[Music] the human defense system this video is all about how the body resists disease and fights infection and it's part one of three videos so when we think of the human defense system we think of building immunity and immunity is the body's ability to resist infection and that's a really important definition the agents that want to cause disease and infection are pathogens and they're defined as disease-causing organisms so some bacteria fungi and viruses would be classed as pathogenic and disease-causing the human defense system is made up of the general and the specific defense system the best way to think of the general defense system is the body as a castle surrounded by a moat and these pathogens want to gain entry so your body is going to have certain systems in place to prevent the entry of every pathogen if possible and if they do manage to breach the walls or gain entry it's going to deal with them in the same way so each of them in the same way whereas this specific defense system is a very tailored approach to a specific or particular pathogen and it involves the production of antibodies so for the rest of the video were concerned with the general defense system we know it's not specific it's a similar response regardless of what the pathogen is and most of it is tasked with preventing them entering in the first place but if they do enter the general defense system will use inflammation white blood cells specialized defense proteins all used as part of this general defense system the first part of the general defense system is your skin it's a physical barrier so this barrier prevents the entry of pathogens and it's important that this barrier is not cracked or broken and so sebum is this oil that's secreted in the skin it's made by the sebaceous gland and it lubricates the skin it's one of its functions and this prevents it from drying and cracking so that's an important role of sebum as well but sebum also has chemicals in it that prevent the growth of bacteria and fungi also Nexxus mucus mucus is a sticky substance that traps pathogens and it's produced by mucous membranes mucus membranes are these thin layers of cells that you find in many places of the body lining many of our tracks for example our respiratory system is lined with mucous membranes our digestive tract is blind mucous membranes you encounter them in the reproductive systems male and female so many places you find mucous membranes that produce mucus one of the things to consider as well that mucus contains lysozyme eat this enzyme that breaks down bacterial cell walls also remember that the lining of your Airways as well as being lined with mucus producing cells is also lined with ciliated cells cells that have these hairlike projections these cilia and the cilia will waft mucus trapped pathogens upwards to your pharynx to your throat where they'll be swallowed the mucus will be swallowed and then the pathogens will be dealt with by the hydrochloric acid in your stomach not only is lysis Army found in mucus it's also found in tears sweat and saliva and remember lysosome II is an enzyme that breaks down bacterial cell walls the next part is the hydrochloric acid in the stomach it kills many microorganisms another part of the general defense system is the role played by beneficial bacteria so there's a mutualism they get something and we get something we both benefit for example there are bacteria in the vagina that produce lactic acid this creates a really acidic environment that pathogenic organisms don't like and also there are those bacteria that live in the large intestine and their presence suppresses the growth of other pathogenic bacteria so that was the first part of the general defense system we've gone through all of the barriers all of the systems in place to prevent the entry of pathogens the skin the sebum lysozyme e mucous membranes and cilia stomach acid and the presence of beneficial bacteria so now we have to discuss what happens if barriers are breached so if the pathogens or toxins entered the blood or the tissues the general defense system relies greatly on white blood cells in particular the monocytes we remember the as being the munchers because their phagocytes phagocytes and gulf and destroy other cells for example bacterial cells are parts of other cells and when these phagocytes are particularly large their macrophages macrophages resided the tissues they can Patrol as well some of them can move around looking for invaders and you would find high numbers of them in the lymphatic tissues for example in your spleen and your tonsils so this is phagocytosis in the picture here you see this big blue macrophage surrounding bacteria so it's going to engulf them and then secretes enzymes onto them to destroy the bacterial cells so we now know that white blood cells in particular monocytes which are phagocytes that means they can do phagocytosis these are crucial to the general defense system but we're particularly concerned with these large Faygo sites these macrophages and we just remember them because we say big munchers inflammation is a very important part of the general defense system it's generally signified by areas becoming swollen red hot and painful if you have all over inflammation its fever why does the area become swollen red and hot well part of it is down to ventilation the arterioles in that area widening and this brings more blood to the area and in particular more white blood cells and the white blood cells that you're particularly interested in are the macrophages next it's the complement system just know its name it's a system of proteins and when activated that results in many different actions for example some of these proteins will clump together and burst bacterial cells others are involved in attracting macrophages cells that are infected by viruses release this protein interferon and interferon then travels to uninfected cells warning them they produce chemicals and these chemicals prevent viral replication so interferon interferes with viral replication so let's just sum up everything this slide summarizes the first line of defense the first part of the general defense system is a barrier system so you've got the skin the sebum the mucus the cilia the hydrochloric acid the lysis I me the enzyme that breaks down bacterial cell walls are not forgetting those bacteria that produce lactic acid and those good bacteria in your large intestine this is a summary of the second line of defense the second part of the general defense system so it's firstly all to do with those white blood cells those monocytes which are phagocytes their munchers and were particularly interested in macrophages and they will do phagocytosis then there's the inflammation basically hot sore and swollen all to do with extra blood going to the area bringing those white blood cells then we've got viral infected cells releasing interferon which signals to non infected cells to get ready to prepare and then we have the complement system that system of proteins that destroys bacteria and also marks up other pathogens for destruction by macrophages so at this stage make sure you can define immunity define pathogen that you can give the outline of what the general defense system is so this is really quick you can do this on one a4 page so basically summarize the first line of defense and summarize the second line of defense a bit like I did at the end of the presentation and know all about monocytes and what phagocytosis is the best of luck with all of your revision the key to doing well is past papers practicing lots of exam questions and writing your own notes the best of look