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hello and welcome to met simplified the immune system is the basic defense system of the body that protects us from harmful pathogens and diseases the immune system consists of various types of cells and different proteins that kill the harmful invading microorganisms and protects our body from disease in this video we will discuss about the human immune system what is a basic structure of the human immune system and how it functions then we will also look
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at some of the factors which affect your immune system and the differences between the innate and acquired immunity you can get the lecture handouts from this video and all our other previous videos by clicking the join button below you can also join our community at patreon.com this will also unlock some of the cool features like behind the scenes of these videos exclusive content early notifications and much more so let's begin with the immune system the
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overall function of the immune system is to prevent or limit infection when the immune system first recognizes invasion by pathogens it responds to address the problem if an immune response cannot be activated when there is sufficient need problems arise like infections and other diseases on the other hand when an immune response is activated without a real threat or is not turned off once the danger passes different problems arise such as allergic reactions and
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autoimmune diseases let's look at the basic structure of the immune system the immune system essentially consists of three layers of defense that protects our body from various types of attacks from microorganisms and even nonliving things like toxins metals etc each layer consists of different mechanisms of immunity and when one layer is breached or invaded the mechanisms of the layer below it come into action until the attack is successfully controlled the first and basic layer of human immune
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system is the barrier immunity below which is the innate immunity and finally we have the adaptive immunity or the acquired immunity let's decode these terms one by one and understand about the basic structure of the human immune system so the first layer defense in human immune system is the barrier immunity and the most important part of para immunity is of course the skin skin is considered as the largest organ of human body with an average surface area of one point seven three meter
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square in simple terms physical barriers prevent pathogens such as bacteria and viruses from entering the organism the skin not only provides a physical barrier that prevents any pathogens from entering your body but it also provides protection by means of chemical and biological barriers skin cells produce and secrete important antimicrobial proteins that kill the invading microorganisms the skin also contains immune cells that help to stop the microbes from invading our body
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shedding of skin epithelium also known as desquamation helps to remove bacteria and other infectious agents that may have adhered to the skin surface similar types of barrier immunity is also provided by many other surfaces present inside our body including the surface lining of our respiratory system the gastrointestinal system the genital urinary system and the surface lining of our nose and pharynx all these types of surfaces provide a physical barrier that
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prevents the attack from pathogens and they also provide various types of chemical anti microbials which try to stop the invading pathogens at a very early stage for example the surface lining of our respiratory system has these small hairlike projections that are known as respiratory cilia a special property of the Celia is that they have a particular direction of movement by virtue of which they remove any foreign material that may have entered our lungs while breathing this provides a strong
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physical barrier that prevents buildup of microorganisms and other foreign material in our lungs defects in the function of Celia are very common in smokers which leads to higher incidence of chest infections the respiratory surface also provides various types of antimicrobial chemicals like surfactants mucus and defensins which help to stop the invading microorganisms our stomach releases strong acids with a very low pH that kills most of the microorganisms
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that we accidentally ingest while eating the tears in our eyes also contains special antimicrobial proteins like lysozyme that kill many pathogens the constant flushing of Tears also prevents any buildup of foreign material in our eyes which is also an example of barrier immunity so this was the first line of defense of our immune system and this was known as the barrier immunity now what happens when a microorganisms say a bacteria or a virus evades our barrier immunity and
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is successful in entering our body in that case the microorganism is met by our next layer of immune system that is known as the innate immunity now to understand about the innate immunity you have to first understand about the meaning of the word innate the word innate is made up of two words in and Nate in means inside and Nate means born so innate is something that you are born with now why this is known as innate immunity this is because the innate immunity is present in our body from the
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time we were born meaning it is already present when we take birth this is in comparison to a third layer of immunity that is adaptive immunity that develops after we were born the innate immune system is an older evolutionary defense strategy as compared to the adaptive immunity that developed later the innate immunity is nonspecific meaning it does not have special mechanism of action for different types of pathogens we will discuss the differences between the
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innate and the adaptive immunity later in this video now per se the barrier immunity is also a part of the innate immunity since it is also presents in Spurs but for understanding this topic it is better to divide these types of immunity into three categories now let's talk about the innate immune system in detail the defense system of the innate immunity consists of the various types of cells and the complement system let's first talk about the various types of cells of
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the innate immune system and look at their basic functions the different types of cells in our innate immune system are neutrophils mast cells basophils dendritic cells eosinophils monocytes macrophages and NK cells or the natural killer cells all these cells are type of white blood cells or WBC's also known as leukocytes leuco meaning white and sites meaning cell the neutrophils are the most abundant immune cells making up about 60 to 70 percent of the total population of
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immune cells they form an essential part of the innate immune system one word you will hear a lot in this immune system is the word fake-o cytosis Fei Jie means eating and cytosis means by a cell so Faygo cytosis in simple terms is cell eating neutrophils are a type of phagocytes that detect and eat the pathogen within the cell within the cell the neutrophils release various enzymes that kill and digest the pathogen they are normally found in the bloodstream
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and are short-lived and highly mobile as they can enter paths of tissue where other cells or molecules cannot neutrophils are usually the first cells to respond to any infection or inflammation this is due to their heightened ability to sense what's going around the body by detecting special chemical signals released by pathogens and by our own body cells that tell them what's going around in the body if you look at a neutrophil it has some characteristic features the first thing
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you would notice is the multi lobe nucleus of the cell this is a normal appearance of the nucleus and this is a reason why neutrophils are also known as polymorphonuclear leukocytes polymorphonuclear meaning the nucleus of the cell has multiple morphologies meaning some neutrophils have two lobes in their nucleus some three or four or five so there are multiple morphologies the nucleus of these neutrophils can have so they are also known as the polymorphonuclear leukocytes another
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characteristic feature you would notice in the structure of these cells is the presence of large number of channels in the cytoplasm on an average about 200 to 250 granules are present in each neutrophil and these granules contain many different types of enzymes chemicals and cytokines that have numerous functions in our immune system the neutrophils release enzymes like milo peroxidase defensins serine proteases and various cytokines that have numerous functions in our immune
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system they're also released several other chemicals like alkaline phosphatase NADPH oxidase like zoos I'm that help in eliminating these pathogens like I told you they are phagocytic cells that detect and eat a pathogens like bacteria upon ingesting the bacteria the bacteria is contained in this bubble like structure known as the fake ozone this phagosome gets fused with lysosome the granule of the cell which contains the lysosome in them which is a type of enzyme the
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combination leads to formation of a Faygo lysosome very cellular enzymes kill the bacteria and digest it the next type of vibra cells we have are known as the EU NFL's USANA Phil's also have a similar-looking nucleus two neutrophils but it usually has only two lobes hence named as a goggle shaped nucleus they also contain numerous cellular granules that contain different types of chemicals and enzymes in normal individuals you know Phil's make up about one to three percent of
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the white blood cells and are responsible for combating multicellular parasites and certain bacterial infections there are also a sauna fills that play a vital role in fighting infections when unchecked you know Phil's are responsible for tissue damage and inflammation in many diseases including asthma another type of WBC of the innate immune system is the base of film basophils are the least common of the w pcs representing about 0.5 to 1% of the circulating white blood cells
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basophils have a very important role in fighting the parasitic infections of the body in addition to fighting parasitic infections basophils play our role in preventing blood clotting as basophils contain heparin they are also implicated in various allergic reactions
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marcelles are a type of immune cells that reside in the connective tissue and in the mucous membranes like the lining of our respiratory and gastrointestinal system mast cells are associated with wound healing and defense against pathogens but are often associated with allergy and anaphylaxis which has serious allergic reactions that lead cause death marcelles also have numerous granules in them that contained abundant quantities of histamine and heparin histamine
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dilates blood vessels which produces the characteristic signs of inflammation and recruits neutrophils and macrophages they also help to link the innate and adaptive immunity to fight against pathogens the next two important cells that we have in the innate immune system are the monocytes and the macrophages macrophages from the Greek word meaning large eaters are large phagocytic leukocytes which are able to move outside of the vascular system by migrating across the walls of blood
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vessels and entering the areas between the cells in pursuit of invading pathogens similar types of cells when present circulating in the blood are known as the monocytes we call neutrophils eosinophils and basophils as polymorphonuclear cells as a name indicated their nucleus contained multiple lobes if you look at the word monocyte this literally means cell with one local nuclear and as you can see the nucleus of monocyte in macrophage is round to oval with only one lobe the
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binding of bacterial molecules to the receptors on the surface of a macrophage triggers it to engulf and destroy the bacteria through the generation of reactive oxygen species pathogens also stimulate the macrophage to produce chemokines which are special chemicals that attract other immune cells to the site of infection another type of innate immune cell that we have in our body is the tender it Excel the word dendrite means branches and these are known as dendritic cells
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because they have branch like projections from these cells dendritic cells are present in those tissues that are in contact with the external environment such as the skin and inner lining of nose lungs stomach and intestines the dendritic cells are a type of antigen presenting cells antigen presenting cells detect the pathogens and they take the antigens that are present on the surface of these pathogens two lymphocytes lymphocytes are cells of adaptive immunity that we
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will discuss in a bit the dendritic cells present these antigens to the lymphocytes and this leads to attack on the pathogen by these lymphocytes and the antibodies they produce so they are known as the antigen presenting cells as they present the antigen to the lymphocytes dendritic cells are also known as the Langerhans cells after the scientists who discovered them type 1 interferons secreted mainly by dendritic cells play a central role in the body's defense against viruses the last cell
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type that we will discuss in the cells of the innate immunity are the natural killer cells or the NK cells NK cells are the component of the innate immune system that does not directly attack the invading microbes rather NK cells destroy our own cells that have become defective such as tumor cells or virus infected cells so these are various types of cells that are present in our innate immune system apart from the physical and chemical barriers and various types of cells the
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innate immune system also has a special type of defense mechanism known as the complement system
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the compliment system is a set of about 20 proteins and it is known as the compliment system as it complements the action of the antibodies and other cells in destroying the pathogens meaning the complement system helps the antibodies and other immune cells to destroy the invading microbes many species have complement systems including the non mammals like plants fishes and some invertebrates too the basic mechanism of action of the complement system is as follows whenever
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any pathogen enters a body it gets recognized by antibodies present in our blood the binding of antibody to the pathogen is the most important factor for the activation of complement system after it is activated a cascade of different enzymes acts on the surface of the microbe to kill it after it is activated a cascade of different enzymes acts on the surface of the microbe to kill it the complement system has many different mechanisms of action but if you want to learn about the complement
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system in more detail make sure to watch the video on the topic of complement system on our channel links are in the description below so this was about the innate immune system the type of immunity that is present since birth it is nonspecific and comparatively weaker as compared to our third line of defense that is the adaptive immunity the adaptive immune system also known as the acquired immune system or more rarely the specific immune system is composed of highly specialized systemic
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cells and processes that eliminate the pathogens or prevent their growth adaptive immunity is not present since birth and it is created in response to exposure to a foreign substance that is why the name adaptive immunity as it adapts accordingly to the type of threats that we are exposed to
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when a pathogen invades our first and second line of defense it is met by the adaptive immunity which mainly consists of lymphocytes and the antibodies they produce and when a particular pathogen enters our body for the first time the response of the adaptive immunity is minimal as it doesn't recognize this pathogen yet it remembers his exposure to the pathogen and stores an immunological memory of this encounter so if you draw the first response of the adaptive immune system on a graph it
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would look something like this upon subsequent exposure to the same pathogen there is an amplified response of the adaptive immune system sending multiple types of lymphocytes and antibodies that are specific for that pathogen only this helps in successfully eliminating the pathogen the system is highly adaptable because once encountered the immunological memory of that pathogen remains in our system forever and upon subsequent invasion by the same pathogen
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a full mounted defense system is already present in our body the cells of the acquired immune system are the T lymphocytes and the B lymphocytes lymphocytes are a subset of leukocytes meaning they are also types of white blood cells B cells and T cells are the major types of lymphocytes the human body has about two trillion lymphocytes constituting 20 to 40% of the WBC's their total mass is about the same as a brain or a liver the peripheral blood contains 2% circulating
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lymphocytes the rest of them move within the tissue spaces and the lymphatic system the adaptive immune system is divided into two main types the humoral immunity which is due to the B lymphocytes and the cellular immunity which is due to the t lymphocytes the T lymphocytes are again divided into two major types the helper T cells and the cytotoxic or the killer T cells the cytotoxic or the cd8 T cells have a major role in killing the pathogens by directly interacting with invading
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microbes whereas the helper T cells or the cd4 T cells have a indirect but a very important role in our immune system the helper T cells are responsible for the proper functioning of the rest of the immune cells including their close cousins the cd8 cells they secrete large number of growth factors and their cytokines that are essential for maturation of other types of immune cells one of the most deadliest diseases of our century AIDS or acquired immunodeficiency syndrome acts by
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killing our cd4 or the T helper cells only the number decreases so much that it cripples our whole immune system and our body gets overwhelmed by a lot of infections that do not usually occur in normal healthy person the other major type of lymphocyte in our blood are the B lymphocytes which are responsible for the humoral immunity the b-lymphocytes produce a special type of protein known as the antibody which looks something like this as you can see it is a y-shaped structure in which the
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terminal end of the protein is specially designed to recognize and capture antigens that are present on the surface of bacteria and other pathogens this of course happens after the B lymphocytes have had their first contact with the pathogen earlier which led to an immunological memory stored inside these cells upon subsequent encounter with the same pathogen by the B lymphocytes the cells produce a large number of antigen specific antibodies that recognize and
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capture the invading pathogen now the antibodies do not destroy these invading pathogens by themselves but activate a number of different mechanisms of our immune system including the complement system and the various types of Fable it excels like neutrophils one of the very important function of these antibodies is known as the opsonization this in simple words just means sugarcoating a pill to make it more tasty now what these antibodies do is that when they
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recognize a particular pathogen they attach to it and they completely coat it with lots of antibodies this is known as opsonization the coated cell acts like a signal to other immune cells like the neutrophils which come and digest the coated cell therefore the antibodies mark the pathogens so they can be destroyed by other immune cells now there are five different types of antibodies with different roles if you want to learn more about the structure of antibody and its function and the
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complement system make sure to watch these videos on our channel links are in the description below the last section of our basis of immune system will be the differences between the innate and adaptive immunity when we look at how each type of immunity develops the innate immunity is something that is present since our birth while the adaptive immune system is a type of immunity that develops after we are born talking about specificity the innate immunity is nonspecific whereas the adaptive
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immunity is very specific and I hope you are clear with the meaning of the word specificity here innate immunity is nonspecific as it doesn't have any specialized defense systems for different types of pathogens rather it uses a common defense system to kill all the types of pathogens and a single immune defense mechanism of the innate immunity is able to defend against a wide variety of pathogens this is in contrast to the specific immune system that has special types of antibodies and
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cells that are specific and act only on the pathogens they recognize when we look at the time that each system takes to respond to an infection the innate immune system has a very rapid response to any infection since this type of immunity is already present in our body while the adaptive immune system is slow to respond as it needs the first exposure to develop a memory of the pathogen if we look at the potency of each system the innate immune system is less potent as compared to the adaptive
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immunity which just means that the adaptive immune system has more power to kill pathogens since of course it has cells and antibodies that are made specifically for that pathogen one important difference between the innate and the adaptive immune system is that the innate type of immunity is generally inherited from parents and passed off to the offsprings while the adaptive immunity is not passed from the parents to the offspring hence it cannot be inherited if we look at the evolutionary
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basis the innate immunity is older and is found in both vertebrates and invertebrates while the adaptive immune system has been developed recently and is found only in vertebrates the various components of the innate immune system of physical and chemical barriers phagocytic leukocytes dendritic cells and natural killer cells while the adaptive immune system is composed of T cells B cells and the antibodies they produce so this was a basic overview about the human immune system as I told
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you previously you can get the lecture handouts from this video and the flashcards as well by joining our channel click the join button below you can also support our channel by joining our community at patreon.com all links are in the description below thank you so much for watching this video see you in the next one
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