Body Logistics Flashcards
What is embryology?
The study of progression from a single cell to a baby in 9 months.
Where does fertilisation usually occur?
In the ampullary region of the fallopian tube (also known as uterine tube)
Millions of sperm enter the female reproductive tract. Why does only one sperm fertilise the secondary oocyte?
- Some die due to the acidic environment of the vagina
- Cilia in the fallopian tube traps some sperm
- Not all sperm have the optimum structure to allow them to swim through to the Fallopian tube
- The secondary oocyte is covered in a protective layer of cells called the corona radiata. Only one sperm breaks through this and reaches the membrane as the corona radiata hardens after this occurs and the egg produces chemicals to prevent other sperm from entering.
When must sperm enter the female reproductive tract for fertilisation to occur?
5 days before ovulation
How long are sperm/secondary oocytes viable for?
Sperm=5 days
Secondary oocyte=12-24 hours
What do sperm require for fertilisation?
Capacitation- the tail of the sperm moves faster causing the plasma membrane to alter
How many cells does a zygote begin with?
2 cells
How does the egg and sperm combine to form a diploid set of chromosomes?
When the sperm reaches the membrane of the secondary oocyte, the membranes of the sperm and secondary oocyte fuse and the contents of the sperm enters the egg. The presence of the sperm pronuclei triggers the completion of meiosis II in the egg pronuclei. Microtubules pull the two pronuclei together to form a diploid set of chromosomes.
What are two potential mechanisms of a male contraceptive pill?
- Cell penetrating peptides that enter sperm and prevent them from moving.
- Blocking sperm power kick using a progesterone receptor antagonist. The progesterone receptor is on the sperms tail and the female hormone activates the receptor triggering a cascade of reactions that make the tail of the sperm move rapidly towards the egg.
Define embryonic age.
Time since fertilisation
Define gestational age.
Time since last menstruation. Embryonic age minus 2 weeks.
Define germinal stage.
Time from fertilisation to end of second week.
Define embryonic period.
Time from the third to end of eighth week
Define foetal period.
Time from beginning of ninth week to birth at 38 weeks.
What is hatching and why is it essential?
Hatching is the process of a blastocyst losing the zona pellucida. This is essential for implantation to occur.
What differentiates the morula and blastocyst?
Morula-By 3 to 4 days after fertilisation, the dividing cells of the embryo forms a spherical shape that looks like a mulberry.
Blastocyst-By 4 to 5 days after fertilisation, a cavity forms within this ball of cells.
When does implantation occur?
6th day after fertilisation
What is the function of the zona pellucida in the blastocyst/morula?
Prevents it from adhering to the oviduct
Stops morula from enlarging (limited food source) so cells divide by reduction division, more cells but overall structure remains the same size
Where does implantation usually occur?
Superior, posterior part of uterus in the endometrium