SLE132 Biology Form And Function Online Lecture PDF

We're going to talk about Osmo regulation. For a little bit today. So when talking about that, it's important to recall the. The these A aspects of diffusion and osmosis. So hopefully, you've all heard of this, and you're very familiar with it. Diffusion is simply the passive movement of molecule...

We're going to talk about Osmo regulation. For a little bit today. So when talking about that, it's important to recall the. The these A aspects of diffusion and osmosis. So hopefully, you've all heard of this, and you're very familiar with it. Diffusion is simply the passive movement of molecules or particles from an area of high concentration to a place of lower concentration, resulting in the equalization of concentration. So in this example, here we have a plasma membrane that. This particular molecule. Can diffuse through freely. So if you, if you increase the concentration of this molecule on one side of the. Lipid membrane. Through time it will make its way through into the side of plasm, so into the inside the cell, and over time you'll end up with an even sole concentration on both sides of the membrane. So pretty, pretty straightforward, the solutes, 1, 2 equilibrate as long as they're allowed to get through that barrier. The example on the right here. So osmosis is just a particular type of diffusion. And osmosis is the movement of solvent molecules. So this is usually water in most of what we talk about in biology. From an area of lower solute concentration to a place of higher concentration through a semi permeable. So if you look at this example, here on the left hand side, we have a situation here where we have. A high, so the water is represented by the orangey color in the background. Here, remember, water is molecules as well. H. 2 o. So water is represented here in orange, and then there's a low concentration of some ion represented in the purple dots here. If this is a semi permeable membrane, so it allows water molecules to get through. But it does not allow these ion molecules, these ion atoms to get through. Then you'll end up with this situation. The water will make its way through. To try and even up the the balance of the solvent and the solute. So this membrane is permeable to water, but not to the to the solute. Then water will move through this way, and you'll end up with this situation here, where the concentration is the same on either side, but the vault. Obviously the volume is higher on this side, because water has made its way over there to even up the the sole concentration. So hopefully that makes sense. So now Osmo, regulation Firstly, Osma regulation in animals that live in water. Again, we have conformers and regulators, just like we were talking about with temperature. So we have. We had thermoers, and we had thermo regulators. Well, we have the same thing with Osmo regulations. So the regulation of our water and ions in our bodies. So Osmoconers A lot of marine invertebrates. So Osmoconers. So that means if the If the Osmallity. So just to recap whatsmality is. This is the number of particles. Per leader of solution. And it's it's usually expressed as Millies. So this is kind of as an example. It would be the amount of salt in water. So osmores. They don't regulate their internality, they just let it drift with whatever's going on outside the body. So that's. That's kind of pretty basic animals invertebrates. Then you get Osmo regulators. And so they. To enable their cells to function optimally. They want to keep the Osmality in the body within certain type bounds, so they don't want the internal body, fluctuating on what water they might be. Transiting through. So there they regulate their Osmality. Inside the body. And here the example is marine fish, but it's all fish. So freshwater fish and marine. They are all osmo regulators. So this is an example here of Osma regulation in Freshwater, up the top. And also regulation in salt water down the bottom. So obviously salt water has a lot of. Solutes in it a lot of salt, whereas freshwater doesn't have much at all. So for the freshwater example at the top here. We have movement of water in blue. And movement of ions represented. So in fresh water. You're going to have a lot of water wanting to move into the body because. The fish is trying to maintain a higher salute. Concentration in the body, which means lower concentration. That's where our cells work optimally. So water is gonna be coming in, and ions are gonna be leaving to try and equilibrate with the fresh water around it. So fresh what fresh water, fish. Do to counter this if they drink very little water. Because water is always trying to make its way in through the gills and through other parts of the body. They actively take up ions. And they excrete lots of water. So really dilute urine. And they excrete small amounts of ions to try and retain them within the body. And this is all done at the level of well, a lot of it's done at the level of the kidney. So, and we'll be talking about how they do that, how the kidney functions to. Keep a hold of ions and get rid of water, or vice versa. A fish in seawater has the opposite problem. So the water. The water is gonna want to be leaving the body to try and get into equilibrium because there are more solutes outside. And then ions are gonna be pushing their way in because the fish is trying to maintain a lower ion concentration in the body than what sea water is. So if you think about it, fresh water levels are right down here. Salt water ion levels are right up here. Fish, and us ourselves prefer something that's kind of in the Middle East, a little bit low of the middle, so fresh order and salt water, both of them in both of those, the bodies requiring to either push. Keep pushing ions out or bringing more in, because they want to be in this middle. In this, roughly, the middle. So I sold waterfish. I drink a lot of water, so a lot of it goes through the digestive system. And. Like create really concentrated urine. So urine has a lot of ions in it. And they try and retain a lot of the water because it's it's wants to move its way out all the time. So. We're gonna go through some of the. Some of the processes within the body that enables to maintain. Maintain kind of homeostasis in terms of their osmotic. Environment. That was freshwater animals. Where there's plenty of water around. Obvious. I mean, that was water living animals where there's plenty of water around. Obviously, because they're living in it. Land animals have a different problem. Land animals. It's all about water preservation. We don't necessarily have. Great access to water all the time. So a lot of our physiological systems have adapted and evolved for water preservation. So we lose water through lots of different mechanisms in urination via faeces and throughout respiratory organs. So if you're thinking of it, if you think of a dog panting, that's to lose. Heat. But they use a lot of they a lot of water is evaporated in that heat loss. So lots of water is being used up all the time. And we get our water, obviously from drinking and eating moist food. The water and ion levels are controlled by the kidneys. Especially. And there are also some specialized specialized systems and organs at various different species have. To help with maintaining water and iron balance. So here is an example here. So this is a marine bird. Marine birds have these nasal salt glands that sit up above the eyes here. If you delve into these. Salt glands, and look a bit more closely. You see that there are blood vessels, so arteries and veins. That are coming in close proximity. To these secretary tubules. So we've spoken about. We've spoken about epithelial cells. Like this in the middle here, and we've spoken about Count. So in this example you have. So all of the salt that these sea birds are taking up. They're eating fish all the time. Marine fish and marine fish have a lot of salt in them all the time, so the birds are having to try and get rid of a lot of that salt from their body. So the salt is in the blood. Comes into these. Into these salt plans. And and salt is passed. Across this epithelial, these thin layer of epithelial cells. Into the lumen of this tubules. And that makes its way down to the central duct. And then the central duct is kind of around the nostril area, and then this. High salt concentration, fluid. Runs along the beacon drips off. So this is a way that marine a lot of marine birds can get rid of a lot of the salt out of their system, because they're consuming a lot in their diet. And in addition to. Sold We have a lot of nitrogenous. So all animals have to deal with nitrogenous waste. This mostly comes from protein consumption. So any protein. A waste product from it is. Ammonia, so that this is a pretty simple molecule ammonia. And the it's not used for anything else in the body, so it needs to be excreted. But it's highly toxic. So it needs to be diluted if you're going to try and transport it. And excreta as is. So the only animals that that handle ammonia without converting it. Mostly aquatic animals that have access to a lot of water. So many invertebrates, and also aquatic species, like telios, fish. So as mentioned. Ammonia is highly toxic. It gets 3 up arrows here. That means that it needs a lot of water in order to transport it through our body and through the fisher's body and excret it. But the benefit of this is that it doesn't take much energy. So if you're able to excrete. This basic. But toxic molecule, because you've got lots of water. Then. You don't have to convert the ammonia into anything else first, st so that reduces the energy that's required to get rid of it. You just keep flushing it out with lots and lots of water that is really plentiful. On land. Most animals don't have that luxury of having plentiful water. So us, and other mammals, and a lot of amphibians, and some marine species in particular. So sharks and rays. They convert ammonia to urea. That conversion is done in the liver. And it takes some energy to convert ammonia into a more complex molecule. So. More energy to do it. But the benefit is, it's less toxic. It doesn't get as many up arrows as ammonia does. And therefore it doesn't take as much water if you're going to transport it and flush it out of the system because it's not as toxic. Some animals have gone a step further, and they generate this molecule called uric acid. You can see here that this molecule is really quite complex. So it does take more energy to put to piece this molecule together. So here energy gets 3 up arrows. But the benefit is that it's really has quite low toxicity. Uric acid, and therefore doesn't need much water at all to flush it out of the system. So birds is an obvious one here. So if you've ever had the Unfortunate or fortune to get on by a bird. You'll see that it's a white. Heisty substance. That's uric acid, so it can be rather than liquid, because. It has really low toxicity. So it doesn't need a lot of water to be able to transfer transport through the body, because it's not very toxic at all. So there are different molecules that are used to get rid of nitrogenous. A lot of this is done at the kidney, and so this is a. A video here that does a good job of explaining of the kidney. Better than I can do. So I will press play here, and you can have that. Process Explained. Of course. Teenagers. If only they could keep their bedroom a little cleaner. Slumberland essentials, mattresses offer a protection. Hi, it's Paul Anderson. And in this video I'm going to go through the basics of the urinary system. The major organs in the urinary system are going to be the kidneys, and their major role is in waste excretion. They're cleaning our blood and solid waste from the blood is eventually gonna leave our body as urine. Now, in addition to doing that, they also regulate blood volume, blood pressure, blood. Ph, they regulate important electrolytes and metabolites in our body. The kidneys are incredibly important. Without them you'll die unless you're hooked up to a kidney dialysis machine. But that's gonna require going 3 times a a week, 4 to 5 HA day hooked up to a machine just to clean your blood. Now, in addition to the kidneys, we also have other parts of the urinary system, including the ureter, the bladder, and the urethra. In males and females the urinary system is essentially identical except for the length of the urethra itself. Now, what's the role of the kidney? The role is to produce urine. From there it's transported to the bladder through the uid, and then from there it's stored, and eventually. That's how we lose this waste. But you might be thinking to yourself, what is urine? Well, urine is mostly water. So 90 to 95% of urine is going to be water. But the rest of it is going to be solid waste, both inorganic and organic waste, like urea, uric acid and inorganics like toxins and certain salts as well. If we look at the structure of the kidney on the outside, we're gonna have the renal cortex. Renal simply means kidney. So we've got the outer layer of the kidney, and then on the inside we have the renal medulla, and then on the center we have the renal power. Pelvis is gonna be a hollow opening. And this is where all the nephrons are gonna enter into. They're gonna they're gonna get rid of their urine. And that's eventually gonna go through the uiter. Now, if we look inside the kidney itself, we find the whole thing is just filled with blood vessels. Around. 20% of cardiac output is going through the kidneys. So that's a massive amount of blood that's going through the kidneys. How does it do that? Well, it comes in through the renal artery out through the renal vein. But there's a huge amount of surface area inside the kidneys itself. From there we go into smaller arteries and smaller arteries, then arterials and capillaries, and then eventually the blood is going to come out. But the important waste excretion is going to take place. As we get to those center blood vessels. So let's zoom into that, and let's zoom into the functional unit of the kidney, which is going to be the nephron. So if we look at where these blood vessels are found, into the nephron, through the afferent arterial, and then it goes into the glomerulus or the glomerular capillaries. At this point you essentially have a dead end. The blood is flowing in, and it comes to a dead end. That dead end is inside something called the bowman. Capsule. At this point. We're gonna have filtration. A lot of that blood plasma is squirting out of the capillary, and it's eventually going to move into the urinary system. From there the blood goes through the afferent arterial. And so at this point. We've got filtration taking place is where we're actually filtering the blood. Now, if you look at the blood vessels, they continue to go and wrap around the rest of the nephrom, the peritubular capillaries, before they're eventually going to lead. What's going on. All of this surface area is secretion and reabsorption secretion is when we're taking material that's in the blood that wasn't filtered out. But we're getting rid of that. And also there's some material in the filtrate glucose. Water, for example, that we want to reabsorb. So we're going to take that back into the circulatory system. So if we remove the circulatory system now, we can kind of see what that nephron looks like. 1st part's going to be the renal core puzzle right here, if we look at what's taking place there, that's where that filtration occurs. So at this point we call this a filtrate. From there. It's going into a number of different renal tubules. The 1st one is going to be the proximal convoluted tubule means close to the renal core puzzle, convoluted mean. It's just folded over and over in many different dimensions. We're increasing the surface area. There. What's going on at this place. Is that we're reabsorbing material. We're reabsorbing solutes water. We're taking that back into our circulatory system. From there the renal tubules are gonna flow down into what's called the loop of Henley. We have a descending limb of the loop of Henley, and during that we're really absorbing a lot of the water. And then, as we have the ascending limb of the loop of Henley, we're reabsorbing a lot of that sodium and chloride. A lot of that salt are coming back into our body. If we look at where we are inside the kidney itself. As we go down into the loop of Henley, we've entered into that regional medulla, and if you think about what's going on as we move farther and farther down we've set up a counter current exchange. We're doing is we're increasing the salt levels as we move farther and farther down into that renal medulla that makes it easier for us to take back more of that water in the descending limit of the loop of Henley, and also in the collecting duck. From there we're moving into the distal convoluted tubule and then into the collecting duck. If you think about where this collecting duct is going, you can see that we're getting a bunch of other nephrons that are connected to it, as well. From the here. It's eventually going into that center of the kidney, the renal pelvis. And eventually it's gonna leave as urine. Now, what's going along in that distal convoluted tubule and the collecting duct. Is, we have variable secretion and reabsorption of solutes and water. So, in other words, sometimes we're getting rid of waste, and sometimes we're taking that back into the into the body. Now, a lot of this is under hormone control. So, for example, a really important hormone is vasopressin or Adh, an a diuretic hormone. And what that's gonna do is it's going to affect the distal convoluted tubule and the collecting duct itself. And what it does is it essentially. Shuts down the flow of water outside our body, and so we can get a signal. If we sense how much, how much water there is in our blood, we can get a signal. That means we have to hold on to that. Or we can have a signal that says we want to release that water, and it's eventually as urine. If we look at where it goes from here. All of that waste that comes out of the nephron is emptying out eventually into the pelvis, into the urine, and it's stored in the bladder itself. From there we can eventually conduct that to the environment. And so that's how the urinary system works. It's really simple. It's also really really important, and I hope that was helpful. Okay, hopefully, that was helpful. This diagram here just goes through a little bit more of what was just in that video. So. So essentially. The field comes in up here at the bowman's capsule. You have changes in Osmality that are occurring as water is taken out in the descending loop. In the test. Descending part of the loop of Henley. You have souls and other solutes, being. Being taken out of the of the group of Henley on the ascending loop. There's. So there's passive transport is represented in blue. Active transport is represented in red. Remember, active transport takes energy for it to happen. So atp is required, whereas passive. So essentially, the end result is that. The the kidney is an excellent organ for helping us pull water back out when we need it. And take salts out when we, when we don't need them. And depending on how much access we have to water, the urine will be more or less concentrated. Depending on that. And this is all done through current kind of exchange and solute and water moving down diffusion, concentration gradients. And through through osmosis as well. So I won't go into any more detail on that, because hopefully, the video did a pretty good job of doing it. And we've got a bit more to get through. But any more questions on that, just pop it on the unit site, on the discussion board. And we can get around to that. Okay. So the video mentioned that the kidney, for example, can be controlled through the anti hormone. So that was just an example of one of these. Of. In that case a hormone that can be used to regulate the functioning of the kidney. So there's lots of. This intercellular communication that's going on throughout all of our bodies all the time. So here are some examples via secreted molecules. So the communication can happen via. Molecular communication. So like secreted molecules. And it can also happen via electrical communication through our nerves. So we're gonna touch on both of those. But here's some examples of. Of communication via secreted. To begin with. So up the top. Here on the left, we have an example of what's called endocrine. So this is where a. A secretary, cell. So here is triggered for some reason. To release the signalling. These go into the bloodstrip. So 1st I go into the into extracellular space and then into the bloodstream, and then they're transported via the bloodstream to all parts of the body. And so there's lots and lots of cells that will be exposed to these, to these molecules, these Whatever it might be, a hormone, it might be in it any kind of signaling, but only the cells that have the right receptors on their surface are gonna respond to it. You don't want every cell responding to every signal all the time. So in this example, here, you see, these cells appear, they don't have the right receptor on the surface, so they're not being stimulated by the mole. That's coming through only the cells that have the right receptor on them. Being triggered by the molecule, and then that will elicit some response. Power. Crime signalling is a similar kind of thing, but it happens locally. So the the secreted molecules don't go into the bloodstream, and they're not distributed all throughout the body. It happens really locally. So the molecules are secreted by these secretory cells, and there's local attachments to cells that have the right receptors. And then they respond in whatever way is appropriate. Auto crime signalling is essentially. Cells talking to themselves. So these are where cells secrete molecules, and they also have. Receptors on the surface that bind those molecules, and that stimulates the cell to do more of what it was doing. You can also have arrangements like this where you have, which is kind of similar to the power signaling where you have a signaling cell, right adjacent target cell. And you have what's called gap junctions. So these are connections. Between the cells that can be opened and closed. And so these signalling molecules can be passed directly through each of the cell. In each of the cell membranes from the signaling cells, the target cell. Additionally, you can have neurons involved in this. So here are some examples where. Neurons are involved with. So you have. Electrical and molecular signalling. So in this example, synaptic. You have a neuron. That's. Connect that's almost connected to. To a cell, a target cell. At the at this point down here. Called the sign Ups. There is a little gap here. But the neuron triggers release of these molecules, and they just bridge this very small. Gap across the sign Apps, and they bind to receptors. And then that initiates a response. And then another example is neuroendocrine. So rather than the neuron being in almost direct contact with the cell, the the neuron. Releases signalling molecules into the bloodstream, and then they are distributed throughout the body, and when they find cells that have the right receptors, those cells. Responses initiated. So. Lots of different methods of communicating throughout the body for all of our different functions to occur. So all of these. Signalling molecules. They're kind of messaging molecules. And we refer to them as hormones when they're produced and transported through our body. There are 3 main groupings that we are interested in here, so there are Peptides. There are steroids. And there are derivatives of amino acids, usually tyrosine. So to step through these. And some of the main differences. So Peptides. They are They're they need to be formed by other by larger proteins. So they're cleaved. They're chopped down to produce the peptide. As a which we call a pro hormone. And they are stored in vesicles. So I remember vesicles inside the. Inside the cell. So in the cytoplasm there's vesicles in there. So they're stored in those vesicles. These peptide hormones there. Most of them are polar and water soluble, so they're hydrophilic. So they can travel freely in the blood because they dissolve in water, and the blood is largely water. They can't, because they're hydrophilic. They can't cross cell membranes by themselves, because, remember, cell membranes a lipid bilayer. And hydrophilic molecules can't get through that hydrophobic. Bilayer in the middle, so they need. They attach to receptors on the outside of cells, and then that triggers something else to happen because they can't move through the cell membranes themselves. These are often fast on set, because they're already stored. So it's fast onset, so things can happen quite quickly. With these Peptide. Hormones. And here are some examples of peptide hormones down the bottom. Here. Steroid hormones are. produced from cholesterol. These are released immediately, so they're produced and released. They're generally nonpolar. So they're hydrophobic. So they do need carrier proteins to travel through the bloodstream, so they don't dissolve well in blood, so they need to bind to another carrier protein, which helps them to dissolve in the blood and be transported through the body. But because they. Can, because they're hydrophobic. They can move through cell membranes once they get to the target cells so they can make their way through the cell membrane, and they can bind 2 things with inside the cell, so they don't have to bind to receptors on the outside of the cell. They can move their way through the cell membrane and bind to things inside, and that can trigger gene expression. They can. They can travel all the way into the nucleus and trigger something in there like gene expression. And examples of these are cortisol, testosterone. These amino acid derivatives are a bit of a mix, more of a mixed bag. They? They're usually stored before release. But the storage mechanism can vary some polar. Some aren't. So depending on whether they're polar and hydrophilic or not. Sometimes I have to be bound to a protein to transport through the blood, and sometimes. They don't have to be. Sometimes they dissolve in blood, sometimes they can make their way across cell membranes, sometimes they can't, etc. So they're a little bit of a more of a mixed bag. And there are some examples down the bottom here of. Different amino acid. Derived hormones. So just to give you a picture of a couple of these. So here's a water soluble hydrophilic hormone. So we'll go from a here over to this panel here in a second. So here you can see that these water soluble hormones are secreted by the cell. They make their way into the bloodstream. They don't need any carrier proteins, because they can dissolve easily in the blood. But they make their way to the target. And they bind to some receptor, some protein receptor on the target cell. They can't get through the cell membrane themselves. The binding to this targets receptor causes a cascade of events which we call a signal transduction pathway. Different molecules are formed. Lots of different things can happen. You can have a response in the cytoplasm of the cell, or you might have something that continues on into the nucleus. And that's where the DNA is, remember. And so that's where you can get gene regulation occurring as soon as you start to modify as soon as you start to transcribe messenger, Rna. And then take that outside the nucleus, and it can be produced into a new protein to do something that the cell needs it to do. Now the lipid, soluble hormone, just to visualize this. It's secreted by cells. It can't dissolve in the blood, so it needs to be bound to transport. Protein, and then it makes its way to the cell, to the target cell. Because it's lipid, soluble, and hydrophobic. It can make its way across the cell membrane, and it can make its way all the way into the nucleus. If necessary, it combines to various receptors. It can stimulate. Gene expression, for example. So it might say, we need to produce more. More of some kind of protein. And then, so that messenger Rna. Is produced. Goes into the cytoplasm, where the Soc reticulum. Oh, the endoplasmic reticulum! Sorry. Produces the new protein. Alright, so Where are all of these? Hormones produced in the human body. They're produced in various different locations. So here is. He. Here is a diagram of the what we call the endocrine tissues and the organs. So these are the. Tissues and organs that are involved in the production of. Hormones. We've spoken about melatonin. So this is the one. This is the hormone that helps to regulate our sleep patterns our Circadian rhythm. So this is produced in the pineal gland. Up here! In the in the head, in the brain. We have a hypothalamus which is also up there, which hopefully lots of you have heard about. So these this. This is intricately linked with the pituitary gland. And the pituitary gland produces things like growth, hormone. Which is obviously involved in tissue growth. Prolactin which is involved in lactation. And oxytocin, which is also involved in secretion of milk in females. The thyroid gland here, so thyroid gland produces a couple of different hormones, thyroxin and triadine which we refer to as T. 4 and t. 3. For simplicity, the para thyroid glands they produce para, thyroid, hormone. Which is involved in calcium regulation in the body. So you can see the thyroid is here. In our neck region. That's why you can get swelling there sometimes. For people have might have thyroid issues. So I the adreno glands closely associated with the kidneys. They produce cortisol. Epinephrine, North epinephrine. These are involved in the fight or flight response. So it's adrenaline. The pancreas in another hormone producing organ, it produces insulin and glucagon. These are, you would have heard of these in diabetes so insulin and glue, insulin. Lowers like glucose levels and glucagonates an increase in like glucose levels. In females that have a uterus and ovaries. This is where oestrogen produced and in males have testes. This is where androgens, like testosterone produced, and then the thymus. Up here as well. Umasson's are involved in a lot of immune triggering immune responses. So. Quite a few different endocrine tissues and organs in our bodies that are all producing different things. To help our bodies function correctly. We've spoken about positive and negative feedback loops. So just as a further example here of how these kind of positive and negative feedback loops regulate the secretion of hormones. So we have a negative feedback oops. Sorry. Have a negative feedback loop on the left hand side. Here. So this is an example of. Of the secretion of the secret in hormone. So the example is when the food has, when food that we have eaten goes through the stomach. That's very acidic in the stomach, and then the food passes into the duodenum, which is the start of the small intestine. It has a low ph, it's quite acidic. And we don't want that. So these endocrine. In the duodenum. They release these. Hi, everybody. It looks like Tim's lost Internet connection. He's still got about 8 to get through, so if he doesn't come back, then I can ask him if he can just do a short recording of those last slides that he was going to explain. But otherwise we will just sit here and wait for to see whether he can get back in or not. Is that okay with everybody? Thanks, Amy. Yeah. Great. Sarah's asked. If there's a lecture next week. Yes, there is. It'll be the final lecture next week. I had another student asking. But student. Students asking questions about assessment tasks. Unfortunately, I'm not involved. With any of the assessment in this unit. So I'm not up to speed with what is going on. It's a really good idea that you post those on the discussion board. And then one of the campus coordinators can answer that question. Tim said something at the beginning of the lecture about the the feedback, and. Getting on and doing that. I. Didn't catch what he said, but. Did anyone else notice when he said that the peer review opens. Because there was a question about when the Peer Review would be. To, Neil said that it's open now. So the student who asked about that. Okay, so there's a couple of you saying that it's not working. So I will refer that on to the unit chair and to Tim and ninky as well. In fact, I can sort of get an email off to them. Right now, so I don't forget. To do that. Okay, I would. I will send a message directly to the unit chairs. I'll email them and just ask them to get onto that. Hi. Okay, we have Tim back, so I will. I will go away. Sorry. My computer just had a catastrophic. Collapse. Which is not ideal from a timing perspective. So. Just quickly before you head on there's an issue. Students are not able to do their peer reviews. They're only able to do their self assessments. A few of them have tried. So that's something that will need to be chased up afterwards. Thing. Okay, yeah, I can chase that up. Oh dear! Okay, if there are any problems with that coming through, just let me know. Otherwise I will just keep rolling here. Where were we? So. Endocrine cell in the duodenum releases a hormone secretin that makes its way throughout the entire body. The target cells at the pancreatic cells. So they're the ones that have the receptors on them that are specific for this hormone. And they generate a response, and this response is bicarbonate into the bloodstream and takes it to the duodenum. So this bicarbonate helps to buffer ph, so it raises the Ph back up again. So this is a negative. Feedback loop, because a low Ph is causing a response. For there to be a higher ph, so it's a negative feedback loop. Positive feedback loop is where a stimulus generates more of the same stimulus. So Of young on the nipple. Causes. Neural stimulation, this triggers a response in the hypothalamus. So there's sensory. Sensory stimulation at the nipple which translates, transfers the signal to the hypothalamus. Up here. You get oxytocin release. And mature, and with the hyperalamus linking in with the pituitary gland. The oxytocin goes into the blood vessels, circulates through the body, and the target cells are the memory glands. A smooth muscle in the mammary glands. So this stimulates a smooth muscle to contract even more so to release even more milk. So the the stimulus. Triggers. Even more milk release until the cycling stops, and then that positive feedback will stop and the milk release will ease up. I'm not going to go into this, but that's just an example of how the brain and the And endocrine systems are working together in a moth. This is on the unit site, I believe. This as well. Just another example of how the. The nervous system, and so the hypothalamus. Is, is. Working with. So you've got neuro secretary cells here that are causing the production of neuro hormones. I mean the in the posterior pituitary. And then here's an example of the hypothalamus, a new secretary cell. Triggering release factors. So sometimes a hormone isn't. Stimulated to be. Released immediately. There's a precursor to that. And so that's a releasing factor. So then the releasing factor makes its way somewhere, and then, that triggers the release of the actual hormone that does does more. Again. Sorry I'm not gonna be able to go into this in a huge amount of detail. But other examples of the. Of the nerves and the hormone cascade pathways working together. Is in the release of. Our thyroid various thyroid hormones. So release is triggered in the hypothalamus again, up in the brain. This triggers the pituitary to. This is a thyroid, stimulating hormone, so that's released into the bloodstream. It makes its way to the thyroid, which is where the. Cells are that have the particular receptors for this hormone and that triggers the thyroid to start releasing this T. 3 and T. 4. Their purpose is to is to regulate our metabolic rate. So these these hormones that are produced at the cause our metabolic rate to go up or down. And if we increase our metabolic rate. That's gonna increase heat production. Because we learned that. Any metabolic activity. Is going to is going to generate more heat as well. And then you get this negative feedback loop, where, if the body. Gets too warm, or the metabolic rate is high enough. Then it feeds back and stops the production. Neurons. Neurons and glial cells. So we've learned a little bit about neurons. And you should remember that they often look a lot like this. So they have the dendrites, that kind of. Branch out. Here's the cell membrane, and then there's a nucleus here. They also have these long extension, which is called an axon. And this is where the electrical signal is transported down, and then it connects up with other Other other dendrites, or whatever it might be, to trigger a response down here. These axons are usually covered in a myelin sheath. So this is just a protective barrier around the axons, and it helps with the signal transduction. And there's these oligodendrocytes which. Produce the myelin And also involved in. In protection of the axons, as well. And there are these gaps between the myelin sheets, which are called nodes of Randy. Glial cells are intimately associated with neurons. So here you have the neuron and the axon under here. So this is in the an example. In the central nervous system. Glial cells are all of these other cells that are associated with the the neuron. So these astrocytes. Are involved in providing nutrients to the axon. Microglia cells are involved in helping to defend the axon from anything and these epidimal cells. Produce like cerebral cerebral fluid, so it helps to bathe the axon and protect it as well. And again, you have these myelin sheaths and the oligodendrocytes. Here the peripheral nervous system. He's the neuron in orange here, and so you can barely see it. It's covered in the satellite cells, and they help to protect it. Check to provide nutrients, etc. It's the Shwan cells that produce the myelin sheath. In the peripheral nervous system, and you can see the axon is is running through. Here. Types of neurons. They can be. They can be kind of categorized, based on either their function or their structure. You have sensory neurons. So these are the ones that Are behind our eyes, you know, is under our skin, so you can imagine if we touch something hot. A signal is is. Rapidly transmitted to our brain. So this sensory neuron ends up. Transferring an electrical signal to our brain, our brain and our central nervous system is full of these into neurons, and they transmit information very quickly to one another. They're all very densely packed. And then our brain makes a decision about what the appropriate response is, and it quickly sends a signal to our motor neurons. And these are the ones that. Can make us pull our hand away from something hot. So you know how quickly this happens. Right? If you touch something hot, it's only a millisecond before you recognize a hot and you pull your hand away. So that's how quickly these neurons are firing information up to our brain and back to back to the location where a response is required. They can also have different structures. So you can have ones like this unique polar. Doesn't have any dendrites. These are mostly found in invertebrates, can have bipolar neurons that have axons heading in both directions. Multipolar. So this is where there's lots of dendrites, etc, etc. And finally, I just wanted to touch on. In on membrane potential resting membrane potential. So this is, it's a key point. That cell membranes they have. Inside the cell is a slightly lower charge, so it's a negative charge compared with outside the cell. This is how most sales are. So they have this. They have this slight difference in electrical charge between the inside and outside, and this is driven by That's driven by what we call electrochemical potential energy. So electrochemical means that there. Electrical charge and chemicals that are associated with driving this. Potential energy difference. So the chemical potential is driven by different solutes. Inside and outside. So ions. And because a lot of this. Cause. A lot of the solutes do have a charge associated with them. You end up with this electrical difference as well. And so these things are going on. All the time. And there's twoing and involved. But ultimately, once they're kind of in equilibrium. The balance causes there to be a slightly negative charge inside the cell, compared with outside the cell. An important thing to remember is that there's a high concentration of potassium ions inside the cell. And a higher concentration of sodium ions outside of the cell. And it's this it's this difference in these 2 ions that generate a lot of these electrochemical. Difference. So this is the final side here. Sorry we've gone. We're kind of gone right to time here. But as an example here. So this is inside the cell, in the cytoplasm. You can see there's lots of potassium ions. And outside the soul there's a lot more sodiums. But the net charge is positive outside. And negative inside. And that's due to various different reasons. We have these. Potassium, binding. Proteins that are inside the cell, and they act to bind potassium and neutralize their charge. So that takes some positive charge and neutralizes it. We also have some free. Chloride ions, which have a negative charge associated with them inside the cell. So definitely go and do your reading on the unit site. But the ultimate result here from all these things that are going on is that we end up with a slightly negative charge inside the cell versus outside the cell. And that's what sets our resting what we call a resting membrane potential. And that's critical for.