Embryology 1 Flashcards
What are the three phases of pregnancy?
Pre-embryonic phase 0-3 weeks
Embryonic phase 4-8 weeks
Foetal phase 9-40 weeks
What are the cells that produce the sperm cells and the ova?
Spermatogonium
Oogonium
Where are the Spermatogonium and Oogonium found?
Gonads
What is the contents of a sperm cell?
22 chromosomes, 1 X, or 1 Y
What is the contents of an ovum?
(22+X)
3 polar bodies
What fuses to from the zygote?
(pro)Nucleus of sperm enters and fuses with (pro)nucleus of ovum
Creates diploid cell, ZYGOTE
What part of the sperm enters the ovum?
Only the nucleus
Rest of the cell is left behind
What happens during week one of pre-embryonic phase?
- Zygote forms, divides to form blastocyst
- Moves through uterine tube, to reach uterine cavity
Why are zygotes always unique?
No two sperm/ova are the same
Which parent is mitochondrial disease inherited from?
Mother
What does a zygote become after dividing?
Morula
Solid ball of cells
What day is a blastocyst formed?
Day 5/6 of pre-embryonic phase
Why is the blastocystic cavity formed?
Increasing number and size of cells makes it more difficult to get nutrition to central core of cells
How is the blastocystic cavity formed?
- Cells accumulate at one end to form an inner cell mass.
- The outer lining of cells is called the trophoblast.
How long does the first cell division take?
36 hours
What happens on day 5/6?
Blastula has formed
Reaches uterine cavity ready to implant in it
What is required for the the dividing zygote/ morula/ blastocyst fallopian tube to move and reach the uterine cavity?
Requires healthy ciliated epithelium
When is ectopic pregnancy likely to occur?
- Cilia function is abnormal
- Pregnancy occurs in uterine tube
- Complications include rupturing of uterine tubes
What is the endometrium?
Mucous membrane lining uterus
Thickens during menstrual cycle in preparation for possible implantation of an embryo
When does the placenta start to develop?
Start by day 6 of 1st week, when implantation occurs in the uterine endometrial layer
What starts to form at week 2?
- Sacs, membranes and cord to nourish human conceptus (baby) start to form
- Cells that later form embryo form a bilaminar disc
What is the role of the chorion?
Burrowing
What cells are initially called to trophoblasts?
Cells that form the outer cell mass
What forms the chorion?
trophoblast
What does the Chorion do?
- Implantation process (chorionic villi)
- Forms part of the placenta
- Secretes human Chorionic gonadotropin (HCG) (used to detect pregnancy)
What is the function of HCG?
Tells ovary to continue producing oestrogen and progesterone so endometrium does not get shed
What is used to test for pregnancy?
HCG
Present in urine
What is the decidua basalis?
part of the endometrium deep to the implanted conceptus.
What is the decidua?
Area in endometrium where blastocyst implants
Which part of the endometrium contains more blood vessels?
Decidua basalis
When does HCG content increase until?
Increase till around 12 weeks gestation
What is the change in structure of the inner cell mass?
Cells of the inner cell mass form a 2–layered flat disc called the BILAMINAR DISC
What is the name of the two cell cavities formed by the inner cell mass?
2 cavities now begin to form
- Amniotic cavity (A)
- Yolk sac (Y)
What are the names of the different layers of the Bilaminar disk
Top - Epiblast
Bottom - Hypoblast
What is the name of the abbreviated structures?
AC – Amniotic cavity
CC – Chorionic cavity
AL – Allantoic cavity
YS – Yolk sac
How does the chorion handle the blood of the embryo?
Prevents maternal blood and embryo blood to mix?
Look
What are the main functions of the placenta?
Main functions:
- Foetal nutrition
- Transport of waste and gases
- Immune etc
Which part of the placenta is smooth?
Foetal part and surface: smooth with foetal blood vessels and end of umbilical cord
Which part of the placenta is rough?
Maternal part: Decidua basalis of endometrium
Rough and has maternal blood vessels
When is the placenta mature?
By 18-20 weeks
How are fraternal/dizygotic twins formed?
How does an identical twin/monozygotic twin formed?
Summary of Weeks 1 and 2
