Fertilisation & Embryology Flashcards
Where does fertilisation take place?
In the fallopian tube specifically in the ampulla. Once fertilisation occurs, the fertilised egg (zygote) moves to implant itself into the endometrium.
What is an ectopic pregnancy?
When the zygote implants itself outside the uterus i.e: fallopian tube. This occurs to women with STD and pelvic infections.
What is the life span of an egg and sperm?
- the egg can live for a maximum of 48 hours.
- the sperm can live for a maximum of 3-4 days.
What happens after sexual intercourse?
Around 200-500 million sperm is ejaculated and only a few reach the egg. Those that do, come in contact with the corona radiata and the zona pellucida which allows access to only one spermatozoa to enter the ovum. Only the head of the spermatozoa actually enters the ovum.
Once the spermatozoon has been penetrated the cell membrane of the ovum, alters its configuration to prevent any other from entering.
When is fertilisation likely to occur?
Fertilisation is more likely to happen when intercourse takes place more than 48 hours before or 24 hours after ovulation.
What happens during the onset of fertilisation?
the DNA in the nucleus of the spermatozoa is released which triggers the final meiotic division by the female chromosomes.
Two sets of female chromosome is created which then only one joins with the male chromosome → CREATING 46 CHROMOSOMES AND IS NOW CALLED A ZYGOTE.
What forms after a zygote?
The zygote moves along the fallopian tube for 3-5 days and meiotic cell division takes place.
The zygote is still contained in the zona pellucida while its dividing to prevent adhering to the mucosa.
Eventually ZYGOTE → MORULA (undifferentiated cells).
MORULA → BLASTOCYST
CELLS SPECIALISATION BEGINS.
When is fertilisation completed?
Completed at day 11.
What happens during implantation?
5 days after fertilisation, the blastocyst lies close to the endometrium for a day or two.
This allows the trophoblast to secrete an enzyme which breaks down the surface of the endometrium → where the blastocyst can be nourished.
Small finger-like projections (chorionic villi) develop around the entire blastocyst that aids implantation.
Some chorionic villi will continue to develop into the mature placenta while the remainder will from the chorionic membrane which lines the uterus.
What happens to the Decidua?
Endometrium is known as DECIDUA
Influence of the high levels of hormones, decidua thickens and nourishes the blastocyst during the pregnancy.
The area in which the blastocyst implants heals and covers over.
The portion beneath the embedded blastocyst becomes the decidua basalis
Decidua capsularis is the portion that covers the blastocyst.
What can cause miscarriages?
Clotting disorders can create miscarriage as the blastocyst can’t attach to the endometrium.
if women are diagnosed with clotting disorders they are given aspirin.
Or a miscarriage can just be that the embryo has a genetic disorder
Where does the blastocyst implants itself?
near the fundus anterior
but with an IVF pregnancy, the blastocyst implants near the cervix.
What is an embryo?
Developing mass of cells from implantation until 8 weeks gestation.
What are the formation of two enclosed cavities called?
The amniotic sac: is filled with fluid that will eventually surround the embryo.
Yolk sac: provides nourishment for the trophoblast.
The embryo develops between these two sacs called the embryo disc and three layers develop in this region:
Ectoderm: the layer closest to the amniotic sac and will form the skin and the CNS of the embryo.
Mesoderm: the central layer in which bones, muscles, heart, blood vessels and internal organs including the kidneys will form.
Endoderm: the layer closest to the yolk sac with form the digestive and respiratory system as well as the glands and mucous membranes.
What happens during day 13 of embryonic life?
Chorionic villi begin to secrete human chorionic gonadotrophin (hCG) and stimulates the corpus luteum to continue producing the hormones necessary. → this is done until the placenta is mature enough to take over.
