It begins with a bit of discomfort and soon becomes a pressing sensation that's impossible to ignore. Finally, it's all you can think about, and out of sheer desperation, you go on a hunt for a bathroom until "ahh." Humans should urinate at least four to six times a day, but occasionally, the pressures of modern life forces us to clench and hold it in. How bad is this habit, and how long can our bodies withstand it? The answers lie in the workings of the bladder, an oval pouch that sits inside the pelvis. Surrounding this structure are several other organs that together make up the whole urinary system. Two kidneys, two ureters, two urethral sphincters, and a urethra. Constantly trickling down from the kidneys is the yellowish liquid known as urine. The kidneys make urine from a mix of water and the body's waste products, funneling the unwanted fluid into two muscular tubes called ureters. These carry it downward into the hollow organ known as the bladder. This organ's muscular wall is made of tissue called detrusor muscle which relaxes as the bladder fills allowing it to inflate like a balloon. As the bladder gets full, the detrusor contracts. The internal urethral sphincter automatically and involuntarily opens, and the urine is released. Whooshing downwards, the fluid enters the urethra and stops short at the external urethral sphincter. This works like a tap. When you want to delay urinating, you keep the sphincter closed. When you want to release it, you can voluntarily open the flood gates. But how do you sense your bladder's fullness so you know when to pee? Inside the layers of detrusor muscles are millions of stretch receptors that get triggered as the bladder fills. They send signals along your nerves to the sacral region in your spinal cord. A reflex signal travels back to your bladder, making the detrusor muscle contract slightly and increasing the bladder's pressure so you're aware that it's filling up. Simultaneously, the internal urethral sphincter opens. This is called the micturition reflex. The brain can counter it if it's not a good time to urinate by sending another signal to contract the external urethral sphincter. With about 150 to 200 milliliters of urine inside of it, the bladder's muscular wall is stretched enough for you to sense that there's urine within. At about 400 to 500 milliliters, the pressure becomes uncomfortable. The bladder can go on stretching, but only to a point. Above 1,000 milliliters, it may burst. Most people would lose bladder control before this happens, but in very rare cases, such as when as a person can't sense the need to urinate, the pouch can rupture painfully requiring surgery to fix. But under normal circumstances, your decision to urinate stops the brain's signal to the external urethral sphincter, causing it to relax and the bladder to empty. The external urethral sphincter is one of the muscles of the pelvic floor, and it provides support to the urethra and bladder neck. It's lucky we have these pelvic floor muscles because placing pressure on the system by coughing, sneezing, laughing, or jumping could cause bladder leakage. Instead, the pelvic floor muscles keep the region sealed until you're ready to go. But holding it in for too long, forcing out your urine too fast, or urinating without proper physical support may over time weaken or overwork that muscular sling. That can lead to an overactive pelvic floor, bladder pain, urgency, or urinary incontinence. So in the interest of long-term health, it's not a great habit to hold your pee. But in the short term, at least, your body and brain have got you covered, so you can conveniently choose your moment of sweet release.
憋尿開始時有一點不舒服 不久後就變成無法忽視的壓迫感 最後,尿急是唯一你能想到的事 並且非常急迫地 需要去尋找洗手間,直到「啊」 人每天至少排尿 4 至 6 次 但現代生活的壓力迫使我們 有時候不得不憋尿 這種習慣有多糟糕 而我們的身體能憋多久? 答案就在膀胱的運作原理 膀胱是骨盆內的一個卵圓形囊袋 環繞這個構造的還有其他器官 共同組成整個泌尿系統 兩個腎臟 兩條輸尿管 兩個尿道括約肌 及一個尿道 從腎臟持續徐徐流下的是 稱為「尿液」的黃色液體 腎臟從水和身體廢物的 混合物中製造出尿液 滴漏出這無用的液體 進入兩條肌肉管子──即「輸尿管」 往下進入一個 稱為「膀胱」的中空器官 這器官的肌肉壁是由 「逼尿肌」的組織所構成 當尿液注入膀胱時,逼尿肌會放鬆 讓膀胱能像氣球般膨脹 當膀胱脹滿,逼尿肌就收縮 尿道內括約肌會自然而然地張開 讓尿液排出 呼咻一聲,尿液向下流進尿道 在尿道外括約肌之前突然止住 這運作就像水龍頭 當想延遲解尿時,你就緊閉這括約肌 當要解尿時 你可自主地打開水閘排尿 但怎樣才能意識到膀胱滿了沒有 而知道何時去解小便呢? 逼尿肌的內層 有數百萬個「牽張接受器」 當膀胱填充時會被觸動 它們沿著神經傳送訊號 到薦椎區的脊髓 然後會有一個反射訊號傳回至膀胱 使逼尿肌輕微地收縮 還有膀胱壓力增加 使你感覺到它脹滿了 同時,尿道內括約肌打開 這稱為「排尿反射」 若現在不方便解尿 大腦能抑制這反射 傳送另一個訊號 使尿道外括約肌收縮 膀胱內尿量達到 150 到 200 毫升時 就足以伸張膀胱的肌肉壁 讓你感受到有尿液在裡面 大約 400 至 500 毫升時 尿意的壓迫感令人感到不舒服 膀胱可以繼續擴張,但是有極限 超過 1000 毫升就可能爆裂 大多數人在爆裂發生前 膀胱就會失控 但在極罕見的情況 例如一個人無法感覺需要排尿 這嚢袋可能會疼痛地破裂 而需要外科手術來修補 但在正常情況下 你要排尿的決定會阻止大腦 向尿道外括約肌傳送訊號 這使得外括約肌放鬆 並使膀胱內的尿液排光 尿道外括約肌是骨盆腔底的肌肉之一 它支撐尿道和膀胱頸 幸好有這些骨盆腔底的肌肉 因為當咳嗽、打噴嚏、大笑 或跳躍導致加壓於此系統時 會造成膀胱漏尿 而骨盆腔底的肌肉會密封此部位 直到你方便解尿為止 但憋尿太久 排尿太快 或解尿時缺乏適當的身體支撐 久而久之可能讓 這肌肉懸帶衰弱或過勞 如此會導致骨盆底部過度活動 膀胱疼痛 尿急 或尿失禁 所以為了長期健康著想 憋尿不是好的習慣 但至少短時間來說 身體和大腦會協助你 讓你能方便地選擇愜意解尿的時間