Embryology Flashcards
Define spermatogenesis.
A spermatogonium with 46 chromosomes undergoes meiosis and forms 4 sperm (X or Y).
Define oogenesis.
An oogonium with 46 chromosomes undergoes meiosis and forms 1 ovum (X) and 3 polar bodies.
Define fertilisation.
Several sperms surround the ovum, but only one penetrates. The pronucleus of the sperm enters and fuses with the pronucleus of the ovum to form a zygote.
What is a zygote?
The genetically unique first cell in the body.
Diploid - 46 chromosomes.
Moves through the uterine tube to reach the uterine cavity.
What does a zygote divide into?
A morula - a solid mass of cells.
As the number and size of cells increases, nutrition to the central core of cells becomes difficult, and a blastocyst cavity develops.
How are the different linings of cells formed in a morula?
Cells accumulate at one end to form an inner cell mass.
The trophoblast is the outer lining of cells of the blastocyst.
What occurs in the first week after fertilisation?
The pre-embryonic phase.
Ovums are released from the ovary.
Fertilisation occurs in the fallopian tube.
What is an ectopic pregnancy?
This could occur when the cilia function of the uterus is abnormal.
What is a chorion?
The trophoblast divides to form the chorion, and develops finger-like processes called chorionic villi.
What are some functions of the chorionic villi?
Implantation.
Forms part of the placenta (in due course).
Secretes human chorionic gonadotropin (hCG), which is used to detect pregnancy.
What is implantation?
At ~7 days, the blastocyst begins to burrow into the uterine wall (endometrium).
The chorion plays an important role in this.
What is the decidua basalis?
Part of the endometrium deep to the implanted conceptus. It is maintained by hCG (secreted by the chorion).
What occurs until ~12 weeks of gestation?
Maternal blood and urine levels of hCG increase.
What do the cells of the inner cell mass form?
The bilaminar disc - a two-layered flat disc.
This forms the amniotic cavity (above the epiblast) and the yolk sac (below the hypoblast).
What other cavities are attached to an embryo?
Allantoic cavity - increases in size as the yolk sac decreases in size, containing waste.
Chorionic cavity - the fluid in which the embryo floats.
