跟读练习: The Composition and Function of Blood - 通过视频学习英语口语
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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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本课的词汇与口语要点
这节口语课以视频“The Composition and Function of Blood”为素材。 视频中反复出现的词有：blood, cell, platelet, protein, plasma。 这段视频共有 53 个句子、1298 个单词可供跟读。 讲话部分时长为 9:57。 说话人语速平稳，每分钟约 130 个词，很适合跟读。 只有 76% 的单词属于英语最常用的 3,000 词，词汇难度较高。
视频中的重点词汇
视频中 15 个值得学习的单词，附发音和释义：
| 单词 | 发音 | 释义 |
|---|---|---|
| tissue 名词 | /ˈtɪʃ.(j)u/ | 纸巾 |
| plasma 名词 | /ˈplæzmə/ | 等離子體 /等离子体 |
| oxygen 名词 | /ˈɑksɪd͡ʒən/ | 氧 |
| vessel 名词 | /ˈvɛsəl/ | 船隻 /船只, 船 |
| fluid 名词 | /ˈflu.ɪd/ | 流體 /流体, 液體 /液体 |
| molecule 名词 | /ˈmɑ.lɪ.kjul/ | 分子 |
| component 名词 | /kəmˈpoʊ.nənt/ | 元件, 部件 |
| plug 名词 | /plʌɡ/ | 插頭 /插头 |
| nucleus 名词 | /ˈnuː.kli.əs/ | 核心, 核 |
| universal 形容词 | /ˌjunəˈvɜɹs(ə)l/ | 宇宙的 |
| bone 名词 | /boʊn/ | гўдў, гўдўзы |
| refer 动词 | /ɹɪˈfɜː/ | 談到 /谈到 |
| hence 副词 | /ˈhɛns/ | 從這裡 /从这里, 從這兒 /从这儿 |
| tear 动词 | /tɛɹ/ | 撕, 撕破 |
| substance 名词 | /ˈsʌbstəns/ | 物質 /物质 |
视频中出现的短语动词
| 单词 | 释义 |
|---|---|
| eat up 动词 | 吃光 |
视频中的语法
说话人最常用的结构，并附上视频中的原话：
| 结构 | 视频中的用法 |
|---|---|
| 被动语态 be + 过去分词 — 强调发生了什么，而不是谁做的 | is technically considered · is comprised · are separated |
| 定语从句 who / which + 从句 — 补充说明人或事物 | elements, which are · bloodstream, which is · leukopoiesis, which is |
需要注意的发音
说话人用了 4 次缩略和弱读形式，例如 don't, can't, we've。请按听到的简短形式来说。
- “th” 音: smooth /smuːð/, erythrocyte /əˈɹɪθɹəˌsaɪt/, pathogen /ˈpæθəd͡ʒn̩/
- “sh” 和 “zh” 音: tissue /ˈtɪʃ.(j)u/, extension /ɪkˈstɛnʃən/, essentially /ɪˈsɛnʃəli/, infection /ɪnˈfɛkʃən/, structural /ˈstɹʌk(t͡)ʃəɹəl/
- 长单词——注意重音位置: universal /ˌjunəˈvɜɹs(ə)l/, essentially /ɪˈsɛnʃəli/, technically /ˈtɛk.nɪˌkəl.i/, continuously /kənˈtɪnjuəsli/, recipient /ɹəˈsɪp.i.ənt/
中文母语者容易读错的音：
- /v/ — 不要读成 /w/，上齿轻触下唇: vessel /ˈvɛsəl/, universal /ˌjunəˈvɜɹs(ə)l/, virus /ˈvaɪ.ɹəs/, involve /ɪnˈvɑlv/, protective /pɹəˈtɛk.tɪv/
- 词尾辅音 — 要读清楚，后面不要加元音: bind /ˈbaɪ̯nd/, fluid /ˈflu.ɪd/, component /kəmˈpoʊ.nənt/, plug /plʌɡ/, nucleus /ˈnuː.kli.əs/
- /r/ 和 /l/ 的区别: universal /ˌjunəˈvɜɹs(ə)l/, briefly /ˈbɹiːfli/, structural /ˈstɹʌk(t͡)ʃəɹəl/, harmful /ˈhɑɹmfl̩/, regulate /ˈɹɛɡ.jə.leɪt/
如何用这段视频练习
- 先完整听一遍视频，不要开口，记下不认识的单词。
- 用正常速度逐句跟读，每句重复到你的节奏与说话人一致为止。
- 录下自己的声音并与原声对比，特别注意 tissue, plasma, oxygen 这类单词。
什么是跟读法？
跟读法 (Shadowing) 是一种有科学依据的语言学习技巧，最初开发用于专业口译员的培训，并由多语言者Alexander Arguelles博士普及。这个方法简单而强大：您在听英语母语原声的同时立即大声重复——就像是一个延迟1-2秒紧跟说话者的影子。与被动听力或语法练习不同，跟读法强迫您的大脑和口腔肌肉同时处理并模仿真实的讲话模式。研究表明它能显着提高发音准确性，语调，节奏，连读，听力理解和口语流利度——使其成为雅思口语备考和真实英语交流最有效的方法之一。