Ovulation is the crucial event when a mature egg suddenly breaks out of the ‘dominant’ follicle, and as the pictures below show it’s a bit like a small volcano erupting! The egg get’s pushed out of the follicle in about 15ml of fluid, and the tentacle-like ends of the fallopian tube then literally ‘sweep’ over the surface of the ovary to ‘catch’ the egg and bring it safely within the tube.
Egg’s are very large cells surrounded by a tough membrane called the ‘zona pellucida’ (Latin for ‘membrane derived from the egg’) and the membrane nourishes and protects the egg for 12-24 hours after it’s ovulated. Nearly all eggs are fertilised in the first few hours after ovulation in the ovary end of fallopian tubes, on around day 14 of the cycle. Although it’s essential that only one sperm fertilizes the egg it requires team-work with at least 40 sperm needed to break through the zona pellucida. Once a sperm fuses with the egg’s membrane and it’s genetic material enters the egg, the zona transforms into an impenetrable barrier to prevent any other DNA entering it (this will cause an unviable pregnancy).
The fertilised egg becomes an embryo when it divides into two cells, and cells of the embryo continue to divide in a ball until there are 70 to 100 cells. At this point the shell of the zona pellucida begins to degenerate which allows the embryo to increase in size and it enters the blastocyst stage with a central, fluid-filled cavity. The embryo takes a about a week to negotiate the 2-3 inches of fallopian tube to reach the uterus, where it must implant to start a pregnancy.
There are cilia cells in the fallopian tubes with little ‘hairs’ that beat to push the embryo towards the uterus. Ideally the cilia push the embryo so it arrives in the womb during the ‘window of implantation’ when the womb’s most receptive. As the embryo has no direct blood supply while it’s in the fallopian tube, and is growing all the time, it needs to get nourished another way, which is from secretions from ‘peg’ cells that line the tubes. There are a number of problems that embryo’s can experience in the tubes:
- The secretions from peg cells can get too thick and sticky (particularly an issue for ‘heavy’ types), which can slow or block the embryo’s progress in the tube
- Obstructions from scars or infections can impede or block the embryo’s way, which tends to be ‘stuck’ or ‘hot’ type issues
- The timing of the embryo’s arrival in the womb is outside the ‘window of implantation’ which reduces the chance of implantation (usually ‘cold’ and ‘stuck’ type issues)
- There’s insufficient nourishment from ‘peg’ cells for the embryo to properly develop and grow, and this can affect ‘hot’, ‘cold’, ‘tired’ or ‘pale’ types!
When an embryo implants in the womb the placenta releases ‘human chorionic growth hormone’ (hCG) which stimulates the corpus luteum in the ovary to increase its production of progesterone. The high levels of progesterone prevent the start of new menstrual cycles and promotes an increasingly blood-rich structure to the womb lining and the huge changes that the immune system needs to make for a successful pregnancy; the more you know, the more of a miracle each baby becomes!