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Hi, this is Tom from zerodefinals .com.
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This video was designed to give an overview of immunology, so that you understand all the basic features of the immune system.
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It will also help you to return to this video once you've already learned the details,
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so that you can again fit those details back into the bigger picture about how the immune system works.
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The immune system can be categorized into the innate immune system and the specific immune system.
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The innate immune system consists of the components that are already at the location of the infection
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and respond immediately with a generalized response.
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The specific immune system involves specialized T and B cells
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that are waiting in places away from the site of infection
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and then when they're activated they launch a specialized system
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that fights the specific invading pathogen the specific immune system takes a little
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while longer to recognize the infection particularly
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when a pathogen is invading the body for the first time
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so in this video we're going to cover both of these systems
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and also talk about a system called the complement system
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that works alongside the innate and specific immune systems let's look at what happens
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when a pathogen invades the body initially there are physical barriers that need to be broken before an infection can take place.
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The skin is an example of one of these barriers.
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Most invaders will get stuck at this barrier, however occasionally an invading pathogen will get through, such as when there's a cut in the skin.
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As well as the skin, there's other physical barriers, such as the mucosa of the respiratory system, the gastrointestinal tract, and the urinary tract.
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There are also chemical barriers that help destroy harmful pathogens before they can cause any infection, such as the hydrochloric acid in the stomach,
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lysozyme in sweat and tears, and lactic acid in the vagina.
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Let's look at the initial responses of the immune system once an invading pathogen has broken through the physical
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and chemical barriers to infection.
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Three things happen.
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Number one, macrophages recognize the pathogen and activate the innate immune system.
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Number two, dendritic cells pick up antigens from the pathogen
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and then head off in the blood
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and lymphatic systems to track down the relevant T and B cells of the specific immune system and activate them.
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And number three, the invading pathogen activates the complement system directly via the lectin pathway and the alternative pathway
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And we'll talk a bit more on those later
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First let's look at how the innate immune system provides an immediate response to infection
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The first to respond are the macrophages
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They recognise pathogens by specific characteristics that occur on pathogens but don't occur on cells of the body
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These characteristics are called pathogen -associated molecular patterns, or PAMPs.
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They recognise PAMPs using various receptor types, including toll -like receptors.
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At this point, I need to talk briefly about a process called phagocytosis.
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Now, phagocytosis is the process that macrophages and other phagocytes like neutrophils use in order to destroy pathogens.
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So what happens is once they've recognized the pathogen they start to wrap their cell membrane around
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that pathogen and absorb them to with inside their cell.
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The pathogen is then left inside something called a phagosome
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and this phagosome fuses with surrounding lysosomes that provide digestive enzymes
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that then break down that pathogen destroying it and also processing all of the components into harmless waste products.
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If the invading pathogens are harmless enough
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that the macrophages can deal with them alone then they're cleared and it goes no further.
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If the attacking army is too great the macrophages need help
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so they release cytokines which are signaling proteins sort of like local hormones
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that sound the alarm of an infection in the local area.
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This leads to a process called inflammation.
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One of the most important actions of these cytokines is to recruit and activate more cells of the immune system, such as macrophages, monocytes and neutrophils.
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Monocytes are precursors to macrophages that float around in the blood.
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Once they enter tissues, they differentiate into macrophages and can then carry out all the processes that macrophages normally carry out.
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Neutrophils are another type of phagocyte that circulate in the blood and can enter the tissues and help by destroying invading pathogens.
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The inflammatory response also involves a number of other processes that help to contain and fight the infection.
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These are vasodilation, increased vascular permeability, mast cell activation and degranulation,
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releasing more cytokines that further stimulate the inflammatory response, activation of the clotting system, and activation of the kinin system.
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Inflammation itself actually stimulates macrophages and neutrophils to secrete more cytokines, notably chemicals called interleukins.
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This is known as the acute phase response, and it leads to a more systemic inflammatory response.
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this involves sending cytokines specifically interleukin 1 to the brain to tell it to produce a fever
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that leads to high temperatures that are poorly tolerated by many pathogens
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and cause reduced appetite and lethargy so that the person conserves more energy
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that can be used to fight the infection
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it also involves sending interleukin 6 to the liver to produce acute phase protein
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that act as something called opsonins and remember this word
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because we'll talk about opsonins in a minute additionally interleukin 8 is released
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that recruits and activates more neutrophils interleukin 2
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and 12 activate natural killer cells and tumor necrosis factor alpha is released
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that does all of these effects by itself as i just mentioned
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i want to take a quick look at opsonins as these are very important in the immune system.
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Opsonins are complex molecules that attach themselves to pathogens
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and make it easier for macrophages and neutrophils to recognize and phagocytose that pathogen.
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I think of them a bit like a fork
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that spears the pathogen so that macrophage can attach to the other end of the fork
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and then use it to eat the pathogen.
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An example of an opsonin that you may have heard of is C -reactive protein or CRP.
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CRP is produced by the liver in response to interleukin -6
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and we actually measure the level of CRP in our patients to assess how much inflammation
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there is in the body
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and it can be a really good indicator of the severity of the infection
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that our patient is suffering with so
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that summarizes the innate immune system a generalized system that recognizes
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and responds to an invading pathogen by causing an inflammatory response
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and recruiting cells
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that destroy the pathogens by phagocytosis next let's look briefly at
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the complement system the complement system works alongside the innate and the specific immune system to help them destroy pathogens
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This involves a series of complement proteins labelled C1 to C9.
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Once the complement system is triggered, the proteins start to activate each other in something called the complement cascade.
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Various products of the complement cascade have important functions such as acting as opsonins,
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triggering further inflammation and directly attacking and destroying the pathogens.
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The complement system is triggered in one of three ways
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The lectin and the alternative pathway are activated directly by pathogens
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and the classical pathway is activated by antibody -antigen complexes that arise from the specific immune system
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And that brings us nicely onto looking at the function of the specific immune system
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The specific immune system involves two characters the T and the B cells and these are both types of lymphocyte.
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They are free to float around the lymphatic system and the blood
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but they spend most of their time in the lymph node and the mucosa -associated lymphoid tissue.
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Think of these lymphoid tissues as army barracks that are full of soldiers
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that are all sat around waiting to get word of an enemy that they've specifically been trained to fight.
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Each pathogen has molecules that are unique to them.
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They're known as antigens.
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Each T cell has T cell receptors that are specific to a single type of antigen.
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B cells have antibodies on their cell membrane that, just like T cell receptors, are specific to a single type of antigen.
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The result is there's millions of different T and B cells that are all specific to a single type of antigen.
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When a new pathogen arrives and causes an infection, The T and B cells that are specific to that pathogen need to be alerted.
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The trouble is they're sat in lymphatic tissue such as lymph nodes while the infection is happening somewhere completely different.
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This is where the dendritic cell comes in.
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These cells are like messengers and they pick up the antigens at the site of the invasion,
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display them on their cell surface and then bring them through the blood and lymphatic system into the lymphatic tissue.
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When they're there all the T and B cells have a look at the antigen and see whether they recognize it.
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When the T and B cells are found that specific to that antigen, those cells become activated.
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So the specific immune response starts with the dendritic cell presenting
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the antigens on the HLA class II molecules to the CD4 cells.
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These CD4 cells, which are a type of T cell, then proliferate and become T helper cells.
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The T helper cells present antigens on their HLA class 1 molecule that can be recognized by CD8 cells, another type of T cell.
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They also secrete cytokines that are responsible for making the CD8 cells proliferate and differentiate into cytotoxic T cells.
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These T helper cells also release cytokines that stimulate B cells to proliferate
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and differentiate into plasma cells that can release large quantities of antibodies
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and memory B cells
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that hang around as part of the immune memory to respond quickly in future inflections with that specific pathogen.
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The T helper cells also travel to areas of infection and
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secrete cytokines that help to recruit monocytes and macrophages to the infected tissue
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and activate the macrophages to cause inflammation and start the process of phagocytosis.
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Cytotoxic T cells are responsible for killing cells that have been infected by pathogens, such as virally infected cells.
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To do this, they need to attach themselves to the infected cell via the T cell receptor
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and the HLA class 1 molecule expressing the relevant antigen protein on the infected cell.
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once they're attached to the virally infected cell they have two killing mechanisms
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that they can choose from the first is called granule exocytosis where they basically spray the infected cell with enzymes
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that destroy the membrane and lead to cell lysis and cell death
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the second is they can activate the fast molecule the fast molecule is like a self -destruct switch
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that once it's activated it causes the cell to undergo apoptosis.
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Plasma cells and antibodies are an essential part of the specific immune system.
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Plasma cells are B cells that have differentiated and become antibody producing cells
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and their job is to produce tons of antibodies that are specific to the invading pathogen.
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These antibodies are proteins
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that are shaped like a Y one end is variable in
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shape to match different antigens whereas the other end is fixed in shape
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and can be recognized by many cells of the immune system these proteins float around the blood
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and attach themselves to antigens that match their specific variable region
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and these antibodies help the immune system fight pathogens in a number of different ways firstly
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they can attach themselves to enemy toxins which themselves are antigens and neutralize their toxic effect.
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Secondly antibodies can attach themselves to the receptors of viruses and bacteria and prevent them from carrying out their function.
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For example it can stop viruses from being able to recognize cells
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that it may want to invade and therefore prevent the viral invasion of that cell.
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Thirdly antibodies can attach themselves to pathogens then clump together to slow the spread of that pathogen down this is called agglutination.
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Finally it can be very difficult for the simplistic receptors of macrophages and neutrophils to recognize certain pathogens.
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Antibodies can act as opsonins that are highly specific to the invading pathogen
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and by attaching themselves to that pathogen acting as upsonins they can help the macrophages
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and neutrophils to recognize and destroy that pathogen.
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That summarizes an overview of the immune system.
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I hope you found this video helpful.
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It was created as part of a set of videos
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that covers everything you need to know about the immune system for medical school
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and practicing as a doctor so go ahead and check out the rest of those videos.
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If you like this one then please like, comment
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and subscribe for more videos to you achieve success in your medical career
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you can also check out the zero to finals website where you'll find notes illustrations practice questions
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and a blog and i hope it's all useful for you and i'll see you in the next video
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Vocabolario e note di pronuncia per questa lezione
Questa lezione di conversazione si basa sul video “Understanding the Immune System in One Video”. Le parole che ritornano più spesso: cell, pathogen, immune, specific, macrophage. Questo video contiene 157 frasi e 2165 parole da ripetere con lo shadowing. Il parlato dura 15:11. Chi parla mantiene un ritmo costante di circa 143 parole al minuto, comodo per lo shadowing. Solo il 73% delle parole rientra nelle 3.000 più comuni dell’inglese, quindi il lessico è impegnativo.
Vocaboli chiave di questo video
15 parole del video che vale la pena imparare, con pronuncia e significato:
| Parola | Pronuncia | Significato |
|---|---|---|
| immune aggettivo | /ɪˈmjuːn/ | immune |
| infection sostantivo | /ɪnˈfɛkʃən/ | infezione |
| invade verbo | /ɪnˈveɪd/ | invadere |
| complement sostantivo | /ˈkɑmpləmənt/ | angolo complementare |
| attach verbo | /əˈtæt͡ʃ/ | legare, appiccare |
| tissue sostantivo | /ˈtɪʃ.(j)u/ | tessuto |
| receptor sostantivo | /ɹɪˈsɛp.tə/ | recettore |
| molecule sostantivo | /ˈmɑ.lɪ.kjul/ | molecola |
| involve verbo | /ɪnˈvɑlv/ | coinvolgere |
| barrier sostantivo | /ˈbæɹi.ə/ | barriera |
| inflammation sostantivo | /ɪnfləˈmeɪ̯ʃən/ | infiammazione |
| recruit verbo | /ɹɪˈkɹut/ | arruolare, reclutare |
| pathway sostantivo | /ˈpæθˌweɪ/ | via |
| inflammatory aggettivo | /ɪnˈflæmət(ə)ɹi/ | infiammatorio |
| trigger sostantivo | /ˈtɹɪɡɚ/ | grilletto |
I phrasal verb che sentirai
| Parola | Pronuncia | Significato |
|---|---|---|
| carry out verbo | /ˈkæ.ɹi aʊt/ | compiere, realizzare |
| check out verbo | investigare | |
| pick up verbo | tirare su, sollevare | |
| get through verbo | /ɡɛt ˈθɹu/ | superare, farcela |
| go ahead verbo | /ˌɡoʊ əˈhɛd/ | procedere, andare avanti |
| track down verbo | rintracciare, scovare |
La grammatica di questo video
Le strutture che chi parla usa di più, con le parole esatte del video:
| Struttura | Nel video |
|---|---|
| Forma passiva be + participio passato — conta ciò che accade, non chi lo fa | was designed · can be categorized · be broken |
| Present perfect have/has + participio passato — un’azione passata che conta ancora adesso | you've already learned · has broken · they've recognized |
| Frasi relative who / which + frase — un’informazione in più su una persona o una cosa | cytokines which are · cells, which are |
Pronuncia a cui fare attenzione
Chi parla usa 15 contrazioni e forme ridotte, come they're, they've, we'll. Pronunciale nella forma breve, così come le senti.
- I suoni “th”: pathway /ˈpæθˌweɪ/, pathogen /ˈpæθəd͡ʒn̩/, lethargy /ˈlɛθ ər dʒi/, thirdly /ˈθɚdli/
- I suoni “sh” e “zh”: infection /ɪnˈfɛkʃən/, tissue /ˈtɪʃ.(j)u/, inflammation /ɪnfləˈmeɪ̯ʃən/, differentiate /dɪf.əˈɹɛn.ʃi.eɪt/, activation /ˌæktəˈveɪʃən/
- Parole lunghe — attenzione all’accento: inflammation /ɪnfləˈmeɪ̯ʃən/, inflammatory /ɪnˈflæmət(ə)ɹi/, differentiate /dɪf.əˈɹɛn.ʃi.eɪt/, activation /ˌæktəˈveɪʃən/, characteristic /ˌkæɹ(ə)ktəˈɹɪstɪk/
I suoni difficili per chi parla italiano:
- /h/ — va soffiata, non è muta: harmless /ˈhɑɹmləs/, helpful /ˈhɛlp.fl̩/, whereas /(h)wɛɹˈæz/, harmful /ˈhɑɹmfl̩/, hormone /ˈhoɹmoʊn/
- Consonante finale — senza aggiungere una vocale dopo: activate /ˈæktɪˌveɪt/, invade /ɪnˈveɪd/, complement /ˈkɑmpləmənt/, attach /əˈtæt͡ʃ/, involve /ɪnˈvɑlv/
- /æ/ — più aperta della “e”: activate /ˈæktɪˌveɪt/, attach /əˈtæt͡ʃ/, barrier /ˈbæɹi.ə/, pathway /ˈpæθˌweɪ/, inflammatory /ɪnˈflæmət(ə)ɹi/
Come esercitarsi con questo video
- Ascolta tutto il video una volta senza parlare e annota le parole che non conosci.
- Fai shadowing frase per frase a velocità normale, ripetendo ognuna finché il tuo ritmo coincide con quello di chi parla.
- Registrati e confronta con l’originale, facendo attenzione a parole come immune, infection, invade.
Cos'è la tecnica dello Shadowing?
Shadowing è una tecnica di apprendimento delle lingue supportata da studi scientifici, originariamente sviluppata per la formazione dei traduttori professionisti e resa popolare dal poliglotta Dr. Alexander Arguelles. Il metodo è semplice ma potente: ascolti un audio in inglese di madrelingua e lo ripeti immediatamente ad alta voce — come un'ombra che segue il parlante con un ritardo di solo 1–2 secondi. A differenza dell'ascolto passivo o degli esercizi di grammatica, lo shadowing costringe il tuo cervello e i muscoli della bocca a elaborare e riprodurre simultaneamente i modelli di discorso reale. La ricerca dimostra che migliora significativamente la precisione della pronuncia, l'intonazione, il ritmo, il discorso connesso, la comprensione dell'ascolto e la fluidità del parlato — rendendolo uno dei metodi più efficaci per la preparazione alla prova di speaking dell'IELTS e per la comunicazione reale in inglese.