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您了解精子嗎？精子是從何而來的？

出處：網(wǎng)絡(luò)收集 日期：2024-07-05 09:57:24 編輯：秩名

同女性一樣，男性的下丘腦同樣有規(guī)律地分泌促性腺激素釋放激素，即促使垂體分泌促卵泡激素和黃體生成激素。促卵泡激素刺激睪丸細(xì)胞并驅(qū)使生殖細(xì)胞產(chǎn)生精子；黃體生成激素促使睪丸細(xì)胞分泌睪丸激素。睪丸激素使男性具備一定的外部特征和性沖動，并協(xié)助精子成熟。精子在睪丸生成，在附睪成熟，最后通過陰莖排出。男性在發(fā)身期結(jié)束時通常是在12～16歲年齡段,就具備了這種能力。
 
睪丸在身體的腹部形成，出生時降到陰囊，袋狀形的陰囊將睪丸與身體隔離。如睪丸未降到陰囊或自身發(fā)育不完善，通常會導(dǎo)致精子數(shù)量減少，這也是不育的原因之一。大多數(shù)男性的睪丸通常會不對稱，一個比另一個大一些，在陰囊的位置也略高些。
 
陰囊的作用是使睪丸保持正常的溫度，以便產(chǎn)生精子。由于睪丸懸于體外，其溫度比人體內(nèi)的正常溫度略低。當(dāng)氣溫較低時，陰囊就緊縮，其目的是使睪丸處于暖和的狀態(tài)。睪丸的溫度升高，陰囊就變得松弛，使它們可以吸收更多的空氣。但對氣溫的極度影響，陰囊卻無能為力，如長時間泡熱水澡，睪丸長期置于高溫之下，所產(chǎn)生的精子數(shù)量就會減少，或產(chǎn)生的精子不正?；虿换钴S。這些副作用要經(jīng)過兩個半月才能消失。
 
體內(nèi)的促卵泡激素可刺激滋養(yǎng)細(xì)胞分泌營養(yǎng)物，以供精子成長之用。發(fā)身期過后，年輕的男性會經(jīng)常產(chǎn)生精母細(xì)胞，1秒鐘約1 000個。精母細(xì)胞轉(zhuǎn)化為精子需要74天的時間，精子最前端的部分含遺傳物質(zhì)，中間部分提供迅速移動的能量，鞭狀形的長尾巴起推進(jìn)作用。
 
為完成精子的發(fā)育過程，正在成熟的精子游入附睪，一直緊緊盤繞在超纖細(xì)管道，在每個睪丸的后部可以觸摸到。附睪是精子完成發(fā)育過程的地方。成熟的精子可以依靠自身的力量移動，進(jìn)入輸精管，輸精管是將精子從附睪輸送至尿道的管道，在射精前精子一直在此逗留。
 
正常男子的身體，每天可以產(chǎn)生數(shù)百萬個精子，其中約40％是有缺陷的。這些精子或是頭部的形狀不正常，或是有1個以上的精頭，或是遺失了部分遺傳物質(zhì)。精子的形成過程并非完美，這也是人體產(chǎn)生大量精子的原因之一。另外，生殖系統(tǒng)感染也會損害精子的質(zhì)量。
 
正常男子每次所射出的是精子和精液的混合物，約含2～6毫升的液體；每毫升含2000萬到2億個精子。有些男子射精后，每立方厘米的液體中精子的含量不足2000萬，這在某種程度上也會影響生育能力。射精后，如可移動精子的數(shù)量少于500萬，生育能力就會受到極大的影響。
 
輸精管將精子從附睪輸送至尿道。性交達(dá)到高潮時，精子與精液通過前列腺排出，形成射精。男性的尿道有兩重功能。當(dāng)排尿時，它負(fù)責(zé)傳送膀胱的尿液。性交時，它負(fù)責(zé)排出精液。當(dāng)進(jìn)入性高潮時，膀胱和尿道之間的開口就會關(guān)閉以阻止尿液滲入精液。射精后過一小會兒排尿系統(tǒng)才能恢復(fù)功能。
 
當(dāng)性交達(dá)到高潮時，男性骨盆的肌肉、前列腺和輸精管的肌肉壁都會收縮，促使精液從尿道通過陰莖排出。每次射出的精液中精子的含量通常達(dá)數(shù)千萬。
 
如果在排卵期前后發(fā)生性交，女性宮頸分泌的黏液的稠度可以使精子順利通過。通過黏液的眾多精子在5～10分鐘之內(nèi)迅速進(jìn)入子宮再進(jìn)入輸卵管。因為精子在宮頸和生殖道的存活時間為48小時，所以精子游動的速度就顯得至關(guān)重要。
 
如果輸卵管保持通暢，精子就會迅速游向卵子，輸卵管收縮和卵子自身分泌的化學(xué)物質(zhì)和激素對精子的游動也起推波助瀾的作用。當(dāng)許許多多的精子擠在卵子周圍迫不及待地想進(jìn)入時，它們不可避免地與卵子的細(xì)胞群相撞，這些精子就會分泌一種酶來分解這些細(xì)胞。數(shù)以千計的精子會在幾小時之內(nèi)死亡，但卵子的細(xì)胞群會消失，在劫后余生的精子面前會呈現(xiàn)出卵膜。大量的精子又會附著在這一保護(hù)層上面，最后一個精子穿透進(jìn)入，而后為防止其他精子的進(jìn)入卵膜便迅速關(guān)閉。
 
研究人員一直想知道那個從千軍萬馬中殺出的精子與其他精子相比有什么區(qū)別或優(yōu)勢？目前得出的結(jié)論是完成這一壯舉的精子必須被“激活”。精子的頂端部不僅含有染色體，而且布滿了一種被稱作頂體膜的東西。在精子進(jìn)入卵子之前，頂體膜中的部分酶就開始變得興奮起來，這是一種必要的頂體反應(yīng)。被激活的酶沿著輸卵管的方向徐徐前進(jìn)，為精子進(jìn)入卵子開路。頂體膜任何地方的異常都可導(dǎo)致男性不育。
 
精子與卵子融合在一起之后，兩者的染色體也組合在一起形成1個具有新的遺傳組合的細(xì)胞。這個新細(xì)胞約16個小時就分解1次。新的染色體組合也會不斷復(fù)制給每個新分解出的細(xì)胞。這個不斷繁殖的細(xì)胞群進(jìn)入輸卵管，然后再進(jìn)入子宮。如果這些細(xì)胞群能在子宮內(nèi)膜成功著床，在以后37周的時間內(nèi)就會不斷獲得營養(yǎng)。它先是通過子宮內(nèi)膜，然后是胎盤。胎盤上面血管密集。在胎兒出生前，胎盤負(fù)責(zé)提供胎兒發(fā)育所需的氧氣和營養(yǎng)物質(zhì)。

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