Fertilisation Flashcards
What process of cell division applies to gametes?
Meiosis
How long can an unfertilised oocyte survive?
12-72 hours
How many sperm does each ejaculation contain and what percent reaches the ovum?
Around 300 million sperm
Around 15%
What is fertilisation?
The fusion of the nucleus of a male gamete with the nucleus of a female gamete to produce a new cell called a zygote
What enzyme does the sperm release to allow penetration through the zona pellucida?
Hyaluronidase
What is the process that sperm are required to go through to enable it to fertilise an oocyte?
Capacitation
Where does capacitation of the sperm take place?
In the uterine tubes
What does the acrosome of the sperm react with when it reaches the ovum?
The zona pellucida
Outline what happens when the sperm reaches the egg in regard to the chemical reactions
- The entry of the acrosome into the egg surface causes a cortical reaction or change
- Chemical reactions cause the ovum to swell, altering the zona pellucida making it impermeable to other sperm
- The sperm nucleus reaches the cytoplasm, where the tail will detach
- The cortical granules within the cytoplasm fuse with the plasma membrane to make the vitelline layer impenetrable to other sperm
What is polyspermy?
This is a condition where more than one sperm nucleus interacts with the female nucleus, creating an unviable zygote
What does fertilisation result in?
A new nuclei containing genetic material from both the sperm and ovum resulting in a diploid cell
How long does the process of fertilisation within the uterine tube take place
24 hours
Name the three developmental periods of the zygote with timescales
Pre-embryonic period week 0-2
Embryonic period weeks 2-8
Fetal period 8 weeks until birth
What happens within the first week of the pre-embryonic stage?
Within the first week, the zygote travels along the uterine tubes towards the uterus, during this travel the zygote goes through cleavage
Outline what happens day 1-3 of the pre-embryonic stage
Day 1- the zygote splits into 2 cells
Day 2- the zygote has split into 4 cells
Day 2.5- the zygote has split into 8 cells
Day 3- the zygote has split into 16 cells and then 32 cells and is now known as the morula
What does the morula develop into when a fluid filled cavity appears?
A blastocyst
What surrounds the outside of the blastocyst?
The trophoblast (this is a single layer of cells)
What is the inner cell mass within the blastocyst called?
The embryoblast
What is the fluid filled cavity of the blastocyst called?
The blastocoele
Outline what happens to the blastocyst when it enters the uterus
It lies free for approximately 2-3 days
On around day 6, it embeds into the endometrium
The trophoblasts become sticky and secrete substances that digest the endometrium
Outline of implantation
Villi make their way into the decidua where they branch and contain blood vessels of the developing embryo to allow gaseous exchange between the mother and embryo
By day 12, the conceptus is completely embedded in the compact layer of the endometrium and is covered by the overlying uttering epithelium
At implantation, what formations take place?
Trophoblasts become the placenta and chorion
Embryoblast becomes the embryo, amnion, and umbilical cord
The trophoblasts differentiate into two distinct layers, the inner cytotrophoblasts and the outer syncytiotrophoblasts
Syncytiotrophoblasts are formed from the outer layer of trophoblasts
Cytotrophoblasts are trophoblasts that haven’t formed synctiotrophoblasts
What two types of cells does the embryoblast differentiate into?
Embryonic epiblast- this is closest to the trophoblast and becomes the embryo and amniotic cavity
Hypoblast- this is closest to the blastocyst cavity and becomes the yolk sac
What process are the three layers of epiblast cells developed through?
Gastrulation
Name the three layers of epiblast cells and what they form
Ectoderm- This forms the epidermis later of the skin, hair, and nails. It also forms the nervous system
Mesoderm- This forms the muscle, skeleton, dermis of skin, connective tissues, urogenital glands, blood vessels, and blood and lymph cells
Endoderm- This forms the epithelia lining of the digestive, respiratory, and urinary systems, and glandular cells
What is the role of the corpus luteum in fertilisation?
Human chronic gonadotrophin is secreted into the maternal blood stream
It releases progesterone and oestrogen
The release of progesterone suppresses menstruation
