The uterus & fallopian tubes are where the action really happens; where egg meets sperm and along which the growing embryo journey’s to reach the womb, which it’ll hopefully call ‘home’ for the next 9 months. The delicate but dynamic structures of the fallopian tubes are about 10cm (3 inches) long and are an extension of the uterus that are held in place near the ovaries by ligaments to make the link between eggs in ovaries and the womb. Rather confusingly they’re also called ‘uterine tubes’, ‘oviducts’, and ‘salpinges’ and these are sometimes part of medical terms like ‘hydrosalpinges‘.
Fallopian tubes functions are:
- They link the uterus to the ovaries so sperm can reach and fertilise an egg
- They nourish sperm so they can survive for up to five days after ejaculation
- The tube’s finger-like ends (fimbriae) ‘sweep’ over the ovary to ‘catch’ an egg after ovulation and fertilisation is usually near the end of the tube
- Little hair-like cells called ‘cilia’ that line the walls of the tubes actively ‘push’ the growing embryo towards the uterus. After five to six days of travelling along a tube the embryo enters the womb to implant about a day later
- The developing embryo is nourished by specialised ‘peg’ cells that line the tubes
The uterus (womb) is an expandable “baby carrier” that’s made up of three layers, which from the inside out are:
- The endometrium lines the inside of the womb and is where embryos implant
- The myometrium is the smooth muscle that makes up the bulk of the womb
- The perimetrium is the loose connective tissue that surrounds the uterus
The womb is usually held in the pelvic cavity by lots of ligaments in a forward position, but it may be ‘tipped’ backwards in a ‘retroverted’ position, but don’t worry as the positioning of the uterus doesn’t affect fertility.
Structure and function of the endometrium
The endometrium lining is made up of two distinct layers of cells:
- The ‘functional layer’ is the top layer and it’s where an embryo attaches and implants, if not, it’s shed in the menstrual bleed
- The ‘basal layer’ lies beneath the ‘functional layer’, it’s attached to the muscle of the myometrium and the ‘functional layer’ grows from it, but it’s never shed
In the first (follicular) phase of the cycle high levels of estrogen produced by follicles growing in the ovaries stimulate the cells of the functional layer to multiply. The more estrogen, the thicker the endometrium can grow, and young women typically have thicker womb linings than older women as they usually have more follicles per cycle.
In the second (luteal) part of the cycle the corpus luteum releases progesterone, and this stimulates the cells in the functional layer to change their structure to maximise the chances of implantation. The endometrium becomes much richer in blood supply, more spongy and sticky as glands alter its surface, plus the