Pratique du Shadowing: The Composition and Function of Blood - Apprendre l'anglais à l'oral avec la vidéo
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Professor Dave here, let's learn about blood.
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Of all the substances within the human body, blood is one of the more familiar ones, as we've all had an injury that involves bleeding.
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For a long time, it was not well understood exactly what blood is,
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or what it does, we just knew that if you lose enough of it, you die.
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But we now have an intimate understanding of this fluid, as well as the circulatory system,
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whose function it is to continuously pump blood around the body.
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We will get to this system in a moment.
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First let's examine blood itself, what it's made of, and why it is so critical for human life.
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First, let's mention that blood is technically considered a connective tissue, and as such, it is the only fluid tissue in the body,
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full of fibrous proteins.
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It is comprised of formed elements, which are blood cells suspended in a fluid called plasma.
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If we place blood in a centrifuge, it will separate into its components.
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The densest section is comprised of erythrocytes, or red blood cells, and the least dense section will be the yellowish plasma.
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They are separated by the buffy coat, a white layer containing platelets, as well as leukocytes, otherwise known as white blood cells.
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As a whole, blood is responsible for distributing various substances around the body,
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most notably oxygen, which we can't survive very long without up, but it also carries nutrients absorbed from the digestive tract,
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and hormones secreted by endocrine organs.
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Blood also delivers waste products to the organs that will dispose of them, like the carbon dioxide that we exhale.
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Beyond this, blood serves to regulate pH in various tissues, maintain body temperature, and prevent infection.
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Let's discuss each component of blood now, beginning with plasma.
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This is a sticky fluid made mostly of water, but also containing a variety of proteins, nutrients, ions, gases, and hormones.
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The most abundant plasma protein is called albumin, which contributes significantly to plasma's osmotic pressure,
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and this is followed by a variety of globulins which bind to certain molecules for transport.
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Moving to the formed elements, these are erythrocytes, or red blood cells, leukocytes, or white blood cells, and platelets.
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Red blood cells and platelets are interesting in that they don't possess all the typical organelles, and they don't divide.
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They are replaced by stem cells in the bone marrow.
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Red blood cells are very numerous in the bloodstream, and they are shaped like flattened discs with depressed centers.
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There is no nucleus, not much of anything inside other than lots of hemoglobin.
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This is the protein that allows for the transport of oxygen throughout the bloodstream, which is picked up in the lungs,
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and then released for tissue cells throughout the body.
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There are other proteins as well that have structural or protective functions, but hemoglobin will be the focus here.
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This is the structure of hemoglobin.
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It is made of a protein called globin, consisting of four polypeptides, two identical alpha chains, and two identical beta chains,
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each of which is bound to a heme group with iron at the center.
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The iron in this heme is able to bind to an oxygen molecule in reversible fashion, so that it can bind and then release when necessary,
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so each hemoglobin can bind four oxygen molecules.
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And there are around 250 million hemoglobins per red blood cell,
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so one red blood cell can transport one billion oxygen molecules cells.
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Blood cells are produced through a process called hematopoiesis, and this occurs in the red bone marrow,
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which is a soft network of connective tissue found on certain blood capillaries, and which contains hematopoietic stem cells.
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For erythrocytes, this is more specifically called erythropoiesis,
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and billions of new red blood cells are made every day to maintain a nearly constant number,
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given that red blood cells function properly for only about three months, only to be destroyed by macrophages,
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which are a phagocytic type of white blood cell.
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Next, let's look at leukocytes, or white blood cells, which unlike the far more abundant red blood cells,
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are complete cells with nuclei and organelles.
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These are part of the immune system, which we will discuss in greater detail later,
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but for now we will just understand that these help us defend against pathogens and other harmful things tissues.
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These use the circulatory system to get around the body, but they can also slip out into other connective tissues to do their work.
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There are two types of white blood cells,
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granulocytes and agranulocytes, which differ in the presence or absence of granules.
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The three types of granulocytes are neutrophils, which kill bacteria, eosinophils, which kill parasitic worms,
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and basophils, which contain histamine that attracts other white blood cells to a site of inflammation.
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Agranulocytes, on the other hand, can be lymphocytes, which fight viruses and tumors, and also give rise to plasma cells,
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which produce antibodies, which we will discuss later, or they can be monocytes, which become macrophages that can eat up intruders.
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Leukocytes are produced by leukopoiesis, which is stimulated by certain chemical messengers.
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Lastly we get to the platelets.
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These are fragments of large cells, called megakaryocytes.
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These fragments are essential during blood clotting, which happens when blood vessels are damaged,
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as platelets can plug up any holes or tears to seal things off.
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They flow through the bloodstream in an inactive state unless needed, dying every ten days or so, and constantly regenerated.
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Megakaryocytes form due to repeated mitotic cycles that do not perform cytokinesis,
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so So the result is one huge cell with a multi -lobed nucleus.
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This then presses against a sinusoid, and its extensions burst to release the platelets.
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These platelets are important during hemostasis, which is the process by which the body will stop bleeding through vascular spasm,
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platelet plug formation, and then coagulation, or blood clotting.
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This essentially means that where there is damage to a vessel,
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smooth muscle will contract, platelets will plug the tear,
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and a protein called fibrin will form a mesh to patch everything up.
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Once the vessel has healed, the clot is removed through a process called fibrinolysis, so that there is no blockage in the vessel.
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So those are the components of blood.
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We can look at a diagram like this one to see how these arise during hematopoiesis.
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We can also briefly mention the different blood types that humans can exhibit.
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These are A, B, AB, and O.
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These have to do with glycoproteins and glycolipids found in the plasma membranes of red blood cells.
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A and B refer to two different agglutinogens that can be found in these membranes, so blood group A has one of them,
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B has the other, AB has both, and O has neither.
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This is important for blood transfusions, because if someone's body only recognizes A and gets blood with B,
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the new blood cells will be recognized by antibodies as foreign and destroyed, which can be fatal.
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So someone with AB blood can receive any blood, since both A and B will be recognized, hence they are universal recipients.
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And someone with O blood can give blood to anyone, since there are no markers to be recognized, hence they are universal donors.
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There are also RH blood groups which refer to agglutinogens called RH factors, and for For these, a person is either positive or negative.
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This is reported along with the ABO blood group by tacking on positive or negative to the end, giving us groups like O positive,
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A negative, and so on.
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And with that, we are familiar enough with the structure
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and function of blood that we can begin to examine the circulatory system as a whole, so let's move forward and do just that.
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Vocabulaire et conseils d’expression pour cette leçon
Cette leçon d’expression orale s’appuie sur la vidéo « The Composition and Function of Blood ». Les mots qui reviennent le plus souvent : blood, cell, platelet, protein, plasma. Cette vidéo contient 53 phrases et 1298 mots à répéter en shadowing. La partie parlée dure 9:57. Le locuteur parle à un rythme régulier d’environ 130 mots par minute, confortable pour le shadowing. Seuls 76 % des mots font partie des 3 000 mots les plus courants en anglais, le vocabulaire est donc exigeant.
Vocabulaire clé de cette vidéo
15 mots de la vidéo à retenir, avec leur prononciation et leur sens :
| Mot | Prononciation | Sens |
|---|---|---|
| tissue nom | /ˈtɪʃ.(j)u/ | tissu |
| plasma nom | /ˈplæzmə/ | plasma |
| oxygen nom | /ˈɑksɪd͡ʒən/ | oxygène |
| vessel nom | /ˈvɛsəl/ | vaisseau |
| fluid nom | /ˈflu.ɪd/ | fluide, liquide |
| molecule nom | /ˈmɑ.lɪ.kjul/ | molécule |
| component nom | /kəmˈpoʊ.nənt/ | composant |
| plug nom | /plʌɡ/ | fiche |
| nucleus nom | /ˈnuː.kli.əs/ | noyau |
| universal adjectif | /ˌjunəˈvɜɹs(ə)l/ | universel |
| bone nom | /boʊn/ | os |
| refer verbe | /ɹɪˈfɜː/ | référer |
| hence adverbe | /ˈhɛns/ | d'ici |
| tear verbe | /tɛɹ/ | déchirer |
| substance nom | /ˈsʌbstəns/ | substance |
Les verbes à particule que vous entendrez
| Mot | Sens |
|---|---|
| eat up verbe | dévorer |
La grammaire de cette vidéo
Les structures que le locuteur utilise le plus, avec les mots exacts de la vidéo :
| Structure | Dans la vidéo |
|---|---|
| Voix passive be + participe passé — l’accent est mis sur ce qui arrive, pas sur qui le fait | is technically considered · is comprised · are separated |
| Propositions relatives who / which + proposition — une précision sur une personne ou une chose | elements, which are · bloodstream, which is · leukopoiesis, which is |
Prononciation à surveiller
Le locuteur utilise 4 contractions et formes réduites, comme don't, can't, we've. Prononcez-les sous leur forme courte, telles que vous les entendez.
- Les sons « th »: smooth /smuːð/, erythrocyte /əˈɹɪθɹəˌsaɪt/, pathogen /ˈpæθəd͡ʒn̩/
- Les sons « sh » et « zh »: tissue /ˈtɪʃ.(j)u/, extension /ɪkˈstɛnʃən/, essentially /ɪˈsɛnʃəli/, infection /ɪnˈfɛkʃən/, structural /ˈstɹʌk(t͡)ʃəɹəl/
- Mots longs — placez bien l’accent: universal /ˌjunəˈvɜɹs(ə)l/, essentially /ɪˈsɛnʃəli/, technically /ˈtɛk.nɪˌkəl.i/, continuously /kənˈtɪnjuəsli/, recipient /ɹəˈsɪp.i.ənt/
Les sons difficiles pour les francophones :
- /h/ — il se souffle, il n’est pas muet: hence /ˈhɛns/, hormone /ˈhoɹmoʊn/, heal /ˈhiːl/, harmful /ˈhɑɹmfl̩/, hemoglobin /ˌhimoʊˈɡloʊbɪn/
- /tʃ/ et /dʒ/ — à ne pas adoucir en « ch » et « j »: oxygen /ˈɑksɪd͡ʒən/, patch /pæt͡ʃ/, messenger /ˈmɛs.ən.d͡ʒɚ/, macrophage /ˈmækɹɔʊː.feɪd͡ʒ/, blockage /ˈblɑkɪd͡ʒ/
- /r/ anglais — langue recourbée, sans frotter la gorge: universal /ˌjunəˈvɜɹs(ə)l/, refer /ɹɪˈfɜː/, tear /tɛɹ/, hormone /ˈhoɹmoʊn/, comprise /kəmˈpɹaɪz/
Comment s’entraîner avec cette vidéo
- Écoutez la vidéo en entier une fois sans parler et notez les mots que vous ne connaissez pas.
- Répétez phrase par phrase à vitesse normale, en reprenant chacune jusqu’à ce que votre rythme corresponde à celui du locuteur.
- Enregistrez-vous et comparez avec l’original, en faisant attention à des mots comme tissue, plasma, oxygen.
Qu'est-ce que la technique du Shadowing ?
Le Shadowing est une technique d'apprentissage des langues fondée sur la science, développée à l'origine pour la formation des interprètes professionnels. Le principe est simple mais puissant : vous écoutez de l'anglais natif et le répétez immédiatement à voix haute — comme une ombre suivant le locuteur avec un décalage de 1 à 2 secondes. Les recherches montrent une amélioration significative de la précision de la prononciation, de l'intonation, du rythme, des liaisons, de la compréhension orale et de la fluidité.