Conception: How It Works
To become pregnant, the following steps must occur:
- Sperm transport. 精子必须被储存并运送到受精地点.
- Egg transport. 排卵必须发生,卵子必须被试管“捡起”.
- Fertilization and embryo development. Union between the sperm and egg must result.
- Implantation. 胚胎必须在子宫内植入并开始生长.
These steps are described below.
Sperm transport
The transport of sperm depends on several factors:
- 精子必须能够推动自己通过女性阴道和子宫颈的环境.
- This environment, which is under cyclic hormonal control, 在不破坏精子的情况下接受精子一定是有利的吗.
- 精子必须具有转化为能穿透卵子细胞膜的形式的能力(获能)。.
Following ejaculation, 精液形成一种凝胶,保护它不受阴道酸性环境的影响. 这种凝胶在20到30分钟内由前列腺中的酶液化. 这种液化对释放精子很重要,这样才能进行运输. The seminal plasma is left in the vagina.
受保护的精子以最大的活力穿过保护子宫入口的宫颈粘液层. During ovulation, this barrier becomes thinner and changes its acidity, creating a friendlier environment for the sperm. 宫颈粘液作为精子存活期的储存库.
Once the sperm have entered the uterus, 收缩推动精子向上进入输卵管. 第一个精子在射精后几分钟进入试管. 然而,第一个精子很可能不是受精精子. 活动精子可以在女性生殖道中存活长达5天.
Egg transport
卵子运输从排卵开始,到达子宫后结束. 排卵后,纤毛状或指状的输卵管末端扫过卵巢. Adhesive sites on the cilia, which are located on the surface of the fimbriae, 负责取卵和移卵到试管中. The cilia within the tube, 以及由卵子运动引起的肌肉收缩, create a forward motion. Transport through the tube takes about 30 hours.
Conditions such as pelvic infections and endometriosis 会永久损害输卵管的功能吗, due to scarring or damage to the fimbriae.
Fertilization and embryo development
排卵后,卵子只能在12到24小时内受精. Contact between the egg and sperm is random.
一旦卵子到达试管的特定部分, called the ampullar-isthmic junction, it rests for another 30 hours. 受精——精子与卵子结合——发生在输卵管的这一部分. 然后受精卵开始快速下降到子宫. 在试管中休息一段时间似乎是受精卵完全发育和子宫准备接受卵子所必需的.
输卵管缺陷可能会影响运输,增加输卵管妊娠的风险, also called ectopic pregnancy.
卵子周围的膜称为透明带,在受精过程中有两个主要功能. 首先,透明带含有人类精子特有的精子受体. 其次,一旦被精子穿透,这层膜就变得无法被其他精子穿透.
穿透之后,一系列的事件为第一次细胞分裂奠定了基础. The single-cell embryo is called a zygote. Over the course of the next seven days, 人类胚胎在有丝分裂过程中经历多次细胞分裂. At the end of this transition period, the embryo becomes a mass of very organized cells, called a blastocyst. It's now believed that as women get older, 由于卵子质量下降,这一早期胚胎发育过程日益受损.
Implantation
Once the embryo reaches the blastocyst stage, approximately five to six days after fertilization, 它从透明带孵化出来,开始在子宫内着床.
在自然界中,50%的受精卵在女性月经未来之前就丢失了. In the in vitro fertilization (IVF) process as well, 胚胎可能会开始发育,但不能进入囊胚阶段——囊胚阶段是那些注定要成为胎儿的细胞与那些将成为胎盘的细胞分离的第一阶段. The blastocyst may implant but not grow, 或者囊胚可能会生长,但在检测到怀孕的两周时间之前停止发育. 子宫的接受性和胚胎的健康对着床过程很重要.
加州大学旧金山分校健康医学专家已经审查了这些信息. 它仅用于教育目的,并不打算取代您的十大赌博平台排行榜或其他医疗保健提供者的建议. 我们鼓励您与您的供应商讨论您可能遇到的任何问题或疑虑.