跟讀練習: The Integumentary System - 通過影片學習英語口語
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It’s Professor Dave, let’s look at the integumentary system.
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With some basics covered regarding two of the types of tissue in the human body, we are ready to start looking at some of the different systems found in the body, and we are going to start with the outermost system, which is called the integumentary system.
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This is made up of the skin that covers and protects all your other body parts, as well as its derivatives, like certain glands, as well as hair and nails.
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Let’s look at the structure and function of these components now.
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The skin is a remarkable organ, acting as the first line of defense from the elements that surround us.
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It keeps bacteria out, and water and heat in, so let’s check out the structure of skin.
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Our skin is made of two regions, a thin outer layer, which is the epidermis, and a thicker inner layer, called the dermis.
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The dermis, which is a tough layer of fibrous connective tissue, is vascularized, getting its nutrients from the bloodstream.
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The epidermis, which is made of epithelial tissue, is avascular, so it gets nutrients by diffusion through the tissue fluid from the dermis.
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In addition, below the dermis is the subcutaneous layer, also called the hypodermis.
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This is made predominately of adipose tissue, and it anchors the skin to other structures below.
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Now let’s zoom in on the epidermis, the thin outer layer of the skin.
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This is made of keratinized stratified squamous epithelium, made of four different cell types in five layers.
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The deepest layer, the one attached to the dermis, is called the stratum basale, meaning basal layer.
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This is made of a single row of cells, most of which are called keratinocytes.
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These are rapidly dividing all the time, pushing new cells up into the layers above, to help regenerate dead skin, and producing lots of keratin as they do so.
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This is necessary because millions of dead keratinocytes rub off your skin every day, due to friction, and even more from your hands and feet, so these constantly dividing cells in the stratum basale ensure that a new epidermis forms every few weeks, so that we always have our skin intact.
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This layer also contains melanocytes, which produce melanin, and tactile cells, which act as the sensory receptor for touch.
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Above this is the stratum spinosum, meaning prickly layer.
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This section is several layers of cells thick, and is full of cells with a weblike system of intermediate filaments attached to desmosomes.
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They look kind of spiky, so they are sometimes called prickly cells.
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Here we can also find dendritic cells, which ingest foreign substances and activate the immune system, which we will talk about later.
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Next is the stratum granulosum, or granular layer.
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This is four to six cell layers thick, and in this section, keratinization begins as cells continue to move their way upwards from the basal layer.
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This is when the cells get far enough from the dermal capillaries below to receive sufficient nutrients, so the cells fill up with keratin as they die, and they flatten while the organelles disintegrate.
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This makes the cell tougher and scalier, which allows for the outer layers to better protect the body.
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Above this is the stratum lucidum, or the clear layer.
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This is two or three cell layers thick, made of dead keratinocytes that have become flat and clear.
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This is where they begin to aggregate into arrays called tonofilaments.
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And lastly, there is the stratum corneum, or horny layer.
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This outermost section is twenty to thirty cell layers thick, and all of these cells are anucleated, meaning the nucleus has disintegrated.
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So it’s incredible to think that all the cells covering the outside of your body are actually dead, but they are dead in a specialized way, with thick plasma membranes surrounding lots of keratin.
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These dead cells protect all the living ones inside from all the outside dangers.
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With the epidermis covered, let’s go a little deeper and talk about the dermis.
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This is made of strong and flexible connective tissue, and is full of nerves and blood vessels.
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This is also where hair follicles begin.
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The dermis has two sections, the papillary layer, and the reticular layer.
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Descending from the epidermis we enter the papillary layer, which is very thin, made of areolar connective tissue and a loose network of collagen and elastic fibers.
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This leaves room for defensive cells to patrol the area for bacteria that may have made it through the skin.
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The word papillary refers to the projections from the surface of this layer, which are called dermal papillae, that stick out into the epidermis above.
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These contain lots of tactile cells as described previously.
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In areas where there is lots of friction, like the hands, these papillae sit on mounds called dermal ridges, which cause ridges in the epidermis as well, which are meant to enhance the gripping ability of the fingers, and they are visible as the lines on our fingertips that make our unique fingerprints.
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Below this papillary layer sits the reticular layer, which is most of the dermis, and it is made of dense fibrous connective tissue that is arranged irregularly.
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A network of blood vessels sits below this, just before the hypodermis.
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What else can we say about the skin?
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We mentioned that the stratum basale also contains melanocytes, which produce melanin.
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This is a pigment molecule, and this is one of the components of the skin that determines its color, and protects the skin from ultraviolet radiation.
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The other pigments responsible for skin color are carotene, which is yellow-orange, and hemoglobin, which is red when oxygenated.
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We will discuss this molecule in more depth later in the series.
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That wraps things up for the skin, so let’s just briefly touch on the other components of the integumentary system, which are called skin appendages.
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First, there is hair.
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Of course most of us have lots of hair on our heads, but there is also hair all over the body, including eyelashes and nose hairs, and these all have specific protective functions.
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So what is a hair made of exactly?
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As it turns out, a hair is a flexible strand made largely of dead, keratinized cells.
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This is hard keratin, which is a bit different from the soft keratin found in cells of the epidermis, which makes them more durable, and not as flaky.
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Hairs are produced by hair follicles.
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These possess a root, which is the part deep inside the follicle where keratinization is happening, and a shaft, the part closer to the surface of the skin and then extending outside the body, where keratinization is complete.
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The hair itself consists of three layers of cells.
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The innermost is the medulla, containing large cells and soft keratin.
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Next is the cortex, which is several layers of flattened cells.
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And lastly there is the cuticle, which is a single layer of overlapping cells, the most keratinized cells in the hair.
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As for the follicle the hair sits in, this also has some structure to it.
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In general, a hair follicle is a pocket that folds down from the surface of the epidermis down into the dermis, about four millimeters below the surface.
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The deep end then expands slightly to form a hair bulb.
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A bundle of nerve endings attach to the bulb and act as a receptor, responding to any bending of the hair and alerting the brain in case an insect is there, or something of the like.
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A little bit of dermal tissue called a hair papilla protrudes into the bulb, which supplies signals and nutrients to the hair so it can grow.
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The wall of each follicle has a few layers.
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The outermost is the peripheral connective tissue sheath, derived from the dermis.
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Next is the glassy membrane, derived from the basal lamina.
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And then there is the innermost epithelial root sheath, derived from the epidermis.
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This last section has an external part and an internal part, which thins as it approaches the bulb.
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The cells that actively divide are found in the hair matrix, which push existing cells upwards as they divide, causing the hair to grow.
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In addition, each follicle has an arrector pili.
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This is a small bundle of muscle cells that can contract and pull the follicle in such a way that the surface of the skin dimples out, producing what we refer to as goose bumps, when cold or afraid.
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Our body hair is pretty sparse so this no longer serves much purpose, but for much furrier mammals it is an important defense mechanism for trapping heat and intimidating enemies.
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Hair can either be vellus hair, which is pale and fine, or terminal hair, which is darker and more coarse, like hair of the eyebrows and scalp.
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The nails found on our fingers and toes are also part of the integumentary system.
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These are products of a modification of the epidermis.
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Just like with hair, in contrast to the soft keratin of the skin, nails contain hard keratin, making them great tools for scratching or picking up objects.
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Each nail has a free edge, which is the very tip, then a body, which is most of what we see, and then a proximal root, which is embedded in the skin.
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The part of the epidermis the nail sits on is called the nail bed, and the nail grows out of the nail matrix, which pushes the nail outwards across the nail bed as these cells divide.
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There are also skin folds overlapping the borders of the nail which are called nail folds, sitting on the lateral and proximal borders, and the latter extends onto the nail as the eponychium.
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At the edge of the finger is the hyponychium, where dirt tends to collect.
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The last part of the integumentary system we must mention is the vast collection of glands that can be found.
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First up are the sweat glands, also known as sudoriferous glands.
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These are found almost everywhere on the surface of the skin, totalling up to around three million.
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There are two types of sweat glands.
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The first is called eccrine, or merocrine sweat glands.
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Most of them are of this type, and it consists of a coiled tube.
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Secretion occurs in the dermis, and the resulting fluid, or sweat, travels through the tube towards a funnel-shaped opening called a pore.
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Sweat is ninety-nine percent water, but it contains some salts and metabolic wastes, among other things.
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Sweat is also secreted by apocrine sweat glands, which are far fewer, found only in certain areas, and secrete fat and protein components along with the normal mixture, which is the cause of body odor.
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Ceruminous glands and mammary glands are also types of apocrine glands, which produce earwax and breast milk.
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Beyond sweat glands there are sebaceous glands, also known as oil glands.
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These are branched alveolar glands that secrete sebum, which is made of oily lipids.
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This will soften and lubricate hair and skin, slowing water loss and killing certain bacteria.
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So that covers the basics of the integumentary system, which consists of skin, hair, nails, and glands.
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This system acts a barrier, separating what’s outside of us from what’s inside of us.
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It has the ability to repair quickly, regulate body temperature, and respond to stimuli outside of the body, among other things.
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Now that we have this system covered, let’s head inside the body and check out the rest.
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關於本課
在這一節中，您將學習關於人體外骨骼系統的重要知識，尤其是皮膚的結構和功能。通過分析外皮層、真皮層及其各自的組成部分，您將能夠更好地理解皮膚在保護身體方面的關鍵作用。此課程還將提供專業術語的列表，有助於加深您的英語理解，尤其是在有關人體解剖的討論中。通過觀看相關影片並進行影子跟讀，您將能更流利地使用這些術語，提升您的英語口語能力。
關鍵詞彙與短語
- 皮膚 (skin)
- 表皮 (epidermis)
- 真皮 (dermis)
- 角質層 (stratum corneum)
- 黑色素 (melanin)
- 毛囊 (hair follicle)
- 免疫系統 (immune system)
- 角質形成細胞 (keratinocyte)
練習提示
進行英語影子跟讀時，建議您選擇這段影片的慢速片段，專注於每個單詞的發音和語調。可以在觀看影片時暫停，先重複其內容，然後嘗試自己說出這些生詞。在練習中，注意模仿老師的語音語調，這樣有助於提高您的英語發音與流利度。執行影子跟讀時，請確保在熟悉的環境中進行，這樣的方式能讓您專注於練習而不受干擾。結合看YouTube學英語的資源，您可以利用影片中豐富的視覺資訊，加深對相關詞彙的理解，同時通過shadow speech的練習，進一步增強您的口語表達能力。
通過這些建議，您將能夠更好地吸收和應用本節中的知識，提升您的英語交流能力。請儘量將學習過程與日常生活結合，應用所學的詞彙與短語，形成自然流利的表達。
影片中的語法
說話人最常用的結構，並附上影片中的原話：
| 結構 | 影片中的用法 |
|---|---|
| 被動語態 be + 過去分詞 — 強調發生了什麼，而不是誰做的 | is called · is made · is vascularized |
| 定語從句 who / which + 從句 — 補充說明人或事物 | system, which is · layer, which is · dermis, which is |
| 現在完成時 have/has + 過去分詞 — 過去發生但與現在仍有關聯的事 | have become · has disintegrated |
什麼是跟讀法？
跟讀法 (Shadowing) 是一種有科學依據的語言學習技巧，最初開發用於專業口譯員的培訓，並由多語言者Alexander Arguelles博士普及。這個方法簡單而強大：您在聽英語母語原聲的同時立即大聲重複——就像是一個延遲1-2秒緊跟說話者的影子。與被動聽力或語法練習不同，跟讀法強迫您的大腦和口腔肌肉同時處理並模模擬實的講話模式。研究表明它能顯著提高發音準確性，語調，節奏，連讀，聽力理解和口語流利度——使其成為雅思口語備考和真實英語交流最有效的方法之一。