Here’s a detailed account of my experience at the egg and what I noticed …
The Nucleus is the heart of the egg cell and contains most of the genetic material in the form of chromosomes. This is where the genes are situated. An egg, like a sperm, contains half the number of chromosomes as a normal cell, i.e. 23 each. Once an egg and sperm combine during fertilisation the resulting embryo then has the normal 46 in total.
The Cytoplasm is a gel-like substance which holds all the cell’s other internal structures, called organelles. It is in the cytoplasm that all the cell’s activities take place to keep it alive and functioning properly. Amongst the more important organelles are structures called mitochondria which supply most of the energy for the cell.
The Zona Pellucida (or egg wall) is an outer membrane of the egg. This structure helps the sperm to enter the egg through its hard outer layers. The egg wall hardens with age and can be a cause for non-fertilisation of an egg. ‘Assisted Hatching’ is a process whereby small openings are created using various techniques (mechanical, chemical or laser) on the egg wall to allow the developing cluster of cells to ‘hatch’. Without this opening, they would not be able to break out of their tough shell and implantation of a pregnancy would not occur.
The Corona Radiata surrounds an egg and consists of two or three layers of cells from the follicle. They are attached to the outer protective layer of the egg, the zona pellucida, and their main purpose is to supply vital proteins to the cell.
How big is a human egg?
The human egg, or ovum, is one of the largest cells in the human body. Having said that, it is still very small and measures approximately 0.12 mm in diameter, which means that you would need 9 of them to fill a millimetre and if you laid 100 of them side by side they would sit on a line 12 mm (1.2. cm) long.
How are eggs produced?
Eggs are produced in the ovaries, and every woman normally has two of these situated towards the back of the abdomen below the kidneys. The eggs grow from tiny cells inside the ovaries, going through various stages of development, called oogenesis, until they are released once a month during ovulation. Usually each ovary takes turns releasing eggs every month; however, if there was a case where one ovary was absent or dysfunctional then the other ovary would continue providing eggs to be released.
How many eggs are there in an ovary?
A woman is born with approximately half a million potential eggs, or follicles, in each ovary. From birth onwards she will not produce any more and in fact these will steadily decline over her lifetime and be absorbed by the body in a process known as atresia.
By the time of puberty, the million original follicles will have reduced to about 300,000 and they will continue to decline right through until the menopause. With each menstrual cycle a dominant follicle will recruit a potentially mature egg, which is released into the fallopian tube at ovulation.
Given an average span of 40 years between puberty and menopause with one egg being released per month, this means that only 400-500 eggs in total are released. Few or no follicles remain at menopause, and any that still remain, are unlikely to mature and become viable eggs because of the hormonal changes that happen with the menopause.
How does an egg develop?
At the beginning of each menstrual cycle, a group of 10 – 20 primary follicles begin to develop under the influence of Follicle Stimulating Hormone (FSH). By around day 9 of the cycle, only one healthy follicle normally remains, with the rest having degenerated. On approximately day 14 of the cycle, a surge of Luteinising Hormone(LH) occurs, which causes the mature follicle to ovulate approximately 24 – 36 hours later.
What’s different in an egg donation cycle?
To donate eggs, a donor is stimulated with a synthetic version of the same hormone that is naturally produced (FSH) in order to encourage the growth of the whole group of 10-20 follicles. This encourages the eggs to develop to the same stage of maturity as the one to be released. Rather than letting ovulation naturally occur, this is triggered by medication and the eggs are surgically removed 36 hours later, placed in a dish in an incubator, ready for fertilisation.
What is egg quality?
Egg quality is about how capable an egg is of being fertilised and going through the developmental stages to form a viable embryo. This is largely determined by two factors: the number of chromosomes present within the egg, and the energy supply of the egg. Both of these tend to reduce over time which means that age is one of the biggest factors affecting egg quality in a woman, with the quality gradually declining as she gets older. This is the main reason that egg donors need to be below 35 years, as this is the age when the egg quality begins to reduce.
Other factors that affect egg quality are life style issues such as smoking, drinking, drugs (medical or otherwise) and general health.
