Lecture 2

corona radiata and zona pellucida

Zygote

The pronuclei of the male and female come together and chromosomes line up for mitosis

Rapid cell division without cell growth

16-32 cell phase

Cells produced by cleavage after fertilization

Ball of cells with a fluid filled cavity. Occurs between days 4-5.

1. Embryoblast/inner cell mass. Forms the embryo proper.
2. Trophoblast/outer cell mass. Forms the fetal part of the placenta, called the chorion.

The zona pellucida degrades so that the blastocyst can "hatch". This allows for implantation because the blastocyst is "sticky".

Day 6 or 7

1. Released oocyte through ovulation
2. Fertilization in the Fallopian tube with 24 hours of ovulation
3. 2 cell stage at at day 2
4. 4 cell, 8 cell, and morula stage occurs days 3-4
5. Blastocyst stage hatched in day 5 in uterus
6. Implantation occurs on day 6

They die

Can survive for 6 days, takes 30 minutes to 6 days to reach the uterine tube

200-500

The posterior wall of the uterus

1 in 100 pregnancies are ectopic, majority are Fallopian tube (95-98%)

1. In the ovary
2. Uterine tube
3. Abdonimal messentrary cavity
4. Implantation low in the uterus, close to cervix

Developed in the 70s, used to assist people with reproductive issues

1. Hormones used to get ovaries to release mature oocytes
2. Oocytes are aspirated from follicle
3. Oocytes are placed in Petri dish with sperm
4. Oocytes are grown to 8 cell stage (day 3) or blastocyst stage (day 5)
5. Embroys are transferred into uterus via catheter

corona radiata and zona pellucida

-Zona pellucida is weakened from laser or needle so blastocyst has an easier time hatching
-Helpful if zona pellucida is thickened (i.e. older women)

-A cell is removed from the 6-8 cell zygote and the DNA is tested for chromosomal abnormalities
-The zygote compensates for the loss and continues to develop normally

1. Embroyo gets two fluid filled cavities (the amniotic cavity and the yolk sack)
2. The inner cells of blastocyst flatten into a two layered disk (bilaminar disk or embryo). Has the epiblast and hypoblast.
3. The trophoblast invades uterus and becomes the cytotrophoblast and syncytiotrophoblast

Cytotrophoblast is interior to the syncytiotrophoblast and is responsible for cell growth
Syncytiotrophoblast has no clearly defined border and synthesizes hormones

End of second week

-Occurs due to implantation of blastocyst
-Occurs near 28th day
-1/3rd of women experience

-50% of pregnancies result in spontaneous abortions
-Majority happen within the first 10 weeks and most are due to chromosomal abnormalities

-Any substance that disrupts development and causes birth defects
-Not often impacted, but if they are, it's all or nothing

-Erodes uterine blood vessels and empties content into spaces called lacunae
-Oxygen and nutrients diffuse across the syncytiotrophoblast

Forms after 12 days, just outside of the yolk stack and amnion

Around day 13. Begins when the cytotrophoblast and syncytiotrophoblast for chorionic villi, which project into the luncane that are filled with maternal blood

Inner lining of the uterus/endometrium (decidua)

Trophoblast -> cytotrophoblast and syncytiotrophoblast -> chorion

15-20 weeks for amniocentesis
10-13 weeks for chorionic villi sampling (no neural tube defects can be detected)

It is the start of gastrulation. It creates a left-right and cranial-caudal division, midline axis, and ventral/dorsal (already set with disk stage).

It is a solid rod that runs down the midline of the embryo. It is formed from mesoderm cells.

Ectoderm, Mesoderm, and Endoderm. Three layers formed during week 3.

Most common tumor in newborns. Caused by the remnants of a primitive streak. It is a made up of tissues from all three germ layers.

It is caused by too little mesoderm in the caudal region due to problems during gastrulation. Leads to fusion of lower limbs to different extents. (i.e. Sirenomelia- mermaid syndrome is most severe form)

Gastrulation establishes midline and right from left. This condition is where organs are in a mirror image arrangement due to problems during gastrulation.

The embryo folds in several directions to form a C-shaped cylindrical tube.

Week 3-8

The nervous system and cardiovascular system

Between weeks 3 and 8. Major structural abnormalities that can result because organs are developing.

Ectoderm (epidermis and NS), Mesoderm (middle stuff), and Endoderm (gut tube)

The nucleus pulposus

The ectoderm thickens, folds, and invaginates downward. Forms: neural tube and neural crest.

It is a hollow tube that gives rise to the CNS. (brain, brain stem, spinal cord). Closes 26-28 days.

Ectoderm cells that fail to be incorporated into neural tube and become neurons whose cells bodies are in PNS (Schwann and Satellite cells)

NS issues, head and neck issues (i.e. cleft lip and palate)

Paired blocks of mesoderm

Day 26, Day 28

Anencephaly and spina bifida, indicated by increased alpha fetoprotein levels, prevented by folic acid supplements

They begin to fold underneath embryo

During the folding, the endoderm and a part of the yolk space become enclosed by embryo, forming gut tube that runs the length of the embryo

Folding encloses the embryo in the amniotic cavity and creates the primary body cavity (coelom)

Epidermis, CNS, ganglia, and PNS, neural crest, head mesenchyme

Filler, CT, bone, cartilage, muscle, blood, blood vessels, heart, lymph, and most GU

Gut tube, trachea, lung, tonsils, thyroid, parathyroid, lower GU

Vitelline duct

At the end of week 4 when the vessels in yolk sac, chorion, and connecting stalk are hooked up

Week 4

Weeks 3-8

Week 9-38

Clinical gestation is calculated based on the last menstral period, so it is the fetal age plus two weeks

18-20 weeks