last main theme in physiology circling back to this idea of homeostasis is what are the control systems that allow us to establish homeostasis anytime there is a failure in establishing homeostasis this leads to some diseased state so if you think about your body temperature right for your body temperature you have some sort of input signal and usually this is going to be some sort of sensory information that sensory information has to be processed and it is usually processed by the central nervous system so the central nervous system consists of the brain and the spinal cord so one of these two regions are going to process this information and decide what an outcome should happen or what response should be triggered so there's an output signal and usually this is a motor signal that will distribute the signal to maybe muscles maybe change uh motion of some sort so when we look at these systems there are these feedback systems that help to maintain balance so think about body temperature if you're hot you sense that you're hot you process that information hey i'm hot and then there's an output signal to your sweat glands to release sweat and that evaporation of the sweat cools you down now you cool down to the point where you no longer register that you're hot okay now if the reverse happens let's say you're cold you sense this information your controller then sends an output that signals the muscles to begin to rhythmically contract so you shiver to generate that heat through friction you only do that until your body temperature rises okay once your body temperature rises past a specific set point you sort of shut off that feedback loop and so this is known as a negative feedback loop where you have a stimulus it generates a response and the response decreases the intensity of the stimulus so that you are around a set point this mechanism is how homeostasis occurs in the human body positive feedback on the other hand you have a stimulus and the response actually increases the intensity of the stimulus so there are two main examples of positive feedback and this is never homeostatic the first is clot formation and the second is childbirth so if you have some sort of injury you want to as quickly repair the damage as possible or at least mitigate bleeding out and so you want to have more and more clot proteins clotting factors involved to seal off so that you don't bleed out so once again if we look at these examples with a positive feedback you get damage and you keep on recruiting platelets and clotting factors and you keep on doing that until the job is done until the temporary patch is in place so that you're not bleeding out with negative feedback you're always oscillating around a set point so as we used the example earlier it's hot you sweat to cool down once you're cold you detect that you shiver to raise your body temperature up and you're constantly oscillating around that and whether we're talking about ph or salt balance or water balance this is the primary mechanism that is going to allow you to establish homeostasis