For most of history, humans had no idea what purpose the heart served. In fact, the organ so confused Leonardo da Vinci, that he gave up studying it. Although everyone could feel their own heart beating, it wasn't always clear what each thump was achieving. Now we know that the heart pumps blood. But that fact wasn't always obvious, because if a heart was exposed or taken out, the body would perish quickly. It's also impossible to see through the blood vessels, and even if that were possible, the blood itself is opaque, making it difficult to see the heart valves working. Even in the 21st century, only a few people in surgery teams have actually seen a working heart. Internet searches for heart function, point to crude models, diagrams or animations that don't really show how it works. It's as if there has been a centuries old conspiracy amongst teachers and students to accept that heart function cannot be demonstrated. Meaning that the next best thing is simply to cut it open and label the parts. That way students might not fully grasp the way it works, but can superficially understand it, learning such concepts as the heart is a four-chambered organ, or potentially misleading statements like, mammals have a dual-circulation: one with blood going to the lungs and back, and another to the body and back. In reality, mammals have a figure-eight circulation. Blood goes from one heart pump to the lungs, back to the second heart pump, which sends it to the body, and then back to the first pump. That's an important difference because it marks two completely different morphologies. This confusion makes many students wary of the heart in biology lessons, thinking it signals an intimidating subject full of complicated names and diagrams. Only those who end up studying medicine compeltely understand how it all actually works. That's when its functions become apparent as medics get to observe the motion of the heart's valves. So, let's imagine you're a medic for a day. What you'll need to get started is a whole fresh heart, like one from a sheep or pig. Immerse this heart in water and you'll see that it doesn't pump when squeezed by hand. That's because water doesn't enter the heart cleanly enough for the pumping mechanism to work. We can solve this problem in an extraordinarly simple way. Simply identify the two atria and cut them off, trimming them down to the tops of the ventricles. This makes the heart look less complicated because the atria have several incoming veins attached. So without them there, the only vessels remaining are the two major heart arteries: the aorta and pulmonary artery, which rise like white columns from between the ventricles. It looks -- and really is -- very simple. If you run water into the right ventricle from a tap (the left also works, but less spectacularly), you'll see that the ventricular valve tries to close against the incoming stream. And then ventricle inflates with water. Squeeze the ventricle and a stream of water squirts out of the pulmonary artery. The ventricular valves, called the tricuspid in the right ventricle and the mitral in the left, can be seen through the clear water opening and closing like parachutes as the ventricle is rhythmically squeezed. This flow of water mimics the flow of blood in life. The valves are completely efficient. You'll notice they don't leak at all when the ventricles are squeezed. Over time, they also close against each other with very little wear and tear, which explains how this mechanism continues to work seamlessly for more than 2 billion beats a heart gives in its lifetime. Now, anyone studying the heart can hold one in their hands, make it pump for real and watch the action unfold. So place your hand above your own and feel its rhymic beat. Understanding how this dependable inner pump works gives new resonance to the feeling you get when you run a race, drink too much caffeine or catch the eye of the one you love.
長久以來 人類對心臟的作用可說是一無所知 這個器官甚至複雜到 讓達文西都放棄去了解它 雖然大家都能感受自己的心跳 但是我們並不清楚它跳動的功用 現在我們知道心臟是輸送血液的幫浦 但這個現象在以前卻不容易知曉 因為若是暴露心臟或被取出 身體會迅速死亡 而且我們也無法透視血管內部 即使可能 血液本身是不透明的 使觀察心臟瓣膜如何運作更加困難 即使到了 21 世紀 只有少數手術人員 實際看過跳動中的心臟 在網路上搜尋心臟的功能 也僅能找到粗略的模型、圖解及動畫 且都無法確實描述心臟機能 數百年來 老師與學生似乎普遍相信 人類不可能演示心臟的功能 意味著只能退而求其次 剖開心臟,給各部位命名 雖然這樣無法讓學生 完整掌握心臟的功能 但至少能大概了解其基本構造與功能 並學到一些概念 像是心臟有四個腔室 或產生一些易誤導的論斷 例如哺乳動物行雙循環 一條輸送血液到肺部,再回到心臟 另一條則輸送血液來回全身 實際上,哺乳動物 血液循環呈「8」字型 第一次跳動輸送血液來回肺部 然後第二次跳動輸送血液至全身 如此周而復始 上述兩種循環的差異非常重要 因為這是兩個完全不同的生理形態 許多學生對此感到困惑 因而擔憂在生物課上學到心臟構造 覺得這是一門恐怖的學科 學名繁雜,圖解難懂 只有最終學習醫科的學生 才完全理清心臟究竟是如何運作的 於是心臟功能的謎題逐漸明朗 歸功於醫學生觀察心臟瓣膜的運作 現在想像你是一名醫學生 你首先會得到一顆新鮮完整的心臟 可以是羊或豬的 把它浸入水中 你會發現即便你擠壓它 它也不會輸水 這是因為進入心臟的水還不夠 導致幫浦功能無法運作 要解決這個問題很簡單 只要找到兩個心房 並將其切除 切到心室上端 這樣心臟就看起來不那麼複雜了 因為心房連接著數條靜脈 所以切掉心房後 就只剩下兩條主要的動脈 分別是大動脈與肺動脈 像圓柱一樣豎立在兩心室之間 這樣看起來也的確就簡單多了 如果你把水注入右心室 左心室也可以,但是效果沒那麼好 你會看到瓣膜關閉 阻擋水流入心室 之後整個心室都被灌滿了水 這時如果你擠壓右心室 水會從肺動脈噴出來 瓣膜有不同的名稱 在右心室稱作三尖瓣 左心室的則是二尖瓣 注水時 瓣膜會像降落傘一樣開合 只要你同時有節奏地擠壓心室 這種水流模擬了血液循環 心臟瓣膜的功能卓越 你會發現擠壓心室時 它完全不會漏水 心臟瓣膜運作時常常閉合 但這過程幾乎沒有磨損 這解釋了心臟為何 得以長時間完美運作 在人一生中,跳動超過二十億次 現在,學習心臟科的人 可以實際拿一顆心臟 讓它跳動 藉此觀察心臟的運作過程 你也可以把手放在胸前 感受心臟韻律的跳動 在了解我們賴以生存的心跳如何運作後 我們就能更深刻的體會心跳的意義 不論是跑步 攝取過多咖啡因 或是與愛人四目相對時